What role does electrode size play in current density and comfort?

• A. Larger electrodes increase current density
• B. Smaller electrodes reduce focal contraction
• C. Larger electrodes lower current density and increase comfort
• D. Electrode size has no effect on comfort

Answer: (C)

The main idea here is how electrode size changes the current density at the tissue interface and how that affects comfort during NMES. Current density is the current divided by the contact area of the electrode. When you use a larger electrode, the same current is spread over a bigger area, so the current density at any given point is lower. That means the nerves and skin near the electrode are stimulated more gently, which reduces uncomfortable sensations and the risk of skin irritation or overheating. Conversely, smaller electrodes concentrate the current into a smaller area, increasing current density, which tends to produce stronger, more focal contractions and can feel more uncomfortable.

So, using larger electrodes lowers current density and increases comfort. The other ideas don’t fit because increasing electrode size does not raise current density, and smaller electrodes don’t reduce focal contraction—they tend to make it more focal and sometimes more intense.