F waves and motor unit size

✍ Scribed by Dr. Reinhard Dengler; Dr. Andon Kossev; Dr. Kai Wohlfahrt; Dr. Margot Schubert; Dr. Josef Elek; Dr. Werner Wolf

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 391 KB
• Volume: 15
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/mus.880151013

✦ Synopsis

M responses and twitch contractions were evoked in single motor units (MUs) of the first dorsal interosseus muscle by intramuscular microstimulation of motor axons. Two-hundred nine MUs were studied in 21 subjects. Thirty-five MUs (17%) showed F waves in addition to M responses. Twitch force was used to provide an indirect measure of MU size; additionally, twitch contraction time was measured. There was no select group of MUs generating F waves with regard to the above contraction parameters. However, four of five MUs with very high twitch forces, above 70 mN, generated F waves. We conclude that MUs of all sizes produce F waves with similar probability. Only few MUs with very strong twitch forces, i.e., very large MUs, may be more subject to F-wave production and may be involved in the generation of the so-called repeater F waves.