If you're working on muscular fitness I'd focus more on the amount of weight you're lifting, along with then number of reps, and the type of excersises you're doing
It's shown to increase stamina
You don’t explain very well but the sentence it’s true
Malevolence is the right answer
I mean, find what you want to work on when feeling mentally unstable. I guess just make a goal to what you want to achieve when doing this.