Postexercise protein-carbohydrate and carbohydrate
supplements increase muscle glycogen in men and women
M. A. TARNOPOLSKY,1 M. BOSMAN,2 J. R. MACDONALD,2
D. VANDEPUTTE,2 J. MARTIN,2 AND B. D. ROY2
Departments of 1Medicine and 2Kinesiology, McMaster University,
Hamilton, Ontario, Canada L8S 4K1
gender; sex differences; defined formula; exercise
of the provision of nutrients after exercise
has become a popular subject in recent years (3, 11, 26).
It is known that carbohydrate (CHO) supplements
provided within the first several minutes of completion
of exercise result in a more rapid repletion of muscle
glycogen compared with the same supplement provided
2 h after completion of exercise (11). The mechanism
responsible for this observation is thought to be related
to the combined effect of insulin and contractionstimulated glucose transport via GLUT-4 transporters
(6). The migration of these transporters from intracellular stores to the sarcolemma and t tubules of muscle is
partially mediated by phosphatidylinositol 3-kinase
(8). The practical implication of these findings is that
it may be possible to accentuate glycogen repletion by
THE TIMING
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merely altering the timing of nutrient provision (i.e.,
providing nutrients shortly after exercise termination).
It has been suggested that a combination protein
(Pro) and CHO supplement provided immediately postexercise may potentiate insulin release and, hence,
glycogen repletion (26). For example, Zawadzki and
colleagues (26) found that the insulin rise and glycogen
repletion rate was 39% greater with a combined ProCHO compared with a CHO supplement. The confounding factor in this latter study was the provision of 43%
more energy in the Pro-CHO trial compared with the
CHO trial; thus two variables changed simultaneously.
Therefore, one purpose of the present study was to
compare the rate of glycogen resynthesis after endurance exercise when the energy content of both the
postexercise supplement (CHO compared with CHOPro-Fat) and the 24-h energy intake of all trials was
held constant.
In addition, almost all of the research that has been
conducted to examine postexercise supplements has
used male subjects exclusively (5, 11, 26). Aside from
the inherent gender bias, there is also accumulating
evidence that there are sex differences in the metabolic
response to endurance exercise (22–24). These differences may be related to our recent finding that men, but
not women, increase muscle glycogen concentration in
response to an increase in dietary CHO content from 60
to 75% of energy intake (21). Therefore, a second
purpose of this study was to examine postexercise
glycogen repletion in both sexes.
We had three a priori hypotheses. 1) There would be
no difference in the rate of glycogen repletion between
CHO and CHO-Pro-Fat supplements, yet there would
be a greater rate of glycogen repletion compared with
placebo (Pl). 2) The glycogen repletion rate for women
would be less than that observed in men. 3) Women
would have a lower respiratory exchange ratio (RER)
during endurance exercise (indicative of greater lipid
oxidation).
METHODS
Subjects. Two groups of male (n 5 8) and female (n 5 8)
athletes volunteered for the study. The study was approved
by the McMaster University Human Ethics Committee, and
written informed consent was obtained after the experimental procedures, risks, and benefits were explained to each
subject.
Men were recruited who had a peak O2 consumption
(V̇O2 peak) of at least 55 ml · kg21 · min21. Women were matched
to the men by training history and required a V̇O2 peak of at
least 50 ml · kg21 · min21. Equalized matching based on these
parameters was confirmed by the similarity in V̇O2 peak when
expressed per kilogram lean mass (Table 1).
0161-7567/97 $5.00 Copyright r 1997 the American Physiological Society
1877
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Tarnopolsky, M. A., M. Bosman, J. R. MacDonald, D.
Vandeputte, J. Martin, and B. D. Roy. Postexercise proteincarbohydrate and carbohydrate supplements increase muscle
glycogen in men and women. J. Appl. Physiol. 83(6): 1877–
1883, 1997.—We have previously demonstrated that women
did not increase intramuscular glycogen in response to an
increased percent of dietary carbohydrate (CHO) (from 60 to
75% of energy intake) (M. A. Tarnopolsky, S. A. Atkinson, S.
M. Phillips, and J. D. MacDougall. J. Appl. Physiol. 78:
1360–1368, 1995). CHO and CHO-protein (Pro) supplementation postexercise can potentiate glycogen resynthesis compared with placebo (K. M. Zawadzki, B. B. Yaspelkis, and J. L.
Ivy. J. Appl. Physiol. 72: 1854–1859, 1992). We studied the
effect of isoenergetic CHO and CHO-Pro-Fat supplements on
muscle glycogen resynthesis in the first 4 h after endurance
exercise (90 min at 65% peak O2 consumption) in trained endurance athletes (men, n 5 8; women, tested in midfollicular
phase, n 5 8). Each subject completed three sequential trials
separated by 3 wk; a supplement was provided immediately
and 1-h postexercise: 1) CHO (0.75 g/kg) 1 Pro (0.1 g/kg) 1
Fat (0.02 g/kg), 2) CHO (1 g/kg), and 3) placebo (Pl; artificial
sweetener). Subjects were given prepackaged, isoenergetic,
isonitrogenous diets, individualized to their habitual diet, for
the day before and during the exercise trial. During exercise,
women oxidized more lipid than did men (P , 0.05). Both of
the supplement trials resulted in greater postexercise glucose
and insulin compared with Pl (P , 0.01), with no gender
differences. Similarly, both of these trials resulted in increased glycogen resynthesis (37.2 vs. 24.6 mmol · kg dry
muscle21 · h21, CHO vs. CHO-Pro-Fat, respectively) compared
with Pl (7.5 mmol · kg dry muscle21 · h21; P , 0.001) with no
gender differences. We conclude that postexercise CHO and
CHO-Pro-Fat nutritional supplements can increase glycogen
resynthesis to a greater extent than Pl for both men and
women.
1878
GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
Table 1. Subject characteristics
Men (n 5 8) Women (n 5 8)
Characteristic
Weight, kg
Age, yr
Lean body mass, kg
Body fat, %
V̇O2 peak, ml · kg21 · min21
V̇O2 peak, ml · kg LBM21 · min21
72.9 6 5.4
22.1 6 2.2
64.6 6 5.2
11.4 6 2.6
56.9 6 2.65
63.8 6 2.6
Significance
(P value)
61.1 6 8.5
20.3 6 0.89
47.4 6 4.3
21.9 6 5.5
51.7 6 2.4
65.1 6 3.5
,0.01
NS
,0.001
,0.001
,0.05
NS
3.8 6 0.25
7.7 6 2.9
5.1 6 0.7
NS
NS
NS
Training history
Time training, yr
Frequency, h/wk
Duration, h/wk
4.2 6 1.5
6.8 6 2.6
4.7 6 1.1
Values are means 6 SD; n, no. of subjects. LBM, lean body mass;
V̇O2 peak, peak O2 consumption; NS, not significant. P values by
independent t-test.
Table 2. Timing of nutrient delivery
Trial
Post-Ex (0 1 1 h)
1100
1400
CHO/Pro/Fat
Isoenergetic
(66% CHO,
23% Pro,
11% Fat)
1 g/kg CHO
(100% CHO)
Sucralose
Lunch
Snack
Supper 1
Placebo
Lunch
Snack
Lunch
Snack
Supper 1
Fat/Pro
Supper 1
CHO/Pro/Fat
CHO
Placebo
1700
Lunch, snack, and supper were identical for each subject in each
trial, based on habitual dietary intake values. CHO, carbohydrate;
Pro, protein; Ex, exercise.
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All female subjects were eumenorrheic for at least 6 mo
before testing, and three were taking oral contraceptives. The
women were tested during the midfollicular phase of their
menstrual cycle. This phase was chosen for a more accurate
ability to determine the onset of the follicular phase (day 1 of
menses) compared with the luteal phase (ovulation) and also
for comparison with our previous work (17, 22).
Design. The subjects participated in a Pl-controlled, doubleblind three-part trial. Trial 1, CHO-Pro-Fat, was 66% CHO,
23% Pro, 11% Fat. Specifically, CHO 5 56% sucrose and 46%
glucose polymer from corn syrup solids; Pro 5 milk protein;
Fat 5 canola, sunflower, and corn oil, with vitamins, minerals, and flavoring (commercially available sports drink, MeadJohnson, Canada). Trial 2, a CHO-only trial, included 100%
CHO, as described above. Trial 3 used, as a Pl, Sucralose
(sucrose derivative not recognized as CHO by the body, as
well as vitamins, minerals, and flavoring). Each subject
completed all three trials with 3–4 wk separating each trial.
Each trial was 5 days in length and was identical in terms of
exercise, diet timing, and prescription (see Experimental
protocol). The trial sequence was randomly chosen. However,
because of an error by the technician who blinded the study,
all subjects participated in each trial in the same sequence
[i.e., all subjects received the supplements in the same order
listed above, yet both they and the other investigators were
blinded to the supplement allocation (double blind)].
Within 2 wk of the experimental trials, V̇O2 peak was determined on an electrically braked cycle ergometer by using a
computerized open-circuit gas-collection system as previously
described (17). V̇O2 peak was considered to be the highest
value recorded during a standard incremental cycle ergometer protocol, with termination of the test after O2 consumption (V̇O2) values reached a plateau for three readings, RER
was .1.12, and subjects could not sustain pedal revolutions
at ,60 revolutions/min (rpm) despite vigorous encouragement. Body density was determined by hydrostatic weighing,
and percent body fat was calculated as described (17).
All subjects collected 4-day diet records, which were analyzed by using a nutritional analysis software package (Nutritionist IV; First Data Bank, San Bruno, CA). For each subject,
individual diets were designed that were both isoenergetic
and isonitrogenous for the three trials. The only parameter
that was different was the composition of the postexercise
supplement on day 1 (practice day) and day 5 (test day). For
example, on the Pl-testing trial, the Pl drink was given
postexercise and a CHO-Pro-Fat supplement was provided
with supper. The reverse was true for the CHO-Pro-Fat trial;
namely, the Pl supplement was provided with supper. For the
CHO trial, a Pro-Fat supplement was provided with supper
(Table 2). Thus, over a 24-h period, the energy and nutritional
composition of each trial was identical (Table 3). Diets were
rigidly controlled over the 5-day experimental protocol for
each of the three trials. Subjects were instructed to eat only
the prepackaged diets provided on days 1, 4, and 5. Individual
checklist diets were followed on the alternate days (days 2
and 3). Compliance was assessed by analyzing the diet
checklists that were returned by each subject. Furthermore,
on the days when food was prepackaged, they returned any
uneaten food for weighing. The apparent energy intake
compliance was .96% of that distributed.
Experimental protocol. During each 5-day experimental
period, subjects adhered to the postexercise regimen to
simulate a typical training schedule: on days 1 and 5, subjects
exercised on a cycle ergometer at a power output preset to
elicit 65% of V̇O2 peak for 90 min. Day 1 was designed as a
controlled trial practice session in preparation for day 5 and
was performed in the evening (from 1700 to 2000), with
postexercise supplements identical to that described below
for day 5. No exercise was performed in the 24 h before each of
these testing days. On day 2, subjects arrived at the laboratory in a fasted state (at 0700–0900) and performed a
high-intensity ride to exhaustion at a preset load designed
to elicit 75% of V̇O2 peak. The ride was terminated when
subjects could not sustain pedal revolutions of .60 rpm.
Subjects cycled for 45 min at 65% of V̇O2 peak on day 3 and
rested on day 4.
On day 5, subjects arrived in a fasted state (at 0700–0900),
and a 22-gauge plastic catheter was inserted into the antecubital vein for blood sampling. Blood samples were then
collected into prechilled, heparinized tubes every 30 min
during exercise and every 20 min up to 2 h postexercise.
Additional samples were collected at 3 and 4 h postexercise,
and the catheter was then removed. These tubes were centrifuged immediately, and aliquots of plasma were stored at
250°C for subsequent analysis of glucose and insulin.
After the exercise was completed, a muscle biopsy was
obtained from the vastus lateralis by using a suction-modified
Bergstrom needle-biopsy technique. A supplement (CHO-ProFat in trial 1, CHO in trial 2, and Pl in trial 3) was given
immediately after the muscle biopsy [time 0 (t 5 0)] and at 1 h
(t 5 11) after the first supplement. A second needle biopsy
was performed on the contralateral vastus lateralis 4 h after
the first supplement (t 5 14). All biopsy samples were blotted
and dissected free of visible connective tissue, quenched in
liquid nitrogen, and then stored at 250°C for later analysis of
muscle glycogen.
During each trial, 24-h urine collections were completed
over day 4 (rest) and day 5 (exercise). Aliquots were taken and
stored at 250°C for subsequent analysis of creatinine and
total urea nitrogen.
1879
GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
Table 3. Habitual and trial nutritional data
Nutritional Data
Diet
Habitual
Men
Women
CHO/Pro/Fat
Men
Women
CHO
Men
Women
Placebo
Men
Women
%Fat
%CHO
%Pro
Pro, g · kg21 · day21
kcal/kg
3,218 6 1,328
2,059 6 363*
31 6 7
26 6 6
52 6 10
60 6 6
17 6 6
14 6 2
1.95 6 1.2
1.23 6 0.31*
44.1 6 17.7
34.5 6 8.8*
50 6 20.8
44 6 10.8*
3,223.3 6 1,303
2,099.4 6 351*
31 6 6
26 6 6
53 6 10
61 6 6
17 6 6
15 6 2
1.97 6 1.2
1.26 6 0.31*
44.6 6 18.3
35.1 6 7.8*
50.1 6 20.5
44.9 6 10.6*
3,230.5 6 1,299
2,066.8 6 297*
34 6 6
27 6 9
53 6 9
45 6 4
17 6 6
14 6 2
2.0 6 1.2
1.22 6 0.3*
44.8 6 18.2
34.5 6 7.8*
50.3 6 20.4
44.2 6 9.6*
3,222 6 1,301
2,099.4 6 351*
31 6 6
25 6 9
53 6 10
61 6 6
17 6 6
15 6 2
1.94 6 1.3
1.26 6 0.31*
44.7 6 18.2
35.1 6 8.5*
50.1 6 20.5
45.1 6 10.4*
Total kcal
kcal/kg LBM
Values are means 6 SD. * P , 0.05 compared with men.
RESULTS
Substrate oxidation. The RER values over the 90 min
of exercise were significantly lower for women compared with men for all three trials (CHO-Pro-Fat:
0.902 6 0.04 vs. 0.934 6 0.03, women vs. men, respectively; CHO: 0.882 6 0.04 vs. 0.902 6 0.03, women vs.
men, respectively; Pl: 0.896 6 0.03 vs. 0.918 6 0.02,
women vs. men, respectively; P , 0.005). There were no
significant gender or time differences in V̇O2 or heart
rate for any of the three trials (Table 4). There were no
differences between the trials in 24-h urea nitrogen or
creatinine. There was a trend for 24-h urea nitrogen
and creatine to be greater on the exercise day compared
with the rest day [not significant (NS)]. There were no
differences between men and women in 24-h urea
nitrogen and creatinine. The total energy cost of the
90-min exercise bout at 65% V̇O2 peak for the men was
1,214, 1,198, and 1,214 kcal for the CHO-Fat/Pro, CHO,
and Pl trials, respectively. Similarly, the total energy
cost for the women at 65% V̇O2 peak was 910, 899, and
963 kcal for the CHO-Fat/Pro, CHO, and Pl trials,
respectively. Lipid contributed to ,29% of the total
energy cost for the women and 23% for the men of the
90-min exercise bout over the three trials (P , 0.005).
Table 4. Substrate utilization and O2 consumption
during trials
Urea Nitrogen/
Creatinine, g/day
Trial Diet
CHO/Pro/
Fat
Men
Women
CHO
Men
Women
Placebo
Men
Women
RER
Rest
Exercise
%V̇O2 max
Heart
Rate,
beats/
min
0.934 6 0.03 9.05 6 1.6 9.3 6 3.2 66.9 6 0.3 153 6 2
0.902 6 0.03* 8.5 6 2.6 9.86 6 3.2 64.6 6 0.6 155 6 2
0.902 6 0.03
0.882 6 0.04*
8.9 6 2.8 10.1 6 2.8 63.1 6 0.8 160 6 5
9.7 6 3.2 9.3 6 1.9 63.8 6 1.1 154 6 2
0.918 6 0.02
0.896 6 0.03*
9.2 6 3.1 9.7 6 4.5 63.1 6 1.7 159 6 3
9.5 6 3.1 10.1 6 3.4 63.5 6 1.7 153 6 4
Values are means 6 SD. Exercise data [respiratory exchange ratio
(RER), maximal O2 consumption (V̇O2 max), heart rate] are collapsed
across 90 min of exercise. * Values are significantly lower for women
compared with men; P , 0.005.
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Plasma and urine. All plasma samples were assayed for
insulin by radioimmunoassay (Diagnostics Products, Los
Angeles, CA). Glucose was determined by spectrophotometry
(kit 135, Sigma Diagnostics, St. Louis, MO). Intra-assay
coefficient of variation for glucose and insulin was ,5%.
Rest and exercise 24-h urine collections were assayed by
using spectrophotometry to determine urea nitrogen (procedure 640, Sigma Diagnostics) and urine creatinine (kit 555-A,
Sigma Diagnostics).
Muscle glycogen analysis. Before analysis, the muscle
samples were lyophilized and powdered, and any visible
remaining blood or connective tissue was removed before
weighing. Glycogen concentration was determined by a
method adapted from that described by Bergmeyer (1). Briefly,
160 µl of NaOH were added to ,2.0–4.0 mg of dry muscle
(dm) tissue and mixed thoroughly. After incubation at 80°C
for 10 min, 640 µl of a combined acid-buffer solution (HClcitrate) were added to neutralize the sample. Then 40 µl of a
reagent solution were added [in mM: 375 triethanolamine,
150 KOH, 112.5 Mg(Ac)2-H2O, 3.75 EDTA-Na2-H2O], along
with 5 µl of 45 mM ATP solution, 5 µl of 60 mM dithiothreitol
solution, and 10 µl of 30 mM NAD solution. Background
absorbance measures were then made with an ultraviolet
spectrophotometer at 340 nm (model 1201; Shimadzu, Tokyo,
Japan). Then 4 µl were added of a combined glucose 6phosphate dehydrogenase/HK solution (200 units of glucose
6-phosphate dehydrogenase with 200 U HK, dissolved in 800
µl doubly distilled water; Sigma Chemical, St. Louis, MO).
Absorbance at 340 nm was then measured 15 min after the
addition of the enzyme solution. Background absorbance was
then subtracted from the reaction absorbance, and the obtained value was plotted against a glycogen standard (Sigma
Chemical) curve for determination of glycogen concentration.
Muscle glycogen concentrations are presented as millimoles
of glycogen per kilogram of dm weight per hour.
Calculations. Muscle glycogen resyntheses rate was calculated from the equation: Rate 5 (Gpost 2 Gpre )/t, where Gpre is
the muscle glycogen concentration immediately postexercise,
Gpost is the muscle glycogen concentration 4 h postexercise,
and t is the time between the two biopsies.
Statistics. Muscle and blood data were analyzed by using
repeated-measures analysis of variance (gender 3 time 3
condition) (version 5.0 Statistica, Statsoft, Tulsa, OK). When
a significant interaction was found, Tukey’s post hoc analysis
was used to locate the pairwise differences. Integrated area
under the curve data for glucose and insulin was analyzed by
using a one-way repeated-measures analysis of variance
(version 5.0 Statistica). P , 0.05 was accepted as statistical
significance. Values are expressed as means 6 SD.
1880
GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
CHO contributed 75% of the energy cost of the three
trials for the men and 68% for the women (P , 0.005).
Pro contributed 2% to the energy cost of the 90 min of
exercise for the men and 3% for the women (NS;
calculated from RER and urea by using equations from
Ref. 9).
Insulin and glucose. There were no differences in
plasma insulin concentrations between the trials at the
beginning of exercise, at the end of exercise, and at the
time of the second biopsy. Plasma insulin concentrations were significantly higher for the CHO-Pro-Fat vs.
the Pl condition at the time points 20, 40, 60, 80, and
120 min postexercise (Fig. 1B; P , 0.01). Similarly, the
CHO condition significantly elevated plasma insulin
concentrations at 20, 40, 60, 80, 100, and 120 min
postexercise compared with the Pl (P , 0.01). The total
integrated area under curve for insulin was significantly greater for both the CHO-Pro-Fat trial (about
threefold) and the CHO trial (about fourfold) vs. the Pl
trial (21.66 vs. 26.2 vs. 6.34 µIU · l21 · h21 in CHO-ProFat vs. CHO vs. Pl trials, respectively; P , 0.01). There
were no significant differences between men and women.
There were no differences between the three trials in
plasma glucose concentration at baseline or during
exercise. The CHO trial resulted in significantly higher
plasma glucose at 40, 60, 80, 100, and 120 min com-
pared with the Pl trial (P , 0.01; Fig. 1A). The
CHO-Pro-Fat trial resulted in an increase in glucose vs.
the Pl trial, although only the 40-min time point was
statistically significant (P , 0.05). The area under the
glucose curve was not statistically different between
the CHO-Pro-Fat and the CHO trial (4.75 vs. 5.35
mM/h, respectively) but these were both greater than
the Pl trial (4.06 mM/h; P , 0.05; Fig. 1A, right). There
were no significant differences between men and women.
Glycogen. The rates of postexercise muscle glycogen
recovery for both the CHO-Pro-Fat and the CHO trials
were significantly higher (P , 0.05) compared with the
Pl trials [in mmol · kg dm21 · h21 (men vs. women, respectively): CHO-Pro-Fat, 25.5 vs. 23.5; CHO, 40.0 vs. 34.5;
Pl, 3.0 vs. 12.0]. There were no significant differences in
muscle glycogen recovery rates between men and women
for any of the three trials (Fig. 2). For both the
CHO-Pro-Fat and the CHO trials, the muscle glycogen
concentration was significantly higher (P , 0.001) at
t 5 14 h compared with the immediate postexercise
time point (t 5 0) (CHO-Pro-Fat, from 142.4 6 69 to
245.2 6 75 mmol/kg dm; CHO, from 163.4 6 53.6 to
312.8 6 56 mmol/kg dm). The Pl trial did not result in
an increased muscle glycogen concentration after 4 h
(from 210 6 68 to 237 6 80 mmol/kg dm; NS). Post hoc
analysis demonstrated that the glycogen concentration
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Fig. 1. A: plasma glucose concentration
during and after (p) endurance exercise
at 65% peak O2 consumption for each
trial; BL, baseline; CHO, carbohydrate;
Pro, protein. Data for men and women
were collapsed because there was no
main effect for gender. Right: integrated area under the curve (AUC). B:
plasma insulin concentration at same
time points for each trial (collapsed
across genders). Right: integrated AUC.
* P , 0.05 compared with placebo.
GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
at t 5 0 was greater for the Pl trial compared with the
CHO-Pro-Fat and CHO trials (P , 0.01).
DISCUSSION
We have demonstrated that postexercise muscle glycogen resynthesis rates are similar for both CHO and
isoenergetic CHO-Pro-Fat supplements and that both
of these are greater than for a Pl. Contrary to our other
hypothesis, the resynthesis rate was similar for men
and women.
Some have questioned the practical value of postexercise supplements because of the observation that muscle
glycogen concentrations were not different 8 and 24 h
after exercise cessation when CHO was provided immediately or after a 2-h time delay (16). However, there
are several examples where early postexercise supplementation may be of practical benefit: 1) when an
athlete is training or competing more than once per
day, 2) when an athlete exercises in the evening on one
day and again the next morning, and 3) when an
athlete may not be able to consume a high-CHO diet
over the ensuing 24-h postexercise period.
The finding of similar postexercise insulin responses
with different supplements is consistent with some (5,
18a) but not all (21, 26) studies. Zawadzki and colleagues (26) found that plasma insulin concentrations
and glycogen resynthesis rates were greater for CHOPro compared with CHO supplements. However, it is
not possible to separate the cointervention of added
energy intake (143%) from the macronutrient compositional changes in their study (26). Our finding of no
difference in glycogen resynthesis between isoenergetic
CHO and CHO-Pro-Fat supplements suggests that
energy intake may have contributed to the observations in the latter study (26). The finding of similar
insulin and glucose responses was also confirmed in
other studies where isoenergetic CHO and CHO-Pro (5)
and CHO-Pro-Fat (unpublished observations by B. D.
Roy and M. A. Tarnopolsky) were compared after
resistance exercise. It may be argued that the minimal
fat content of the supplement used in our study may
have confounded the results by inhibiting gastric emptying and, thus, potentially inhibiting the rapid provision of CHO to the muscle and CHO-Pro to the pancreas for insulin release. We do not feel that gastric
inhibition was a factor, because insulin rose rapidly in
the CHO-Pro-Fat trial and was not statistically different from the CHO trial at any time after the supplement. Furthermore, over a 24-h period after endurance
exercise, the addition of similar amounts of fat to the
diet did not impair glycogen resynthesis in a study of
eight well-trained endurance athletes (3). The CHO
source used in the current study was sucrose (contains
fructose) and glucose polymers rather than glucose in
the study by Zawadzki et al. (26). However, there were
very similar insulin responses observed in Zawadzki’s
study (26) compared with the present study. Thus it is
unlikely that this could have altered the results. Furthermore, the most important comparison in the present study was that between the CHO and CHO-ProFat trial, and the CHO source was identical in these.
It could also be argued that the order of the trials in
our study could have influenced the results. However,
we found no difference between the trials in V̇O2, heart
rate, RER, insulin, or glucose during exercise. Because
we studied trained endurance athletes who were accustomed to this training intensity and we separated the
trials by nearly 1 mo, a training effect would be further
negated. However, the postexercise glycogen concentration was significantly greater for the Pl trial compared
with the other trials because of two outliers (1 in each
gender). These subjects were predominantly runners,
and it is possible that they developed a more efficient
cycling form in subsequent trials. A greater reliance on
the gastrocnemius and hamstrings (by use of toeclips)
would reduce the work of the quadriceps muscles.
Lower glycogen concentrations can result in greater
glycogen resynthesis rates per se (18, 27). However,
this difference is only significant when muscle glycogen
concentrations are ,120 mmol/kg dm (18). The 27%
difference in glycogen concentration between the two
supplement trials compared with the Pl trial fell within
the range (120–280 mmol/kg dm) that has been shown
to have no effect on glycogen resynthesis rates (18).
Furthermore, the postexercise glycogen values for the
CHO-Pro-Fat and CHO trials were nearly identical,
and the comparison between these two trials was the
most important measurement in the present study.
A strength of the present study was the provision to
each of the subjects in each trial of prepackaged diets
that were isoenergetic to the subjects’ habitual diet. We
also controlled for 24-h energy intake by providing
complimentary blinded supplements later in the day to
ensure that the macronutrient composition over the
24-h period was consistent. This is important to examine the true effect of the timing of macronutrient
provision not confounded by supplemental energy. A
practical advantage of this approach is that we have
found that women and those on restricted energy
intakes are reluctant to consume additional energy.
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Fig. 2. Rate of glycogen resynthesis for each trial over first 4 h
postexercise. Open bars, men; solid bars, women. * P , 0.05 compared
with placebo.
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GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
We thank Roxanna Birsan for technical assistance.
This work was supported by a grant from Mead-Johnson, Canada.
Address for reprint requests: M. Tarnopolsky, Depts. of Neurology,
Physical Medicine, and Kinesiology, Rm. 205, Ivor Wynne Centre,
McMaster Univ., Hamilton, Ontario, Canada L8S 4K1 (E-mail:
[email protected]).
Received 29 May 1997; accepted in final form 28 July 1997.
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Another advantage of combination postexercise supplements is that they provide ‘‘balanced’’ macronutrients.
For example, if one were to give a 1 g/kg CHO drink
after exercise at t 5 0 and 11 h to a woman weighing 60
kg, the energy content would be 480 kcal. With an
energy intake of ,2,000 kcal, this would amount to
,25% of daily intake as a simple sugar. If this were
part of a habitual diet, it might limit intake of vitamins,
calcium, iron, and other minerals (25) that may be of
particular concern for the female athlete (7, 12). Furthermore, habitual endurance training increases protein requirements for male (14, 23) and female (17)
athletes.
Our group has previously demonstrated that men,
but not women, increased muscle glycogen concentration in response to an increase in dietary CHO from 60
to 75% of energy intake (24). The results of the present
study, however, were contradictory to our a priori
hypothesis and did not show a difference between the
genders in the rate of glycogen repletion. This is an
important finding for female athletes, who may have a
limited ability to supercompensate (24). Whether the
provision of supplements in the early postexercise
period may permit glycogen supercompensation in
women remains to be explored.
Our finding of a lower RER for the women in the
present study has been demonstrated in three of our
previous studies (17, 22, 24) and by others (2, 15, 10).
The RER finding indicates a greater lipid and lesser
CHO oxidation for women during endurance exercise at
65% V̇O2 peak. We found a trend toward a higher urea
excretion on the exercise day for both men and women.
This suggested a trend toward an increased whole body
protein oxidation consequent to the exercise stress (17).
Contrary to our work in nutrient supplementation after
resistance exercise (unpublished observations by B. D.
Roy and M. A. Tarnopolsky), we did not demonstrate a
suppression of urea excretion for the two supplement
trials compared with the placebo trial. This may relate
to differing metabolic situations after these types of
activity. After resistance exercise, for example, we
found that the reduction in urea excretion for the early
supplement trial paralleled a decline in 3-methylhistidine excretion (indicative of lesser myofibrillar protein
degradation) (18a). Although 3-methylhistidine was
not measured in this study, it is unlikely that habitual
endurance exercise at 65% V̇O2 peak would be associated
with myofibrillar protein breakdown (4). Therefore, the
trend toward an increased urea excretion on the exercise day was likely caused by an increased protein
oxidation during (13, 17) and not after exercise.
In summary, we have demonstrated that, compared
with a Pl drink, CHO and CHO-Pro-Fat supplements
when given early after endurance exercise result in
more rapid glycogen resynthesis rates. Importantly,
this finding is true for both male and female athletes.
GLYCOGEN REPLETION IN MEN AND WOMEN AFTER EXERCISE
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1883
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