title: Reproducibility of tendon jerk reflexes during a voluntary contraction.
abstract: OBJECTIVE
  The present study explored whether testing tendon jerks during voluntary contraction of the test muscle would improve reproducibility by effectively 'clamping' the excitability of the motoneurone pool at firing threshold.
  
  
  METHODS
  Tendon jerk reflexes of soleus, tibialis anterior and vastus lateralis and the soleus H reflex were recorded in 12 healthy subjects at rest and during voluntary contractions of 10-20% of maximum. Recordings were repeated 8-10 times in 5 subjects, in whom reflex symmetry was also determined.
  
  
  RESULTS
  Not all tendon jerk reflexes could be recorded at rest, and the variability of latency and amplitude was high. All reflexes could be recorded in each subject during contractions. The latency of tendon jerk reflexes decreased by approximately 2 ms during contractions, but H-reflex latency decreased by only 0.2-0.3 ms. For the tendon jerks, an asymmetry of >3.0 ms at rest and >2.5 ms contracting would be outside 3 SD of the normal mean. In repeat studies, the coefficient of variation of reflex latency was <4% for the tendon jerk.
  
  
  CONCLUSIONS
  A voluntary contraction could potentiate the tendon jerk by a number of mechanisms, but the most important is probably enhancement of the excitability of the motoneurone pool. The present techniques should increase the value of tendon reflex testing when assessing possible peripheral nerve, plexus and root disturbances.
authors.affiliation: Department of Neurology, Prince of Wales Hospital, Prince of Wales Medical Research Institute, and University of New South Wales, Sydney, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Uysal
authors.forename: I
authors.initials: I
authors.lastname: Mogyoros
authors.forename: D
authors.initials: D
authors.lastname: Burke
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D015203:Reproducibility of Results; D013710:Tendons / Q000502:physiology*