Freestanding Power Stack Hi-Low
The tricep muscle located on the back of the arm is a single muscle unit with three heads, the medial, lateral and long head. The long head is biarticular, originating at the scapula and inserting on the elbow. The long head extends the lower arm, extends the shoulder and adducts the shoulder bringing the upper arm alongside the chest.
The medial tricep is a deep part of the muscle overlapped by the long and lateral heads of the tricep. Its origin is the middle of the humerus and also attaches to the elbow. The middle head is active at all times during elbow extension.
The lateral head of the tricep is on the outside or lateral side of the arm and originates on the upper part of the humerus and attaches to the olecranon process of ulna along with the other two heads.
Placing your hands on a straight bar on a tricep pulldown in a prone position, that is palms down, has the greatest activation of the lateral portion of the tricep. If the same movement is done in a supine or palms up position the long head portion has greater muscular stimulation. The medial head participates in both actions.
A point to remember - first stand tall with your arms at a right angle as if you were to place them on a tricep pressdown bar - as you turn your hands into a palms up position, the upper arm becomes closer to the chest, as the long head of the tricep is involved in shoulder adduction.
Keeping your arms close to your side and hands in a supinated position, pressing a weight down activates and develops more of the long head portion of the tricep muscle.
In the same position when you pronate your hands the elbows move farther away from the chest, which activates more of the lateral head of the tricep during a weighted pressdown.
Consider grip variance when you are Getting the triceps Strong on a Pendulum Power Stack.