Glycogen and Resistance
Training
Todd Astorino, M.S. and Len
Kravitz, Ph.D.
Studies Reviewed:
Haff, G. G., et al. 1999. The effect of carbohydrate supplementation on
multiple sessions and bouts of resistance exercise. Journal of Strength and
Conditioning Research, 13, (2), 111-7.
Leveritt, M. & Abernethy, P. J. 1999. Effects of carbohydrate restriction
on strength performance. Journal of Strength and Conditioning Research, 13, (1),
52-7.
The Role of Glycogen in Aerobic and Resistance Exercise
The role of glycogen (stored carbohydrate in muscle) in aerobic exercise has
been clearly shown to be associated with increased work output and duration
(Haff et al., 1999). Carbohydrate is the body’s preferred substrate during
endurance exercise due to its more efficient energy yield per liter of oxygen
consumed. Previous resistance training research suggests that weight training is
associated with a consequential depletion of muscle glycogen stores. For
instance, Robergs et al. (1991) demonstrated that subjects performing 6 sets of
leg extensions at 35% and 70% of 1RM resulted in a decrease in muscle glycogen
by 38% and 39%, respectively. This article will review two recent articles that
further elucidate the role of glycogen in resistance exercise. It is hoped that
the personal trainer will gain a better understanding as to the appropriateness
of carbohydrate replenishment recommendations for clients engaged in resistance
exercise programs.
Energy for Resistance Exercise
Due to the intense and short-term nature of individual bouts of resistance
training, it would seem likely that this activity would be highly dependent upon
muscle glycogen for ATP provision. High-intensity exercise of short duration
(&Mac178; 30 seconds) is characterized by a rapid breakdown of phosphocreatine
for the production and use of ATP, as well as stimulation of glycogenolysis
(breakdown of glycogen) and glycolysis (breakdown of glucose), with a lesser
contribution of oxidative metabolism.
In a study by Tesch et al. (1986), nine bodybuilders completed five sets each of
front squats, back squats, leg presses, and leg extensions to fatigue,
comprising 30 minutes of exercise. Biopsies of muscle samples were obtained from
the vastus lateralis before and immediately after exercise. Muscle glycogen
concentration was 26% lower post-exercise, a rather modest decline considering
the demanding exercise protocol completed. This led the authors to conclude that
energy sources in addition to muscle glycogen support heavy resistance training.
Data from Essen-Gustavsson and Tesch (1990) with nine bodybuilders performing
the same exercise regimen (as above) revealed a 28% decrement in muscle glycogen
content as well as a 30% decrease in muscle triglyceride content. This suggests
that intramuscular lipolysis (breakdown of triglycerides) may also play a role
in energy production during repeated high-intensity exercise. Overall, research
suggests that intramuscular glycogen is an important fuel supporting weight
training exercise, but not the only substrate.
Effects of Carbohydrate Restriction and Aerobic Exercise on Strength
Performance
Recent research has demonstrated that depleted muscle glycogen stores in
conjunction with aerobic exercise compromises strength performance (Levitt &
Abernethy, 1999). Subjects (5 young men and one woman) performed resistance
exercise under a control (CON) condition (no strenuous exercise for at least 48
hours prior to testing) and after a carbohydrate restricted program (EXP). The
EXP condition included 60 min of submaximal cycling and four 1 minute bouts of
maximal exercise, followed by 48 hours of reduced carbohydrate intake. The
resistance exercise consisted of three sets of squats (80% 1RM) and 5 sets of
isokinetic knee extensions, all at different contractile speeds. In comparing
the CON to the EXP testing condition, the most observable difference was noted
in squat performance, with no significant differences in the knee extension
trials. There was a decrease in the average total number of repetitions in Set 1
(CON=18 reps vs EXP=12 reps) and Set 2 (CON=13.5 reps vs EXP=10.33 reps).
However, there was no difference between the CON and the EXP groups at any of
the five contractile speeds of isokinetic knee extensions.
In explaining the differing outcomes of the squat sets versus the knee
extensions sets (to an aerobic and carbohydrate restricted program), the authors
summarized previous research that has depicted substrate utilization differences
in the type of exercise. Isometric exercise has been shown to be impaired by
reducing glycogen content while no change has been seen in isokinetic exercise.
The authors hypothesized the differences in the present study were also due to
the type of exercise. The isokinetic exercise bouts consisted of relatively
short duration (1.5 to 7.5 seconds) versus the sets of squats (approximately 30
seconds per set). It was felt the energy production of the isokinetic exercise
was predominantly due to the breakdown of creatine phosphate while the
utilization of glycogen was much more apparent in the longer lasting squat
exercise regime.
The Effect of Carbohydrate Supplementation on Multiple Sessions and Bouts of
Resistance Exercise
For athletes completing multiple high-intensity strength training sessions
per day, maintenance of muscle glycogen stores is critical. In a study by Haff
et al. (1999), six resistance-trained men ingested a 250 gram carbohydrate
supplement or placebo during a morning training session, rested for 4 hours, and
then performed a second session consisting of multiple sets of light-intensity
squats (55% 1RM) to exhaustion. During the second training session, the number
of sets and repetitions performed were markedly higher with the carbohydrate
consumption, and subjects were able to exercise for 30 minutes longer. The
authors concluded that athletes engaging in multiple exercise sessions per day
(ranging from mild to high intensity) will receive a performance advantage with
carbohydrate ingestion via maintenance of intramuscular glycogen stores, due to
greater glycogen resynthesis during recovery. In addition, the carbohydrate
supplementation not only increased workout performance, it markedly increased
workout duration.
Practical Application
For the recreational athlete participating in weight training, consideration
of muscle glycogen stores is most satisfactory maintained with a well-balanced
and calorically-sufficient diet. It is necessary for personal trainers to
consider the exercise habits and goals of their weight training clients before
prescribing carbohydrate supplementation to benefit exercise performance. So as
not to let clients get carried away, it is meaningful to remind them that an
excess of carbohydrate intake, exceeding bodily energy expenditure needs, will
result in weight gain. However, it is apparent from these two studies reviewed
that individuals doing concurrent aerobic exercise with high-intensity
resistance training and/or completing multiple training sessions per day should
be concerned with maintenance of glycogen stores, since glycogen depletion may
reduce work output and duration.
References
Essen-Gustavsson, B. & Tesch, P. A. 1990.
Glycogen and triglyceride
utilization in relation to muscle metabolic characteristics in men performing
heavy-resistance exercise. European Journal of Applied Physiology, 61, 5-10.
Haff, G. G., et al. 1999. The effect of carbohydrate supplementation on
multiple sessions and bouts of resistance exercise. Journal of Strength and
Conditioning Research, 13, (2), 111-7.
Leveritt, M. & Abernethy, P. J. 1999. Effects of carbohydrate restriction
on strength performance. Journal of Strength and Conditioning Research, 13, (1),
52-7.
Robergs, R. A., Pearson, D. R., Costil, D. L., Fink, D. D., Pascoe, M. A.,
Benedict, C. P., Lambert, C. P., and Zachweija, J. J. (1991). Muscle
glycogenolysis during differing intensities of weight-resistance exercise.
Journal of Applied Physiology, 70, 1700-1706.
Tesch, P. A., Colliander, E. B., & Kaiser, P. 1986. Muscle metabolism
during intense, heavy- resistance exercise. European Journal of Applied
Physiology, 55, 362-6.
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