Do electrode leads or polarity matter for producing a motor response?

• A. Yes
• B. No
• C. Only With Direct Current
• D. Only With Alternating Current

Answer: (B)

Motor contractions happen when the nerve fibers near the active electrode reach their excitation threshold from the applied current. In most therapeutic stimulators, the current is biphasic or alternating, so polarity reverses with each pulse and there’s no net charge. That means which lead is positive or negative doesn’t change whether a motor response can be produced—the key factors are the current’s amplitude and pulse duration, and where the electrodes are placed to target the right nerves. You can swap the leads and still get the same contraction if you keep the same path and parameters. Using direct current with a single polarity can affect skin comfort and electrode interface, but it doesn’t change the basic ability to evoke a motor response in the standard biphasic/alternating setups.