National Physical Therapy Examination (NPTE) Practice Exam

In a patient 4 weeks post knee arthroscopy, what is the most appropriate pulse duration for functional electrical stimulation (FES) targeting the quadriceps?

1. Pulse duration - 250-300 msec; 10 sec on, 50 sec off

2. Pulse duration - 150-170 msec; 10 sec on, 20 sec off

3. Pulse duration - 250-300 msec; 10 sec on, 20 sec off

4. Pulse duration - 150-170 msec; 10 sec on, 50 sec off

The correct answer is: Pulse duration - 250-300 msec; 10 sec on, 50 sec off

In the context of functional electrical stimulation (FES) targeting the quadriceps, particularly in a patient who is 4 weeks post knee arthroscopy, selection of an appropriate pulse duration is crucial for effective muscle contraction. A pulse duration of 250-300 msec is typically used for larger muscle groups like the quadriceps, as this range allows for optimal muscle fiber recruitment and effective contraction. Using this pulse duration helps facilitate a stronger contraction, which is essential for re-educating the muscle following surgery, where the quadriceps may have experienced disuse or atrophy. The frequency of stimulation, indicated by the "on" and "off" times, is also important. The proposed 10 seconds on and 50 seconds off provides adequate recovery time for the muscles, which is beneficial for sustaining muscle activity without fatigue—especially important in the early stages of rehabilitation. In contrast, shorter pulse durations, such as the ones mentioned in the other choices, may not adequately stimulate larger muscle fibers necessary for effective quadriceps engagement in this post-surgical context. Therefore, the parameters established in the first choice are best suited for promoting muscle strength and rehabilitation in this scenario.