Where should the electrode be placed to generate a motor response?

• A. Place on tendon insertion
• B. Place on muscle belly
• C. Place over nerve trunk
• D. Place over bone

Answer: (B)

When you want a motor response from surface stimulation, focus the stimulus where the muscle is most excitable and easily activated. Placing the active electrode over the muscle belly places the current directly into the muscle tissue near the motor endplates, so the stimulus effectively recruits motor units and produces a clear, controlled contraction. This location provides a more reliable and localized response with less current than other sites.

If you stimulate over a tendon insertion, the tendon is less responsive to electrical current, so the contraction may be weaker or inconsistent. Stimulating over a nerve trunk can trigger a motor response, but it often activates multiple muscles and can be less comfortable or less specific. Stimulating over bone isn’t effective because bone conducts poorly, so the current doesn’t reach the muscle well.