What is usually the lowest frequency for motor unit recruitment in FES for shoulder subluxation?

• A. 60 pps
• B. 35 pps
• C. 20 pps
• D. 80 pps

Answer: (B)

To hold a shoulder in place with FES, you need a contraction that is steady and fused rather than a series of separate twitches. That means picking a frequency high enough to produce a smooth, tetanic contraction, but not so high that fatigue and discomfort become a problem. The lowest frequency that reliably achieves this smooth, continuous contraction is a mid-range rate. At that level, motor units fire in a coordinated, sustained way to support the joint, whereas lower frequencies tend to produce intermittent twitches that won’t control the shoulder effectively. Higher frequencies offer diminishing returns in held force and simply increase fatigue, so starting at this mid-range rate provides the best functional balance for preventing shoulder subluxation.