Anchor a band overhead and press the triceps to lockout.
Keep your elbows fixed and high, only your forearms should move.
Both elbows tucked beside your head, forearms driving up to lockout, this puts the long head of your triceps under stretch at the bottom of every rep. The band pulls hardest right as you reach full extension, matching the squeeze instead of dying off the way overhead free weights do. It is a pure isolation move, nothing else on the muscle list, just triceps from stretch to lockout.
Arm position. Overhead, the long head of the triceps starts fully lengthened, which pushdowns never achieve. Training a muscle from its stretched position is a stimulus you cannot replicate with your arms at your sides, so overhead work rounds out triceps training.
Both work. Standing on it is quicker and self-adjusts to your height, while an overhead anchor gives a smoother line of pull. Pick whichever keeps the band tracking close behind your head without scraping it.
The band is beating your triceps, so your shoulders are recruiting help. Go a band lighter or grip with less stretch, then keep the elbows aimed at the ceiling. Fixed elbows are the whole exercise.
