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
Arteriovenous oxygen difference diff. The maximum a-vO diff is also usually greater in trained athletes than in untrained individuals. This is a result of aerobic exercise leading to hypertrophy of the slow twitch muscle fibres mainly due to increased capillarisation. The increase in capillary beds in the muscle means that blood supply to that muscle can be greater and diffusion of oxygen, carbon dioxide, and other metabolites increases. With training the muscles also improve in their ability to extract oxygen from the blood and process the oxygen, possibly due to adaptations of the mitochondria and an increase in the muscle's myoglobin content. Research