Mostly running at a leisurely pace - most people use many of their muscles when they run - I was doing 5km three times a week. Additionally, I was doing 2x1hr a week of karate practice (a whole body workout), And the occasional random set of 20 pushups / 20 sit-ups / 20 squats, probably 2-3 times a day.

I should note that anything aerobic like running was easy, anything anaerobic (like karate sparring) was not, but it wasn’t painful either.

I did pay attention to electrolytes - especially magnesium and potasssiun - I got cramps when water fasting and not supplementing.

I know my body well, and I think that’s essential to be able to continue - e.g. to know it is magnesium that’s needed now, and not (as one might think) the body is eating itself.

Don’t know how to learn that skill though.