The upside to muscle loss with inactivity:

Strength and muscle mass is rapidly restored with re-training.

Ten days of disuse in young males decreased muscle strength by -30% and muscle mass (volume) by -4%.

But just 9 resistance exercise sessions over 21 days was enough to not just restore, but supercompensate these losses:

✅Muscle strength: +14% above baseline
✅Muscle mass (volume): +19% above baseline

Muscle can be rapidly lost—but quickly regained too.