A-System, Power Twister Alternative with Adjustable Resistance Get stronger, burn fat, increase muscle using this exercise-anywhere device. Chest exerciser, arm machine, and upper body trainer. Adjustable tension levels, make your exercises easier or more difficult. Feel yourself getting stronger in time as you increase the resistance. Spring hidden behind metal frame, eliminating discomfort associated with using power twisting devices. Solidly constructed, made of metal (with rubber covered handles), not cheap plastic.