How can you recruit more motor units electrically?

How can you recruit more motor units electrically?

• A. Increase electrode size
• B. Increase phase charge by increasing amplitude and/or pulse duration
• C. Increase frequency only
• D. Shorten pulse duration

Answer: (B)

In electrical stimulation, the number of motor units that are recruited is driven by the amount of charge delivered with each pulse. The phase charge equals the current amplitude times the pulse duration. Delivering more charge per pulse means more axons reach their excitation threshold, so more motor units are recruited and a stronger contraction results. Increasing amplitude or lengthening the pulse duration directly increases that phase charge, which is why this is the best way to recruit more motor units. Frequency, on the other hand, changes how often the recruited motor units fire (the rate of contraction) rather than how many are recruited. Shorter pulse durations deliver less charge and recruit fewer units, while longer durations or higher amplitudes that stay within safety limits raise recruitment. Electrode size can influence current density and spread, but the fundamental lever for recruiting more motor units is increasing the phase charge. Remember to stay within recommended safety limits for charge per phase and charge density.

In electrical stimulation, the number of motor units that are recruited is driven by the amount of charge delivered with each pulse. The phase charge equals the current amplitude times the pulse duration. Delivering more charge per pulse means more axons reach their excitation threshold, so more motor units are recruited and a stronger contraction results. Increasing amplitude or lengthening the pulse duration directly increases that phase charge, which is why this is the best way to recruit more motor units.

Frequency, on the other hand, changes how often the recruited motor units fire (the rate of contraction) rather than how many are recruited. Shorter pulse durations deliver less charge and recruit fewer units, while longer durations or higher amplitudes that stay within safety limits raise recruitment. Electrode size can influence current density and spread, but the fundamental lever for recruiting more motor units is increasing the phase charge. Remember to stay within recommended safety limits for charge per phase and charge density.