Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights.

Repeated exercise, or wasting, can change the way key genes work.

There's a lot of talk about lean muscle compared to bulk muscle, but experts say it's not worth differentiating the two. Learn why.

Skeletal muscle is the type of muscle that controls movement. Problems with these muscles can be minor, life-threatening, or ongoing problems that make it hard to perform basic daily activities.