Lower toward your skull, press back up, all triceps.
Keep your upper arms stationary and pointing at the ceiling, only the forearms swing.
With the upper arms locked vertical, bending at the elbows to bring the dumbbells beside your head strips everything away except the triceps lengthening and contracting. Travelling just past the ears puts the muscle under load at a longer stretch than pushdown-style work reaches, and the palms-in dumbbell grip keeps the wrists and elbows in a comfortable line. It earns its place as the lying triceps builder that trains the stretch, the half of the growth equation cable work often misses.
Skullcrushers isolate the triceps, only the elbow moves, while close-grip bench is a compound press where the chest and shoulders share the load. Press heavy for strength, then skullcrush to target the triceps directly.
Travelling beside and just past the head lengthens the triceps further, especially the long head, and keeps the dumbbells from hovering over your face. Deeper stretch, safer path.
Extend fully but don't slam into a hard lockout. A firm squeeze at the top finishes the contraction, while snapping into lockout just transfers load to the joint and gives the muscle a rest it hasn't earned.
