typical stimulation protocols used in clinical fes involves trains of electric pulses. biphasic, charged balanced pulses are employed as they improve the safety of electrical stimulation and minimize some of the adverse effects. pulse duration, pulse amplitude and pulse frequency are the key parameters that are regulated by the fes devices. the fes devices can be current or voltage regulated. current regulated fes systems always deliver the same charge to the tissue regardless of the skin/tissue resistance. because of that, the current regulated fes systems do not require frequent adjustments of the stimulation intensity. the voltage regulated devices may require more frequent adjustments of the stimulation intensity as the charge that they deliver changes as the skin/tissue resistance changes. the properties of the stimulation pulse trains and how many channels are used during stimulation define how complex and sophisticated fes-induced function is. the system can be as simple such as fes systems for muscle strengthening or they can be complex such as fes systems used to deliver simultaneous reaching and grasping, or bipedal locomotion.