Which fiber type does NMES primarily stimulate?

Which fiber type does NMES primarily stimulate?

• A. Type I
• B. Type IIA
• C. Type IIB
• D. Type IIx

Answer: (C)

Electrical stimulation activates nerves directly, so recruitment follows the excitability of motor neurons rather than the normal gradual order you see with voluntary contraction. The larger-diameter motor neurons, which innervate fast-twitch fibers, reach the activation threshold more readily under surface NMES. Among the fast-twitch fibers, the Type IIB (fast glycolytic) fibers have the largest neurons and the most fatigable profile, so they are the ones most prominently recruited by NMES. That combination produces the strong, quick contractions typical of NMES, but with quicker fatigue. Slow-twitch Type I fibers are less responsive to standard NMES intensities, and Type IIa fibers, while fast, aren’t as readily recruited as Type IIB under typical parameters. So, the primary fiber type stimulated by NMES is Type IIB.

Electrical stimulation activates nerves directly, so recruitment follows the excitability of motor neurons rather than the normal gradual order you see with voluntary contraction. The larger-diameter motor neurons, which innervate fast-twitch fibers, reach the activation threshold more readily under surface NMES. Among the fast-twitch fibers, the Type IIB (fast glycolytic) fibers have the largest neurons and the most fatigable profile, so they are the ones most prominently recruited by NMES. That combination produces the strong, quick contractions typical of NMES, but with quicker fatigue. Slow-twitch Type I fibers are less responsive to standard NMES intensities, and Type IIa fibers, while fast, aren’t as readily recruited as Type IIB under typical parameters. So, the primary fiber type stimulated by NMES is Type IIB.