Answer: during exercise, lactate builds up in muscles and causes a burning pain in the affected muscle
Explanation: Exercise increases the energy needs of the muscles used. Increased energy generation requires increased oxygen. If energy demands exceed the body’s ability to supply oxygen, muscle tissues switch from aerobic to anaerobic respiration.
In anaerobic respiration pyruvate is reduced to lactate. Energy production is <10% as efficient as aerobic respiration, so it must be at a high rate.
C3H4O3 + 2NADH + 2ADP + Pi —> C3H6O3 + 2NAD+ + 2ATP
Reducing intensity of exercise or taking breaks can give the body a chance for recovery. Aerobic fitness will increase ability to supply oxygen.
After exercise, lactate is converted back to pyruvate and to replenishing glucose via gluconeogenesis. The enzyme lactate dehydrogense catalyses the pyruvate/lactate reaction in both directions.
The cumulative effect of exercise and converting lactate back to pyruvate creates an ‘oxygen debt’ which is why we breathe heavily after exercise.
Exercise can lead to dehydration (e.g. sweating) which decreases metabolic efficiency. Additional water intake before during and after exercise prevents dehydration.
It has also been shown that light exercise in the recovery phase after strenuous exercise improves the rate of lactate removal
Menzies et al. Blood lactose clearance during active recovery after an intense running bout depends on the intensity of the active recovery. J. Sports Sci 2010; doi 10.1080/02640414.2010.481721
