What is overtraining? A. overloading the muscles too often
B. progressing through exercises too quickly
C. muscles that aren't adapting quickly enough
D. when muscles start atrophying

A) overloading the muscles to often

Explanation:

You have to allow your muscles to fully recover after a workout. Since when you workout your tearing the fibers in your muscles, and during your rest period your allowing your body to rebuild those fibers and during that process they add more fibers to your muscle. Making your muscles bigger and stronger.