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2015-12-09
The Interactive Effects of Beta-Alanine and
Resistance Training on Muscular Endurance in
Older Adults
Christopher H. Bailey
University of Miami, [email protected]
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UNIVERSITY OF MIAMI
THE INTERACTIVE EFFECTS OF BETA-ALANINE SUPPLEMENTATION AND
RESISTANCE TRAINING ON MUSCULAR ENDURANCE IN OLDER ADULTS
By
Christopher Hayes Bailey
A DISSERTATION
Submitted to the Faculty
of the University of Miami
in partial fulfillment of the requirements for
the degree of Doctor of Philosophy
Coral Gables, Florida
December 2015
©2015
Christopher Hayes Bailey
All Rights Reserved
UNIVERSITY OF MIAMI
A dissertation submitted in partial fulfillment of
the requirements for the degree of
Doctor of Philosophy
THE INTERACTIVE EFFECTS OF BETA-ALANINE
SUPPLEMENTATION AND RESISTANCE TRAINING ON
MUSCULAR ENDURANCE IN OLDER ADULTS
Christopher Hayes Bailey
Approved:
________________
Joseph F. Signorile, Ph.D.
Professor of Kinesiology and Sport Sciences
_________________
Arlette Perry, Ph.D.
Professor of Kinesiology and
Sport Sciences
________________
Kevin Jacobs, Ph.D.
Associate Professor of Kinesiology
and Sport Sciences
_________________
Dean of the Graduate School
________________
Nicholas Myers, Ph.D.
Associate Professor of Educational and Psychological Studies
BAILEY, CHRISTOPHER HAYES
(Ph.D., Exercise Physiology)
The Interactive Effects of Beta-Alanine Supplementation
(December 2015)
and Resistance Training on Muscular Endurance in Older
Adults
Abstract of a dissertation at the University of Miami.
Dissertation supervised by Professor Joseph F. Signorile.
No. of pages in text. (50)
Muscular endurance is a major neuromuscular factor affecting independence and fall
probability in older persons. PURPOSE: To determine the effects of sustained-release
beta-alanine supplementation alone or in combination with a resistance training program
on muscular and daily activity-based performances in older adults. METHODS:
Twenty-seven subjects, 60-82 years of age, were randomly assigned to one of four groups
for a 12-week intervention: 3.2g/day placebo without resistance training, 3.2g/day betaalanine without resistance training, 3.2g/day placebo with resistance training, or 3.2g/day
beta-alanine with resistance training. Before and after the intervention, subjects’
anthropometric, Physical Functional Performance 10, Senior Fitness and upper and lower
body strength and endurance assessments were performed. Upper and lower body
strength and endurance tests included one-repetition maximum (1RM) and 20 repetitions
power tests at 50% 1RM using pneumatic resistance equipment. RESULTS: Twentyseven subjects completed post-testing. Beta-alanine was well tolerated with only 1
subject reporting any side effect (muscular aches). Multiple 4 (group) x 2 (time) mixed
design ANOVA’s indicated no significant group x time interactions (p > .05) for any
anthropometric or performance measures except 1RM leg press (p = .010). A post-hoc
analysis revealed significant improvements in 1RM leg press for both the resistance
training groups (p < .001); while no significant between group difference was detected.
For the 20-repetition chest and leg press tests, no differences were detected for time,
group or time x group interactions (p < .001). When untrained and trained groups were
compared, significant effects of time (p < .001) and repetition (p < .001), and significant
repetition x training status (p < .01) and time x repetition by training status interactions
(p = .019) were detected. Pairwise t-tests with Bonferroni adjustment (p < .0025) for
both tests revealed only one difference between pretest and post-test across repetitions for
the untrained group; while the training group showed significant increases across time for
multiple repetitions. When comparing pretest and post-test power patterns across
repetitions for chest press, there were nearly linear declines with a lack of significant
differences between pretest and post-test for the untrained group. In contrast, the trained
group showed a more rapid decline in power across repetitions during pretest than during
post-test. For the untrained group during leg press, no significant differences were
detected across repetitions for pretest or post-test; however, the trained group presented a
pattern of gradual increases in power and changes in significance across repetitions.
CONCLUSION: Although beta-alanine had no effect on any measures, the resistance
training program did affect fatigue patterns.
ACKNOWLEDGEMENTS
I thank the Department of Kinesiology and Sport Sciences for supporting me
through my undergraduate and graduate studies. I thank my dissertation advisor, Dr.
Joseph Signorile for his time and guidance throughout the dissertation. I also appreciate
the help of my two student assistants, Amanda Luiso and Caitllin Lowe. The
contribution of beta-alanine and placebo tablets by Natural Alternatives International
(San Marcos, California) is greatly appreciated and was essential for the testing of my
research hypotheses.
Thank you to my parents, Joan and William for always being there.
iii
TABLE OF CONTENTS
Page
LIST OF FIGURES .....................................................................................................
v
LIST OF TABLES ......................................................................................................
vi
Chapter
1
INTRODUCTION .........................................................................................
Resistance Training to Promote Independence .............................................
Beta-Alanine ..................................................................................................
Purpose of the Study ......................................................................................
1
3
4
8
2
METHODS .....................................................................................................
Subjects ..........................................................................................................
Experimental Design .....................................................................................
Testing Protocol .............................................................................................
Training Protocol ...........................................................................................
Supplementation Protocol .............................................................................
Statistical Analysis ........................................................................................
9
9
10
10
11
12
12
3
RESULTS ........................................................................................................
14
4
DISCUSSION .................................................................................................
17
5
PRACTICAL APPLICATIONS FOR FUTURE RESEARCH ......................
23
WORKS CITED…………… ......................................................................................
24
FIGURES…………… ................................................................................................
30
TABLES……………………………………………………………………………...
37
iv
LIST OF FIGURES
Figure 1.1. Muscle fiber distribution changes with aging
Page 30
Figure 1.2. Potential benefits of beta-alanine supplementation used in
conjunction with resistance training for muscular endurance Page 31
Figure 2.1. Study design for investigating the effects of beta-alanine
supplementation and resistance training on muscular
endurance
Page 32
Figure 3.1. Comparative changes in power across repetitions for pretest
versus post-test in the untrained group for the chest press
Page 33
Figure 3.2. Comparative changes in power across repetitions for pretest
versus post-test in the trained group for the chest press
Page 34
Figure 3.3. Comparative changes in power across repetitions for pretest
versus post-test in the untrained group for the leg press
Page 35
Figure 3.4. Comparative changes in power across repetitions for pretest
versus post-test in the trained group for the leg press
Page 36
v
LIST OF TABLES
Table 2.1. Baseline characteristics of subjects participating in the study
Page 37
Table 2.2. Muscular endurance training program
Page 38
Table 3.1. Results of anthropometric measures of subjects participating
in the study
Page 39
Table 3.2. Results of the Physical Functional Performance Test-10
(PFP-10)
Page 40
Table 3.3. Results of the Senior Fitness Test (SFT)
Page 41
Table 3.4. Results of the tests of strength (1RM) for the chest press and
leg press
Page 42
Table 3.5. Comparative paired T-tests for pretest versus post-test of the
chest press across repetitions in untrained subjects
Page 43
Table 3.6. Comparative paired T-tests for pretest versus post-test of the
chest press across repetitions in trained subjects
Page 44
Table 3.7. Comparative paired T-tests for pretest versus post-test of the
leg press across repetitions in untrained subjects
Page 45
Table 3.8. Comparative paired T-tests for pretest versus post-test of the
leg press across repetitions in trained subjects
Page 46
Table 3.9. Analysis of the change in power patterns over time across
repetitions for the chest press in the untrained group
Page 47
Table 3.10. Analysis of the change in power patterns over time across
repetitions for the chest press in the trained group
Page 48
Table 3.11. Analysis of the change in power patterns over time across
repetitions for the leg press in the untrained group
Page 49
Table 3.12. Analysis of the change in power patterns over time across
repetitions for the leg press in the trained group
Page 50
vi
Chapter 1: Introduction
Skeletal muscle function declines with age1 due to a number of factors that may
be explained by changes in the properties of the skeletal muscle and nervous system that
result in decreased muscle mass2, strength3, power4, and endurance5. The age-related
decline in muscle mass is often termed sarcopenia6; however, this definition is often
expanded to include reductions in specific functional measures.
For example, the criteria applied by the European Working Group on Sarcopenia
in Older People to define this condition include a skeletal muscle index (SMI) < 8.87
kg/m2 in men and < 6.42 kg/m2 in women7 and a gait speed is below 0.8 mˑs-1 7. With
aging, the loss in muscle mass is also commonly accompanied by changes in the
properties of skeletal muscle. Lexell et al2 noted that aging results in a selective decline
in the size of type II fast-twitch fibers, while type I slow-twitch fiber size is often well
preserved. The type II fibers also decrease in number with age, while the quantity of type
I fibers may increase8.
Changes in the properties of skeletal muscle with aging may be explained by a
number of factors. Lee et al8 noted that in elderly populations, there is little demand for
the activation of fast-twitch fibers, resulting in a shift away from fast-twitch towards
slow-twitch fiber dominance. Throughout the aging process, there is also a reproportioning of muscle fiber types through constant denervation and reinnervation9.
Lexell et al2 noted that these changes were most likely explained by reductions in motor
neurons in the lumbosacral spinal cord10. Therefore, changes in fiber type associated
with aging might be explained by fast-twitch fibers that underwent denervation and were
1
2
subsequently re-innervated by slow-twitch motor units. A summary of these changes can
be found in Figure 1.1.
Three major components of skeletal muscle that have been identified as crucial to
the ability to carry out activities of daily living include muscle strength, power and
endurance. The relationship of muscular endurance to ADL is an area of study that
requires further investigation. Muscular endurance can be broadly defined as “…the
ability to perform multiple repetitions against a set of submaximal loads”11 or “…the
ability to maintain a specific power output”11. It can also be subdivided into two
categories, relative and absolute muscular endurance. Relative muscle endurance is “a
measurement of repetitive performance related to maximum strength”;12 while, absolute
muscular endurance is “a measurement of repetitive performance at a fixed resistance”12.
Finally, decreases in strength result in concomitant reductions in absolute muscular
endurance13.
In his book, Bending the Aging Curve, Signorile11 explains the importance of
muscular endurance to an elderly individual’s ability to perform ADL, which is a critical
component for maintaining independence. ADL (i.e. carrying groceries, lifting
household items etc.) require absolute amounts of strength, meaning that for a given
activity performed by an older individual compared to a younger individual, the older
individual will likely require a greater proportion of his or her maximum strength14.
Therefore, age-related declines in muscular strength result in a loss of absolute muscular
endurance13 because the higher the intensity of an activity, the shorter the time the
activity can be sustained15. This greater demand causes an earlier onset of fatigue and
3
may result in injury16. In older adults (65 and older) endurance decreases significantly
with increasing age5.
Endurance has also been identified as a significant predictor of fall risk in older
adults5. For example, older women who had fallen within the past 18 months had lower
muscular endurance than older women who had not13. In the introduction to their paper
on older persons’ abilities to perform ADL, Hortobágyi et al16 noted that as older persons
work at high levels of their functional capacities, fatigue levels tend to be high for this
population increasing the probability of injury. Schwedner et al suggests that fatigue
after performing ADL may compromise the ability of an individual to generate sufficient
muscle force to prevent a fall13. Finally, muscular fatigue also results in reduced
proprioception11,17.
To summarize, reduced muscle strength leads to decreased muscular endurance
engendering an early onset of fatigue during daily activities and increased injury
potential.
Resistance Training to Promote Independence
Resistance training may mitigate age-associated declines in muscular strength,
power, and endurance. In a meta-analysis on strength training in older adults, Liu et al
concluded that resistance training increases strength18; and Adams et al19 noted that
absolute endurance improved with resistance training in older adults. Through increasing
muscle strength, and therefore increasing absolute muscular endurance, ADL become less
demanding, resulting in a delayed onset of fatigue and improved levels of performance.
Furthermore, a study by Pu et al indicated that submaximal endurance was improved via
progressive resistance training in older women with chronic heart failure 20. Resistance
4
training has also been shown to be effective in improving muscle power in older adults21.
Training interventions designed to address these areas of age-associated declines may
improve older individuals’ capacities to live independently and reduce their risk of
falling. Previous studies have demonstrated that a resistance training program was
effective in improving performance on the Continuous Scale-Physical Functional
Performance test (CS-PFP)22,23 and other measures of physical function24.
Beta-Alanine
Beta-alanine is an amino acid that is produced in the liver25, but it can also be
found naturally in the diet26. Beta-alanine combines with histidine to form carnosine27
and is the rate-limiting substrate for carnosine synthesis in skeletal muscle27. Artioli et al.
concluded that because it is the limiting factor to carnosine synthesis, beta-alanine
supplementation provides the best approach for increasing muscle carnosine content27.
Numerous research studies have confirmed the effectiveness of beta-alanine for
increasing muscle carnosine concentrations28-34. Del Favero et al. demonstrated a
significant increase in muscle carnosine content of the gastrocnemius in elderly subjects
(60-80 years of age) receiving beta-alanine supplementation for twelve weeks 29
indicating that the biochemical pathways involved in synthesizing carnosine (at normal
and supraphysiological capacities) are well preserved in older subjects.
Research on beta-alanine supplementation in older adults has indicated that it may
improve physical performance measures such as physical working capacity at fatigue
threshold35. Given its potential to increase muscular endurance36, beta-alanine
supplementation may have the capacity to attenuate some of the declines in skeletal
muscle function that occurs with age. Beta-alanine supplementation has been evaluated
5
in aging populations (greater than 55 years) in only two studies 29,37. In a study
examining the impact of beta-alanine on time-to-exhaustion during a submaximal cycling
task, del Favero et al,29 found that taking 3.2 g/day of beta-alanine in 2 daily doses of
1.6g (consisting of two 800mg sustained release tablets) was successful at increasing
carnosine content after 12 weeks and resulted in improvements in time to exhaustion on
both submaximal and progressive treadmill tests. In the second study, Stout et al37 found
statistically significant improvements in physical working capacity at fatigue threshold
(PWCFT) using 2.4g/day (consisting of 3 daily doses of one 800mg capsule) of betaalanine; however, muscle carnosine content was not evaluated. Neither study reported
any negative side effects29,37.
A number of mechanisms have been proposed to explain the possible benefits of
elevated muscle carnosine content through beta alanine supplementation on muscular
endurance including: improved calcium sensitivity in muscle fibers38, enhanced release of
calcium in Type I muscle fibers38, improved antioxidant activity39,40, and increased
buffering in skeletal muscle41. The greatest benefits of carnosine may be associated with
its effect on calcium sensitivity in muscle fibers. Muscle force can vary based upon
changes in calcium sensitivity even when calcium concentration remains constant42.
Several phenomena associated with fatigue may result in reduced calcium sensitivity
including increases in inorganic phosphate and a decrease in pH43. Carnosine’s
attenuation of this response may aid in delaying the onset of fatigue.
Beta-alanine supplementation is reported to pose a low risk of side effects and is
well tolerated in human subjects. For example, beta-alanine does not produce significant
changes in any blood or urinary markers29. Acute doses above 10mg·kg-1·bw-1 may
6
result in a flushing sensation31 that occurs approximately 20 minutes after ingestion31 and
may take up to an hour to subside31. The flushing sensation was first described by Harris
et al in 200631 and was subsequently referred to as paraesthesia27,39,44-48. Paraesthesia
appears to be largely avoidable through the use of doses below 10mg·kg-1·bw-1 31 or
extended-release tablets46. Sale et al49 noted that although other researchers had
presented a number of pathways that may explain the occurrence of paraesthesia, it has
yet to be determined with certainty what causes this phenomenon.
Previous research has indicated that beta-alanine supplementation alone can
positively influence a number of performance measures including increased time to
exhaustion on submaximal and incremental treadmill tests29 and increased PWCFT, both
indicators of enhanced muscular endurance37.
Although no studies examining the combination of resistance training and betaalanine supplementation have been reported in older adults, there are a number of studies
that have examined this combination in younger populations. Beta-alanine has been
reported to attenuate the decline in force production during repeated isokinetic knee
extensions30 in sprint athletes undergoing training before the competitive season. In
males that were physically active, beta-alanine supplementation improved both the time a
knee extension was held at 45% of the subject’s maximal voluntary isometric contraction
(MVIC)36 and the impulse (the average force multiplied by how long the contraction was
held at a force greater than 95% of the target force)36. Additionally, beta-alanine
supplementation increased training volume in college football players50,51. Despite
carnosine content not being enhanced by training alone in the short term33,34,52 and the
combination of training and supplementation with beta-alanine not having an additive
7
effect on carnosine content34, the combination of these two interventions could still prove
to be beneficial. Although it has yet to be investigated in elderly populations, both Stout
et al37 and del Favero et al29 indicate that beta-alanine supplementation may enhance a
resistance-training regimen. By delaying the onset of fatigue, beta-alanine
supplementation may improve individuals’ tolerance of resistance training programs and
increase training volume for those new to regular physical activity. By affecting these
variables, increases in overload levels and resultant enhanced improvements in skeletal
muscle function may occur.
As noted previously, a number of changes in skeletal muscle that occur with aging
contribute to reduced skeletal muscle function. These impairments may contribute to
lower ADL performance, as well as an increased risk for falling. Beta-alanine
supplementation may improve ADL performance through increased muscular endurance
as a result of increased carnosine content, and by increasing training volume thereby
providing a greater training stimulus to induce muscular adaptations. High-volume
resistance training programs have been found to be more effective for improving
muscular endurance than lower volume programs53; therefore, these programs may
reduce fatigue-related declines in ADL performance and reduce fall risk. Providing betaalanine as an intervention to improve muscular endurance that training alone may not
provide, might serve as a new approach to improve functional performance for older
persons. A summary of the potential benefits of combining beta-alanine supplementation
with resistance training is presented in Figure 1.2.
8
Purpose of the Study
The purpose of this study was to determine if beta-alanine supplementation
combined with endurance-based resistance training could increase gains in muscular
endurance and functional performance to a greater extent than endurance-based resistance
training alone in older adults. This purpose was fulfilled by testing the following
research hypotheses.
Research Hypotheses 1.
There will be greater improvements in muscular endurance and ADL performance
in men and women above the age of 60 when beta-alanine supplementation is
combined with resistance training compared to a group receiving resistance
training alone or two groups not receiving resistance training.
Null Hypothesis 1.
Beta-alanine supplementation combined with resistance training will not result in
changes in muscular endurance/ADL performance that are significantly different
from than any other group.
Research Hypothesis 2.
There will be greater improvements in muscular endurance and ADL performance
for men and women above the age of 60 supplementing with beta-alanine but not
resistance-training compared to a non-training group taking a matching placebo.
Null Hypothesis 2.
The changes in muscular endurance and ADL performance for the beta-alanine
group not performing resistance training will not differ from the placebo group
receiving no resistance training.
Chapter 2: Methods
Subjects
Recruitment, testing and training of subjects were conducted in accordance with
procedures approved by the University of Miami’s Human Institutional Review Board
(IRB). Subjects were recruited using flyers posted on the University of Miami campus,
presentations in the community, contacting individuals who had participated in previous
studies in our laboratories, and through referrals by friends and family members of
subjects already participating in studies in our laboratories. Subjects were between 60
and 90 years of age, lived independently without assistance, did not have sarcopenia (gait
speed ≥ .8 m s-1 and/or skeletal muscle index (SMI) ≥ 8.87 kg/m2 in men and ≥ 6.42
kg/m2 in women7), and were free of significant cognitive impairment and medical
conditions that would interfere with participation in the study. Cognitive impairment was
evaluated using the Mini-Mental Questionnaire. Individuals were excluded if they scored
below 2354. Medical conditions were reviewed using a health history questionnaire.
Individuals that responded “yes” to any item on the Physical Activity Readiness
Questionnaire (PAR-Q)55 or were 70 years or older were required to obtain clearance
from their physicians before beginning the exercise program. An additional
questionnaire was used to screen individuals for the use of other supplements (including
beta-alanine) and to assess their physical activity levels. No subjects were included in the
study if they had any previous history of beta-alanine supplementation or any recent
history (6 months) of resistance training. Subjects were informed of the potential risks
and benefits associated with the study and written consent was obtained from all
9 10
individuals prior to participation. Baseline characteristics for the subjects can be found in
Table 2.
Experimental Design
The study utilized a double blind, randomized, placebo controlled trial design.
Subjects were randomly assigned to one of four groups. Subjects assigned to the
treatment group were provided a 12 week supply of 800mg sustained released tablet betaalanine (two 1.6g doses per day (totaling 3.2g per day); subjects assigned to the placebo
group were provided a tablet similar in appearance and weight containing maltodextrin
placebo. The treatment and placebo groups were further divided into an exercise group
and a non-exercise group. Natural Alternatives International (San Marcos, CA) provided
the coded extended release beta-alanine and placebo tablets. A summary of the study
protocol can be found in Figure 2.1.
Testing Protocol
Upon arrival at the laboratory for their first testing session, subjects’
anthropometric measurements including height, weight, body composition, and skeletal
muscle mass were obtained. Height was measured using a Detecto Scale (Detecto Corp.,
Webb City, MO), and weight and body composition were measured using a Tanita BC
418 single-frequency Bioelectrical Impedance Analysis (BIA) device (Tanita Corp.,
Arlington Heights, IL). ADL performance was then evaluated using components of the
Senior Fitness Test (SFT)56 and the short Physical Functional Performance Test-10
(PFP-10)57. Subjects’ one-repetition maximums (1RM) for chest press and leg press
were evaluated using computerized pneumatic machines (Keiser Air 420, Keiser Corp,
Fresno, CA). To determine 1RM on the pneumatic leg press machine, subjects started
11
with a 10-repetition warm-up at 25% of their bodyweight. The second warm-up was 5
repetitions at 35% of their bodyweight. All subsequent attempts were single repetitions
at progressively higher weights until 1RM was achieved. Between the warm-up and
single repetition attempts a 1-minute rest period was provided. For the 1RM on the
pneumatic chest press machine, a similar warm-up and test protocol was used with the
same number of repetitions and rest period duration but at 10 and 20% of the subject’s
bodyweight. On a second testing day muscular endurance was evaluated by having
subjects perform 20 repetitions of the chest press and leg press as fast as possible at 50%
of their 1RM on the same pneumatic machines. Before the muscular endurance tests, the
same warm-up protocols for the chest press and leg press machines were used. Mean
power, peak power and the change in peak power over the 20 repetitions were evaluated
using dedicated software (Keiser Corp, Fresno, CA).
Training Protocol
The resistance-training protocol was adapted from ACSM guidelines for
improving muscular endurance (see Table 2.2)58. Subjects were instructed to perform 2
sets of 15-25 repetitions on each of the 11 computerized pneumatic machines. Subjects
were allowed 1-2 minutes of rest between sets and little to no rest between machines.
The order of the machines was alternated between upper and lower body. When subjects
completed 25 consecutive repetitions, the resistance was raised for the following set.
Larger increases were done for machines involving larger muscle groups (i.e., leg press)
and smaller increases for machines involving smaller muscle groups (i.e., seated bicep
curl). Before starting the training program, subjects randomized into the exercise groups
were shown proper form and technique on each of the 11 pneumatic machines.
12
Individuals were then tested for their 1RM on each machine. All training was supervised
by an ACSM Certified Exercise Physiologist (ACSM EP-C).
Supplementation Protocol
After completing the 2nd day of testing, subjects were randomly assigned to one of
the four groups. If the subject was assigned to a non-exercise group, he or she was given
the coded supplement or placebo so dosing could begin the following morning. For
subjects assigned to an exercise group, they began taking the supplement or placebo on
the first training day following their familiarization with the exercise equipment.
Statistical Analysis
Following completion of the study, the data were summarized and analyzed
without knowing which group of subjects had received, the supplement or placebo. A 4
(beta-alanine with resistance training, beta-alanine without resistance training, placebo
with resistance training, placebo without resistance training) x 2 (pretest, post-test) mixed
design ANOVA was used to determine group differences, time differences, and group x
time interactions. Additionally, two 2 (resistance training, control) x 2 (beta-alanine,
placebo) x2 (time) x 20 (repetition) mixed design ANOVA were used to evaluate
declines in power across 20 repetitions at 50% 1RM for chest press and leg press.
Significance for all analyses was set a priori at α = .05. When significant main effects or
interactions were found Bonferroni post hoc tests were used to determine the sources.
Effect size was evaluated using partial eta square. A power-analysis using G*Power 3.1
software59 employing an effect size of η2 = .167, based upon previous data for changes in
strength measures with beta-alanine supplementation in older adults by McCormack et
al35, and moderate correlation between time points (r =.3) indicated a minimum required
13
sample size of 24 subjects to achieve a desired power of 80%. When these planned
analyses were completed as described in the study proposal submitted to the IRB, the
code was broken to permit interpretation of the performance of the supplement and
placebo treated groups. The group given bottle A were identified as members of the
supplement groups and the group given bottle B were in the placebo groups. Thus,
neither the study subjects nor any of the investigators had knowledge of whether subjects
were taking beta-alanine or placebo during data collection or preliminary data analyses.
Chapter 3: Results
Fifty-four individuals consented to participate in the study. A total of 36 subjects
completed baseline testing and were randomly assigned to one of the four groups.
Twenty-seven individuals completed testing at the end of the study. Table 2.1 contains
the baseline characteristics of the subjects that completed the study. Figure 2.1
summarizes the number of subjects from each group who failed to complete the study and
the reasons for each event.
The 4 x 2 mixed design ANOVAs for the anthropometric measures of weight,
body composition, fat free mass, and skeletal muscle index (SMI) revealed no significant
effects of time or group x time interactions (Table 3.1). The 4 x 2 mixed design ANOVAs
for the individual tests of the PFP-10 (Table 3.2) revealed significant effects of time for
the jacket test, pot carry test (time), washer test, grocery carry test (weight), and the 6minute walk test, p ≤ .038, but no significant group x time interactions. The 4 x 2 mixed
design ANOVAs for the individual tests of the Senior Fitness Test (Table 3.3) revealed
significant effects of time for only the 30 second arm curl test (p = .001); but no
significant group x time interactions. Next, the 4 x 2 mixed design ANOVAs that
evaluated 1RM leg press and chest press produced significant effects of time for both
measures; however, there was a significant group x time interaction for 1RM leg press
(F(3,23) = 4.803, p = .010, η2p = .385) (Table 3.4). A post-hoc analysis revealed significant
improvements in 1RM leg press for the training group taking beta-alanine (mean
difference = 103.125, 95%CI = 58.344 to 147.906, p < .001) and the training group
taking the placebo (mean difference = 130.625, 95%CI = 85.844 to 175.406, p < .001).
An independent samples t-test indicated no significant differences in the change in 1RM
14
15
leg press performance for the training group taking beta-alanine compared to the training
group taking the maltodextrin placebo (t(14) = -.826, p = .423). A 2 x 2 mixed design
ANOVA indicated a significant effect of time for training volume (F(1,14) = 37.671, p <
.001, η2p = .729), but no group x time interaction (p > .05).
In examining results for the 20-repetition endurance test, no differences were
detected for average or peak power for time, group or time x group interactions (p ≤
.001). Because there was no significant difference between the supplement and placebo,
the four groups were collapsed to two groups, untrained and trained. For the fatigue
analysis of the chest press, there was a significant effect of time (F(1,24) = 15.134, p =
.001, η2p = .387) and repetition ( F(19, 456) = 42.162, p < .001, η2p = .637), and significant
repetition by training status ( F(19, 456) = 6.458, p = .003, η2p = .212) and time by repetition
by training status interactions (F(19, 456) = 1.814, p = .019, η2p = .070). For the fatigue
analysis of the leg press, there was a significant effect of time (F(1,23) = 18.156, p < .001,
η2p = .441) and repetition (F(19, 437) = 24.265, p < .001, η2p = .513). Additionally, there
was a significant time by repetition by training status interaction (F(19, 437) = 1.939, p =
.010, η2p = .078). Multiple pairwise t-tests with Bonferroni adjustment (p<.0025) for both
the chest press and leg press revealed no significant differences between pretest and posttest across repetitions for the untrained group during chest press (Table 3.5) and only a
single significant difference for leg press across all twenty pairwise comparisons (Table
3.7). In contrast, the training group showed significant increases across time for
repetitions 9 and 12 -20 for the chest press (Table 3.6) and 6, 9-16 and18-20 for the leg
press (Table 3.8).
16
In an analysis of the change in power across repetitions over time all analyses
with the exception of the post-test values for leg press, no significant difference was seen
between the first repetitions and all subsequent repetitions in the testing set. This was
likely due to the poor initial performance at the initiation of the testing set as obviated by
examining these initial repetition scores. When comparing pretest and post-test power
patterns across repetitions, there was a similar nearly linear decline seen for the untrained
group for chest press, and the lack of significant differences between pretest and post-test
values for the untrained versus the trained individuals mentioned above was clearly
visible (Figure 3.1, Tables 3.5, 3.9). In contrast, the trained group showed a more rapid
decline in power across repetitions during pretest than during post-test where there was a
discernable plateauing of power across repetitions 2 through 17 as can been seen in
Figure 3.2 and Tables 3.6 and 3.10. Additionally, the differences between pretest and
post-test scores presented in Table 3.6 are visually evident in Figure 3.2. When
comparing pretest and post-test power patterns across repetitions, for the trained versus
untrained groups during leg press, the differences were even more apparent. For the
untrained group, not significant differences were detected across repetitions for either the
pretest or post-test (Table 3.11) and the lack of significant differences between pretest
and post-test scores presented in Table 3.7, is easily seen in Figure 3.3. In contrast, the
trained group presented a completely different pattern of power production across
repetitions for pretest versus post-test. Table 3.12 shows a pattern of gradual increases in
power and changes in significance across repetitions. This pattern and the differences
seen between pretest and post-test values presented in Table 3.8 are illustrated in Figure
3.4.
Chapter 4: Discussion
The principal finding of the study was that beta-alanine supplementation did not
have a significant impact on anthropometric measures, ADL performance, or measures
on tests of strength and endurance in older adults. A secondary finding was that the
while the resistance training intervention, independent of supplementation, also had no
significant effect on the aforementioned measures, with the exception of leg press
strength, it did result in alterations in the patterns of power production across the 20repetition pneumatic fatigue test.
The lack of effect of beta-alanine on body composition and daily performance
measures in the older adults who did not receive resistance training in this study reflects
the results presented in a study by del Favero et al,29 which examined the impact of this
supplement on performance in 18 healthy elderly subjects, 60-80 years of age (10
women, 8 men). Twelve subjects received 3.2 g of beta-alanine per day for 12 weeks,
while controls received a placebo. Similar to our findings, these researchers reported no
significant improvements in anthropometric measures or for the sit-to-stand or timed upand-go tests compared to the control group. However, they did report a significant
increase in time-to-exhaustion on a treadmill test performed at 75% of the difference
score between subjects' ventilatory anaerobic threshold and VO2peak. The difference in
results between our 20 repetition fatigue test and their treadmill test is central to the
question being addressed during our study. Clearly the endurance testing protocol used
by del Favero et al targeted the classic use of beta-alanine to enhance cardiovascular
endurance, while our 20 repetition leg press and chest press tests are more representative
of neuromuscular endurance. While there is some relationship between these two
17
18
variables, it is clearly tentative. For example, a comparative analysis between Canadian
firefighters and the general population indicated that the firefighters exhibited higher
muscular endurance, but lower cardiovascular endurance, than the general population60.
Additionally, in a study by Mayorga-Veag et al that examined the impact of a circuit
training on muscular and cardiovascular endurance in children 10-12 years of age, these
researchers reported strikingly different effect sizes for muscular (30s sit-ups: g=0.68,
bent arm hang: g=.65) and cardiovascular ( 20m endurance shuttle run: g=0.37)
endurance measures61. These results illustrate the tenuous relationship between these two
variables as would be expected by the diverse physiological mechanisms involved in
each62,63. Similarly, McCormack et al35 reported no significant changes in body
composition or grip strength in older adults, aged 70.7 ± 6.2 y, due to the administration
of an oral nutrition supplement containing fat, protein, carbohydrate with or without betaalanine at doses of 800 or 1200 mg. Significant improvements in a sit-to-stand test were
seen with the supplement; however, no additional benefit was seen due to the addition of
beta-alanine35. And finally, both beta-alanine conditions produced significant increases
in physical working capacity at fatigue threshold, a cardiovascular assessment, for both
beta-alanine conditions over the non-alanine matched supplement.
Other trials with beta-alanine have examined measures more consistently based
on neuromuscular rather than cardiovascular endurance. Similar to our results, Kendrick
et al33 noted no greater improvements in isoinertial or isokinetic strength, arm curl
muscular endurance, in male Vietnamese physical education students taking beta-alanine
compared to those taking the placebo during a resistance training program. In contrast,
Hoffman et al50 found an additive effect of beta-alanine when supplemented with creatine
19
in collegiate football players on a number of outcomes including lean body mass, percent
body fat and training volume. The divergence in results between their results and those
of our study may be due to a number of factors including, differences in the age of the
subjects, the training interventions, or possible additive or synergistic effects of creatine
and beta-alanine. However, the levels of interaction between these two supplements
could not be determined, since beta-alanine alone was not given to a test group in their
study. Their results for peak and average power during a 30s Wingate test and 20
repetition jump test reflect the same lack of impact by beta-alanine as shown in the peak
and average power results from the 20 repetition chest press and leg press tests included
in the present study. Although Hoffman et al50 indicated that the lack of improvements in
power may have been due to difference in the nature of the power testing compared to the
training during their intervention, this conclusion should be explored more carefully since
these result were also evident in our study where the testing methods were consistent with
the training intervention. Two later studies by Hoffman et al indicated beta-alanine
supplementation alone increased training volume51,64 but there were also differences in
the subjects, training program, and dosing protocol.
The lack of a significant effect of training on fat free mass and body composition
agrees with previous research findings by Marsh et al using a training program with the
same training frequency, duration, and pneumatic equipment as seen in the current
study65. They suggested that significant changes in muscle mass might be seen in
interventions of longer duration65; however, another more mechanistic, explanation
should be considered when examining our results and those of Marsh et al. As noted by
Brad Schoefield66, the most effective muscle hypertrophy programs incorporate
20
metabolic stress and moderate tension levels. Such programs incorporate multiple sets of
multi-joint and single joint exercises using loads allowing between 6 and 12 repetitions
with rest intervals between sets of 60–90 seconds. Additionally, he contends that some of
the sets should incorporate concentric muscular failure. And finally, the concentric and
eccentric repetitions should be performed at 1–3s and 2-4s, respectively. Clearly, the
training pattern used during the current study differed dramatically from that proposed for
hypertrophy-based training. In fact, the patterns of change seen across the 20 repetition
fatigue test reflects the training continuum proposed by Campos et al.67, who showed that
although four sets of low repetition training (3–5 RM) with 3 min recovery periods and
three sets of intermediate repetitions (9–11 RM) with 2 min rest could improve muscle
endurance as measured by increased repetition number at loads of 60% 1RM, two sets of
high repetition training (20–28 RM) with 1 min rest produced significantly greater
improvement.
With the exception of 1RM leg press, the current training program did not
significantly improve any performance variable of strength, endurance, or ADL. These
results are in contrast to other studies utilizing resistance training in older adults. A
training intervention of longer duration (24 weeks), with similar intensity (50% 1RM) but
lower repetitions (13 instead of 15-25) conducted 3 days/week resulted in significant
improvements in muscular strength and endurance for the chest press and leg press, as
well as a decrease in stair climb time in older adults with a similar age range (60 to 83) to
that in the current study68. Another study with older women indicated that a low intensity
(14 repetitions at 40%1RM) for 3 days/week) training program of 52 weeks was effective
at increasing leg muscle strength69. Additionally, other training programs reported
21
significant improvements in physical function. A 20-week resistance training program
significantly improved performance on the chair rise test and stair climb test70; while a 16
week power training program found significant improvements in overall score on the CSPFP-1023. The difference seen between these studies and the current study may be
attributable to a number of factors. First, due to the targeting of endurance through
multiple repetitions required a lower loading pattern and may have produced a reduced
stimulus for strength development. Second, the duration of the current study was
substantially less than that seen in the aforementioned studies. And finally, the nature of
the functional tests used was more attuned to testing strength and power, than muscular
endurance. In contrast, the current study’s results are similar to another study using
pneumatic equipment for a training program of similar duration and frequency which
reported no significant improvements in the 400m walk, timed chair rise, or self-reported
function using the WOMAC scale in subjects with knee osteoarthritis71. As noted by
these researchers, the lack of transfer may have been due to the different biomechanical
nature of the test tasks and the training program. While this explanation may be
applicable to our study, a further explanation may be the lack of improvement seen in
strength and power with our protocol. Although most physical performance outcomes
did not reveal significant group by time interactions, some measures had large effect sizes
including grocery carry weight and 1RM chest press; while many others exhibited
moderate effect sizes. Therefore, a larger sample size may have yielded additional
significant group by time interactions for these variables.
Limitations of the study included the duration of the intervention, duration of the
testing protocols and lack of dietary controls. The PFP-10 and Senior Fitness Test contain
22
many tests with short durations (i.e. the 30-second chair stand test and 30-second arm
curl test) that may have limited the ability of these batteries to discern improvements in
muscular endurance related to beta-alanine administration. While the moderate effect
sizes seen in the grocery carry tests and six-minute walk tests support this contention,
further research is necessary to confirm its legitimacy. Finally, no dietary controls were
imposed during this study and this may have introduced a source of inter-subject
variability.
Chapter 5: Practical Applications for Future Research
The results of this study suggest that further research should be conducted to
examine the effect of beta-alanine in conjunction with training in older adults using
training methods of greater duration (i.e., 24 or more weeks). Such interventions could
provide a longer-term stimulus for structural and functional changes and enable longer
periods to engender changes in fat free mass and body composition. Additional measures
that could be incorporated into future studies are self-reported questionnaires which
assess ADL, instrumental activities of daily living (IADL) and perceived physical
capacity. Further research should also examine the effect of beta-alanine and resistance
training both independently and together on the effects of fatigue using tests of endurance
with longer duration, either through the use of more repetitions on machine based tests, or
greater time to completion for tests simulating ADL. Examination of the development
and decline of muscle power across repetitions during resistance exercise in this study
represents a promising direction for evaluating muscular endurance in older adults.
Future research should examine the possibility of using this test of muscular endurance to
predict declines in ability to do ADL.
23
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FIGURES
Figure 1.1. Muscle fiber distribution changes with aging
Aging
Reduced # of motor neurons
Fast-twitch fiber
denervation and
reinnervation by slower
motor neurons
Reduced physical activity
Reduced # of fast-twitch
fibers
30
31
Figure 1.2. Potential benefits of beta-alanine supplementation used in conjunction with
resistance training for muscular endurance
Resistance training program for
muscular endurance
Beta-alanine supplementation
(+)
! Muscular endurance
(+)
! Performance on tests of ADL
with a muscular endurance
component
(+)
(+)
(+)
Training Volume
32
33
Figure 3.1. Comparative changes in power across repetitions for pretest versus post-test
in the untrained group for the chest press
34
Figure 3.2. Comparative changes in power across repetitions for pretest versus post-test
in the trained group for the chest press
35
Figure 3.3. Comparative changes in power across repetitions for pretest versus post-test
in the untrained group for the leg press
36
Figure 3.4. Comparative changes in power across repetitions for pretest versus post-test
in the trained group for the leg press
37
TABLES
Table 2.1. Baseline characteristics of subjects participating in the study
38
Table 2.2. Muscular endurance training program
Intensity
50% 1RM
Repetitions
15-25
Speed of repetitions
Moderate to fast
Sets per Exercise
2
Recovery between sets 1-2 minutes
Training Frequency
3 days per week (full body)
Progression
Increased load when 25 full repetitions were performed
39
40
41
42
43
Table 3.5. Comparative paired T-tests for pretest versus post-test of the chest press
across repetitions in untrained subjects
Repetition
Mean Difference±SE
Lower 95% CI
Upper 95% CI
t
df
p
1
-18.5±15.9
-53.8
16.9
-1.163
10
.272
2
-7.7±11.1
-32.4
17.0
-.693
10
.504
3
-19.5±9.2
-39.9
1.0
-2.121
10
.060
4
-12.2±8.2
-30.5
6.0
-1.492
10
.166
5
-18.0±7.4
-34.5
-1.5
-2.437
10
.035
6
-11.5±7.0
-27.1
4.1
-1.644
10
.131
7
-11.4±6.2
-25.2
2.4
-1.840
10
.096
8
-13.7±9.5
-34.9
7.4
-1.447
10
.179
9
-12.1±8.2
-30.3
6.1
-1.486
10
.168
10
-9.6±6.7
-24.7
5.4
-1.429
10
.184
11
-12.1±9.3
-32.8
8.5
-1.308
10
.220
12
-14.2±8.3
-32.8
4.3
-1.710
10
.118
13
-9.0±8.4
-27.7
9.8
-1.064
10
.312
14
-13.9±10.1
-36.5
8.7
-1.372
10
.200
15
-11.0±9.4
-31.9
9.9
-1.168
10
.270
16
-16.1±11.9
-42.9
10.7
-1.357
9
.208
17
-11.2±10.8
-35.2
12.9
-1.036
10
.325
18
-2.1±8.9
-22.0
17.7
-.240
10
.815
19
-4.9±10.3
-27.8
18.0
-.478
10
.643
20
-9.7±7.9
-27.4
7.9
-1.228
10
.247
*Bonferroni adjustment, p < .002
44
Table 3.6. Comparative paired T-tests for pretest versus post-test of the chest press in
trained subjects.
Repetition
Mean Difference±SE
Lower 95% CI
Upper 95% CI
t
df
p
1
-11.9±12.2
-37.9
14.1
-.975
15
.345
2
-29.6±9.4
-49.7
-9.6
-3.153
15
.007
3
-21.8±10.1
-43.4
-0.3
-2.163
15
.047
4
-19.8±10.8
-42.8
3.2
-1.836
15
.086
5
-23.5±10.4
-45.6
-1.3
-2.261
15
.039
6
-24.9±7.6
-41.0
-8.8
-3.289
15
.005
7
-26.4±7.6
-42.5
-10.3
-3.499
15
.003
8
-28.1±8.3
-45.8
-10.3
-3.372
15
.004
9
-32.0±6.7
-46.3
-17.6
-4.752
15
.000*
10
-22.5±8.5
-40.6
-4.4
-2.645
15
.018
11
-29.5±7.7
-45.9
-13.1
-3.834
15
.002
12
-34.4±7.3
-49.9
-18.8
-4.706
15
.000*
13
-35.8±7.8
-52.4
-19.1
-4.587
15
.000*
14
-39.2±7.5
-55.1
-23.2
-5.240
15
.000*
15
-38.9±7.4
-54.7
-23.1
-5.243
15
.000*
16
-39.9±6.8
-54.4
-25.4
-5.858
15
.000*
17
-39.7±6.8
-54.1
-25.3
-5.875
15
.000*
18
-39.3±7.5
-55.2
-23.3
-5.241
15
.000*
19
-42.1±7.2
-57.5
-26.7
-5.832
15
.000*
20
-39.2±7.7
-55.6
-22.7
-5.070
15
.000*
*Bonferroni adjustment, p < .0025
45
Table 3.7. Comparative paired T-tests for pretest versus post-test of the leg press in
untrained subjects.
Repetition
Mean Difference±SE
Lower 95% CI
Upper 95% CI
t
df
p
1
-66.6±26.8
-126.3
-6.9
-2.484
10
.032
2
-80.9±32.5
-153.3
-8.4
-2.486
10
.032
3
-98.5±18.8
-140.3
-56.6
-5.237
10
.000*
4
-67.8±21.2
-115.1
-20.5
-3.194
10
.010
5
-57.5±23.2
-109.3
-5.7
-2.473
10
.033
6
-41.7±21.9
-90.5
7.0
-1.908
10
.085
7
-76.4±19.8
-120.5
-32.3
-3.858
10
.003
8
-59.0±26.5
-118.0
-0.1
-2.231
10
.050
9
-77.2±21.7
-125.7
-28.8
-3.552
10
.005
10
-49.6±15.5
-84.2
-15.0
-3.193
10
.010
11
-60.1±24.8
-115.4
-4.8
-2.421
10
.036
12
-50.3±23.3
-102.2
1.7
-2.156
10
.057
13
-55.5±25.4
-112.2
1.2
-2.182
10
.054
14
-33.0±28.8
-97.1
31.1
-1.147
10
.278
15
-41.3±18.6
-82.8
0.2
-2.216
10
.051
16
-39.9±33.5
-124.4
24.9
-1.486
10
.168
17
-39.7±29.0
-100.8
28.3
-1.252
10
.239
18
-39.3±20.0
-76.2
12.7
-1.592
10
.142
19
-42.1±21.5
-69.2
26.5
-.995
10
.343
20
-39.2±22.0
-93.1
4.7
-2.013
10
.072
*Bonferroni adjustment, p < .0025
46
Table 3.8. Comparative paired T-tests for pretest versus post-test of the leg press
in trained subjects.
Repetition
Mean Difference±SE
Lower 95% CI
Upper 95% CI
t
df
p
1
-94.9±28.7
-156.1
-33.7
-3.306
15
.005
2
-95.5±42.8
-186.7
-4.4
-2.235
15
.041
3
-144.4±45.6
-241.5
-47.3
-3.171
15
.006
4
-151.4±47.3
-252.2
-50.7
-3.204
15
.006
5
-154.4±42.9
-245.9
-62.9
-3.596
15
.003
6
-154.6±36.6
-232.7
-76.5
-4.220
15
.001*
7
-147.3±43.4
-239.7
-54.8
-3.396
15
.004
8
-151.3±45.1
-247.4
-55.2
-3.355
15
.004
9
-166.6±35.4
-242.1
-91.1
-4.706
15
.000*
10
-174.2±41.6
-263.0
-85.5
-4.183
15
.001*
11
-143.0±37.2
-222.3
-63.7
-3.843
15
.002*
12
-142.9±36.5
-220.7
-65.2
-3.920
15
.001*
13
-162.9±44.1
-256.9
-68.9
-3.695
15
.002*
14
-150.2±41.0
-237.6
-62.7
-3.661
15
.002*
15
-160.9±36.8
-239.3
-82.5
-4.373
15
.001*
16
-177.3±44.1
-271.2
-83.4
-4.024
15
.001*
17
-155.1±42.8
-246.4
-63.9
-3.623
15
.003
18
-164.0±42.7
-255.1
-72.9
-3.838
15
.002*
19
-151.3±37.6
-231.4
-71.1
-4.023
15
.001*
20
-137.0±35.1
-211.9
-62.2
-3.901
15
.001*
*Bonferroni adjustment, p < .0025
47
Table 3.9. Analysis of the change in power patterns over time across repetitions for the
chest press in the untrained group.
Pretest
Post-test
Repetition #
Mean ± SE
Letter
Mean ± SE
Letter
1
233.0±37.8
A
242.3±39.3
A
2
244.2±41.7
A
246.4±39.3
A
3
239.0±39.8
A
254.5±39.7
AB
4
239.9±39.5
A
247.6±37.8
ABC
5
232.2±38.6
A
246.8±37.4
ABCD
6
229.3±37.8
A
237.0±36.3
ABCDE
7
221.2±36.8
A
229.2±35.9
ABC E
8
218.1±34.9
A
228.8±35.6
ABC E
9
211.6±34.4
A
221.5±34.3
ABC E
10
208.6±33.2
A
215.0±32.5
ABCDEF
11
202.1±32.2
A
212.0±33.2
ABC E G
12
194.8±30.6
A
207.2±31.6
ABC E G
13
192.8±30.1
A
200.0±30.1
ABCDE G
14
185.1±28.4
A
197.5±30.8
ABC E G
15
180.7±27.9
A
190.3±29.6
ABC E G H
16
172.3±25.3
A
186.9±29.5
ABC E G H
17
171.5±25.3
AB
181.4±28.7
ABCDEFGH
18
170.2±25.6
AB
171.6±27.4
A
H
19
165.3±24.9
ABC
169.2±26.9
A
H
20
154.3±23.7
A C
163.9±25.3
AB
Repetitions having the same letters are not significantly different from one another.
48
Table 3.10. Analysis of the change in power patterns over time across repetitions for the
chest press in the trained group.
Trained Chest Press
Pre
Post
Repetition
Mean ± SE
Letter
Mean ± SE
Letter
1
203.5±29.7
A
215.4±24.1
A
2
214.2±32.9
A
243.8±29.3
AB
3
220.6±32.1
AB
242.4±28.6
ABC
4
220.4±32.2
AB
240.3±27.2
BCD
5
219.9±32.2
AB
243.4±27.5
ABCDE
6
216.8±30.3
AB
241.7±27.4
ABCDE
7
215.2±30.2
ABC
241.6±28.2
ABCDEF
8
210.3±31.1
ABC
238.4±28.6
ABCDEFG
9
210.1±29.8
ABCD
242.1±28.6
ABCDEFG
10
215.7±32.4
ABCD
238.2±30.0
ABCDEFGH
11
207.1±30.6
ABCDE
236.6±30.3
ABCDEFGH
12
201.4±30.3
ABCDEF
235.8±30.9
ABCDEFGH
13
197.6±29.5
ABC EFG
233.4±32.2
ABCDEFGHI
14
193.8±29.6
ABCDEFGH
233.0±31.5
ABCDEFGHIJ
15
188.8±28.1
AB
FGH
227.7±30.8
ABCDEFGHIJK
16
183.8±28.4
A
H
223.7±30.1
ABCDEFG IJK
17
177.8±26.6
A
F HI
217.5±29.1
ABCDE G I K
18
171.4±24.8
A
F HI
210.7±28.3
A CD
19
168.5±26.0
A
210.7±27.9
A
20
161.6±25.1
A
200.8±26.6
A
IJ
D
G IJK
Repetitions having the same letters are not significantly different from one another.
IK
49
Table 3.11. Analysis of the change in power patterns over time across repetitions for the
leg press in the untrained group.
Untrained Leg Press
Pre
Post
Repetition
Mean ± SE
Letter
Mean ± SE
Letter
1
430.7±49.8
A
497.3±64.8
A
2
527.9±82.3
A
608.8±84.9
A
3
528.3±81.1
A
626.7±88.9
A
4
535.0±79.8
A
611.7±75.7
A
5
563.9±78.1
A
621.4±81.2
A
6
566.9±72.7
A
608.6±81.3
A
7
559.8±75.5
A
636.2±81.4
A
8
564.8±73.5
A
623.9±78.1
A
9
566.0±75.1
A
643.2±80.8
A
10
579.9±81.0
A
629.5±72.8
A
11
577.7±85.3
A
637.8±78.9
A
12
598.6±86.9
A
648.9±76.1
A
13
591.1±85.8
A
646.8±76.8
A
14
599.9±89.4
A
632.9±70.9
A
15
591.1±81.2
A
632.4±80.4
A
16
592.2±90.6
A
642.0±72.4
A
17
594.0±87.0
A
630.3±79.6
A
18
614.7±82.1
A
646.5±77.1
A
19
616.9±85.1
A
638.2±76.1
A
20
588.0±80.3
A
632.2±70.7
A
Repetitions having the same letters are not significantly different from one another.
50
Table 3.12. Analysis of the change in power patterns over time across repetitions for the
leg press in the trained group.
Trained Leg Press
Pre
Post
Repetition
Mean ± SE
Letter
Mean ± SE
Letter
1
408.4±57.3
A
503.3±44.8
A
2
490.7±74.4
A
586.2±57.7
AB
3
470.9±65.2
A
615.3±60.6
ABC
4
497.3±69.5
A
648.8±63.0
BC
5
498.0±73.1
A
652.4±67.0
ABC
6
507.5±70.8
A
662.1±66.3
BC
7
512.4±72.4
A
659.6±70.3
ABC
8
521.6±80.2
A
672.9±67.3
BC
9
511.8±77.7
A
678.4±69.2
BC
10
500.3±59.2
A
674.5±68.9
BC
11
529.0±74.8
A
672.0±70.0
BC
12
528.6±70.6
A
671.6±67.7
BC
13
529.4±79.1
A
692.3±70.9
BC
14
534.8±71.4
A
684.9±71.1
BC
15
533.1±76.7
A
694.0±69.5
C
16
537.8±74.3
A
715.1±76.5
C
17
544.0±75.7
A
699.2±69.7
BC
18
525.5±74.3
A
689.5±71.5
BC
19
530.6±70.3
A
681.8±70.2
BC
20
537.5±73.9
A
674.5±70.1
BC
Repetitions having the same letters are not significantly different from one another.