The fast inward turn of shoulder and forearm at contact — the whip behind every overhead. Shoulder internal rotation delivers up to 66% of shuttle speed in the smash.
Pace in badminton is a timing problem, not a strength problem: in the smash, internal rotation of the shoulder supplies up to 66% of shuttle speed, and the elbow extension angle accounts for a further 51.5% of the variance in speed. What coaches call pronation is exactly that turn — shoulder first, forearm behind it, all of it in the last few centimetres before the shuttle. The classic fault is a tense arm: squeeze the handle, drag the stroke out of your shoulder, and you block the rotation while asking your wrist to do work it can never do. Keep the grip loose and only tighten it at contact. You don't learn this on the smash but on the high clear — same movement, more time to get it right. What often goes unnoticed: the follow-through is part of the stroke. It decelerates the rotation under control and protects the rotator cuff that every overhead loads.