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Keywords:

  • electrical stimulation;
  • joint angle;
  • muscle strength;
  • rate of torque development;
  • tenascin-X deficiency

Abstract

Introduction: Ehlers–Danlos syndrome (EDS), a connective tissue disorder, may lead to impaired contractile function of lower limb muscles. Methods: To test this hypothesis and to understand the possible mechanisms involved, isometric function of the thigh muscles was investigated at different joint angles (30°, 60°, and 90° of knee flexion) in 7 tenascin-X (TNX)-deficient EDS patients. Results: There was reduced maximal voluntary torque of the knee extensors (but not knee flexors) across all joint angles in the patients. Time to reach maximal rate of torque development was delayed, and voluntary activation capacity was reduced in patients compared with controls, particularly at 30°. Conclusions: EDS is associated with muscle weakness, most likely due to increased compliance of the series-elastic component of muscle tissue and failure of maximal voluntary muscle activation. Further research is required to understand the influence of reduced voluntary activation on the severe fatigue reported by EDS patients. Muscle Nerve, 2013