Which statement correctly describes electrode polarity and placement for NMES on a muscle?

Which statement correctly describes electrode polarity and placement for NMES on a muscle?

• A. Negative electrode placed on motor point and positive at the opposite end
• B. Positive electrode placed on motor point
• C. Both electrodes on the same muscle belly
• D. Negative electrode placed on the distal tendon

Answer: (A)

The key idea is how NMES activates muscle fibers efficiently. The electrical current works best when the cathode (negative electrode) is placed over the motor point—the spot on the muscle where a small amount of current most easily triggers a motor neuron to fire. By putting the negative electrode there, you depolarize the nerve efficiently, producing a strong, controlled contraction with less overall current. Placing the positive electrode (anode) at the opposite end completes the circuit and directs the current through the muscle, supporting a coordinated contraction across the muscle belly. This setup—negative over the motor point and positive at the far end—minimizes the current needed and tends to be more comfortable and effective. If the positive electrode were placed on the motor point, you wouldn’t be targeting the most excitable site as efficiently, requiring more current for the same contraction. Placing both electrodes on the same muscle belly reduces the current’s path through the tissue, leading to a less uniform or weaker contraction. Putting the negative electrode on the distal tendon also misses the motor point, making stimulation less efficient and potentially more uncomfortable.

The key idea is how NMES activates muscle fibers efficiently. The electrical current works best when the cathode (negative electrode) is placed over the motor point—the spot on the muscle where a small amount of current most easily triggers a motor neuron to fire. By putting the negative electrode there, you depolarize the nerve efficiently, producing a strong, controlled contraction with less overall current.

Placing the positive electrode (anode) at the opposite end completes the circuit and directs the current through the muscle, supporting a coordinated contraction across the muscle belly. This setup—negative over the motor point and positive at the far end—minimizes the current needed and tends to be more comfortable and effective.

If the positive electrode were placed on the motor point, you wouldn’t be targeting the most excitable site as efficiently, requiring more current for the same contraction. Placing both electrodes on the same muscle belly reduces the current’s path through the tissue, leading to a less uniform or weaker contraction. Putting the negative electrode on the distal tendon also misses the motor point, making stimulation less efficient and potentially more uncomfortable.