It is well known that carbohydrate intake improves endurance exercise capacity and performance. As such, in the 1980’s, a large number of studies investigated the efficacy of carbohydrate loading strategies on performance – a strategy adopted by many endurance athletes today. In addition, the ingestion of carbohydrate during exercise, at a rate of 1g per minute, has been found to improve performance during exercise lasting longer than 60-90 minutes. This performance improvement occurs as a result of a potential sparing of liver and muscle glycogen stores with an increase in carbohydrate oxidation from blood glucose.
Restricting carbohydrate intake
Despite the well-documented evidence to show carbohydrate ingestion improves performance, there is emerging research to suggest benefits of restricting carbohydrate. This was discovered by using a training schedule involving training in the morning followed by training in the evening, without carbohydrate intake between sessions. The research has shown that restricting carbohydrate availability enhances oxidative adaptations improving the capacity to use lipids to provide energy, thereby sparing muscle glycogen stores. This approach has been called train-low: compete-high. For this to be an effective strategy, some and NOT all training sessions are undertaken with low muscle glycogen stores, whilst competition is always undertaken with high carbohydrate availability.
If you get this strategy wrong – you’ll soon know about it! You will struggle to maintain a high pace and you will put yourself at risk of injury and illness. The train-low session should involve reduced exercise intensity to reflect the limited carbohydrate availability; therefore this strategy should only be used during times when exercise intensity is not crucial to the session.
One of the additional problems with this strategy is the increase breakdown of proteins when exercise is undertaken with reduced glycogen stores. Effectively, your body has to use protein as an energy source and as a result, lean muscle mass could be reduced. To overcome this, protein could be consumed before, during or after exercise to help maintain protein synthesis.
Caution should be taken to ensure this strategy is well designed and incorporated into training at specific periods. Training low has the benefit of shifting metabolism towards oxidising lipids. However, whilst our muscles effectively increase enzyme activity involved in lipid metabolism, enzymes involved in carbohydrate metabolism is down regulated. The gut also needs to be trained to increase the capacity for carbohydrate delivery. Therefore, if you train in a low state too frequently, when it comes to race day, your gut and muscles will effectively forget how to metabolise carbohydrate.