Your triceps is the large muscle on the back of your upper arm, the part between your shoulder and elbow. When you straighten your arm out or push something away from you, like doing a push-up or throwing a ball, your triceps does most of the work.

This muscle actually connects to your bones in three different places near your shoulder. You can feel your triceps working by placing one hand on the back of your other arm while you straighten that arm out completely.

The triceps works opposite to your biceps, the muscle on the front of your upper arm. When you bend your elbow to lift something toward you, your biceps contracts while your triceps relaxes. When you straighten your arm back out, your triceps contracts while your biceps relaxes. This back-and-forth cooperation between opposing muscles is how your body creates smooth, controlled movements.

People who do activities like swimming, rock climbing, or gymnastics often develop strong triceps because these activities require lots of pushing and arm extension. Even simple movements like opening a heavy door or tossing a frisbee rely on your triceps to generate power.