Yes, substantial muscle breakdown and atrophy occur within just 5 days of disuse (bed rest or immobilization) in the elderly. Older adults are particularly vulnerable, losing muscle mass and strength at a faster rate than younger individuals, often experiencing significant declines in leg strength after only a few days of inactivity ...
Older adults, especially those over 70, may suffer from muscle loss that is harder to recover, with some losing up to 15% of their strength in a single week of bed rest.
rate of force development (RFD),...While young and old adults demonstrated similar adaptive responses in preventing the loss of skeletal muscle thickness, RFD was retained in the young only.
https://pmc.ncbi.nlm.nih.gov/articles/PMC11330699/