Apparatus and methods for muscle stimulation and control of muscle stimulators are disclosed. In at least one embodiment, an electrical muscle stimulator includes a belt having a plurality of stimulator pads, a pulse width modulator controlled by a feedback loop, the PWM providing output to control voltages of the stimulator pads, and a control unit to control the PWM and feedback loop. In various embodiments, the control unit monitors PWM output values during a rest phase of a cycle of the muscle stimulator, provides a contraction phase, and following a sag after the contraction phase, uses PWM values from the rest phase to set a voltage for a subsequent rest phase of a next cycle.