You've been doing:
Overhead triceps extensions
Bodybuilders have long used the overhead extension to build the long head of their triceps (the part of the muscle that's on the torso side of your arm)-and they've long paid physical therapists to treat the damage they've done to their elbows as a result. The good news is that you can build the same T-shirt-busting triceps with the much safer incline pushdown. Unlike the overhead extension, which allows the triceps to rest somewhat in the top position while your elbow joints take the brunt of the load (endangering the joints' connective tissues in the process), the angle and direction of the cable in the incline pushdown keep all the muscles in your triceps under constant tension throughout the entire movement. At the same time, you never stress the elbow joints directly, ensuring that the heavy weights you lift do maximum damage to the parts that can take it-your triceps.
HERE'S WHAT YOU DO
Set an adjustable bench to a 45-degree incline and place it near a cable station, facing away. Attach a bar to the top pulley of the cable station so that it hangs just behind the bench; now lie on the bench and grasp the bar behind your head with an overhand grip and your hands inside shoulder width. Pull the bar forward so that it stops over your upper chest-now pin your elbows to your sides (you should be in the same position as in a normal pushdown, only reclining on the bench) . Straighten your elbows, pushing the bar down the front of your body as far as you can without moving your upper arms . That's one rep. Perform three sets of eight to 10 reps, resting a minute between sets.