Effects of Caffeine Supplementation on
Women's National League Soccer Players' Performance
By
Niamh Reid Burke
1428322
A thesis submitted in partial fulfillment of
the requirements for the degree of
MASTER OF SCIENCE IN
EXERCISE & NUTRITION SCIENCE
At the
University of Chester
06/10/2016
1428322: Niamh Reid Burke
Table of Contents
1. Declaration of Work ..................................................................................................iv
2. Acknowledgements................................................................................................... v
3. Literature Review ...................................................................................................... 1
3.1.
Abstract ................................................................................................................. 1
3.2.
Caffeine ................................................................................................................. 2
3.3.
Mechanisms of action ............................................................................................ 4
3.3.1.
Increased Fat Oxidation ..................................................................................... 4
3.3.2.
Adenosine Receptor Antagonism ....................................................................... 4
3.3.3.
Increased Adrenaline Production ....................................................................... 5
3.3.4.
Carbohydrate-Sparing ........................................................................................ 6
3.3.5.
Blood Lactate Production ................................................................................... 6
3.3.6.
Increased Calcium Concentration ...................................................................... 7
3.3.7.
Decreased Rating of Perceived Exertion (RPE) ................................................. 8
3.4.
Dosages, Timing and Form ................................................................................. 11
3.5.
Caffeine in Sports ................................................................................................ 15
3.5.1.
Caffeine in Endurance and High-Intensity Exercise ......................................... 15
3.5.2.
Caffeine in Team Sport .................................................................................... 16
3.6.
Females and Caffeine Supplementation.............................................................. 19
3.7.
Conclusion........................................................................................................... 21
3.8.
References .......................................................................................................... 22
(i)
1428322: Niamh Reid Burke
4. Research Project .................................................................................................... 32
4.1.
Abstract ............................................................................................................... 32
4.2.
Introduction.......................................................................................................... 33
4.3.
Methods............................................................................................................... 36
4.3.1.
Participants ...................................................................................................... 36
4.3.2.
Experimental Procedures ................................................................................. 36
4.3.3.
Statistics ........................................................................................................... 39
4.4.
Results ................................................................................................................ 40
4.4.1.
Multiple-Sprint Performance ............................................................................. 40
4.4.2.
Time to Exhaustion .......................................................................................... 41
4.4.3.
Heart-Rate........................................................................................................ 42
4.4.4.
Rating of Perceived Exertion (RPE) ................................................................. 43
4.4.5.
Habitual-Caffeine Consumption ....................................................................... 44
4.5.
Discussion ........................................................................................................... 45
4.5.1.
Multiple-Sprint Performance ............................................................................. 45
4.5.2.
Time to Exhaustion .......................................................................................... 47
4.5.3.
Heart-Rate........................................................................................................ 48
4.5.4.
Rating of Perceived Exertion ............................................................................ 49
4.5.5.
Habitual-Caffeine Consumption ....................................................................... 50
4.6.
Conclusion........................................................................................................... 51
4.7.
References .......................................................................................................... 53
5. Appendices ............................................................................................................. 59
5.1.
Ethical Approval .................................................................................................. 59
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1428322: Niamh Reid Burke
5.2.
Participant Information Sheet .............................................................................. 61
5.3.
Consent Form...................................................................................................... 64
5.4.
Health Screening ................................................................................................. 65
5.5.
Diet Questionnaire ............................................................................................... 67
5.6.
Yo-Yo Intermittent Recovery Test Level 2 Norms ............................................... 71
Table of Figures
Figure 1: Caffeine on multiple sprint performance, values are shown as medians ..................... 41
Figure 2: Caffeine on time to exhaustion, values are shown as medians .................................... 42
Figure 3: Interaction Effect of supplementation and trial, values shown in means and standard
deviation ....................................................................................................................................... 43
Table of Tables
Table 1: Caffeine on collective performance measures, values are shown in means .................. 41
Table 2: Rating of perceived exertion over both trails, values shown are medians .................... 44
Table 3: Norms for Yo-Yo Intermittent Test ................................................................................. 71
(iii)
1428322: Niamh Reid Burke
1. Declaration of Work
I hereby declare that this piece of written work, which I am going to submit as part of my
assessment as a project in the module, Research Project, on the course Exercise and Nutrition
Science (Dublin), is completely my own work and has not been submitted in whole or in part for
assessment for any academic purpose other than in fulfilment for that stated above.
Signed: _Niamh Reid Burke_
Date: _06/10/2016_
(iv)
1428322: Niamh Reid Burke
2. Acknowledgements
I’d firstly like to thank the participants for taking part in this research as they gave up their free
time to volunteer for this research. It wouldn’t have been possible without them. Secondly, I
would like to thank the Women’s National League coaches for allowing me to approach their
players and for helping me recruit the participants needed for the study. Thirdly, a huge thanks
must be given to Santry Stadium for the use of their facility which was kindly offered free of
charge to the researcher, all the staff were of wonderful help and it was all much appreciated.
It is without question that I have to acknowledge the support and help afforded to me by my
supervisor, Dr. Ceri Nicholas, university lecturer and tutor, Stephen Fallows, and phlebotomy
laboratory technician, Ellen Freeborn, for her help in obtaining the equipment and supplements
needed.
Finally, I would like to acknowledge the incredible support I have received from my family, they
are the people that inspire me to be the best I can be. The amount of love they show me is
amazing, thank you all; mam, dad, Cian and Aisling.
(v)
Student Number: 1428322
Department of Clinical Sciences and Nutrition
MSc in Exercise & Nutrition Science – Dublin
Literature Review: Caffeine and Team Sports
………J19425……….
Student J Number
…………2014…………
Year of Intake
……...06/10/2016…….
Date submitted
………..4,400…….….
Word Count
Student Number: 1428322
3. Literature Review
3.1. Abstract
Caffeine has thought to produce an ergogenic effect on performance in a number of ways,
mostly likely is adenosine receptor antagonism, increased rating of perceived exertion, and
increased motor unit recruitment. The recommended dosage seems to be 3-6 mg/kg of
anhydrous caffeine one hour prior to exercise. Research proves caffeine’s positive effects on
endurance and explosive performance, however, intermittent exercise remains ambiguous. Of
the studies completed, limitations in methodology, sample size and varying results have been
observed. Caffeine seems to effect females similarly to males, which would suggest ergogenic
benefits, although, females metabolise caffeine slower. There is extremely limited research in
females and even fewer of a high performance level, therefore, research to investigate the
effects of caffeine on female intermittent (soccer) performance.
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3.2.
Caffeine
Caffeine is the most commonly consumed stimulant which effects the central nervous system,
but unlike others is legal and consumed mainly through coffee and energy drinks. Caffeine’s
benefits were first realised over 100 years ago for its ability to increase muscular performance
(Rivers & Webber, 1907) and was used as far back as the Stone Age (Escohotado & Symington,
1999). Approximately 90% of American adults ingest caffeine every day (Andersen, Jacobs,
Carlsen, & Blomoff, 2006). It has become evident its ergogenic effects are substantial in
endurance performance (Costill, Dalsky, & Fink, 1978; Ivy, Costill, & Fink, 1979; Cole, et al.,
1996; Graham T., 2001; Cox, Desbrow, & Montgomery, 2002; Doherty & Smith, 2005; Burke,
2008; Desbrow, et al., 2012) while literature on short-term high-intensity exercise (Collump,
Ahmaidi, Chatard, Audran, & Prefaut, 1992; Jackman, Wendling, Friars, & Graham, 1996;
Jacobs, Pasternak, & Bell, 2003; Becks, et al., 2006; Wiles, Coleman, Tegerdine, & Swaine, 2006;
Woolf, Bidwell, & Carlson, 2008; Astorino, Firth, & Rohmann, 2008; Beaven, et al., 2008) show
ambiguous results, some showing positive while others negligible effects. Furthermore, results
with intermittent-exercise/team-sport are even more inconclusive. Review articles published to
date investigating caffeine and exercise (Graham, 2001; Paluska, 2003; Rogers & Dinges, 2005;
Doherty & Smith, 2005; Burke, 2008; Tarnopolsky, 2008), show little consideration has to
exercise utilising non-oxidative metabolism including sprint/power based exercise, resistancetraining and team-sports.
Caffeine can be naturally consumed in the diet from chocolate, tea, guarana and coffee. The
American College of Sports Medicine (2008) calculated an average cup of coffee contains
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100mg of caffeine. However, unlike anhydrous caffeine, coffees ergogenic effect is inhibited as
it doesn’t have the same effect as anhydrous caffeine when compared by dosage. One study
took four groups of middle-distance athletes (caffeine 4.45mg/kg, regular coffee of 4.45mg/kg,
decaffeinated coffee, and decaffeinated with caffeine 4.45mg/kg) and had them run at 85% of
their VO² max. The only group to improve their time to exhaustion was the caffeine group with
a nine-minute improvement from 32-minutes to 41-minutes (Graham, Hibbert, & Sathasivam,
1998). Results show that coffee doesn’t affect athletic performance, while anhydrous caffeine
does, as trials using coffee or mixed anhydrous caffeine with coffee, produced no significant
results. However, this study does not examine the effect caffeine may have on the central
nervous system, which may affect perception of effort, reaction time, etc. In 2004, the World
Anti-Doping Agency (WADA) removed caffeine from the banned substance list, meaning
athletes can use the stimulant to a certain limit. The current legal limit for caffeine is ≤5µg/ml in
urinary concentration (World Anti-Doping Agency, 2015).
This document will review all the current literature, critically analyse the available research to
understand the effects of caffeine, the mechanisms of action, the optimal dosage, its relevance
in team sports, and to discover gaps in the current research which could lead to future
research.
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3.3. Mechanisms of action
3.3.1. Increased Fat Oxidation
It was previously thought that caffeine’s main effect on the body was increased fat oxidation,
yet recent research has questioned this as caffeine has been shown to improve short-term
high-intensity exercise (Collump, Ahmaidi, Chatard, Audran, & Prefaut, 1992; Jackman,
Wendling, Friars, & Graham, 1996; Becks, et al., 2006; Wiles, Coleman, Tegerdine, & Swaine,
2006; Beaven, et al., 2008). This type of exercise along with resistance-training fails to use fat
oxidation, as the anaerobic energy system is used in these forms of training and fat oxidation
requires oxygen. In fact, some studies have shown that fat oxidation doesn’t increase with
caffeine supplementation. Raguso, Coggan, Sidossis, Gastaldelli, & Wolfe, (1996) showed a
similar stimulant, namely theophylline, did not increase or alter FFA’s and its only effect was
the stimulant increased resting levels of FFA’s. Therefore, it is more likely fat oxidation is
increased during rest and not during short-term high-intensity exercise.
3.3.2. Adenosine Receptor Antagonism
Graham (2001) believes caffeine’s primary mechanism of action is its ability to inhibit adenosine
receptors. Caffeine obstructs adenosine from binding to its receptors as they are very similar in
structure, caffeine then binds to these sites and leads to a reduction in fatigue (Graham, 2001),
furthermore O’Connor, Motl, Broglio, & Ely (2004) has proven that caffeine increases the body’s
pain threshold, as they tested a moderate dosage (5mg/kg) on quadricep pain-intensity and
found the supplemented athletes reported a dramatically lower pain-intensity compared to
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placebo (p=0.002, mean pain scores; caffeine 2.6±1.5, placebo 3.8±1.7). Additionally, Graham
(2001) states adenosine receptors are found in skeletal muscle, in the heart and brain,
adipocytes, and in smooth muscle, meaning caffeine may work in a number of these sites with
the additional possibility of interacting responses. Therefore, there is no clear way of detecting
which tissues were firstly effected and which tissue provided the enhancement in performance
when supplemented with caffeine.
3.3.3. Increased Adrenaline Production
Caffeine increases the release of adrenaline, or epinephrine, which can trigger a number of
ergogenic responses. Ratheiser, Brillon, Campbell, & Matthews (1998) explain that the
increased release of adrenaline causes an inhibition of insulin production, glycolysis, and
adenosine tri-phosphate (ATP) formation, described in their study. Increased adrenaline in the
body supplies greater amounts of energy to the working muscles, meaning a potential to work
at increased capacities and to react quicker, desirable in team sports. Adrenaline will also
increase mental alertness in the central nervous system (CNS) where caffeine seems to have a
substantial effect, as explained caffeine inhibits adenosine from binding to receptors in the
brain leading to a slower rate to fatigue and an increased level of pain threshold. Moreover,
caffeine has been shown to improve skeletal muscles motor unit recruitment (Walton, Kalmar,
& Cafarelli, 2004), research believes this takes place between the motor neurons and the motor
cortex in the CNS by use of transmission signals. With caffeine supplementation, this allows the
brain to stimulate a larger percentage of muscle to perform during exercise and leads to an
ergogenic effect.
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3.3.4. Carbohydrate-Sparing
With caffeine supplementation its thought carbohydrate-sparing decreases the rate of
glycogen-catabolism in working muscles, which in turn would allow glycogen to be spared until
the dying minutes of a game. Carbohydrate-sparing has been extensively investigated in early
studies by Ivy, et al., (1979), Erickson, et al., (1987) and Graham & Spriet (1991) which found
the athletes supplemented with caffeine showed less glycogen catabolism in muscles over the
first 15 minutes when compared to placebo. It would suggest reliance on carbohydrate for
energy is lessened and fat becomes the main energy source, although as mentioned recent
research shows increased fat-oxiation doesn’t occur. Later studies in 1998 by Chesley, et al, in
2000 by Greer, Friars, & Graham and in 2000 by Graham, Helge, & MacLean, showed muscleglycogen levels were not altered with or without caffeine supplementation, moreover all three
studies used varying intensities and differing times for comparison. Therefore, the literature
would suggest this mechanism is not what causes caffeines ergogenic effect, and there are few
reliable studies investigating this which would suggest otherwise.
3.3.5. Blood Lactate Production
Exercise naturally produces lactate, when supplemented with caffeine it is thought that lactate
levels are increased further. It has to be considered that carbohydrate-sparing reduces blood
lactate levels which should reduce the fatigue in muscles (Coyle, Coggan, Hemmert, & Ivy,
1986). As previously stated, caffeine doesn’t cause carbohydrate-sparing, as there was no
difference in the caffeine or placebo groups (Chesley, et al, 1998; Greer, Friars, & Graham,
2000; Graham, Helge, & MacLean, 2000), it is possible that carbohydrate-sparing does happen
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and that it is counteracted by the increase in blood lactate produced with caffeine
supplementation, although further research is required to confirm this. Others believe that
when blood lactate levels are increased with supplementation, that the pyruvate system is
capable of breaking down the lactate and reproduced as energy and used by the muscles again
(Anselme, Collomp, Mercier, Ahmaidi, & C, 1992). Either theory is possible, yet, both suggest
the supplementation doesn’t cause increased fatigue and so it may be a mechanism of action,
but does not seem to negatively affect performance.
3.3.6. Increased Calcium Concentration
In relaxed muscle fibres, calcium levels are usually low, as exercise begins, the muscles contact
and the calcium concentration increases. These contractions are initiated my calcium ions and it
is suspected that caffeine supplementation increases these muscle contractions which may
increase contractility of muscle fibres to produce more work (Olorunshola & Achie, 2011).
Rosser, Walsh & Hogan (2009) studied whether caffeine supplementation would increase
calcium concentration and handling, as well as fatigue development. Muscle fibres were
isolated and either subjected to caffeinated solution (7µM) or non-caffeinated solution, each of
the fibres was stimulated at different intensities over 60-minutes (0.16, 0.20, 0.25, 0.33, 0.50,
and 1.0 tetanic contractions, in two-minute intervals). The results revealed that caffeine was
not ergogenic towards increasing calcium concentration or handling (calcium concentration
ratio at fatigue, caffeinated; 1.16±0.51, non-caffeinated; 1.16±0.50), and didn’t significantly
increase fatigue development (time to fatigue, caffeinated; 566±125, non-caffeinated; 548±120
s). Rosser, Walsh & Hogan (2009) concluded that any ergogenic effect found during moderate
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or high-intensity muscular performance from caffeine supplementation are caused by
mechanisms outside the muscle fibre.
It has been proposed that an enhanced concentration of calcium within the cells maybe a
possible mechanism of caffeine, however, for this mechanism to have any substantial ergogenic
effect on performance a dose impractical for humans to consume would be necessary.
Additionally, Meyers & Cafarelli, (2005) state an increase in calcium-release is not likely to
induce fatigue during exercise of short-term high-intensity.
3.3.7. Decreased Rating of Perceived Exertion (RPE)
RPE is a scale used to measure exercise intensity level, it is measured using a person’s own
feelings of effort intensity. Borg (1998) has shown it provides an accurate estimate of heart rate
during exercise, even though it is a subjective measure.
Glaister, et al, (2008) found that caffeine decreased fastest sprint time by 1.4% (0.06 seconds)
and slightly reduced multiple sprint time overall also (caffeine: 4.53 seconds, placebo: 4.54
seconds). Although, this ergogenic effect is not replicated with RPE, as the results showed no
significant difference between supplementation (p= 0.713) or in the interaction between
supplement and time (p=0.685). However, taking into account that participants ran faster sprint
times in the first couple of sprints and still reported the same ratings as placebo, this would
indicate caffeine may allow the body to perform greater amounts of work at similar intensities
to that without caffeine. RPE in team sport hasn’t been extensively researched (Ali, O'Donnell,
& Foskett, 2015), however, Schneiker, Bishop, Dawson, & Hackett, (2006) used a prolonged test
(72-minutes; 2 x 36-minute halves) which used multiple sprint work (18 x 4 second sprints with
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active recovery) and found caffeine had the same suppressive effects on RPE as those found by
Glaister, et al, (2008), indicating its potential for use in assessing perception of effort in team
sport. Schneiker, et al, (2006) showed as exercise intensity increased during the multiple sprint
work, so did RPE, heart-rate and sprint-time, in a progressive manner. This would indicate that
RPE as a scale and measurement of perception of effort is an accurate assessment for this
activity, intermittent high-intensity exercise.
Doherty & Smith, (2005) completed a meta-analysis using twenty-one research papers which
implemented double-blind testing methods and controlled using a placebo comparison. The
results proved that caffeine supplementation during continued exercise reduced RPE by 5.6%.
This would indicate RPE is likely to be caffeines main mechanism of action and also indicates
that the CNS may primarily be affected.
To summarise, pin pointing and identifying the primary mechanism of action explaining
caffeine’s ergogenic properties is extremely difficult. The most probable rationale for this
difficulty is the likelihood of caffeine’s ergogenic effects interrelating via multiple factors,
responsive to each other. Meaning one mechanism may trigger another and another, while
some may inhibit other mechanisms also. The most likely factors responsible for the ergogenic
effects are adenosine antagonism, Graham (2001) shows adenosine antagonism works on
varying smooth muscle, which may be effected simultaneously causing interacting responses.
While RPE seems plausible also, as caffeine seems to dampen humans’ perception of effort in
the CNS which allows the body to maintain higher levels of exercise, whether this is due to an
increased pain threshold more research is required. Mechanisms such as increased adrenaline
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and motor-unit recruitment also show adequate evidence to possibly allow for ergogenic
improvements in performance.
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3.4. Dosages, Timing and Form
Caffeine is rapidly absorbed from the stomach and so only requires acute ingestion (Glaister
M. , et al., 2008), highest plasma concentrations occur approximately one hour after ingestion
(Graham, 2001). Early studies advised to ingest caffeine three-hours prior to exercise to allow
adequate time for caffeine-induced lipolysis to occur and maximal levels of free-fatty acids in
the blood (Nehlig & Debry, 1994; Weir, Noakes & Myburgh, 1987). Although, Laurent, et al.,
(2000) proved that the higher levels of FFA’s produced don’t cause any further ergogenic
effect , and so Glaister, et al., (2008) recommendation of one hour seems to be the most ideal
time to exercise after consumption to gain the most benefits, while consumption during
exercise isn’t recommended as caffeine requires a one-hour) to come to maximal concentration
in the blood.
The commonly followed dose in peer-reviewed studies is 3-9mg/kg (Graham & Spriet, 1991;
Douglas & McLellan, 2002; Stuart, et al, 2005; Schneiker, et al, 2006). Anselme,et al, (1992) and
Collump, et al, (1992) used absolute doses, administering 250mg of caffeine to each participant
compared to the previous studies which administered mg/kg. Varying administration between
studies causes a discrepancy in results, as heavier individuals receive a lower dose compared to
lighter individuals. Furthermore, when using a mix of participants including males and females
the results will show even greater variance, which Anselme, et al., (1992); Collump, et al.,
(1992) include. This is due to the fact males and females metabolise caffeine at different rates,
pregnancy and oral contraceptives decrease caffeine excretion from the body caused by steroid
content in the drug and increased steroid levels during pregnancy (Lane, Steege, Rupp, & Kuhn,
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1992). Lane, et al, (1992) also investigated whether sex steroid levels during the menstrual cycle
increased and if this effected caffeine excretion from the body, especially when hormone levels
are at their highest during the luteal phase of the cycle. They found elimination of caffeine was
slower in the luteal phase, which was related to the levels of progesterone found during this
phase, leading to a higher accumulation of caffeine although it is unlikely to cause any
significant changes in most women. Due to this complication, there has been a limited number
of studies using solely females when implementing supplementation.
The accuracy of any study using this absolute dose method can be limited and Graham (2001)
shows this variance may be anywhere up to 20%. Jenkins, Trilk, Singhal, O'Connor, & Cureton,
(2008) used cycle-ergometer testing and athletes worked at 80% VO² max and followed by a
fifteen minute VO² max cycle to exhaustion, these tests were separted by four minutes active
recovery. Compared to placebo, the caffeine group enhanced their performance by 3%, this
proved even a dose as low as 3mg/kg produces an ergogenic effect on performance. Adverse
effects have been observed when the dosage is higher than 9mg/kg including disturbed sleep,
jitteryness, nervousness, inability to focus, mental confusion, and gastrointestinal upset
(Graham & Spriet, 1995). Research recommends to sustain the ergogenic effect and limit the
negative side effects which high doses prove to cause, a moderate dosage of 3-6 mg/kg should
be administered (Graham & Spriet, 1995; Graham, et al, 2000; Schneiker, Bishop, Dawson, &
Hackett, 2006; Carr, Dawson, Schneiker, Goodman, & Lay, 2008; Sokmen, et al., 2008). Finally,
comparing acute supplementation with repeated administration, a single dose of caffeine will
elevate blood caffeine concentrations for anywhere up to eight hours (Graham, 2001), which
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leads investigators to give preference to acute supplementation as smaller repeated doses
seem to provide a similar effect.
Graham, Hibbert, & Sathasivam, (1998) proved that anhydrous caffeine produced the greatest
(p= 0.05) ergogenic effect when compared to caffeine with coffee, decaffeinated coffee, and
decaffeinated coffee with caffeine (all caffeine doses were 4.5 mg/kg). Edward, et al, (2013)
investigated the effects of caffeine gum on cycling performance, eight male cyclists completed
four testing sessions; each of 75% VO2 max for 15-minutes followed by a 7 kJ/kg time trial, gum
was given to participants at either 120-minutes, 60-minutes, or 5 minutes prior to testing.
Results showed that the only trial with significant results proving caffeinated gums ergogenic
effect is the 5-minute prior to exercise consumption. Although to gain the same benefits
athletes would have to consume three-sticks of gum (100mg each) in one-serving 5-minutes
prior to exercising, whereas, anhydrous caffeine in tablet form would allow athletes to easily
consume the correct dosage (3-6 mg/kg). Furthermore, when comparing anhydrous caffeine to
energy drinks containing caffeine it has been found Red Bull and Monster contain
approximately 0.32 mg/ml of caffeine (CaffeineInformer, 2016), an athlete would have to drink
one litre of either to consume the minimal recommended dose of 300 mg of caffeine for an
ergogenic effect to be found. This is unrealistic as that amount of liquid would cause an athlete
to urinate. Additionally, athletes would be consuming 100g of sugar which is three-times a
males recommended daily intake and four-times a females.
Varying doses of caffeine seen in the vast amount of studies is responsible for the inconclusive
results, when examining the evidence present a dosage of 3-6 mg/kg would be recommended.
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Astorino & Roberson (2010) meta-analysis confirms these recommendations as the optimal
dosage for caffeine. Finally, sample size is important when identifying whether the results are
transferable to team sports. A number of tests, (Stuart, Hopkins, Cook, & Cairns, 2005) and
(Schneiker, Bishop, Dawson, & Hackett, 2006), demonstrating positive results of caffeine
enhancing intermittent-high intensity exercise have used relatively small sample sizes, which
affects the statistical power of the study. A larger sample size is recommended to ensure the
relevance and strength of the study. Finally, caffeine in anhydrous form is recommended for
supplementation as it is conveniently consumed, the dosage is easily managed and prescribed,
it causes least disruption to exercise routine, and does not require participants to consume any
other possible nutrient which may alter caffeines ergogenic effect (i.e. carbohydrate). Using
anhydrous caffeine will ensure any ergogenic results found in research studies will be purely
down to the caffeine supplementation once proper protocols and placebo use is established.
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3.5. Caffeine in Sports
3.5.1. Caffeine in Endurance and High-Intensity Exercise
Team sports use a combination of endurance type exercise, i.e. walking, jogging, and shortterm high-intensity exercise, i.e. sprinting, and is classed as intermittent high-intensity sport.
The ergogenic effects of caffeine on endurance, as stated, is established (Costill, Dalsky, & Fink,
1978; Ivy, Costill, & Fink, 1979; Cole, et al., 1996; Graham, 1998; Graham, 2001; Cox, Desbrow,
& Montgomery, 2002; Doherty & Smith, 2005; Burke, 2008; Desbrow, et al., 2012). These
studies use 30-60 minute protocols, where fat is the main energy source. Greer, Friars &
Graham (2000) found 50%of glycogen stores remained after cycling at 80% VO2max to
exhaustion, concluding glycogen wasn’t the limiting factor. Kovacs, Stegen, & Brouns, (1998)
investigated caffeine on power output during endurance exercise, 15 males completed the
equivalent of a one-hour time-trial as quick as possible on a cycle-ergometer. Results showed a
carbohydrate-electrolyte solution didn’t effect performance (time to completion; placebo
62.5±1.3 minutes, placebo plus carbohydrate-electrolyte 61.5±1.1 minutes, power output;
placebo 292±10 W, placebo plus carbohydrate-electrolyte 295±9 W), while with 225mg and
320mg of caffeine results greatly improved (p=0.001, caffeine 225 mg; 58.9±1.0 minute and
p=0.001, caffeine 320mg 58.9±1.2 minutes). Research proves caffeine increases performance.
Short-term high-intensity also seems to be improved but evidence is inconsistent with varying
methods, training status and dosage used. Research shows vast differences with (Anselme,
Collomp, Mercier, Ahmaidi, & C, 1992; Collump, Ahmaidi, Chatard, Audran, & Prefaut, 1992;
Stuart, Hopkins, Cook, & Cairns, 2005; Becks, et al., 2006; Woolf, Bidwell, & Carlson, 2008)
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showing improvements, (Greer, Friars, & Graham, 2000; Paton, Hopkins, & Vollebregt, 2001)
showing diminishing results, and (Greer, MacLean, & Graham, 1998; Astorino, Firth, &
Rohmann, 2008; Beck, Housh, Malek, Mielke, & Hendrix, 2008) showing no effect. Performance
gains found are likely caused by increased motor unit recruitment stimulating a higher portion
of the muslce. When multiple bouts of high-intensity are performed, energy systems switch
(ATP-PC to aerobic), resulting in high-intensity-intermittent exercise.
3.5.2. Caffeine in Team Sport
Team sport comprises of a mixture of endurance and explosive-power exercise, and can
generally be explained as high-intensity-intermittent (HII) exercise. As it is widely accepted that
caffeine can greatly enhance endurance, this provides significant potential for caffeine.
However, the fact the endurance work in HII sports are separated by stages of high-intensity, it
proves difficult to replicate in gym and laboratory settings. As previously stated, caffeine is
likely to increase single bout sprint times and jump height along with a number of other
strength tests, team sports use a high-volume of each of these. Consequently, it becomes tough
to examine the effects caffeine has on athletes. Current research doesn’t seem to provide a
definite answer as to whether HII-exercise will benefit from caffeine supplementation as most
of the studies produce equivocal results. The variance in results is prompted by varying dosage,
training status, and varying testing methods. Stuart, et al., (2005) and Schneiker, et al., (2006)
studied caffeine supplementation in HII exercise, using methods that closely replicated team
sport demands lasting 72 (cycle ergometer, 2x36 minute halves, using 18x4-second sprints
separated by two-minute active recovery at 35% VO2 peak) and 80 minutes (rugby test, seven
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circuits in 2x40 minute halves; using sprint, power, and accuracy exercises) respectively. Both
studies showed 6mg/kg of caffeine 60-70 minutes before testing increased performance, and
moreover determined that caffeine supplementation produced an improvement in HII exercise
similarly to endurance exercise when also supplemented with caffeine. One limitation noticed
in the aforementioned studies is sample size which was ten. Challenging these positive studies,
Paton, et al., (2001) conveyed caffeine supplementations negative effect on repeated sprint
performance. The protocol used 10x20 metre sprints separated by ten seconds rest, although
Nicholas, Nuttall, & Williams, (2000) suggests that this testing protocol doesn’t represent HII
sport well as they contain periods of high-intensity combined with stages of walking and
jogging. In contrast, Glaister, et al., (2008) who used twenty-one active males and used a
repeated-sprint protocol, which consisted of 12x30 metre sprints separated by 35 seconds rest.
This research revealed the possible benefits caffeine supplementation has on sprint
performance in both single and multiple sprint activity. The positive effect on sprint
performance observed in this study is likely due to the testing protocol providing longer resting
time to that seen in Paton, et al., (2001) study. Another finding by Glaister, et al., (2008) shows
that both single and multiple sprint ability is improved, therefore it provides ground for more
specific testing to each individual team sport.
Although there is an abundance of information proving endurance exercise is greatly enhanced,
the amount of information regarding short-term high-intensity exercise is hugely ambiguous
with varying testing methods and likely to cause this. Many review articles give minimal focus
to HII exercise, and mainly focus on once-off explosive exercise and endurance-type exercise
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Student Number: 1428322
(Graham, 2001; Paluska, 2003; Rogers & Dinges, 2005; Doherty & Smith, 2005; Burke, 2008;
Tarnopolsky, 2008). Results have been equivocal as stated with Paton, et al, (2001) finding
negligble effects, whereas Glaister (2008) found positive effects on both once-off explosive
exercise and HII exercise. Astorino & Roberson, (2010) completed a systematic review which
identified 17 studies which showed altered team-sport performance (swimming, rugby,
football, cycling, sprinting, etc), 65% of the 17 studies displayed positive results of caffeine
supplementation increasing performance up to 10%, with mean improvements of 6.5±5.5%.
Compared to studies using laboratory settings, tests simulated by sports-specific methods
displayed increased performance when supplemented with caffeine, proving that testing
methods using laboratory settings are unrealistic, and team sport studies require specific
testing. As each sport differs in demands this is obvious to provide recommendations to various
types of athletes.
In summary, team sports seem to be affected by caffeine in a similar fashion to endurance
exercise, however, more consistent investigation is required using sport-specific testing, welltrained individuals, adequate sample size, and accurate dosing to be able to advise caffeine
supplementation to team sport athletes.
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3.6. Females and Caffeine Supplementation
To date there are very few studies which solely focus on caffeine supplementation in females
during HII exercise, in fact, to the best of the researcher’s knowledge there is only two studies
completed on this topic. Ali, O'Donnell, & Foskett, (2015) studied female athletes undertaking
HII exercise (six 15-minute blocks of treadmill running, each block contained six 2-minute
periods of 40%, 60%, 80%, 40%, 60%, 80% VO2 max followed by one-minute at 60% VO2 max
and then two-minutes at 4 km/hr walking) using a 6mg/kg dose of caffeine while in
combination using oral-contraceptive pills. They found caffeine positively affected RPE, vigor,
and rate of fatigue. This test would indicate caffeine’s potential to positively affect females’
performance, however, testing explosive power and time to exhaustion are two testing
protocols which remain untested. Fernandez-Campos, Dengo, & Moncada-Jimenez (2015)
found an energy drink did not improve physical performance measured by the grip test, vertical
jump test, and anaerobic power test. However, it would appear the energy drink used in this
study did not contain a high amount of caffeine (<2.1 mg/kg), which would have not caused an
ergogenic effect as the suggested minimal dosage of caffeine for ergogenic effect is 3mg/kg
(Astorino & Roberson, 2010). As seen guidelines relating to females are limited, while female
participation in sport is growing (Del Coso, et al, 2011) and taking into consideration the
gender-associated differences; such as differing gender muscle structure, hormone differences,
menstruation cycle in females, and the altered metabolism of caffeine reported, menstruation
cycle increases accumulation of caffeine especially during luteal phase (Lane, Steege, Rupp, &
Kuhn, 1992), investigation is necessary. Due to this differing metabolism of caffeine between
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sexes, studies using male participants cannot be used to form recommendations for females,
especially due to the fact oral contraceptives and menstruation affect caffeine’s metabolism.
The only study to take into consideration these factors is (Ali, O'Donnell, & Foskett, 2015),
however, they target only a couple of mechanisms for testing, therefore more testing in
required.
In summary, caffeine seems to have the potential to positively affect athletic performance in
females including HII exercise, however, it is important to understand that at the luteal phase
female’s reaction times may be slower and caffeine is eliminated from the body at a slower
rate, although it is still thought to have an ergogenic effect. There is extremely limited research
on females and caffeine supplementation and more research is warranted.
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3.7. Conclusion
Caffeine supplementation seems to cause a number of reactions in the body which may cause
an ergogenic effect. However, it is difficult to pinpoint one single mechanism of action, due to
the fact there is multiple factors which are plausible, and the possibility of those having
interacting effects is also likely. While one mechanism may trigger another, the opposite is also
possible that one mechanism may inhibit another. With this in mind, the research seems to
suggest that adenosine receptor antagonism, decrease in RPE, and increased motor unit
recruitment are the most probable mechanisms to produce an ergogenic effect. Following
current literature, it is advised to ingest 3-6 mg/kg of anhydrous caffeine approximately one
hour prior to exercise, as this allows the for peak-caffeine plasma concentration. Research on
intermittent high-intensity, such as soccer, proves equivocal with methodology and results
greatly differing. Furthermore, many of the studies regarding intermittent-exercise have been
completed in a laboratory which as discussed is not transferable to team sport demands.
Research shows that caffeine effects females in a similar fashion to males as comparable
ergogenic effects have been observed, however, metabolism of caffeine in females is slower
due to the menstrual cycle, but this does not seem to effect results. There are extremely limited
studies in females and caffeine consumption, and even fewer using high performing female
soccer players, therefore, due to gaps in current research it would be beneficial to investigate
the effects of caffeine supplementation in Women’s National League soccer players’
performance.
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3.8. References
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Fernandez-Campos, C., Dengo, AL., Moncada-Jimenez, J. (2015). Acute Consumption of an
Energy Drink Does Not Improve Physical Performance of Female Volleyball Players.
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Graham, T., & Spriet, L. (1991). Performance and metabolic responses to a high caffeine dose
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of coffee and caffeine ingestion. Journal of Applied Physiology, 85, 883-889.
Greer, F., Friars, D., & Graham, T. (2000). Comparison of caffeine and theophylline ingestion:
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of muscular endurance. Medicine and Science in Sport and Exercise, 35, 987-994.
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doses of caffeine on cycling performance. International Journal of Sport Nutrition and
Exercise Metabolism, 18(3), 328-342.
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caffeine excretion, and performance. Journal of Applied Physiology, 85(2), 709-715.
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Kumar, S., Mufti, M., & Kaisan, R. (2013). Variation of reaction time in different phases of
menstrual cycle. Journal of Clinical Diagnostic Research, 7(8), 1604-1605.
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in the human female. European Journal of Clinical Pharmacology, 43(5), 543-546.
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Exercise Metabolism, 14, 698-708.
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not by altering firing rates during submaximal isometric contractions. Journal of Applied
Physiology, 99, 1056-1063.
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Sports Medicine, 15(5), 215-223.
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field test that simulates the activity pattern of soccer. Journal of Sports Sciences, 18, 97104.
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reducing leg muscle pain during cycling exercise is unrelated to systolic blood pressure.
Pain, 109(3), 291-298.
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Olorunshola, K., & Achie, L. (2011). Caffeine Alters Skeletal Muscle Contraction by Opening of
Calcium Ion Channels. Current Research Journal of Bi, 3(5), 521-525.
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sprints in team sport athletes. Medicine and Science in Sport and Exercise, 33(5), 822825.
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Schneiker, K., Bishop, D., Dawson, B., & Hackett, L. (2006). Effects of caffeine on prolonged
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30
Department of Clinical Sciences and Nutrition
MSc in Exercise & Nutrition Science – Dublin
Effects of caffeine supplementation on Women’s National League soccer
players’ performance
…………J19425………
Student J Number
…………2014…………
Year of Intake
……...06/10/2016……..
Date submitted
…………4,400…….….
Word Count
1428322: Niamh Reid Burke
4. Research Project
Effects of caffeine supplementation on Women’s National League
soccer players’ performance
Niamh Reid Burke
Department of Clinical Sciences & Nutrition, University of Chester, Parkgate Road, Chester, United Kingdom
Journal article style; Medicine & Science in Sports & Exercise, rationale for choice; recognised
worldwide, proves level of research is of a high quality as it is peer-reviewed, the article would provide
nutritional help to coaches, athletes, and other researchers, add to my academic achievements, and to
receive feedback from experts and professionals in the field.
4.1.
Abstract
Purpose: To determine the effects of acute caffeine ingestion on female soccer players repeated-sprint
performance, time to exhaustion, heart-rate, and rating of perceived exertion. Additionally, to investigate if habitual
caffeine consumption effects supplementation results. Methods: Using a randomised double-blind research design,
18 females from the Women’s National League ingested two-tablets containing either caffeine (400 mg) or placebo
(lactose) 1 hour before completing an indoor multiple-sprint test (12 x 30 metre; separated by 35 seconds rest), and
a multi-stage fitness test (Yo-Yo Intermittent Recovery Test Level 2). Participants attended two-testing sessions 7days apart and consumed either placebo or caffeine on the first session, and the opposite on the second testing
session. Sprint-times were recorded using dual-beam photocells, time to exhaustion was measured in seconds and
metres covered using interval recording on paper. Heart rate was monitored continuously, while RPE was measured
after every third-sprint and every-minute during the multi-stage fitness test. Results: Sprint 3, 4, and 5 in the
multiple-sprint test showed significant results (three sprints p=0.001, sprint 3: caffeine 7.58±1.36, placebo
7.61±1.33, sprint 4: caffeine 7.54±1.35, placebo 7.60±1.31, sprint 5: caffeine 7.56±1.36, placebo 7.60±1.32), while
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1428322: Niamh Reid Burke
sprint 8 and 9 showed a tendency for faster times. Time to exhaustion was significantly improved with caffeine
(p=0.0001, caffeine 428±209 seconds, placebo 345±122 seconds), heart-rate was not significantly different between
trials as no interaction effect was found between trials (p=0.183), RPE overall wasn’t statistically different between
trials (all values were p>0.005) with sprint 12 providing the only significant different rating of perceived exertion
score (p=0.003, placebo 16.3±0.8, caffeine 15.7±0.9). Finally, habitual caffeine consumption wasn’t statistically
different between conditions (time to exhaustion p=0.92, rating of perceived exertion p>0.005, heart-rate p>0.01,
and multiple sprints p>0.004). Conclusion: Caffeine supplementation improves female soccer performance by means
of increased time to exhaustion, tendency to improve multiple-sprint performance, and doesn’t affect heart-rate.
Caffeine does not affect rating of perceived exertion, however, due to the increase in performance seen it is thought
that unchanged RPE allows the body to work at higher intensities for longer. Finally, habitual caffeine consumption
does not affect results as long as an abstention period of 48 hours is undertaken prior to matches. Take home
message: Caffeine in a 400mg dose positively effects female soccer performance and minimal health risks or
negative effects are associated with this supplementation. Caffeine produces a huge positive increase in endurance
capacity, such as time to exhaustion, while also increasing the ability to perform at higher intensities for longer,
reduced perception of effort.
4.2. Introduction
Considered the worlds most used drug, caffeine stimulates the central nervous system (CNS)
and is mainly consumed through natural sources such as tea and coffee. Graham (2001) states
caffeine imposes minimal health risks from consumption. Nowadays its believed approximately
90% of adult-Americans consume coffee daily (Andersen, Jacobs, Carlsen, & Blomoff, 2006). In
2004, caffeine was removed from the World Anti-Doping Agency’s list of prohibited substances,
allowing athletes to use the stimulant to a certain limit of ≤5µg/ml in urinary concentrations
(World Anti-Doping Agency, 2015). Its removal has allowed athletes to exploit its benefits.
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Bell & McLellan (2002) and Kalmar (2005) explain how doses of 4-6 mg/kg of caffeine, is
absorbed quickly from the stomach and reaches peak concentration in the blood after
approximately one-hour. From the mechanisms reported, recent research indicates the CNS is
most likely effected, namely adenosine receptor antagonism and increased motor-unit
recruitment, leading to masking of perception of effort, possible reduction in fatigue, and
increases in neuro-transmitter release. It’s difficult to identify exact mechanisms of action as
the possibility of intracellular action between a number of mechanisms is likely to cause effect.
Caffeines ergogenic effects on endurance is evident (Costill, Dalsky, & Fink, 1978; Ivy, Costill, &
Fink, 1979; Cole, et al., 1996; Graham T., 2001; Cox, Desbrow, & Montgomery, 2002; Doherty &
Smith, 2005; Burke, 2008; Desbrow, et al., 2012), literature on short-term high-intensity
exercise (Collump, Ahmaidi, Chatard, Audran, & Prefaut, 1992; Jackman, Wendling, Friars, &
Graham, 1996; Jacobs, Pasternak, & Bell, 2003; Becks, et al., 2006; Wiles, Coleman, Tegerdine,
& Swaine, 2006; Woolf, Bidwell, & Carlson, 2008; Astorino, Firth, & Rohmann, 2008; Beaven, et
al., 2008), shows equivocal results as some show positive, some neglible, or no effect. When
attention is turned to caffeine and intermittent exercise, the results are even more unclear.
Within review articles examining caffeine and exercise, intermittent-exercise received barely
any attention (Graham, 2001; Paluska, 2003; Rogers & Dinges, 2005; Doherty & Smith, 2005;
Burke, 2008; Tarnopolsky, 2008).
Intermittent-exercise uses a combination of endurance and speed activity, it seems likely
caffeine could benefit this type of exercise, although current literature results prove
ambiguous. Paton, et al, (2001) reports negligible effects on repeated sprinting, although
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participants were tested using a cycle-ergometer which is unfavourable considering they were
testing field team-sport athletes. Additionally, single-beam photocells were used to measure
sprint time which is prone to false triggering due to the single-beam set, whereas dual-beam
photocells are seen as the norm for testing sprint times. Finally, this study used straight-line
running which isn’t very applicable to team-sports as they use frequent and multiple changes of
direction. Similarly, Glaister, et al., (2008) and Crowe, Leicht & Spinks, (2006) failed to use a
combination of speed-strength and endurance-exercise which would seem paramount when
testing sports which are classed as intermittent and combining both components. Stuart,
Hopkins, Cook, & Cairns, (2005) and Schneiker, Bishop, Dawson, & Hackett, (2006) used longer
duration intermittent-exercise of 80 and 72-minutes, respectively, using a combination of
repeated-sprints and endurance-exercise results revealed caffeine has a similar effect on
intermittent-sport to that of endurance, although both had limited sample size (n=9 and n=10,
respectively). Of the studies completed on team-sports using relevant testing methods, virtually
no studies have been conducted on female team-sport athletes. To the best of the authors
knowledge O'Donnell, (2012), Lee, et al., (2014), and Ali, O'Donnell, & Foskett, (2015) are the
only studies completed. The aim of this study is to investigate the gap in current research by
testing high-performing female intermittent-sports players’, using a larger sample size, sportspecific testing, and reliable equipment to determine the effects of acute caffeine ingestion on
female soccer players’ performance. Additionally, to investigate if habitual-caffeine
consumption effects supplementation results.
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1428322: Niamh Reid Burke
4.3. Methods
4.3.1. Participants
Eighteen female Women’s National League player’s volunteered for the study, which was
approved by Chester University Ethics Committee (see appendices, heading 5.1). Before testing
began, participants received testing information, written and verbal instructions to outline the
research being investigated (see appendices, heading 5.2), participants provided written
consent (see appendices, heading 5.3) and required to pass health-screening (see appendices,
heading 5.4). Participants were high-performing female-soccer players competing in the
Women’s National League, the majority of participants had been playing soccer for
approximately 15 years and would be considered well-trained who actively participated in
multiple sprint and endurance work. Diet diaries were used to assess whether participants were
habitual or non-habitual-caffeine consumers and used to show that athletes consumed the
same food 48 hours before both testing sessions as requested (see appendices, heading 5.5).
4.3.2. Experimental Procedures
Participants completed two trials of the multiple-sprint test and multi-stage fitness test, the
multiple-sprint test comprised of 12x30 metre zig-zag sprints separated by 35-seconds rest.
Sprint times were recorded using dual-beam photocells (SmartSpeed, Toca Sports, Republic of
Ireland). The multi-stage fitness test (Yo-Yo Intermittent Recovery Test Level 2) consisted of 20
metre shuttles where participants ran 2x20 metre shuttles followed by a 10 second active rest
and completed the intervals in time to an audio prompt (Team Bleep Test, version 1.3.1,
Bitworks Design, United Kingdom). The testing ended when each participant could not keep up
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with the audio prompt for two consecutive shuttles. Both trials were administered double-blind
and randomised, testing on each day took place at the same time of day and the trials were
seven-days apart. Participants were informed to continue regular diet over the course of the
study, and were required to eat the same food in the 48-hour lead up to both trials to limit any
possibility of results being influenced by nutritional intake. Food intake in this 48-hour lead up
was monitored by use of diet diaries which each participant completed prior to both trials, this
also allowed the researcher to assess each participant’s daily caffeine consumption.
Participants were asked to avoid consumption of caffeine and alcohol, and also strenuous
exercise 48-hours before each trial. They were given a list of caffeinated foods and beverages
for reference to aid abstention from caffeine.
On the day of testing, participants were required to report to the facility one-hour prior to
testing and asked not to consume any food/drinks, then administered either placebo (lactose)
or 400mg of caffeine in tablet form and 200 ml of water, both tablets were identical in colour,
size, and shape. Participants then rested for 45 minutes and briefed on the testing procedures
and the rating of perceived exertion (RPE) scale (Borg scale), before a standardised warm-up
protocol was performed, approximately 10 minutes in length and included two-minutes of
jogging at a moderate pace, dynamic stretching of all muscles, and finally four sprints. The
facility used for testing was an indoor running track with synthetic running surface and the
thermometer was adjusted to 20˚C. Testing began with the multiple-sprint test, participants
initiated each sprint and began 30 cm behind dual-beam photocells (SmartSpeed, Toca Sports,
Republic of Ireland), to avoid incorrect triggering. There were two sets of dual-beam photocells
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used to record sprint times, one set at the start of the course and one at the end. The next
sprint began after 35-seconds rest and participants were instructed when this time had
elapsed. Glaister, et al., (2007) recognized this multiple-sprint running procedure as reliable and
repeatable in their research. Participants were then given ten-minutes to rest and each were
given 200 ml of water. The multi-stage fitness test then took place, participants began the test
at the start of the 20 metre shuttle, the audio tape initiated the first shuttle which participants
were required to jog to the end of the 20 metre course and wait for the audio prompt to return
to the start point. After every 40 metres an active 10 second recovery period is signalled to
participants where they must walk to a 5 metre cone and back in time to start the next shuttle.
Participants continued this pattern until failure, this occurred when participants could not
complete two-consecutive shuttles in time to the audio-tape. Their time and stage of test was
recorded, where time to exhaustion and metres covered could be compared. Krustrup, et al.,
(2003) recognized this multi-stage fitness procedure as reliable and repeatable in their
research.
Heart-rate was continuously monitored during both testing procedures by use of heart-rate
monitors (Fitbit Flex, Fitbit, San Francisco, United States). Heart-rate was recorded at various
key time points in testing, before and after multiple sprint test, and before, two-minutes into,
and after the multi-stage fitness test. RPE was recorded from each individual after every third
sprint and after every minute during the multi-stage fitness test using the Borg scale (Borg,
1998).
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4.3.3. Statistics
SPSS version 22 was used for statistical analysis of the results recorded during this study (SPSS
Inc., Chicago, Illinois). Due to RPE being ordinal data, a two-way ANOVA with repeated
measures could not be implemented and instead the data was split and two individual
Friedman tests were conducted, one to look at the effect of caffeine on RPE during the
multiple-sprint test and a second Friedman test to look at the effect of caffeine on RPE during
the multi-stage fitness test. Results were expressed as median and range, due to the nature of
the data. A two-way ANOVA with repeated measures (supplement x trial) on both factors was
conducted to assess the effects of caffeine on heart-rate. Measures of centrality and spread are
represented as means and standard deviation. Similar to RPE, data not being normally
distributed in the multiple-sprint performance data, a two-way ANOVA with repeated measures
could not be performed and instead a Friedman test was used to measure the effect of caffeine
on multiple-sprint performance. A paired t-test was used to assess the effects on time to
exhaustion by comparing results from the placebo trial to those from the caffeine trial. Results
were presented as median and range. P value was set at 0.05 and Bonferroni correction was
used for multiple comparisons in post hoc analysis. Habitual-caffeine consumption was also
investigated to assess the possibility that significant differences in performance with
supplementation was due to habitual-caffeine consumption, this was examined by conducting
multiple-independent t-tests on heart-rate as the data was normally distributed, using the
Bonferroni correction to allow for the possibility of a statistical error occurring. Results were
displayed using mean and standard deviation, unless stated otherwise. While multiple-sprint
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performance, time to exhaustion, and RPE was analysed using multiple Mann-Whitney U tests
due to data either of ordinal level or normal distribution being violated, the Bonferroni
correction was used in a similar way, and data was displayed as median and range, unless
stated otherwise. Of the 18 participants, six were believed to have high daily caffeine
consumption, where they consumed over 300mg per day. To compare these to low caffeine
consumers, five of the remaining 12 participants were randomly selected as comparison.
4.4. Results
4.4.1. Multiple-Sprint Performance
Figure 1, below, shows the effects of caffeine supplementation on multiple-sprint performance,
while Table 1 shows the effects on collective performance measures. When compared to
placebo, caffeine supplementation caused a 0.08 reduction in fastest sprint time, a decrease of
1.1%. The Friedman test showed there was a statistically significant difference overall in
repeated sprint times (p=0.001). Post hoc analysis with Wilcoxon signed-rank tests was
conducted with a Bonferroni correction applied, resulting in a significance level set at p<0.004.
Results are shown in median and range, unless stated otherwise. Results showed only sprint 3,
4, and 5 (all three p values were 0.001, sprint 3: caffeine 7.58±1.36 and placebo 7.61±1.33,
sprint 4: caffeine 7.54±1.35 and placebo 7.60±1.31, sprint 5: caffeine 7.56±1.36 and placebo
7.60±1.32) were significantly different when compared to placebo, while the rest of the 12
sprints did not show any significant differences. Although, the remaining sprints did not show
any significant difference (p>0.004) sprint 8 and 9 also produced faster times (both sprints
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p<0.05, sprint 8: caffeine 7.58±1.35 and placebo 7.60±1.3, sprint 9: caffeine 7.59±1.28 and
placebo 7.60±1.31). This shows caffeine has a tendency to decrease multiple-sprint times.
7.62
7.6
Time (s)
7.58
7.56
7.54
7.52
7.5
1
2
3
4
5
6
7
8
9
10
11
12
Sprint Number
Placebo
Caffeine
Figure 1: Caffeine on multiple sprint performance, values are shown as medians
Table 1: Caffeine on collective performance measures, values are shown in means
Fastest Sprint Time (s)
Mean Sprint Time (s)
Placebo
Caffeine
Placebo
Caffeine
7.30
7.22*
7.78
7.76
*Significantly different from placebo (P<0.05)
4.4.2. Time to Exhaustion
The intermittent high-intensity exercise was measured using time to exhaustion during a multistage fitness test. Data are represented as medians unless otherwise stated. Of the 18 females
recruited, caffeine supplementation caused an increase in time to exhaustion in 17 participants
compared to placebo, only the first participant did not run as long with caffeine which can be
seen in figure 2. The data was symmetrically distributed, as assessed by a histogram and
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confirmed by the Shapiro-Wilk’s test as p=0.038 and 0.011. Results are presented as median
and range, unless stated otherwise. A Wilcoxon signed-rank test determined that there was a
statistically significant median increase in time to exhaustion (83 seconds/1 minute 23 seconds)
when subjects ingested caffeine (428±209 seconds) compared to placebo (345±122 seconds),
p<0.0001. The results were significantly different, from this we can reject the null hypothesis
and accept the alternative, caffeine supplementation increased time to exhaustion.
Time to Exhaustion (sec)
600
500
400
300
200
100
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Participant
Placebo
Caffeine
Figure 2: Caffeine on time to exhaustion, values are shown as medians
4.4.3. Heart-Rate
The results of a two-way ANOVA revealed that there was no significant two-way interaction
between supplementation and trial (p=0.183), figure 3. The effect of the placebo-trial on heartrate is not statistically different to the effect of caffeine on heart-rate. However, there was a
significant difference in main effect of treatment for both condition and trial separately
(p=0.001, p=0.001). The main effect showed that mean heart-rate was significantly different
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between trials, this is expected as there was two separate tests conducted and heart-rate
increases with exercise.
Figure 3: Interaction Effect of supplementation and trial, values shown in means and standard deviation
4.4.4. Rating of Perceived Exertion (RPE)
The Friedman test displayed a significant difference (p<0.001) in RPE between placebo and
caffeine in both multiple-sprinting and time to exhaustion. This displayed a progressive increase
in RPE over each trial due to an increase in intensity, as seen in table 2. Post hoc analysis with
Wilcoxon signed-rank test was conducted with a Bonferroni correction applied, resulting in a
significance level set at p<0.005. Results are displayed as mean ± standard deviation, unless
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stated otherwise, although data is ordinal SPSS only provided descriptives in mean and
standard deviation. Sprint number 3, 6 and 9 showed no significant differences between
placebo and caffeine (p>0.005, sprint 3: placebo 9.3±0.84 and caffeine 9.4±0.7, sprint 6:
placebo 11.4±1 and caffeine 11.8±0.7 sprint 9: placebo 14.2±1.2 and caffeine 14.2±1), while
sprint 12 showed a significant difference (p=0.003, p=0.003, placebo 16.3±0.8, caffeine 15.7±0.9).
RPE during the time to exhaustion trial showed no significant differences from start to finish, as
all p values were >0.005, the significant difference found initially was due to the progressive
increase in intensity during the multiple-sprint test and multi-stage fitness test. Therefore,
caffeine did not alter RPE in soccer performance testing.
Table 2: Rating of perceived exertion over both trails, values shown are medians
Multiple Sprint Test
Multi-stage Fitness Test
Sprint
Placebo
Caffeine
Minute
Placebo
Caffeine
3
9.3
9.4
1
8
8
6
11.4
11.8
2
10
10
9
14.2
14.2
3
12
12
12
16.3
15.8
4
14
14
5
17
17
6
16
16
4.4.5. Habitual-Caffeine Consumption
The independent t-test used to test for differences in heart-rate between high-caffeine and
low-caffeine consumers, and the Mann-Whitney U test used to test for differences in repeated
sprint performance, time to exhaustion, and RPE between the two groups. There were no
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significant differences found in caffeine supplementation results in time to exhaustion (p=0.92),
RPE (p>0.005), or heart-rate (p>0.01). There was also no significant difference when comparing
repeated sprints (p>0.004), although, three quarters of the twelve sprints showed a significant
difference (p<0.05) before the Bonferroni correction.
Therefore, habitual-caffeine consumers do not seem to have become tolerant of caffeine and
display similar results to those of low consumers.
4.5. Discussion
This research delivers a more concise understanding of caffeine’s effects in team-sport, and
shows the performance responses produced by female-soccer players using caffeine as a
supplement compared to current research. The research addressed gaps in current literature
including; limited research on intermittent high-intensity exercise and in particular team-sports,
limited research conducted on high-performing females, addressed the methodological issues
of research which have displayed caffeine’s positive effects in team-sports by using a larger
sample size and more specific-testing.
4.5.1. Multiple-Sprint Performance
Analysis of multiple-sprint performance revealed fastest sprint-time was reduced by 1.1% (0.08
seconds, p<0.05), similar to that found by Glaister, et al, (2008), who reported a decrease of
1.4% (0.06 seconds). Caffeine supplementation effected overall speed and its possible this may
have occurred from quicker reaction times which would be triggered by the CNS. The CNS
responses have already been identified as a primary mechanism of action, so reaction time may
well have caused this increase in performance, especially when the testing protocol is taken
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into account. Participants performed a 30 metre zig-zag sprint, including a number of changes
in direction testing their reaction time, rather than straight-line sprint as this was to replicate
match demands. Jacobson & Edgley (1987), Liebermann, Tharion, Shukitt-Hale, Speckmann, &
Tulley (2002), and, Ali, O'Donnell, & Foskett (2015) found caffeine decreased reaction times
significantly. These results of overall faster speeds, with the possibility of the results being
caused by enhanced reaction times, will benefit athletes’ performance, as even the most
marginal of gains can prove beneficial especially at elite and high performance level. Caffeine
didn’t significantly affect multiple-sprint performance overall, with the Bonferroni correction
giving an adjusted P value of 0.004, only sprint three, four, and five showed caffeine
supplementation caused significantly lower scores (p=0.001). However, it seems that caffeine
does have a tendency to positively affect multiple-sprint performance as sprint two, eight, and
nine would have had significant results (p<0.05) had the Bonferroni correction not been used.
This would have led to 50% of the multiple-sprints resulting in significant results. A number of
other studies (Schneiker, Bishop, Dawson, & Hackett, 2006; Stuart, Hopkins, Cook, & Cairns,
2005; Glaister M. , et al., 2008) have found caffeine positively affects multiple-sprint
performance, therefore, it is possible but further research is required to confirm this.
Additionally, an important result to note is that caffeine didn’t cause any negative affects
during the multiple-sprint test as results with caffeine supplementation compared to placebo
didn’t display any decrease in performance. This is important to note as (Paton, Hopkins, &
Vollebregt, 2001) found that even a 0.8% impairment or decrease in sprint speed can prove
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detrimental to player performance, as this decrease in speed is linked with loss of possession
when two opposing players are sprinting for the ball.
4.5.2. Time to Exhaustion
Caffeine supplementation significantly increased time to exhaustion (p=0.0001), post hoc
analysis displayed a huge increase in performance with caffeine supplementation giving
participants a 24% increase in time to exhaustion. Compared with placebo caffeine allowed
participants to continue performance 83 seconds longer, which in the Yo-Yo intermittent test is
a significant difference with the average participant covering 650 metres with placebo, which
compared to the norms for this test (see appendices, heading 5.6) is seen as good and above
average, whereas the average participant covered 720 metres with caffeine and this compared
to the norms is rated as an excellent score, with four athletes verging on elite. Although 83
seconds or 70 metres does not seem a huge difference when compared to a soccer match
which last approximately 90 minutes, the results of the Yo-Yo intermittent shuttle test can be
used to assess VO2max. Bangsbo, et al, (2008) published a formula for estimating VO2max from
this test: VO2max (mL/min/kg) = Yo-Yo Intermittent Recovery test result (metres) x 0.0136 +
45.3. Therefore, the average participant with placebo had a VO2max of 54.1, while the average
participant with caffeine had a VO2max of 55.1. Bangsbo, et al, (2008) concluded that the Yo-Yo
intermittent recovery test is valid test to understand athlete’s ability to perform repeated
intense exercise and to monitor improvements or declines in performance. Haugen, Tonnessen,
Hem, Leirstein, & Seiler (2014) found VO2max of 55 mL/kg/min or greater is necessary to
perform at international level in soccer, Haugen, et al, (2014) completed a study on 199 female
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soccer players in Norway with data from players between the years of 1989 and 2007, after
2007 the protocols for measuring VO2max in players changed and therefore comparison was
not possible. The study used international players from Norway and were classed as players
who had played in the Olympic games, World Cup, European finals, qualification games, and/or
training games. Since Norway have been an extremely successful nation in women’s soccer
winning gold and bronze at the Olympic games, gold in the World Cup, and gold and silver in
the European Championships, therefore the data would provide a decent comparison.
Compared to this data, the participants with caffeine supplementation averagely achieved 55.1
mL/kg/min, which suggests with caffeine supplementation that Women’s National League
players’ can compete at a high performance level. By increasing players’ VO2max and time to
exhaustion it benefits their overall performance as players’ require less time to recover, can
cover more ground, and become more efficient in their use of energy. A number of studies
(Bangsbo & Lindsquist, 1992; Castagna & D'Ottavio, 2001; Bangsbo, 1994) have found a
relationship between distance covered and VO2max in team sports.
4.5.3. Heart-Rate
There was no significant difference (p=0.183) found in heart-rate with caffeine
supplementation, this can be seen as a positive finding due to the fact a higher heart-rate leads
to increased energy expenditure due to its thermic effect. The body creates heat when
exercising and sweat rate increases to regulate this increase in temperature, this uses energy
and if a significant difference in heart-rate with caffeine supplementation had been found it
would indicate a higher rate of heat production and sweat regulation causing a higher energy
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expenditure. This is similar to Glaister, et al, (2008) who found a main effect in heart-rate
between caffeine and placebo trials (p=0.009), however, both trials were not significantly
different compared to baseline. Additionally, there were no significant difference in peak heartrate in any of the trials (p=0.064). Glaister (2016) also found that in endurance trained-men
caffeine actually decreased heart-rate but that this effect dissipated as intensity increased.
Furthermore, higher heart-rate can cause discomfort to athletes when the heart races or beats
more frequently. Therefore, it is an advantage that caffeine supplementation does not
significantly alter heart-rate while exercising.
4.5.4. Rating of Perceived Exertion
There was no significant difference in RPE during the sprint test or multi-stage fitness test
(p>0.005) overall. Although, sprint 12 showed a significant difference meaning at the end of the
multiple-sprint test participants rated their exertion lower than in the placebo trial. This may
prove that caffeine allows the body to work at higher intensities for longer, and taking into
consideration the substantial increase found in time to exhaustion (p=0.0001) and the
possibility of caffeine effecting multiple-sprint performance, with more research, it would
indicate RPE is affected. A possible explanation is the effect on the CNS, caffeine may dampen
pain-receptors which would affect the length of time the muscles can work under heavy strain.
O’Connor, Motl, Broglio, & Ely (2004) confirmed this, they found caffeine supplementation
significantly decreased pain-intensity (p=0.002) in participants completing leg-extension
exercise. Additionally, the effect on RPE found confirms the theory that caffeine inhibits
adenosine from binding with its receptors and resulting in delayed fatigue production. In
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conclusion, as RPE was similar in both trials and allows the body to perform a greater amount of
work with caffeine supplementation, this will benefit soccer performance by increasing the
distance covered while preserving energy meaning the player can last longer and under less
stress.
4.5.5. Habitual-Caffeine Consumption
Caffeine supplementation results didn’t significantly change with habitual-consumption in time
to exhaustion (p=0.92), RPE (p>0.005), heart-rate (p>0.01), or multiple-sprint performance
(p>0.004). There was no apparent tolerance formed when caffeine was regularly consumed.
High habitual-caffeine consumption is classed as having an intake >200mg/day (Fredholm,
Battig, Holmen, Nehlig, & Zvartau, 1999), six-participants were high habitual-caffeine
consumers and were compared to six other participants randomly. Similar research by Jordan,
Farley & Caputo, (2012) tested caffeine supplementation on repeated sprint performance in
habitual and naïve consumers, they found no significant differences in sprint times (p=0.33). It’s
possible that the abstention period of 48-hours prior to testing was enough time to reduce the
tolerance to caffeine which may have affected the results, as this abstention period was also
used in both previously mentioned studies (Glaister, et al, 2008; Jordan, Farley, & Caputo,
2012). Van Soeren & Graham, (1998) proved that cessation of caffeine can reduce tolerance
levels back to initial levels similar to naïve consumers. These findings will benefit athletes as
they can manipulate their caffeine consumption in match preparation to ensure the maximam
benefits of caffeine can be achieved.
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4.6. Conclusion
Overall results show multiple-sprint performance (although not statistically significant) has a
tendency towards improved performance. Only three of twelve sprints were significantly faster,
the majority of sprints tended to be quicker compared to placebo. Additionally, fastest sprinttime was significantly quicker and it is thought to be due to improved reactions. Further
research is required to confirm both of the above statements. An important finding regarding
multiple-sprints is; there was no detrimental effect in performance with caffeine. Regarding
time to exhaustion, there was a major increase in performance observed with a 24% increase
with caffeine supplementation. This correlates to higher VO2max results and further distance
covered in soccer. Heart-rate, RPE, and habitual-caffeine consumption showed no significant
affect between placebo and caffeine, which is seen as a benefit to soccer performance. Heartrate remained similar throughout testing, concluding no unnecessary energy expenditure or
discomfort to players. While RPE remained unchanged overall, meaning with caffeine the body
has the ability to buffer pain-receptors and to perform higher intensities of work for longer.
Finally, habitual-caffeine consumption does not seem to effect caffeine’s ergogenic affects, or
more likely the protocol used which had a 48-hr abstention period prior to testing provided
enough time for tolerance levels to dissipate to regular sensitivity levels. Therefore, the
hypothesis that supplementation will reduce sprint-times, and increase time to exhaustion can
be accepted, while the hypothesis that supplementation will increase heart-rate, decrease RPE,
and that high-habitual consumers will be less sensitive to the supplementation can be rejected.
It can therefore be confirmed that caffeine supplementation is recommended to female soccer
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players’ in acute dosage of 400 mg/kg one hour prior to matches. Finally, it is important to note
the limitations of the present study for future research purposes, any future research would
benefit from a larger sample size for statistical power, the supplement being administered per
mg/kg as opposed to an absolute dosage. However, due to the availability and resources in
purchasing the caffeine in this study an absolute dose was more convenient. Finally, this study
shows the possible advantages caffeine has on female soccer performance, however, more
replicable match-testing would provide even greater results, an example of such a test is the
Loughborough Intermittent Shuttle test, which was initially proposed for this research, again,
limited resources forced testing to be reconsidered.
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Krustrup, P., Mohr, M., Ammstrup, T., Rysgaard, T., Johansen, J., Steensberg, A., . . . Bangsbo, J.
(2003). The Yo-Yo intermittent recovery test: Physiological responses, Reliability and
Validity. Medicine and Science in Sport and Exercise, 35(4), 697-705.
Lee, C., Cheng, C., Astorino, T., Lee, C., Huang, H., & Chang, W. (2014). Effects of carbohydrate
combined with caffeine on repeated sprint cycling and agility performance in female
athletes. Journal of the International Society of Sports Nutrition, 11(17), 1-12.
Liebermann, H., Tharion, W., Shukitt-Hale, B., Speckmann, K., & Tulley, R. (2002). Effects of
caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy
SEAL training. Sea-Air-Land. Psychopharmacology, 164(3), 250-261.
O'Connor, P., Motl, R., Broglio, S., & Ely, M. (2004). Dose-dependent effect of caffeine on
reducing leg muscle pain during cycling exercise is unrelated to systolic blood pressure.
Pain, 109(3), 291-298.
O'Donnell, J. (2012). Effect of caffeine supplementation on metabolism and physical and
cognitive function in female intermittent games players. Unpublished, N/A.
Paluska, S. (2003). Caffeine and exercise. Current Sports Medicine Reports, 2, 213-219.
Paton, C., Hopkins, W., & Vollebregt, L. (2001). Little effect of caffeine ingestion on repeated
sprints in team sport athletes. Medicine and Science in Sport and Exercise, 33(5), 822825.
Rivers, W., & Webber, H. (1907). The action of caffeine on the capacity for muscular work.
Journal of Physiology, 36, 33-47.
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Rogers, N., & Dinges, D. (2005). Caffeine: Implications for Alertness in Athletes. Clinical Sports
Medicine, 24, e1-13.
Schneiker, K., Bishop, D., Dawson, B., & Hackett, L. (2006). Effects of caffeine on prolonged
intermittent-sprint ability in team-sport athletes. Medicine and Science in Sport and
Exercise, 38, 578-585.
Stuart, G., Hopkins, W., Cook, C., & Cairns, S. (2005). Multiple effects of caffeine on simulated
high-intensity team sport performance. Medicine & Science in Sport & Exercise, 37(11),
1998-2005.
Tarnopolsky, M. (2008). Effects of caffeine on the neuromuscular system- Potential as an
ergogenic aid. Applied Physiology and Nutrition Metabolism, 33, 1284-1289.
Van Soeren, M., & Graham, T. (1998). Effects of caffeine on etabolism, exercise endurance, and
catecholamine responses after withdrawal. Journal of Applied Physiology, 58, 14931501.
Wiles, J., Coleman, D., Tegerdine, M., & Swaine, I. (2006). The effects of caffeine ingestion on
performance time, speed, and power during a laboratory-based 1km cycling time trial.
Journal of Sports Science, 2006, 1165-1171.
Woolf, K., Bidwell, W., & Carlson, A. (2008). The effect of caffeine as an ergogenic aid in
anaerobic exercise. International Journal of Sport Nutrition and Exercise Metabolism, 18,
412-429.
World Anti-Doping Agency. (2015). 2015 List of Banned Substances and Methods. Retrieved
from World Anti-Doping Agency: http://list.wada-ama.org/list/s6-stimulants/#caffeine
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5. Appendices
5.1.
Ethical Approval
Faculty of Medicine, Dentistry and Clinical Sciences
Research Ethics Committee
[email protected]
Niamh Burke
Portersgate Court
Dublin
Dear Niamh
Study title:
FREC reference:
Version number:
Effects of caffeine supplementation on women’s national league soccer
players’ performance.
1159/16/NRB/CSN
1
Thank you for sending your application to the Faculty of Medicine, Dentistry and Clinical Sciences Research
Ethics Committee for review.
I am pleased to confirm ethical approval for the above research, provided that you comply with the
conditions set out in the attached document, and adhere to the processes described in your application
form and supporting documentation. However, the Committee would like to make the following
recommendations: 
Whilst your justification for a food diary is acceptable there is no reference to completing a food
diary in the PIS or ensuring the same meal will be consumed prior to each testing session. This
should be recast within the PIS.
Please forward an electronic copy of your amendments to [email protected]
The final list of documents reviewed and approved by the Committee is as follows:
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Document
Application Form
Appendix 1 – List of References
Appendix 2 – Summary CV for Lead Researcher
Appendix 8 – Risk Assessment
Appendix 4 – Participant Information Sheet [PIS]
Appendix 3 – Letter(s) of invitation to participants
Appendix 5 - Consent Form
Appendix 7 – Timeline
Appendix 6 – Written permission(s) from relevant personnel (eg.
to use faculties)
Appendix 13 – Project Flow Chart
Appendix 14 – Multi stage fitness test protocol
Appendix 9 – Non-validated questionnaire(s)
Appendix 12 – Gpower calculation
Appendix 11 – Measurement protocols
Appendix 10 – Health screening document
Appendix 15 – Loughborough Intermittent Shuffle test protocol
Response to FREC request for further information or clarification
Version
1
1
1
1
1
1
1
1
1
Date
March
March
March
March
March
March
March
March
March
1
1
1
1
1
1
1
March
March
March
March
March
March
March
1
Please note that this approval is given in accordance with the requirements of English law only. For
research taking place wholly or partly within other jurisdictions (including Wales, Scotland and Northern
Ireland), you should seek further advice from the Committee Chair / Secretary or the Research and
Knowledge Transfer Office and may need additional approval from the appropriate agencies in the
country (or countries) in which the research will take place.
With the Committee’s best wishes for the success of this project.
Yours sincerely,
Professor Ben Green
Chair, Faculty Research Ethics Committee
Enclosures:
Standard conditions of approval.
Cc. Supervisor/FREC Representative
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5.2.
Participant Information Sheet
Effects of Caffeine supplementation on Women’s National League Soccer Players'
Performance
You are being invited to take part in a research study. Before you decide, it is important
for you to understand why the research is being done and what it will involve. Please
take time to read the following information carefully and discuss it with others if you
wish. Ask the lead researcher if there is anything that is not clear or if you would like
more information. Take time to decide whether or not you wish to take part.
Thank you for reading this.
What is the purpose of the study?
The aim of the study is to determine the effects of caffeine supplementation on female
soccer players’ athletic performance. The study will be testing repeated sprint
performance, time to exhaustion, heart rate, and perceived exertion. Additonally, the
study will also investigate if regular caffeine consumption affects supplementation results.
Why have I been chosen?
You have been chosen because you are a Women’s National League player and are over
the age of 18.
Do I have to take part?
It is up to you to decide whether or not to take part. If you decide to take part, you will be
given this information sheet to keep and be asked to sign a consent form. If you decide
to take part, you are still free to withdraw at any time and without giving a reason. A
decision to withdraw at any time, or a decision not to take part, will not effect of you in any
way.
What will happen to me if I take part?
If you decide to take part, you will be given this information sheet to keep and asked to
sign the consent form. This will give your consent for a researcher from the University
of Chester to contact you to invite you to attend testing sessions. You will be asked to
keep a food diary in the 48 hours leading up to testing on day 1. The lead investigator
will then ask you to replicate this diet in the 48 hours in the lead up to testing day 2. This
is to ensure the utmost accuracy of the assessment. On both testing sessions, on arrival
you will be given a supplement to take, it will either be a caffeine tablet or a control
glucose tablet. It is important you abstain from alcohol and caffeine for two days prior to
testing, and to abstain from heavy exercise 24 hours prior to testing. After consumption,
you will be given 45 minutes to relax before a warm-up takes place, the researcher will
ask for you not to consume any food or sugary drinks during this time frame. This is to
ensure the study is reliable. A 15-minute warm-up will be performed immediately before
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the test begins. The test will then commence. Each participant will perform 12x30 metre
sprints of a zig zag course. There will be 35 seconds rest in between sprints. Following
this, the multi-stage fitness test will commence. You will start at one point, when the
audio recording instructs them to begin they run towards the second point. The speed
increases after one minute and the beeps will start to become more frequent requiring
you to make it to the 20m line quicker. If you do not make the line in time for the beep
you will be issued a warning but can continue to run, you have two more beeps to make
up the ground. The test is terminated if you fail to reach the line after the warning is
issued and the two catch-up beeps have passed. After the test you are free to leave.
No-one will be identifiable in the final report and day two and three testing sessions will
take approximately 1.5 hours.
What are the possible disadvantages and risks of taking part?
Most people do not react to caffeine in any adverse way, some individuals may feel a
slight increase in heart rate and feel more alert. However, the dosage specified has been
used in similar studies and has not been known to cause any negative effect and health
screening will be performed prior to participation.
What are the possible benefits of taking part?
As a participant it is possible you may see the benefit of using caffeine in your pre-match
and training preparations. By taking part, you will be contributing to women sport by
offering solid evidence on nutritional supplements for females. This will better inform
governing bodies, parents, athletes and all others with interest in the subject.
What if something goes wrong?
If you wish to complain or have any concerns about any aspect of the way you have been
approached or treated during the course of this study, please contact: Dean of the Faculty
of Medicine, Dentistry and Clinical Sciences, University of Chester, Parkgate Road,
Chester, CH1 4BJ, 0044 1244 513055.
Will my taking part in the study be kept confidential?
All information which is collected about you during the course of the research will be kept
strictly confidential so that only the researcher carrying out the research will have access
to such information. Participants should note that data from this project may be retained
and published in an anonymised form. By agreeing to this project, you are consenting to
the retention and publication of data.
What will happen to the results of the research study?
The results will be written up into a report for submission to the University of Chester as
a thesis. It is hoped that the findings may be used to improve the level of literature
available of the subject. Individuals who participate will not be identified in any subsequent
report or publication.
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Who is organising and funding the research?
The research is funded by the lead researcher and by the University of Chester.
Who may I contact for further information?
If you would like more information about the research before you decide whether or not
you would be willing to take part, please contact:
Niamh Reid Burke
Email: [email protected]
Thank you for your interest in this research.
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5.3.
Consent Form
Title of Project: Effects of Caffeine supplementation on Women’s National League
Soccer Players Performance
Name of Researcher: Niamh Reid Burke
Please initial box
1. I confirm that I have read and understand the information sheet
for the above study and have had the opportunity to ask questions.
2. I understand that my participation is voluntary and that I am free to
withdraw at any time, without giving any reason and without my
legal rights being affected.
3. I agree to take part in the above study.
___________________
Name of Participant
_________________
Date
_____________
Signature
Researcher
Date
Signature
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5.4.
Health Screening
Pre-test Health Questionnaire
Effects of Caffeine supplementation on Women’s National League Soccer Players
Performance
Researcher: Niamh Reid Burke
Name: _________________________________ Test date: ________________
Contact number: ____________________________ Date of birth: ___________
In order to ensure that this study is as safe and accurate as possible, it is important that
each potential participant is screened for any factors that may influence the study. Please
circle your answer to the following questions:
1. Has your doctor ever said that you have a heart condition and that you should
only perform physical activity recommended by a doctor?
YES/NO
2.
Do you feel pain in the chest when you perform physical activity?
YES/NO
3. In the past month, have you had chest pain when you were not performing
physical activity?
YES/NO
4. Do you lose your balance because of dizziness or do you ever lose
consciousness?
YES/NO
5. Do you have bone or joint problems (e.g. back, knee or hip) that could be
made worse by a change in your physical activity?
YES/NO
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6. Is your doctor currently prescribing drugs for your blood pressure or heart
condition?
YES/NO
7. Are you pregnant, or have you been pregnant in the last six months?
8. Have you injured your hip, knee or ankle joint in the last six months?
YES/NO
YES/NO
9. Do you know of any other reason why you should not participate in physical
activity?
YES/NO
10. Has a doctor ever told you to avoid consuming caffeine consumption?
11. Do you smoke?
12. Do you have diabetes?
13. Do you take oral contraceptive tablets?
YES/NO
YES/NO
YES/NO
YES/NO
Thank you for taking your time to fill in this form. If you have answered ‘yes’ to any of
the above questions, unfortunately you will not be able to participate in this study.
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5.5.
Diet Questionnaire
Pre-test Diet Questionnaire
Effects of Caffeine supplementation on Women’s National League Soccer Players
Performance
Researcher: Niamh Reid Burke
Name: _________________________________ Test date: ________________
Contact number: ____________________________ Date of birth: ___________
Please circle your answer to the following questions:
1. Would you consider your diet to be high in caffeine, i.e. drink more than two cups
of coffee, or three cups of tea, or caffeinated soft drink?
YES/NO
2. Do you eat or drink the following; chocolate, coffee, tea, cola,
YES/NO
energy drinks?
3. If yes, please explain how much of each you would approximately consume in a
week?
4. Do you take any nutritional supplements?
YES/NO
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5. If yes, which ones?
Finally, please fill out the diet diary on the following page. It isn’t long and only requires
two days of your diet. Please don’t change your diet for this diary and be completely
honest. The diary is not being judged and will only be seen by the lead researcher. The
purpose of the study is to allow the researcher to ask each participant to eat the same
meal prior to testing day two.
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Below is a diet form as mentioned previously, down the left column is the meal which is
being consumed. Anything additional to breakfast, lunch and dinner consumed can be
placed in the snack section. When entering the food item write it under the column of
day and state how much was consumed, the food does not need to be weighed and a
rough estimation will suffice. Please see an example on the next page, and a blank
entry sheet will be on the following page.
Breakfast
Lunch
Dinner
Snacks
Drinks
Day 1
2 Weetabix, 200 ml slim
milk
1 slice wholemeal toast,
teaspoon of butter and
teaspoon of jam
1 sesame bagel with 2
slices of ham, quarter
avocado, 1 slice of cheddar
cheese, handful of lettuce
and tablespoon of mayo
Spaghetti
bolognaise
(approx. 75g of pasta, cup
full of mince, half a jar of
Dolmio tomato sauce, 1
carrot, 1 onion)
1 packet of chocolate
buttons
1 apple
1 banana
2 rice cakes with 2
tablespoons of peanut
butter
200 ml of orange juice
1
cup
of
coffee
(cappuccino)
250 ml apple juice
500 ml water
Day 2
40g of porridge, 1 cup of
slim milk, tablespoon of
honey,
handful
of
blueberries
200g of pasta salad
(approx. 75g of pasta, 1
tablespoon of pesto, 1
chicken breast sliced, half
red pepper, sweetcorn)
Baked
salmon
fillet,
steamed
broccoli
and
asparagus, half a large
sweet potato roasted
Chocolate nutri-grain bar
Handful of strawberries
2 tablespoons of hummus
and 1 large white pitta
bread
200 ml of orange juice
500 ml water
500 ml Lucozade sport
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Day 1
Day 2
Breakfast
Lunch
Dinner
Snacks
Drinks
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5.6.
Yo-Yo Intermittent Recovery Test Level 2 Norms
Table 3: Norms for Yo-Yo Intermittent Test
Rating
Elite
Excellent
Good
Average
Below average
Very poor
Males
meters
> 1280
1000 - 1280
720 - 1000
480 - 720
280 - 480
< 280
level
> 16.5
15.6 - 16.5
14.7 - 15.6
14.1 - 14.7
12.3 - 14.1
< 12.3
Females
meters
> 800
720 - 800
480 - 720
360 - 480
160 - 360
< 160
level
> 15.1
14.7 - 15.1
14.1 - 14.7
13.2 - 14.1
11.2 - 13.2
< 11.2
71