Different muscles recover at different speeds

You can train your calves more often than your back, and that's not random

Training programs often assume the same rest interval for every muscle group, but recovery research shows the speed at which different muscles bounce back after a load varies noticeably. Larger muscle groups — back, quads, glutes — typically need more time to fully recover after a hard session, often 48–72 hours or more, due to a larger volume of damaged tissue and more pronounced systemic fatigue.

Smaller muscles and ones dominated by fatigue-resistant, slow-twitch fibers — calves, forearms, parts of the core, for example — recover noticeably faster, sometimes within 24–36 hours, partly because of their fiber-type composition and the smaller absolute volume of tissue that needs repairing.

Practical takeaway for programming: you don't need to give every muscle group the same training frequency. Calves or abs can reasonably be trained 3–4 times a week without much overtraining risk, while fully recovering your back or legs after a hard session often calls for at least 48 hours before the next serious load on that same group.