Graph:
Mosso’s ergograph tracing showing muscular fatigue and the effect of rest pauses during repeated voluntary contractions.

Effect of a rest pause:
A rest pause causes partial recovery from fatigue, so the subsequent contractions become stronger and their height/amplitude increases again. It prolongs the total duration of work that can be performed.

This occurs because rest helps restore energy stores, especially ATP and phosphocreatine, improves oxygen supply, and allows removal of fatigue-producing metabolites such as lactate and inorganic phosphate.