Sports nutrition: carbohydrate loading is an important aspect of post exercise recovery

Loading up with carbohydrates during recovery from strenuous exercise promotes a high level of muscle glycogen resynthesis

Loading up with carbohydrates during recovery from strenuous exercise promotes a high level of muscle glycogen resynthesis. But this does not necessarily translate into improved subsequent endurance performance, according to a new British study.

The study examined the effects of carbohydrate intake during a four-hour recovery from prolonged running on muscle glycogen metabolism during subsequent exercise. On two occasions, seven male recreational runners ran for 90 minutes at 70% of maximum oxygen uptake (VO2max) on a treadmill, then took a four-hour rest period followed by a 15-minute run, consisting of five minutes at 60% and 10 minutes at 70% VO2max.

During one of the rest periods, each subject ingested 2.7 litres of an isotonic solution containing 50g of carbohydrate (CHO); during the other they ingested the same amount of solution, this time containing 175g of CHO.

The researchers’ hypothesis was that the high-carb rest period would be followed by a higher rate of muscle glycogen utilisation during the second bout of exercise, leading, by implication, to an improvement in endurance running capacity.

But in fact, although muscle biopsy samples showed a higher rate of muscle glycogen resynthesis after the high-carb trial than after the low one, muscle glycogen utilisation during the second bout of exercise was similar for both trials.

These findings raise the interesting possibility, say the researchers, that muscle glycogen availability may not be the only limiting factor in restoring exercise capacity after recovery from prolonged exercise.

They point out that in previous related studies, a significant amount of muscle glycogen remained at the end of carbohydrate-loaded endurance exercise, suggesting that muscle glycogen depletion might not be the cause of fatigue under these conditions.

‘It is possible,’ they conclude, ‘that availability of liver glycogen might play an important role in restoring exercise capacity… In support of this hypothesis, a recent study showed a positive relationship between the increase in liver glycogen replenishment during a 4h recovery from prolonged exercise and improvement in subsequent exercise capacity. Therefore, further studies are required to examine the relative roles of liver and muscle glycogen repletion in restoring exercise capacity.’

Int J Sports Med 2003;24:452-458

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