Sports Nutrition: Glycogen levels need to be replenished post exercise

Glycogen synthesis: your post-exercise plan

The importance of replenishing muscle glycogen stores as well as fluids after heavy exercise is well understood by sports scientists and coaches. But the relatively recent discovery that muscle glycogen synthesis is more rapid if carbohydrate is consumed immediately after exercise has focused attention on early post-race strategies to promote recovery and enhance subsequent performance.

In a wide-ranging review of the literature in this field, exercise physiologist John L Ivy, of the University of Texas at Austin, points to the evidence that muscle glycogen synthesis is twice as rapid if carbohydrate is consumed immediately after exercise rather than several hours later, and that a rapid rate of synthesis can be maintained if carbohydrate is consumed at regular intervals for a few hours. He explains that the reduced rate of glycogen synthesis observed when ingestion of a carbohydrate supplement is delayed can be ascribed to the development of muscle insulin resistance – apparently a protective mechanism to prevent the development of hypoglycaemia (low blood sugar level) when insufficient glucose is available. Providing a carbohydrate supplement soon after exercise, therefore, enhances the muscle glycogen recovery process by maintaining stable blood glucose levels and preventing the development of muscle insulin-resistance. ‘Moreover’, Ivy poins out, ‘providing the supplement soon after exercise maximises the time for recovery to proceed.’ When a carbohydrate supplement is provided immediately after exercise, its effect on muscle glycogen synthesis eventually decreases as blood glucose and insulin levels decline. But the rate of this decline can be slowed if supplements are taken at regular intervals for several hours after exercise.

Ivy’s key conclusions are as follows:

  • To maximise the rate of muscle glycogen storage during short-term recovery, it is essential that a carbohydrate supplement be ingested as soon after exercise as possible;
  • Supplements should be ingested at frequent intervals, such as every 30 minutes for 4-5 hours, and be concentrated enough to provide 1.2-1.5g carbohydrate (CHO) per kg of body weight;
  • If less carbohydrate consumption is required, a similar rate of glycogen storage can be achieved with the addition of protein and amino acids to the supplement – e.g. 0.8g CHO plus 0.4g PRO per kg of body weight.

‘Furthermore’, Ivy points out, ‘the ingestion of protein with carbohydrate has the added benefit of stimulating muscle amino acid uptake and protein accretion. This could be very important for rapid tissue repair and prevention of muscle soreness during periods of intense training.’

Can J Appl Physiol 2001 26 Suppl S236-45

Isabel Walker

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