National Physical Therapy Examination (NPTE) Practice Exam

A patient receiving neuromuscular electrical stimulation to the quadriceps femoris has no contraction but reports a strong tingling sensation. What alteration should be made to elicit a contraction?

1. Increase in current amplitude

2. Increase in pulse duration

3. Decrease in electrode size

4. Decrease in distance between electrodes

The correct answer is: Increase in pulse duration

To elicit a contraction of a muscle using neuromuscular electrical stimulation (NMES), adjusting the pulse duration is critical. When a patient reports a strong tingling sensation but exhibits no contraction, it indicates that the electrical current is likely stimulating sensory fibers rather than motor fibers. Increasing the pulse duration allows the electrical impulse to remain on longer, which can help recruit the larger motor fibers necessary for muscle contraction. The longer duration increases the likelihood that the current will reach the threshold required to activate these motor units. While increasing the current amplitude could also enhance the stimulation's intensity, if the pulse duration is too short, the stimulation may still only activate sensory nerves. Thus, increasing pulse duration is a more effective and specific adjustment to facilitate muscle contraction in this scenario. Reducing electrode size or decreasing the distance between electrodes can also change the stimulation characteristics, but they are not as directly related to eliciting a contraction when the challenge is already with the stimulation parameters regarding pulse duration.