How soon do we need to eat carbohydrate post-exercise?

There are many ideas that come go and go in sport nutrition, as research develops to allow fact to be separated from fiction. A good example of this is the myth that there is an “anabolic protein window” and therefore protein must be consumed immediately post-exercise. We now know that the anabolic response to a protein feed lasts several hours post exercise and consequently there is no immediate rush to consume your protein feed like we may have been led to believe. But is this also true for carbohydrate?

My students must get sick of me saying “it depends” but when it comes to post-exercise carbohydrate intake it really does depend. If the training session has been light or there is no need to maximally replace muscle glycogen stores then it may be acceptable to wait until you get home and then have your post-training carbohydrate. However, if the training has been hard and you want maximum replacement of carbohydrate ready for subsequent performance then an immediate re-feed can offer several metabolic advantages.

We have known for many years that there is a “window of opportunity” post-exercise to replace muscle glycogen stores above and beyond what would occur if we delay this feed. The reason for this is that glucose transports into muscle (via its transporter GLUT-4) is normally regulated via insulin. However, exercise itself causes GLUT-4 transporters to move to the plasma membrane ready to allow glucose into the muscle cell. This exercise-induced movement of GLUT-4 lasts between 30 minutes and 2 hours’ post exercise and during this phase it is possible to reload muscle glycogen more effectively than delaying the feed.

We have recently examined this hypothesis in rugby players following a simulated game. In one group players were given carbohydrate immediately post game whilst in the other group the feed was delayed by 2 hours, deliberately missing the window of opportunity. Over the next 48 hours both groups consumed a high carbohydrate diet. Two days later we took muscle biopsies to assess glycogen re-synthesis. We observed that glycogen re-synthesis was greater in the group that had the immediate re-feed compared with the delayed re-feed group.  One could therefore speculate that if maximum performance was required in the immediate days following the initial exercise then it is crucial to take advantage of this window.

In terms of how much carbohydrate to consume post exercise, the advice is about 1.2 g per Kg body mass per hour, on the hour, for 3 hours’ post-exercise. For a 75 kg person this is about 90 g of carbohydrate.

A practical refeed strategy following a team sport game may be:

In summary, immediate consumption of carbohydrate post-exercise can be advantageous if maximum performance is required in the days following the exercise. This involves preparation and often bringing food with you. Be organised and take advantage of this window.

References

1.         Dreyer HC, Fujita S, Cadenas JG, Chinkes DL, Volpi E, Rasmussen BB. Resistance exercise increases AMPK activity and reduces 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle. J Physiol. 2006;576(Pt 2):613-24.

2.         Goodyear LJ, Hirshman MF, King PA, Horton ED, Thompson CM, Horton ES. Skeletal muscle plasma membrane glucose transport and glucose transporters after exercise. J Appl Physiol (1985). 1990;68(1):193-8.

3.         Bradley WJ, Hannon MP, Benford V, Morehen JC, Twist C, Shepherd S, et al. Metabolic demands and replenishment of muscle glycogen after a rugby league match simulation protocol. J Sci Med Sport. 2017;In Press.