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 to do so oxygen consumption (VO) may be measured using a spirometer to detect gaseous concentrations in exhaled air compared to inhaled air, while cardiac output can be determined using a Doppler ultrasound. Arterial blood will generally contain an oxygen concentration of around 20 mL/100 mL. Venous blood with an oxygen concentration of 15 mL/100 mL would therefore lead to typical values of the a-vO diff at rest of around 5 mL/100 mL. During intense exercise, however, the a-vO diff can increase to as much as 16 mL/100 mL due to the working muscles extracting far more oxygen from the