ABSTRACT
Exercise needs energy substrate. The two main energy sources during exercise are carbohydrate and fat. In principle, the bodily reserves of these substrates are limited for carbohydrate, but for all practical purposes unlimited for fat. The carbohydrate stores in the human body consist of the glycogen stores in muscle and liver. Muscle glycogen can be used directly by the contractile process. Liver glycogen is utilized after being transported from the liver to the contracting muscle as blood glucose. Gluconeogenetic substrate in the form of lactate, glycerol and alanine are transformed to glucose in the liver, which can then be utilized also. In addition, exogenous glucose can be furnished and utilized during exercise.
