Chemical Physiology of Muscle Contraction

Abstract

The mechanical response of an isolated muscle to an excitant is not accompanied by any oxygen consumption increase; the additional amount of oxygen is not consumed as long as contraction and relaxation have not occurred. Thus, there are two contraction phases, an anaerobic (anoxidative) phase and an aerobic (oxidative) or recovery phase, during which the muscle resumes its previous stage. When the muscle is repeatedly excited in a nitrogen atmosphere, it strongly contracts at the beginning, but it gets quickly exhausted, since between contractions it cannot get the necessary oxygen for its recovery. Lactic acid gathers in the muscle, which becomes stiff. If it gets oxygen at the beginning of its fatigue, the lactic acid disappears and the muscle recovers its initial contraction strength. The lactic acid concentration at which complete skeletal muscle fatigue sets in (i.e. the lactic acid peak) ranges between 0.3 and 06%. In order to release the energy it needs for its contraction, the muscle does not depend on immediate oxidative processes. It continues to contract for a certain amount of time even when it is completely deprived of oxygen.