Electromechanical delay and reflex response in spastic cerebral palsy

Objective: Electromechanical delay (EMD) and reflex response in patients with spastic cerebral palsy (CP) were quantified and compared with those in normally developing individuals. It was hypothesized that the increased muscle stiffness associated with spasticity must make EMD shorter than the EMD of normally functioning muscles. Design: Electromechanical reflex behavior was assessed in a case-control study. Setting: Motion Analysis and Motor Performance Laboratory, University of Virginia, a tertiary clinical referral center and research facility. Participants: A volunteer sample of 12 children diagnosed with spastic CP and 12 age-matched, normally developing children recruited from the local community and clinical services. Results: EMD in the patients with spasticity was significantly shorter than in the normally developing subjects, 40.5 msec and 54.7 msec, respectively. The spastic group also had greater reflex activity, rate of force development, and antagonistic muscle activation. Knee flexion angle did not influence EMD in either group. Conclusions: Increased biomechanical stiffness in spastic muscle results in abnormally reduced EMD. Reciprocal excitation of antagonistic cocontraction was uniquely observed in the spastic group, but did not explain the reduced EMD.