Know about Physiology of Muscle Contraction

Physiology of Muscle Contraction 
Researchers have noted the following aspects of muscle contraction in the laboratory:
All-or-None Law 
When a muscle fiber is stimulated, it behaves in an all-or­none manner; it either contracts completely or not at all. On the other hand, the strength of the contraction of a whole muscle can increase according to how many muscle fibers are contracted. In other words, an entire muscle does not obey the all-or-none law because the total amount of contraction depends on how many muscle fibers are contracted at that time.
Muscle Twitch, Summation, and Tetanus 
A single stimulus causes a muscle to contract and then relax, resulting in a muscle twitch. A muscle twitch can be divided into the latent period (the time between stimulus and initiation of contraction), the contraction period, and the relaxation period. Normally in the body, a muscle receives many impulses in rapid succes­sion. Because of this, tension summates until maximal sus­tained contraction called tetanus is achieved. If the muscle is not allowed to rest, fatigue will set in. Fatigue is apparent when a muscle relaxes, even though stimula­tion is continued. When a muscle fiber fatigues (gives out), it has run out of ATP. The muscles of long-distance runners have been known to fatigue ~hen most of the fibers have run out of ATP, causing the runner to collapse.
Muscle fibers obey the all-or-none lavv, but whole muscles do not. The occurrence of a muscle twitch, summation, or tetanus depends on the frequency with which a muscle is stimulated.