Charles Poliquin Body Position: the Forgotten Training Variable
The triceps has three heads: the long head, the lateral head and the medial head.
Because all three heads of the triceps join at a common tendon to insert on the ulna (elbow bone), it is impossible to purely isolate one single head of the triceps. However, by changing your body position to change the orientation of your upper arm in relation to gravity and to your torso, you can affect the percentage of contribution of each muscle. Here are some specifics:
Incline to Perpendicular: The farther away the arms are from the belly button, the more recruitment there is of the long head of the triceps. Exercises that would fit this definition are triceps extensions performed on an incline bench (incline position) and the overhead triceps extension (perpendicular position).
Flat: Performing triceps exercises on a flat bench will increase the contribution of the lateral and long head of the triceps.Decline: As the arms get closer to the torso, as occurs during exercises performed on a decline bench, there is an increase in the contribution of the medial head of the triceps at the end of the range of motion. However, in the bottom position of the exercise, the prime mover is the lateral head of the triceps.
Also Check put Charles Poliquin’s Top 10 Triceps Exercises for Mass and Strength