title: Insight into motor adaptation to pain from between-leg compensation.
abstract: OBJECTIVE
  Although it appears obvious that we change movement behaviors to unload the painful region, non-systematic motor adaptations observed in simple experimental tasks with pain question this theory. We investigated the effect of unilateral pain on performance of a bilateral plantarflexion task. This experimental task clearly allowed for stress on painful tissue to be reduced by modification of load sharing between legs.
  
  
  METHODS
  Fourteen participants performed a bilateral plantarflexion at 10, 30, 50 and 70 % of their MVC during 5 conditions (Baseline, Saline-1, Washout-1, Saline-2, Washout-2). For Saline-1 and -2, either isotonic saline (Iso) or hypertonic saline (Pain) was injected into the left soleus.
  
  
  RESULTS
  The force produced by the painful leg was less during Pain than Baseline (range -52.6 % at 10 % of MVC to -20.1 % at 70 % of MVC; P < 0.003). This was compensated by more force produced by the non-painful leg (range 18.4 % at 70 % of MVC to 70.2 % at 10 % of MVC; P < 0.001). The reduction in plantarflexion force was not accompanied by a significant decrease in soleus electromyographic activity at 10 and 30 % of MVC. Further, no significant linear relationship was found between changes in soleus electromyographic activity and change in plantarflexion force for the painful leg (with the exception of a weak relationship at 10 % of MVC, i.e., R (2) = 0.31).
  
  
  CONCLUSIONS
  These results show that when the nervous system is presented with an obvious solution to decrease stress on irritated tissue, this option is selected. However, this was not strongly related to a decrease in soleus (painful muscle) activity level.
authors: NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, The University of Queensland, St. Lucia, Brisbane, QLD, 4072, Australia, francois.hug@univ-nantes.fr.
authors: François
authors: F
authors: Hug
authors: Paul W
authors: PW
authors: Hodges
authors: Sauro E
authors: SE
authors: Salomoni
authors: Kylie
authors: K
authors: Tucker
mesh_terms: D000222:Adaptation, Physiological; D005260:Female; D006801:Humans; D007866:Leg / Q000294:innervation / Q000502:physiology*; D008297:Male; D009068:Movement; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D055815:Young Adult