the burst-modulated alternating current stimulators can produce the most force, particularly when applied to large, proximal muscle groups

low stimulus intensities, particularly to more distal musculature, the twin-spiked monophasic pulsed current might be the most comfortable.

Force of muscle contraction and amount of current applied are linearly related

Lowering skin resistance can lower the driving voltage needed for current to penetrate the skin.

Currents with shorter pulse or phase durations require a greater current amplitude to produce a particular muscular force

Burst-modulated alternating current requires the least current amplitude.

Because of the strength-duration relationship of electrical stimulation to motor and pain nerve fibres, pulses wider than 60 ~sec increase the likelihood of recruiting pain fibres

Pulses with longer durations (300 to 400 /olsec) produce a more powerful contraction

Biphasic pulsed stimulators may have either fixed or variable pulse durations

Burst-modulated 2500Hz alternating current has a cycle duration of 400 ~sec

Twin-spiked monophasic pulsed currents have pulse durations of 90 /olsec or less

interference-modulated alternating current stimulators have cycle durations of 250 ~sec

maximum force is produced only at higher frequencies of 60 to 100 stimuli per second

stimulation of skeletal muscle at frequencies as low as 20 pulses per second can greatly reduce muscle fatigue

if the frequency of the electrical stimulation of muscle is gradually reduced during the stimulation period a high force can be maintained throughout the stimulation period.

(!) no commercially available clinical stimulator can be automatically programmed to reduce the stimulation frequency

Duty cycle is defined as ratio of 'on-time' to 'total cycle time' expressed as a percentage

a progressive decrease in muscle fatigue with a progressive reduction in 'on-time'.

Biphasic pulsed stimulators offer controls which allow for a wide range of duty cycles

Interference-modulated alternating current stimulators do not offer duty cycle controls

many burst-modulated alternating current stimulators have only the 2 duty cycles

Amplitude ramp modulation is defined as the gradual, sequential increase or decrease in the peak amplitude ofa series of pulses

A gradual increase in the peak amplitude at the beginning of a series of pulses is designed to gradually increase the number of recruited motor units and gradually increase the force of contraction, and a gradual decrease in peak amplitude at the end produces a smooth, gradual decline in muscle force.

Most stimulators have controls for regulating ramp durations. In electrical stimulation protocols ramps vary from 2 to 4 seconds at the beginning of a stimulation series and I to 2 .seconds at the end

Neuromuscular Electrical Stimulation (NMES) -- AC, pulsed DC (Type of Current) -- stimulation of innervated muscle to restore function including muscle strength, reduction of spasm/spasticity, prevention of atrophy, increase ROM, and muscle reeducation