• agonist activation;
  • antagonist coactivation;
  • cross-sectional area;
  • gastrocnemius;
  • spastic hemiplegia


Introduction: Muscle weakness is present in the paretic limbs of individuals with cerebral palsy (CP). We aimed to determine what neuromuscular factors contribute to weakness in adults with CP during isometric maximal voluntary contractions (iMVCs). Methods: Gastrocnemius anatomical cross-sectional area (ACSA) and agonist and antagonist activation were measured in 11 CP and 11 control adult men during plantarflexion iMVC. Results: Plantarflexion iMVC torque of the paretic leg was 42% and 52% less than in the non-paretic and control limbs, respectively. The paretic gastrocnemius ACSA was smaller than in the control group only. Paretic agonist activation was less than the non-paretic and control groups, whereas antagonist coactivation was higher. Multiple regression analysis revealed muscle activation accounted for 57% of variation in paretic plantarflexion iMVC torque. Conclusions: In individuals with CP, muscle weakness in the paretic limb is attributed primarily to impaired neural activation and, to a lesser degree, ACSA. Muscle Nerve 49: 76–83, 2014