Home of Sports Medicine and Exercise Physiology

Speed-power activities such as 400-m sprinting, and court and field games such as basketball and football, are energetically driven by the combination of immediate and nonoxidative energy sources. However, the importance of nonoxidative, glycolytic energy sources described in this section extend far beyond a role in sustaining activities lasting a few minutes or less. Continue reading.

During short, intense exercise bouts, blood glucose rises above preexercise levels because the autonomic nervous system stimulates hepatic glycogenolysis and in some cases, blood [glucose] actually rises in male athletes during hard exercise. However, the ability of the liver to maintain a high rate of glucose release over time is limited by the amount of glycogen stored and by the activities of the hepatic glycogenolytic and gluconeogenic enzymes. During prolonged exercise, glucose production may be limited to gluconeogenesis because of hepatic glycogen depletion; thus, glucose production may fall below the level required by working muscle and other essential tissues such as the brain. Also, in prolonged exercise leading to dehydration and hyperthermia, shunting of blood flow away from the liver and kidneys occurs. Thus, the levels of gluconeogenic precursors (lactate, pyruvate, alanine) rise, and hepatic glucose production falls. In this case of falling blood glucose, the exercise becomes subjectively more difficult because of CNS starvation and difficulty in oxidizing fats in muscle due to the absence of anaplerotic substrates