Answer: by insufficient oxygen supply
Pain due to decreased blood flow during exercise (often in the legs) is caused by insufficient oxygen supply
Step-by-step explanation:
During exercise, the skeletal muscle are vigorously contracting, and the body consumes oxygen to produce energy faster than it takes in.
Under such conditions, pyruvate (the end product of glycosis) cannot be oxidized due to lack of oxygen. Thus, it is then reduced to lactate and then pain start to be felt in extreme body parts such as the legs.