ABSTRACT
High-intensity exercise is exercise that is non-steady-state exercise, and as such is likely to be maintained for slightly longer than 5 minutes before fatigue ensues. This means that such exercise can be maximal and last for a few seconds or slightly more prolonged. Studies employing muscle biopsy sampling immediately following high-intensity exercise have demonstrated that after 30 s of sprinting 80% of the energy is derived from anaerobic sources. The exercise intensity enabling prolonged activity is dependent on the level of training. The major energy source during such exercise is initially carbohydrate from muscle glycogen and blood glucose, but as the exercise progresses there is a greater dependence on fatty acids either from intramuscular triglyceride stores from adipose tissue. Fatigue for prolonged exercise is due to hypoglycemia, muscle glycogen depletion, or dehydration.
