The biceps and triceps muscles are the major flexors (biceps) and extensors (triceps) of the arm at the elbow joint. The biceps also play a very important role in rotating your forearm during activities such as turning a screwdriver or doorknob. Each of these muscles starts out as tendons near the shoulder, transition to muscles in the middle of the upper arm, then turn back into tendons near the elbow.
They can be injured at any of these locations, but they are most commonly injured where the tendon inserts onto the bone at the elbow. These injuries are very common, and they typically occur after a sudden, forceful movement such as catching something that is falling or quickly lifting a heavy object.