A soldier has many arms and jobs.

Your question, I'd better understand it this way: how long should the soldiers of special forces rest their muscles after intensive training every day? This is one of them.

I think habit is the law of life, and so is muscle. When high-intensity training adapts to muscles, it won't be as tired as when you first started training. Moreover, most of their training is full-body muscle exercise, and nutrition can keep up, so their bodies recover faster.

As for "fitness every other day", this is not an academic term. My understanding is that a certain part of muscle consumes energy after full fitness exercise and needs a rest (not necessarily a day) to replenish energy and enhance physical fitness. Therefore, fitness every other day is only a common phenomenon of mass fitness at present. Friends who know how to keep fit will generally make a good exercise plan and arrange exercise and rest according to their own lives.