Marathon Fueling
Techniques: Physiologic
Understanding and
a Proposed Intake
Schedule
John R. Bennett, MS, CSCS and Michael P. Kehoe, PhD
University of Central Florida, Orlando, Florida
SUMMARY
THIS REVIEW EXAMINES FUELING
TECHNIQUES DURING
PROLONGED ENDURANCE
EVENTS AND PRESENTS A
PROPOSED MARATHON FUELING
INTAKE SCHEDULE. BOTH
TRADITIONAL AND RECENT
PERSPECTIVES IN PHYSIOLOGY
ARE EXPLORED AND PROVIDE
THE BASIS FOR DISCUSSION OF
PROJECTIONS FOR HUMAN
ENERGY POTENTIAL. IT IS THE
INTENTION OF THIS REVIEW TO
FOCUS SPECIFICALLY ON THE
UPPER-ECHELON MARATHONER
AND THOSE COMPETITORS
CONCERNED WITH THE FINITE
POINTS OF PERFORMANCE
RATHER THAN SIMPLY RACE
COMPLETION.
MARATHON FUELING
TECHNIQUES: PHYSIOLOGIC
UNDERSTANDING AND A
PROPOSED INTAKE SCHEDULE
nderstanding an athlete’s metabolic profile may be an individual’s blueprint for success.
Athletes do not intentionally neglect
race nutrition (13,29); many simply do
not understand the need for a nutrition
U
schedule in prolonged events, whereas
others attempt nutrition but may not
fully understand the need. When an
athlete lacks an understanding, the accuracy and effectiveness of any nutritional schedule attempted will likely be
inconsistent or ineffective. This discussion provides a resource for performance specialists and athletes alike
to learn and understand competition
nutrition, avoiding diversion into
training nutrition, an important but
different subject. The foundation of
analysis is for endurance athletes specifically focusing on the marathon.
General intake recommendations and
guidelines exist for prolonged aerobic
activities, including the marathon
(3,18,32,44,52,69). Existing principles
are intended to cover the entire performance spectrum, from first-timers to
world champions. The intention is to
focus specifically on the upper-echelon
marathoner, or those with performances of less than 3 hours, with our
focus primarily towards the elite. This
parameter was established for 2 purposes. Primarily, top-end athletes are
most concerned with the finite points
of performance rather than simply race
completion. Here, the interest lies in
advancing performance by even the
smallest fraction for advantage over
the next athlete, rather than lifeachievement endeavors. Second, elite
athlete performance is less variant.
Although each individual is unique,
science inarguably agrees that athletes
with a strong training history have set
adaptations that have brought them
thus far (6,8,22,58,76,81), whereas
recreational athletes have not necessarily maximized their potentials to the
last percentages. Additionally, elite
athletes have demonstrated their commitment and focus on achieving maximal capacity—they exist in a state of
readiness to breach the next threshold.
ENDURANCE PHYSIOLOGY
In the sports world, intensity mostly
relates to near or supramaximal shortduration bursts associated with power
athletes. For aerobic activity, as compared with an instant effort, the
force put forth is substantially less.
Marathoners, for example, compete at
a pace between 75% and 90% of their
maximum intensity (6,7,27,40,53,76).
By comparison, 100-meter sprinters
KEY WORDS:
caloric cost; endurance; energy;
glycogen sparing; hydration; nutrition;
substrate
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VOLUME 30 | NUMBER 5 | OCTOBER 2008
Copyright Ó National Strength and Conditioning Association
perform almost exclusively in a state of
oxygen debt at 110–120% (8,83). Intensity has several measures, including
heart rate (HR), lactate, and power, but
_ 2) is the most
oxygen consumption (VO
popular aerobic power measure. For
the context of this review, intensity is
relative only to that of prolonged
aerobic performance.
An athlete may start running at a
5-minute mile pace and maintain a
heart rate reserve (HRR) of 75%. However, that continual relative effort shifts
as performance continues, increasing
the heart rate to as much as 95% HRR
before the end of the event (7,26,52).
On the other hand, if an athlete were to
perform solely based on intensity with
85% HRR being the accepted elite
marathon performance norm (7,64),
the pace would have to decline to
maintain a consistent heart rate (35).
At some point, the heart rate may
continue to increase unless the activity
is ceased altogether (21,33,34).
Aerobic intensity truly exists at any
level that uses oxygen for work. However, the focus herein is competition,
a rate rarely performed at below 50%
of maximal effort, even in week-long
ultra-endurance events (29,52,55).
During aerobic competitions lasting
90–180 minutes, top athletes perform
_ 2max (6,7). Even a trained
at 80–90% VO
athlete’s submaximal effort for a
5-minute run becomes near-maximal
exertion by the end of the second
hour. This absolute work rate refers to
the total fuel necessary for the task,
whereas relative work rates suggest the
substrate portioning, which will be
discussed later in the review (58).
With this suggestion, it becomes apparent that the energy systems have
shifted. Regardless of activity, the
systems steadily progress through
a fixed path to eventually end up at
the final state most dependent upon
intensity—duration is secondary only to
the body’s ability to maintain a given
relative intensity (19,56,78). The
2 primary factors affecting duration
at controlled threshold intensity are
energy metabolism and hydration.
METABOLISM
Throughout the majority of the race,
an athlete’s aerobic metabolism taps
into stored glycogen and intramuscular
triglyceride (IMTG) sources, requiring
continued glucose availability for both
efficient fat metabolism and glycogen
sparing (9,23,44,47,81,84). A growing
shift to stored glycogen signifies a
decreasing ability of aerobic metabolism to process anaerobic waste. This
may be demonstrated as an increase in
lactic acid, but before its sharp increase
to the point of detriment (27,38,50,80).
Performance in this range for the
elite athlete requires a fine tuned
carbohydrate–fat usage. Both have
benefits and downfalls. Fatty acid
(FA) oxidation is limited by the availability of carbohydrates (CHO); however, carbohydrate alone is a direct
measure of energy reserve potential to
a marathoner (Figure 1) (4,38,48,53).
If the athlete were performing in a lowintensity event, CHO would be of
much less importance. Figure 1 illustrates the benefit of providing a CHO
energy source for high-intensity aerobic events. Training allows the elite
athlete to burn fat more efficiently and
at a greater intensity (38,52,53,81). The
idea seems antithetical to the rapid
energy source benefit from CHO. The
key for the athlete is to shift energy
reliance from CHO to fat as much as
possible without affecting performance. Even minimal shifts will have
tremendous savings with regards to
sparing
glycogen
sources
(4,17,47,81,84). The elite athlete must
determine a point of diminishing
returns for success.
Glycogen versus glucose. The body
has a limited capacity to perform at
high-intensity levels. Muscle glycogen,
the primary fuel source for marathoners, provides approximately 2 hours of
energy. Performance will decline before muscle glycogen stores are truly
depleted. Decrements may occur as
early as 50% capacity, although some
runners may be able to maintain
performance without decrement until
70%
depletion
(14,19,53,76,84).
Beyond this point, athletes are unable
to maintain marathon intensities, or
often even intensities greater than
_ 2max.
70% VO
The liver stores approximately 20% of
the body’s glycogen, which is much
less than the muscular system, but the
primary hepatic function is blood sugar
maintenance (3,26,38). Jeukendrup and
Jentjens (48) clearly demonstrated that
the liver has a rate limitation to spare
substrate over time rather than overly
rapid use. An important point to
consider is that glycogen yields 4.2
kilocalories (C) per gram, whereas
glucose yields 3.7 C/g (55,83). Research strongly demonstrates a preference for muscle glycogen over
endogenous blood glucose for
several
well-understood
reasons
(14,25,46,47,78,82):
Figure 1. Benefits and drawbacks to metabolic sources.
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57
Marathon Fueling Techniques
1. Intramuscular glycogen is immediately available, not requiring transport to the working muscles.
2. Although glycogen is a more complex substance, the process to yield
energy is more efficient than with
glucose.
3. The amount of circulating blood
glucose is negligible (approximately
5% of the energy potential from
glycogen) for long-duration activities. It is intended more for vital
functions, mental awareness, and
quick energy bursts.
These comparisons also illustrate that
a relatively greater lean mass aids in
athletic performance (5,24). Women
tend to have a proportionally lower
glycogen store simply as the result of
anatomical averages of lower lean body
mass percentages than men. Women,
however, are more efficient users of
lipids (40); whether this factor or
others affect their maximum pace is
beyond this discussion.
Why lipids alone don’t work. Although a lean athlete has greater than
25 times the amount of calories available from fat as compared with CHO,
fat usage actually has several disadvantages (3,9,18,38,81):
1. Intensity must be low enough to
prevent cellular oxygen depletion.
2. Fat metabolism requires more oxygen usage per C expended as
compared with CHO.
3. Fat metabolism requires one CHO
molecule for every FA molecule
metabolized.
4. The most immediate source of fat
for muscles is IMTG. However,
IMTG must first be broken down
to its usable FA parts.
5. Fat metabolism requires nearly
twice as long to provide energy as
aerobic carbohydrate metabolism.
The body adapts well to training
stimuli placing the body at threshold
levels. This teaches the body to use
a slightly greater percentage of fat at
increased intensities (4,6,13,18,23,
76,81,84). Although the percentage is
relatively minimal, with the highenergy yield from lipids, the result is
both statistically and practically significant. Consider the following example.
If an athlete typically uses 90% carbo_ 2max,
hydrate and 10% fat at 85% VO
proper training will allow the athlete to
use 85% carbohydrate and 15% fat at
_ 2max pace. At 120
the same 85% VO
C/mile, that’s a savings of 37 g or 156
C of glycogen, enough to complete 1–
1.7 miles at the same 85% intensity
without depleting carbohydrate energy
reserves. Most elite marathoners that
have hit the infamous wall experience
their crash within the last 6 miles of
their race (32,43,49,53,64). Fats cannot
be metabolized anaerobically and, as
performance intensity approaches the
lactate threshold, the likelihood of fat
being used decreases (79). Hawley (38)
cites traditional concepts suggesting
that this shift comes from a decrease in
plasma FA as the result of a decreased
blood flow to adipose (and an increased flow to muscles for glycogenolysis). Decreased flow to adipose
means less delivered albumin to transport free fatty acids (FFAs). Hawley
references an argument for mitochondrial efficiency. The evidence suggests
that increased glycogen breakdown
may ‘‘inhibit the entry of long-chain
fatty acid. into the mitochondria’’
(38). This inhibition is cyclical: it
results in increased acetyl CoA and
pyruvate, which in turn also inhibit
a particular fatty-acid transferase for
FFA mitochondrial entry. Nonetheless,
no effect has been shown on mediumchain FA.
HYDRATION
Aside from fueling, fluid availability is
the other ultimately limiting factor for
performance. Hydration research on
performance has a longer-standing
history than sports nutrition and deals
with only one fixed factor: water.
Dehydration can begin by several
methods. The main concern in sport
is the hypotonic water loss through
sweat. A dehydration flowchart demonstrates the interrelation of any single
response to all others when losses are
not offset (Figure 2) (12,44).
As a direct result of the sweat lost to
cool the body, blood volume decreases
(11,12,34). With a lower absolute
volume of blood returning to the heart,
ventricular filling volume is decreased,
thereby decreasing stroke volume.
With this decreased stroke volume
combined with a total decrease in
absolute volume, the HR increases to
compensate. A concern with the
compensation is that it has limited
success and creates an increased workload (oxygen demand) on the heart.
Additionally, the increased respiration
rate and often loss of rhythmic pattern
is barely adequate to meet the demands
Figure 2. Dehydration flow chart showing direct and indirect effects of low blood
volume.
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58
VOLUME 30 | NUMBER 5 | OCTOBER 2008
of the respiratory musculature, let alone
the heart and peripheral system
(12,21,33,69,80). The absolute amount
of oxygen delivered is decreased simply
because its medium, the blood, is not
circulating to the working cells in as
high a volume. Combined with the
heart requiring more oxygen for itself
first, the peripheral system must shift
to an increase in anaerobic pathways
to meet the energy demands. Such a
shift also causes an increase in HR. The
overall impact on the HR and relative
blood volume compromises the body’s
ability to cool itself by shunting blood
to the skin for air contact.
The body becomes unable to keep up
with the mitochondrial heat output,
increasing core temperature from fuel
catabolism, up to 80% of the energy
released. Needing blood for continued
work, muscles compete for a greater
percentage of the already-low volume
shunted to the skin for cooling. The
result is less blood to serve the needs of
oxygen and nutrient delivery, as well as
waste elimination. From here, the
previously described pyruvate cycle
begins (3,55,83). As time and intensity
progress, lactic acid levels increase,
with less oxygen available to convert
the pyruvic acid (79). The concomitant
hydrogen ion accumulation inhibits
aerobic metabolism by way of displacing calcium ions. Once below 6.9 pH,
a resulting increase in citrate levels (53)
affects the efficacy of phosphofructokinase, the aerobic rate-limiter. At
this point, myoexcitation becomes
inhibited. Thus, once again, intensity
is the primary controlling factor.
CALORIC COSTS
A variety of methods exist for calculating caloric expenditure, ranging
from research-based mileage expenditure to individual metabolic assessment. However, most methods are
not appropriate for the population or
purpose at hand. Most formulas are
typically for sedentary to average
individuals, although some formulas
do account for levels of fitness (42). No
equation found is specifically appropriate for the elite athlete, let alone one
that specifies between aerobic, anaerobic, or mixed-power athletes.
A few general rules seem to be widely
accepted in sports nutrition, much like
the theoretical 220 beats per minute
maximum HR for exercise calculations.
Bookstore publications for the layperson suggest that running expends
a confounding range of 90–160 C per
mile (1,3,43,53,64). None of these
citations, however, provide clear guidelines about intensity reference for the
population studied—a 7:30 pace may be
_ 2max for one athlete, yet 90%
60% VO
_ 2max for another (5,70). The variVO
ation is likely the result of the wide
range of performance in data collection,
with 50–90% of maximal efforts considered valid to generalization (26,36).
A well-conditioned athlete expends the
same amount of energy on a fixed
distance (24,53) ‘‘regardless of whether
the run takes just over 2 hours, 3 hours,
Table 1
Substrate expenditure per intensity
E system activity
(%)
Expenditure per mile
(C)
CHO
Fat
CHO
Fat
_ 2 max
VO
C/mi
65%
90–160
65
35
58–104
32–56
70%
90–160
70
30
63–112
27–48
80%
90–160
80
20
72–128
18–32
90%
90–160
90
10
81–144
9–16
_ 2 max and CHO percentage identities. No
Fuel rations in highly trained athletes. Note the VO
published research provided specific calorie per mile relations to aerobic intensity. Derived
from references 52, 55, 64, 81, 83.
or 4 hours!’’ (55). Although twice the
duration is spent running at 5 mph as
compared to 10 mph (12 min/mi and 6
min/mi, respectively), the net energy
cost is nearly the same. For most elite
marathoners who weigh less than 75
kg, this suggests the expenditure is well
below the preceding 90–160C/mi
recommendations. Additional research
_ 2 and speed are in
(5,57,76) supports VO
linear proportion. Nonetheless, the
level of efficiency and expenditure is
more weight and heat dependent (24)
between athletes. Individually, it must
be remembered that ‘‘speed increases
heat more than it dissipates it’’ (24).
Although no method calculates precisely how much energy one individual
athlete will expend during a race, 2
items narrow the variability: testing
and experience. An athlete does not
perform the same each time, and each
season is different. The goal is to hone
the estimate as best as possible without
adverse effects (Table 1). Consulting an
appropriate certified sports nutritionist
may prove invaluable, especially when
the level of expertise required exceeds
the scope of practice of a certified
trainer.
STRATEGIES
It is suggested that a marathon is not
a 26.2-mile race, but rather a 6.2-mile
race (32,43,64,69). The trained body
undoubtedly has enough resources to
perform maximally for about 20 miles
(38,53,55) with the final 6.2 residing in
strategy. As illustrated by Table 2, the
human body in top form has enough
energy to perform at maximal aerobic
capacity for about 90–120 minutes
(14,17,19,56,76). Most athletes never
approach this level of intensity for such
duration.
The elite and aspiring-elite athletes
are most interested in the ability to
maximize their capacities. Yet even
with the best training minds, most
endurance athletes still never succeed
on physical ability alone. If the body
only has limited fuel and no formula
exists to internally amplify the energy,
then how does one suggest crossing
this threshold?
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59
Marathon Fueling Techniques
Table 2
Total caloric capacity in trained athletes
Carbohydrate
g
C
Fat
g
C
Total
450–625
1800–2500
Total
5,500–11,000
50,000–100,000
Liver
70–110
250–450
Adipose
7,800
40,000–100,000
350–500
1400–2050
IMTG
161–330
1,513–3,000
5–80
20–80
FFA
*
*
Muscles
Blood sugar
Derived from reference 3, 38, 48, 53, 55, 76, 83.
*FFAs fluctuate with performance activity, and are released products of adipose, so quantification is widely variable.
The key component to superseding
ability is to think outside the body.
Exogenous fuel during performance is
the only way that triathletes, marathoners, tour cyclists, and other longendurance
athletes
can
thrive
(9,28,38,50,78). Fuel intake during
a marathon has 2 reflective purposes:
1. To provide a continual fuel source
for immediate consumption
2. To provide aerobic fuel methods to
spare resources for the last 6.2 miles
Although cited research is inconclusive
on the precise intensity–expenditure
relationship (26,36,70), it seems that,
for a given athlete, the faster the pace,
the greater the calorie burn per minute
(but not per mile) at a constant training
state. The more efficient the runner
(24,70), the lower the calorie burn at
a constant intensity (5,24,57).
FACTORS
Facts recapitulated:
CHO is the primary source of energy
at high aerobic intensities, 80–90%
_ 2max, used during a marathon.
VO
Muscle glycogen is the preferred
source for muscular work.
The body only has enough muscle
glycogen for about 20 miles if using
75–90% of its caloric expenditure
from muscle glycogen.
Consuming 2,000 C during a race is
simply not practical. Intake of a 6%
carbohydrate solution as found in the
most popular commercial fluid-replacement beverages (1,3,69,75) would
require 8.3 liters intake to meet this
requirement. Precompetition gastric
fluid levels are recommended, if tolerated, to be as high as 600 mL
(10,31,62,68,71). If an athlete consumed the recommended 180–240
mL 6–8% solution every 15 minutes
during competition, a fluid quantity
rarely met (25,41,63,67,74), the athlete
would take in 167–223 C/h and only 2
of the 8.3 liters. Elite men complete
marathons in less than 2.25 hours, and
women 2.5 hours, respectively providing a caloric intake of 502 C and
582 C during the race. Adding one
carbohydrate gel pack (usually 110–
120 C) every 45 minutes still leaves the
athlete far short of the supply goal.
A key to remember is that the fuel
cannot be consumed in high gradients
throughout the entire race. If consumed in the beginning, blood glucose
levels would maximize and glycogen
stores would already be maximized,
allowing little influx, raising plasma
glucose (48,61). Continual, smaller
feedings are more feasible for runners
at high intensities. Coggan and Coyle
(14) did not evaluate the marathoner
but did provide a good model of single
feedings. They performed cycle-based
research evaluating single bolus midexercise. The single feeding took place
after the 2-hour time period and used
a 50% concentration. The consumption would be late for the sub-3-hour
runner and a marathoner could not
consume such a high concentration
solution. Furthermore, the decline in
physiologic (blood glucose) and performance (respiratory exchange ratio)
measures in the study were already
declined below desirable levels. Ivy
et al. (45) demonstrated that carbohydrate consumption did not actually
improve performance in the first 60
minutes of exercise but did improve
fatigue resistance in the last 30 minutes
of exercise. McConnel et al. (56)
compared continual feeding of a 7%
solution to a single-dose 21% solution
administered at 90 minutes of exercise.
Continual 7% ingestion allowed athletes to perform more total work and
_ 2max
achieve a higher percentage of VO
with no difference in respiratory exchange ratio. Similarly, athletes are
better able to maintain constant velocities when consuming a 5.5% solution
as opposed to water or a 6.9% solution
(77). Hawley et al. (39) further supported the Jeukendrup and Jentjens
(48) validation of how carbohydrate
oxidation rates are limited to just
greater than 1 g/min, regardless of
how much fuel is consumed, whether
in single or multiple feedings.
Coping with the declining capacity of
endogenous carbohydrates is a challenge. The ultimate limitation falls
with gastric emptying, usually around
1 L/h, decreasing significantly as intensity progresses to more than 70%
_ 2max (20,51,62,65,72). Athletes can
VO
undoubtedly train themselves to be
able to improve ingestion rate. The
solubility provided in a sports drink has
2 benefits: readily accessible fuel and
rapid fluid uptake. The universal 5–8%
concentration provides optimum fuel
while not compromising water uptake
by the small intestine (18,62,75). While
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VOLUME 30 | NUMBER 5 | OCTOBER 2008
tempting to use a greater-concentration fuel, most research has agreed that
a solution greater than 8% slows gastric
emptying (18,23,26,30,75). Furthermore, by pulling fluid into the intestinal
lumen to facilitate absorption, highconcentration fluids can actually invoke a relative dehydration (46,69,73).
Carbohydrates are rapidly taken up in
the duodenum, almost immediately
after passing the pyloric sphincter
(31,51). The glucose-sodium ‘‘facilitative diffusion’’ (55) alters the relative
osmotic gradient, thus pulling water
with it. The duodenum has a capacity
limit; when this limit is reached, the
stomach stops emptying to allow time
for uptake. Furthermore, water shifts
into the small intestine to aid in diluting
the substance (46,48,69).
RACE INTAKE SCHEDULING
Regardless of what research demonstrates or how complex a formula may
be, each athlete must be treated as
unique. It would be ideal to have
a formula to provide a precise intake
schedule for each athlete. However,
such charting would require extensive
data, much of which changes with the
season: age, gender, total mass, lean
_ 2 at
_ 2 (VO
mass, lactic threshold, vVO
_
a given velocity), VO2max, projected
pace, projected acceleration, fatigue
rate, temperature, humidity, sweat rate,
gastric tolerance, and fuel product.
Each factor is a key in determining
an athlete’s caloric expenditure per
mile at separate stages of the race.
Unfortunately, no clean universal formula exists to calculate such precise
expenditure. Even the mild prediction
equations that do exist have an average
population and are not likely to be
accurate for highly trained athletes.
Barring experience and the existence of
such a precise running formula, the
factors discussed herein can lead to
a generic-yet-accurate intake method.
Studies have shown continuous smaller
feedings are as effective as a significant
feeding shortly before fatigue, generally
at the 2-hour mark (15,48,56,78).
Although Coggan and Coyle (15)
showed an improvement of a single
feeding over placebo, there was no
comparison to continual feeding. Before the CHO feeding, there was
a decrement in performance and
metabolism, an undesired undulation
from steady-rate performance. The
benefit is that the continuous feedings
are likely to promote adequate intake
of fluids and calories. Furthermore, less
flux allows a more steady systemic
response, decreasing risk for adverse
reactions.
Competition and climate factors can
make consuming the appropriate
amount of fuel and, especially, fluid
difficult. Single feedings can lead to
discomfort and gastrointestinal (GI)
distress. Furthermore, larger feedings
require more focus on the GI system,
attenuating blood flow from the
muscles (3,33,68). Athletes are safer
at fast paces with continual fueling
attributable to greater oxygen demands
for the muscles (48). If any adverse
event were to occur that prevented the
athlete from taking in sustenance later
in the race, they, at minimum, will have
partially offset caloric fatigue by their
earlier ingestion. A low steady fluid and
fuel intake early helps with prehydration, which is proven to be more
effective in combating dehydration
than any other strategy (54,60,68,79).
With endocrine changes not resulting
in a noticeable decline in energy
reserves until 30 minutes or more, it
is sensible for feedings to occur at some
point thereafter. Race experience and
training with fueling techniques is
paramount. Once a bolus feeding has
occurred,
low-dose
maintenance
should continue. Maintenance allows
the GI tract to remain primed (65,66)
but, more importantly, it also allows
the bolus intake to be of longer
duration as opposed to a spike and
drop-off
in
energy
uptake
(15,17,54,56,59).
APPLICATION
Table 3 provides a basic example of
race fuel strategy based on the analyses
provided in this review. Few racers
maintain an exact pace throughout
a race. Many strategies have racers
progressing after mile 15, whereas
others drastically accelerate after mile
20. Each racer’s fuel chart must
accommodate their strategic aerobic
intensity at each race stage. Note that
the latter stages of the race, however,
have less focus on simple hydration. At
this point, fuel stores are becoming
scarce, and hydration effects are difficult to counter without disturbing
the need for late, low gastric volumes
but high2energy sources (2,66,78).
Wilmore and Costill (83) validate
this point by stating, ‘‘.in later stages
of an endurance event, blood glucose
may make a larger contribution.’’
FUTURE DIRECTIONS
The proposed schedule is undoubtedly
a pilot theory. Several other factors
must be evaluated and accounted for in
developing a true template for other
influences, namely individual sweat
rates (12,37), consumption tolerance
(59,67), running speeds (18), and
environmental conditions (16,28). Decreased CHO proportions must be
considered in the first hour of exercise
(18,45,47,50,78) and in hot conditions
(16,28,30,65). Table 3 intentionally
violates this rule based on anecdotal
experience, but will be modified as
necessary based on future research.
Controlled studies and training sessions allow for ideal time-based intake.
Aside from select events, races are
geared toward per-mileage set-ups to
accommodate an array of paces; therefore, it becomes difficult for the fastest
racers to establish a personal fuel and
hydration resource set-up for the
course. Most races have hydration and
sports drink stops every mile, intermittently including foods and other fuels.
Reasoning from there, race-day fueling
and hydration must be founded on
mileage as opposed to time.
Although in this review we address the
main acceptance of a rough 1 g/min
CHO oxidation rate, other authors
suggest that oxidation rates up to
2 g/min may be possible (14,82). Coggan
and Coyle used very high concentrations
(20% and 50% solutions) of glucose
polymers and sucrose, whereas Wallis
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61
Marathon Fueling Techniques
Table 3
Marathon fueling schedule
Pace
7:00 per mile
Fluid
(mL)
1
7:00
2
14:00
3
21:00
4
28:00
Sport drink
180
5
35:00
Water
180
6
42:00
Gel and water
240
7
49:00
Water
180
8
56:00
9
63:00
10
70:00
11
77:00
Water
180
12
84:00
Gel and water
240
13
91:00
Water
180
14
98:00
15
105:00
16
112:00
17
119:00
Water
240
18
126:00
Gel and water
180
19
133:00
Water
180
20
140:00
21
147:00
22
154:00
23
161:00
Water
180
24
168:00
Sport drink
180
42
144:00
Sport drink
180
42
120:00
25
175:00
Sport drink
60
14
150:00
Sport drink
120
28
125:00
26
182:00
156:00
130:00
26.2
183:24
157:12
131:00
Sport drink
Time
180
180
42
Source
Fluid
(mL)
Time
Water
C
5:00 per mile
Mile
Total
Source
6:00 per mile
C
6:00
5:00
12:00
10:00
18:00
Water
180
24:00
Sport drink
180
42
42
Sport drink
180
42:00
Water
180
48:00
Gel and water
240
54:00
Water
180
42
Sport drink
240
56
120
Sport drink
180
42
78:00
Water
180
Sport drink
180
3180
42
84:00
Gel and water
240
90:00
Water
180
120
Sport drink
240
56
180
42
Water
240
40:00
Gel and water
240
45:00
Water
180
55:00
Sport drink
180
42
60:00
Sport drink
180
42
70:00
Water
180
75:00
Gel and water
240
80:00
Water
180
30:00
120
120
85:00
108:00
90:00
Sport drink
240
114:00
95:00
Water
180
105:00
Gel and water
240
110:00
Water
120
115:00
Sport drink
180
42
Sport drink
120
28
2880
612
120:00
Water
180
126:00
Gel and water
240
132:00
Water
180
3060
56
100:00
120
138:00
598
Sport drink
65:00
96:00
120
20:00
50:00
72:00
102:00
C
35:00
60:00
120
Fluid
(mL)
25:00
36:00
66:00
Source
15:00
30:00
120
Time
612
120
Hypothetical in-race fuel schedule. Notice that the allocation is based on time and not mileage, nor is there any accounting for individualism.
et al. used a specific 11.25% maltodextrin–fructose combination to achieve
these rates. Although both studies
were conducted on cyclists who
have a different tolerance, the results
do hold hope for runners who
generally tolerate lower volumes and
concentrations (67).
A review of the literature seems to
indicate a relationship between percent
_ 2max and percent carbohydrate oxVO
idation (Table 1). The fact that these
percentages mirror one another must
be investigated further. For example,
_ 2max equal or approximate
does 75% VO
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62
VOLUME 30 | NUMBER 5 | OCTOBER 2008
75% carbohydrate oxidation in highly
trained athletes? Jentjens et al. (46) calls
for even more detailed understanding
of carbohydrate type in fueling. Future
expansion on this investigation will
include total concentration and osmolality analysis for total race intake.
A procedure must be set forth for
developing the hydration and fueling
schedule for each runner. A quality
model must be developed that is simple
to follow. With the amount of existing
research, a guiding template is feasible,
where coaches spend their time assessing the athlete and minimal time
perfecting the tool.
John
R. Bennett is the
owner of Athlit
Peak Performance
and consults in
performance enhancement physiology and an Adjunct Professor at the
University of Central Florida.
Michael
P. Kehoe is the
Program Coordinator of the Sports
and Fitness, B.S.
degree program at
the University of
Central Florida.
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