When working with weakness of a muscle, which electrode spacing and sensitivity are used to create an adequate visible signal?

When working with weakness of a muscle, which electrode spacing and sensitivity are used to create an adequate visible signal?

• A. Wide spacing and high sensitivity
• B. Narrow spacing and low sensitivity
• C. Narrow spacing and high sensitivity
• D. Wide spacing and low sensitivity

Answer: (A)

When a muscle is weak, its electrical signal is small, so you need to both sample from a larger area and amplify the tiny voltages. Using wider spacing between surface electrodes increases the area from which potentials are picked up, which tends to yield a larger differential signal as motor units fire. Coupling that with high sensitivity (greater gain) makes these small voltages large enough to be clearly visible on the display. Narrow spacing reduces the signal you collect, and low sensitivity fails to boost the small signal enough, making it harder to see. Wide spacing with high sensitivity thus provides the best chance to obtain an adequately visible signal in a weak muscle.

When a muscle is weak, its electrical signal is small, so you need to both sample from a larger area and amplify the tiny voltages. Using wider spacing between surface electrodes increases the area from which potentials are picked up, which tends to yield a larger differential signal as motor units fire. Coupling that with high sensitivity (greater gain) makes these small voltages large enough to be clearly visible on the display. Narrow spacing reduces the signal you collect, and low sensitivity fails to boost the small signal enough, making it harder to see. Wide spacing with high sensitivity thus provides the best chance to obtain an adequately visible signal in a weak muscle.