As reviewed in other articles on
this site, carbohydrate nutrition is an important determinant of exercise
performance for sports that require repeated bouts of all-out-effort (i.e.
hockey shift) and long distance races. Consuming a carbohydrate-rich meal 3-4
hours prior to exercise, a fructose-rich drink 30 minutes prior to exercise and
the ingestion of 5-8 ounces of a carbohydrate sports drink every 10-15 minutes
during exercise are considered prudent ergogenic (exercise enhancing) strategies
in the field of sports nutrition. This applies primarily to sports activities
executed at a strenuous level and lasting a minimum of 60-90 minutes.
Once the training session or
sports event is over there are two concerns to address with respect to
carbohydrate replenishment. First, the craving within the muscle for
carbohydrate storage is extremely high in the first 2 to 6 hours following the
completion of exercise. Thus, this represents an ideal opportunity to rapidly
drive carbohydrates into the muscles’ carbohydrate fuel tank (glycogen)
thereby helping to prepare the muscle for the next training session or
Secondly, on a more long-term
basis it is important to derive sufficient carbohydrate calories from day to day
as it requires at least 24 hours to fully refuel the muscles’ carbohydrate
fuel tank. Very conveniently the size of the muscles’ carbohydrate fuel tank
doubles with exercise training. So, the key is to completely refuel the tank
between training sessions as greater concentrations of muscle glycogen are
correlated with better performance. This includes improved ability to perform
repeated all-out sprints, better sustained maximum power in long distance events
and the postponement of fatigue. Hence, reloading the muscles’ carbohydrate
stores to a maximum level is deemed to be very desirable for athletes competing
in a wide variety of sports. The ability to store twice as much carbohydrate in
trained muscles versus untrained muscles is known as glycogen super
compensation, which requires sufficient daily carbohydrate intake. For sports
that rely heavily upon carbohydrate energy the athlete’s diet should consist
of 60-70 percent carbohydrates from day to day.
On a more technical level the
rate of post-exercise muscle glycogen storage, when supplied by dietary
carbohydrates is reported to be 5 to 8 mmol/kg/hour, which means at least 20 to
24 hours are required for complete restoration of normal muscle glycogen levels.
The rate of resynthesis is faster if carbohydrates are consumed immediately
following exercise rather than delaying carbohydrate intake by 2 hours. Thus,
athletes should ingest carbohydrates as soon after exercise as possible.
Interestingly, in the early
post-exercise period the optimal carbohydrate intake appears to be 50 grams
every 2 hours aiming for a total carbohydrate intake in 24 hours of 600 grams
(2,400 calories) for athletes involved in strenuous training or tournament
weekends where carbohydrate demanding sports are involved (i.e. basketball,
hockey, swim meets).
Ingestion of simple rather than
complex carbohydrates are preferred between games and events scheduled on the
same day. Examples include sports drinks, sports bars, pancakes, bread, rice,
pasta, potatoes, fruit and fruit juice. Sweet vegetables such as carrots, squash
and sweet potatoes are also a consideration. If the next game or race is less
than 3 hours following the preceding one, then a complete meal is not
recommended. Rather, reliance upon sports drinks, sports bars, fruit juice,
fruit and carrot sticks are viable dietary suggestions.
In the event of over training
that produces muscle soreness, muscle damage and presence of inflammatory cells,
the refueling of muscle carbohydrate (glycogen resynthesis) is reduced,
resulting in poorer performance in future events. The effect of muscle damage
can be partially overcome by the ingestion of increased amounts of carbohydrate.
Thus, athletes should be aware of the potential need of increased dietary
carbohydrate following intense, prolonged exercise that produces muscle damage
From a metabolic standpoint
glucose and sucrose (white sugar) results in faster muscle glycogen resynthesis
than fructose, although fructose may be of more benefit in the restoration of
In summary, in view of the
importance of carbohydrate for performance in many sports, the goal of
carbohydrate nutrition strategies aimed at before, during and after exercise as
well as day to day carbohydrate loading can help to optimize athletic
performance, providing an important competitive edge.
Copyright 1998 Dr. James
Meschino D.C., M.S.
Costill DL and Hargreaves M.
Carbohydrate nutrition and fatigue. Sports medicine 1992; 13; 2:86-92.
Bak JF, Pedersen O.
Exercise-enhanced activation of glycogen synthase in human skeletal muscle.
American Journal of Physiology 248:E957-E963, 1990.
Blom PCS, Costill DL, Vollestadt
NK. Exhaustive running: inappropriate as a stimulus of muscle glycogen
supercompensation. Medicine and Science in Sports and Exercise 19:398-403,1987a.
Blom PCS, Hostmark AT, Vaage O,
Kardel K, Maehlum S. Effect of different sugar diets on the rate of muscle
glycogen synthesis. Medicine and Science in Sports and Exercise
Burke L, Collier G, Hargreaves
M. Effect of glycemic index on muscle glycogen resynthesis following exhaustive
exercise. Submitted for publication, 1991.
Costill DL, Pascoe DD, Fink WJ,
Robergs RA, Barr SI et al. Impaired muscle glycogen resynthesis after eccentric
exercise. Journal of Applied Physiology 69: 46-50, 1990.
Costill DL, Sherman WM, Fink WJ,
Maresh C, Witten M et al. The role of dietary carbohydrates in muscle glycogen
resynthesis after strenuous running. American Journal of Clinical Nutrition 34:
Ivy JL, Katz AL, Cutler CL,
Sherman WM, Coyle EF. Muscle glycogen synthesis after exercise: effect of time
of carbohydrate ingestion. Journal of Applied Physiology 64: 1480-1485, 1988a.
Ivy JL, Lee MC, Broznick JT,
Reed MJ. Muscle glycogen storage after different amounts of carbohydrate.
Journal of Applied Physiology 65: 2018-2023, 1988b.
Kiens B, Raben AB, Valeur AK,
Richter EA. Benefit of dietary simple carbohydrates on the early post-exercise
muscle glycogen repletion in male athletes. Medicine and Science in Sports and
Exercise 22: S88-1990.
O’Reily KP, Warhol MJ,
Fielding RA, Frontera W, Meredith CN et al. Eccentric exercise-induced muscle
damage impairs muscle glycogen repletion. Journal of Applied Physiology
Sherman WM, Costill DL, Fink WJ,
Hagerman FC, Armstrong LE et al. Effect of a 42.2 km footrace and subsequent
rest or exercise on muscle glycogen and enzymes. Journal of Applied Physiology
55: 1219-1224, 21983.
Zachwieja JJ, Costill DL, Pascoe
DD, Robergs RA, Fink WJ. Influence of muscle glycogen depletion on the rate of
resynthesis. Medicine and Science in Sports and Exercise 23: 44-48,1991.