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
Neural control of limb stiffness of the limb contribute to its overall stiffness. The cocontraction of antagonistic muscles, posture of the limb, and stretch reflexes within the limb all contribute to stiffness and are affected by the nervous system. The stiffness of a limb is dependent on its configuration or joint arrangement. For example, an arm that is slightly bent, it will deform more easily under a force directed from the hand to the shoulder than an arm that is straight. In this way, the stiffness of a limb is partially dictated by the limb's posture. This component of limb stiffness is due to the