NMES tends to recruit which type of muscle fiber?

• A. Slow-twitch (Type I)
• B. Fast-twitch (Type II)
• C. Type III fibers
• D. Cardiac fibers

Answer: (B)

Electrical stimulation doesn’t follow the body’s normal order of motor-unit recruitment. Under NMES, larger-diameter nerve fibers are more easily excited by external current, so the fast-twitch motor units they innervate fire first. Those fast-twitch (Type II) fibers generate greater force quickly but fatigue more readily, which is why NMES-evoked contractions are typically driven by Type II fibers. Slow-twitch (Type I) fibers, which are more fatigue-resistant and recruited during voluntary effort, are not the primary drivers with this stimulation. The other options aren’t relevant to skeletal muscle recruitment by NMES (cardiac fibers aren’t skeletal muscle, and Type III fibers aren’t a recognized category).