The classic triceps mass builder, bar to forehead and back.
Don't let your elbows flare out, keep them tucked and pointing forward.
Lying back with the bar over your chest and only the elbows bending puts the entire load on the triceps, stretched hard as the bar approaches your forehead and squeezed hard at lockout. Keeping the upper arms vertical is what separates it from a press, the shoulders stay out of it and the triceps own every centimetre. It has been the default triceps mass builder for decades because nothing else loads the muscle this directly with this much weight.
Usually too much weight and too fast a descent. Slow the lowering phase, cut the load, and switch to an EZ bar so your wrists and elbows sit at a friendlier angle. If the ache persists, rotate in other triceps work for a while and come back.
Skullcrushers load the triceps in a deep stretch, which pushdowns cannot do, so they tend to be the better growth driver. Pushdowns are easier to control and perfect for finishing. Run the crusher first, the pushdown after.
Both are legitimate, and the movement is identical. Most lifters settle on the EZ bar because the angled grip takes strain off the wrists, letting you focus on the triceps instead of your joints.
