Isolation exercises like the tricep kick backs are one of my favorite ways to finish up an #armday and work on that #horseshoe. The triceps are composed of three separate muscles bellies: LATERAL, LONG, and SHORT. All three heads cross the elbow joint and blend into the triceps brachii tendon at the olecranon process of the ulna and serve as primary ELBOW EXTENSORS. The LONG HEAD is the only head the spans across the shoulder joint , and thus will EXTEND THE SHOULDER as well. Because of the different origins of the muscle bellies, you can preferentially bias activation of one head over the other, based on the shoulder position of an exercise.
Exercises in which the shoulder is in flexion (ie overhead extensions, skullcrushers), will lengthen the long head of the triceps and thus preferentially bias recruitment of the long head. On the other head, exercises in which the shoulder is in neutral or flexion (ie tricep kick backs, rope extensions, dips), places the long head at a passively insufficient position - thus, we can preferentially bias recruitment of the lateral and medial heads.
Tricep kick backs need TO BE PERFORMED PROPERLY. Gravity works down folks!! If your extension moment around the elbow is not directed AGAINST gravity, you won't be getting much of a workout!