Hinge forward from the hips until your torso is close to parallel with the floor, back flat, one knee resting on a bench for support if you have one nearby. Your upper arm stays pinned against your ribs, elbow bent to about ninety degrees — that arm does not move for the whole set. Straighten your arm by extending at the elbow only, driving the dumbbell back until it's level with your hip, then pause and feel the tricep lock out. Lower back to the start slowly rather than letting the weight swing. If your elbow drops or your upper arm drifts away from your side, the shoulder starts sharing the work and the tricep loses tension. Keep the motion small and controlled — this is not a movement that rewards momentum.