Muscle contraction occurs when muscle fibers get shorter.
Isometric exercise is a sustained contraction of large muscles, such as weight lifting.
Weight lifting requires  shortening of of the fibers of large muscles.
Weigh lifting requires muscles
[a] to move people
[b] Energy.
[c] stamina
[d] it needs them
[e] shortening
[f] hydration
[g] sensory neurons
[h] Energy