Exercise physiology loss of integrity to the blood brain barrier. Hyperthermia also can lower cerebral blood flow, and raise brain temperature. Researchers once attributed fatigue to a build-up of lactic acid in muscles. However, this is no longer believed. Rather, lactate may stop muscle fatigue by keeping muscles fully responding to nerve signals. The available oxygen and energy supply, and disturbances of muscle ion homeostasis are the main factor determining exercise performance, at least during brief very intense exercise. Each muscle contraction involves an action potential that activates voltage sensors, and so releases Ca ions from the muscle fibre’s sarcoplasmic reticulum. The
Aerobic conditioning able to diffuse more oxygen into their blood than they previously could. Although exercising at lower intensities will improve aerobic conditioning, the most rapid gains are made when exercising close to an individual's anaerobic threshold. This is the intensity at which the heart and lungs can no longer provide adequate oxygen to the working muscles and an oxygen debt begins to accrue; at this point the exercise becomes anaerobic. Anaerobic training intensity for most individuals will be <85-92% of maximum heart rate. Once improvement in aerobic conditioning is apparent, for example in metabolism and oxygen uptake, the body will progressively