The belly of the muscle, or muscle belly, is a term used to described the large mass of muscle that powers the work of movement.

Generally, the muscle belly is located between two tendons that each attach onto adjacent bones. In this way, the tendon of the muscle and/or the muscle itself crosses over a joint, providing movement during contraction and relaxation of the belly.

The amount of movement possible at a joint, or range of motion, is partially determined by the amount of tension present in the belly of the muscle. This, of course, is a factor of range of motion that can be improved with stretching.