Don't worry about losing muscles during running. When the amount of exercise is too large, the body takes out protein from the muscle for a rainy day because of lack of energy, which will happen. Generally, moderate intensity aerobic exercise mainly depends on fat for energy supply, which is fat-reducing exercise, not muscle reduction.

Those high-level long-distance runners are thin, on the one hand, they exercise a lot! There will be a problem of muscle consumption. On the other hand, in order to pursue better sports performance, they deliberately maintain such a body shape (muscles consume a lot of energy, are bulky, and long-distance running is not cost-effective, and strong men have strength but long-distance running is not dominant).

Therefore, it is enough to ensure adequate energy supply, do muscle strengthening training (muscle strength training) and control the amount of long-distance running. Generally speaking, don't run too long at a time (generally controlled within one hour) and don't run too fast (moderate intensity aerobic exercise mainly consumes fat and does the least damage to muscles).

Good endurance (cardiopulmonary function and physical strength) is also very important for muscle exercise. I can't breathe after doing it twice. How do you exercise your muscles? So come on!