Electric current traveling along our nerve, from our brain, is spreading to the muscles and innervate each muscle cell. This electrical current causes molecular reactions between proteins, the actins and myosins filaments. It is the sum of these contractions of motor units that determines the force of muscle contraction.
Molecular interaction between actin and myosin.
A small animation, not to the scale, of a contractile unit.
In real life, our muscle fibers contract in less than a hundredth (1/100) of a second.
Three motor units, at rest and contracted.
Put a thousand of them in-line and you can get an impressive force of contraction.
