Monday, March 18, 2013

Endurance Athletes and Carbohydrates Part 1

A balance in macronutrients is essential in an endurance athlete's diet and we sometimes hear people trying out some funky nutrition shifts such as high fat diet, low carbs diet, etc. One thing is sure, endurance athletes need to have a high proportion of their daily macronutrients intake as carbohydrates (CHO) to perform optimaly. CHO has a lot of functions within the body and I am going to try and make this a series of two or three posts on CHO in relation to exercise, recovery and fatigue.

Carbohydrates and recovery

Heavy aerobic exercise rely mostly on muscle and liver glycogen for fuel. The precious glycogen is stored in limited quantity within the human body and any moderate to hard intensity aerobic effort will be fueled from these reserves. The importance of post-workout refueling is therefore crucial for short and long term improvements. But how does it happen? Why is it so important? Here are some answers on the topic.
Carbs play a major role in the recovery process. Depending on exercise intensity and duration, muscle glycogen stores could be partialy to fully depleted. The average 70kg male has about 400g of muscle glycogen to spare and 100g of liver glycogen. Despite being trainable, the total quantity of stored glycogen remains limited. These reserves generally allow for a sustained moderate-hard effort of 2 hours before being fully depleted.

Post-exercise CHO feeding will ensure the recovery process kicks in by refueling your muscles and liver glycogen stores. A proper post-exercise CHO intake will also help your body trigger all the biological processes to set up training induced adaptations. Fueling back your tanks allows to be ready for your next training sessions. Therefore, better recovery means higher quality/quantity training on a regular basis to achieve your performance goals.

Quite often we can read or hear about the post-workout 30 minutes recovery opportunity window and it's major impact on muscle glycogen synthesis. Though this aspect has been debated, it appears evidence tends to suggest the actual opportunity window is an important part of the post-workout recovery process. Insulin response is high following exercise when CHO is ingested. Tissues sensitivity to insulin and glucose transporters such as GLUT1 and GLUT4 is also higher in the few minutes following hard exercise which would increase their hability to absorb glucose. In that optic, a high glycemic index carbohydrate solution should be prefered when aiming for optimal recovery. Liquid CHO with sodium intake is also favorable to ensure gastric emptying is processed faster.

Traditionnaly, we've been told ingesting a combination of CHO and protein (3:1 to 4:1 ratio) would accelerate the rate of muscular glycogen synthesis. A few experts have studied this issue and it appears coingestion of CHO and protein would only be useful if the quantity of ingested CHO (or total energy) is too low. Drinking a 1,2g/kg/h of a CHO solution (van Loon et al. 2000) would seem like a good approach to post-exercise CHO feeding for optimal recovery.

So what should you learn fro that? The importance of ingesting a liquid CHO solution in the few minutes following hard exercise or competition will enhance the body's capacity to recover. Muscle glycogen synthesis is a slow process which takes some time. Under optimal recovery conditions, 5-7% per hour of total glycogen reserve will be restored. Complete glycogen replenishment can  easily take up to 24 hours to be completed and most of the time 24 hours is not enough. This is a major reason to emphasize post-workout nutritional strategy to achieve your performance goals.

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