title: Positive afferent feedback to the human soleus muscle during quiet standing.
abstract: BACKGROUND
  In this study we investigated the mechanisms responsible for soleus muscle contraction during quiet standing.
  
  
  METHODS
  Subjects stood on a platform that was randomly moved forward or downward or rotated around the ankle.
  
  
  RESULTS
  Downward perturbation caused a short-latency drop in averaged rectified soleus electromyography (SOL EMG). SOL drop increased monotonically with downward acceleration amplitude. Ischemia above the knee abolished or diminished this drop. Ischemia above the ankle had no diminishing effect. Vibration of the Achilles tendon had a diminishing effect on the amplitude of SOL responses.
  
  
  CONCLUSIONS
  The short-latency drop in SOL observed for downward perturbation might be due to a decrease in positive afferent feedback due to the sudden decrease in body weight. This implies the existence of an ongoing afferent feedback loop toward the SOL motoneuron pool from force-sensitive receptors. Both Ia and Ib afferents probably play a role in the responses observed.
authors.affiliation: Center for Sensory Motor Interaction, Aalborg University, Aalborg, Denmark.
authors.forename: Johan
authors.initials: J
authors.lastname: Van Doornik
authors.forename: Christine
authors.initials: C
authors.lastname: Azevedo Coste
authors.forename: Junichi
authors.initials: J
authors.lastname: Ushiba
authors.forename: Thomas
authors.initials: T
authors.lastname: Sinkjaer
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D004576:Electromyography / Q000379:methods; D025461:Feedback, Physiological / Q000502:physiology*; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012146:Rest / Q000502:physiology*