What Happens to Stored Carbohydrate (Glycogen) During Exercise?

The hormone picture that develops during exercise is similar to the one discussed regarding a fasting period; however, there are relative differences. Epinephrine is released from our adrenal glands as a direct effect of exercise.

Quite simply, the greater the exercise intensity, the greater the epinephrine release. Epinephrine stimulates the breakdown of muscle cell glycogen (see Table 4.5 and Figure 4.3). This makes glucose available for the muscle cells hard at work. Epinephrine also promotes the breakdown of glycogen to glucose in the liver. Some of this glucose will then circulate to working muscle to provide support. Cortisol may also be released in response to moderate to intense exercise, particularly as the exercise becomes prolonged (for example, endurance cycling and running). Cortisol will also support the breakdown of glycogen as well as gluconeogenesis in our liver.