Does Carbohydrate Restriction Augment Adaptations From Endurance Training?

The glycogen stored in muscle cells is the primary energy source during endurance exercise such as cycling and long distance running. There have been discussions recently on whether reducing carbohydrate (CHO) intake and training with low levels of CHO in the muscle cell will increase the adaptation from a training session. The proposed increases from training low-CHO include increased cell signalling, gene expression, and increased oxidative enzyme activity. Impey et al. reviewed the literature on this topic. The two main questions included whether there is an exact window or threshold of muscle glycogen that is ideal for training low-CHO. In addition, they questioned if there are greater advantages to being in a state of low-CHO during rest, light exercise, or high intensity training.

The researchers found that although there seems be an ideal threshold muscle glycogen to receiving the benefits of low-CHO training, that level may change from athlete to athlete, and it is unknown how much CHO in the diet over how long of a period is required to reach that level. The threshold might be found by individual athlete experimentation rather than a predefined amount of CHO intake. The primary issue with training at low-CHO is that the quality and intensity of training can be affected by glycogen depletion in the muscle. It can then be questioned if gaining the advantages of training low-CHO are worth the loss of intensity of a training session. The researchers concluded that being in a state of low-CHO during rest and low intensity training sessions would be most advantageous, enabling both the benefits of resting and training low-CHO, but increasing CHO intake before and after high intensity training session to optimize performance.