title: Motor unit firing behaviour of soleus muscle in isometric and dynamic contractions.
abstract: BACKGROUND
  Understanding the detailed control of human locomotion and balance can be improved, when individual motor units can be isolated and their firing rates followed in natural movement of large, fuctionally important muscles. For this reason the present study investigated the motor unit discharge rate (MUDR) in isometric and dynamic contractions of the soleus muscle.
  
  
  METHODS
  Eleven males performed isometric (10-100% MVC) and dynamic (10-40% MVC) plantar flexions. Intramuscular EMG was measured from Soleus with bipolar wire-electrodes and decomposed with custom built "Daisy" software.
  
  
  RESULTS
  The Soleus MUDR was significantly higher in concentric compared to isometric or eccentric contractions at all submaximal force levels (P<0.05). In isometric contractions MUDR increased up to 100% MVC.
  
  
  CONCLUSIONS
  Motor unit discharge properties of a large plantarflexor can be measured in dynamic and maximal contractions. For a given torque output, MUDR is dependent upon contraction type, as set by the major mechanical differences between concentric and eccentric actions.
authors: Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland. jouni.kallio@jyu.fi
authors: Jouni
authors: J
authors: Kallio
authors: Karen
authors: K
authors: Søgaard
authors: Janne
authors: J
authors: Avela
authors: Paavo V
authors: PV
authors: Komi
authors: Harri
authors: H
authors: Selänne
authors: Vesa
authors: V
authors: Linnamo
mesh_terms: D000328:Adult; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque
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