Motoneuron excitability and the F wave

Muscle Nerve. 2003 Jun;27(6):720-7. doi: 10.1002/mus.10388.


For three motoneuron pools that differ in excitability to Ia inputs [tibialis anterior (TA), abductor pollicis brevis (APB), and soleus], F-wave parameters were measured at rest, during voluntary contraction, and following prolonged vibration. There was an inverse relationship between F-wave chronodispersion and F-wave persistence at rest, and this appeared to be related to the ease of recording the H reflex for the motoneuron pool. During a steady voluntary contraction, overall F-wave activity increased in amplitude but decreased in duration for TA and APB. Following vibration of the test muscle at 50 HZ for 10 min there was a long-lasting depression of the H reflexes of TA and APB, but no significant change in F-wave measurements. These findings are consistent with the view that reflex discharges can prevent F waves in low-threshold motor units, and that chronodispersion is affected by the extent of reflex activity; that is, chronodispersion and related F-wave measurements do not measure motor properties exclusively. The findings also suggest that F waves provide a flawed measure of the excitability of the motoneuron pool.

MeSH terms

  • Action Potentials / physiology*
  • Adult
  • Afferent Pathways / physiology*
  • Female
  • H-Reflex / physiology*
  • Humans
  • Motor Neurons / physiology*
  • Muscle Contraction / physiology
  • Muscle Spindles / physiology*
  • Muscle, Skeletal / innervation*
  • Muscle, Skeletal / physiology
  • Neural Conduction / physiology
  • Spinal Cord / physiology*
  • Synaptic Transmission / physiology
  • Vibration