Abstract: The present invention is an exercise machine comprising a booster bar to which is attached a pair of flexible elastic shock cords which have their other ends attached to fixed structural members. The user exercises his arms or his legs by repeatedly pushing against the booster bar, thus stretching and unstretching the shock cords. The unstretched length of the shock cords is adjusted by rotating the booster bar about its axis, thus winding or unwinding, the shock cords around the booster bar. This, in turn, adjusts the force required to stretch the shock cords to a given dimension. The fixed structural member may be a part of a foot-stand or a cot-like backrest.