Some anecdata but, I suffered from very bad muscle injuries from one summer in 2014. I skateboarded hard for two days in a row. Ran 3-ish miles on both days. Two days later I was exhausted but took two ibuprofen and I went to a beach with friends anyway. Where I skated hard at a park for a few hours, then swam, then ran. A day or so later, after not getting the best sleep, on an hour drive home, I pull both quads. The day after I had to call out for a week. I was exhausted and my obliques, core, quads, and arms were beyond sore. I laid around for most of the week.
Your muscles may not get "exhausted" but it seems like there must be some breakdown in the cells that outpace recovery at some point.
When they work, muscles break fibers. The more intensely you work out, the more they break. So you have to rest for them to be rebuilt (and more fit to the exercise), otherwise at some point they give in. The more frequently you train, the more they can withstand.
That seems unlikely given that if he had rhabdo he’d have felt bad enough to need to go to hospital. 20% death rate due to kidney failure is not to be sneezed at.
Your muscles may not get "exhausted" but it seems like there must be some breakdown in the cells that outpace recovery at some point.