In transcutaneous electrical nerve stimulation (TENS) for motor stimulation, which parameter combination is typical?

• A. High Frequency and Short Phase Duration
• B. Low Frequency and Long Phase Duration
• C. Variable Frequency with Medium Duration
• D. High Frequency and Long Phase Duration

Answer: (B)

When you want surface stimulation to cause a muscle contraction, you need enough charge per pulse to recruit motor fibers, but you also want to avoid fatiguing the muscle too quickly. A longer pulse duration (phase duration) does more work per pulse, so motor neurons reach the depolarization threshold more efficiently, allowing you to achieve a contraction at a lower current level and with less discomfort. Pairing that with a lower frequency means the muscle fires less often, producing controlled twitches or a slow, manageable contraction rather than a continuously fused, fatiguing contraction. This combination keeps the contraction effective without overwhelming fatigue or discomfort, which is ideal for motor stimulation.

In practice, this means relatively low frequency—on the order of a few hertz up to perhaps a dozen hertz—and a long phase duration, often several hundred microseconds. High frequency with short duration is typically used for sensory or analgesic effects, not for driving a motor contraction, so the described low-frequency, long-duration pairing is the typical approach for motor stimulation.