Lying triceps extension

EZ bar or dumbbells

Also called skull crushers. With the upper arms angled back toward the head, the long head of the triceps is stretched under load.

What each muscle does in the lying triceps extension

Muscle	Role	Action
Triceps brachii	Primary	Extends the elbow; the long head also extends the arm

Primary muscles are the prime movers; secondary muscles assist or stabilise. The balance shifts with grip, stance, range of motion and technique.