Hold the bar in front of you at shoulder height with both hands, arms extended, and let the weight hang from the rope or strap wound around its middle. Rotate your wrists forward, one hand over the other, winding the rope up around the bar until the weight reaches the top. Then reverse the motion, unwinding it back down under control instead of letting it spin loose. Keep your arms extended rather than bending your elbows to help; the whole point is your wrists and forearms doing the work while your shoulders just hold position.