Quadriceps femoris muscle voluntary force and relaxation capacity in children with spastic diplegic cerebral palsy.

Isometric voluntary force production and relaxation capacity of the quadriceps femoris (QF) muscle was compared between 12 children with spastic diplegic cerebral palsy (CP) and healthy controls, age 10-11 years. Children with CP had less (p < .05) maximal voluntary-contraction force, voluntary activation, and rate of force development than controls. Visual reaction to contraction did not differ significantly in measured groups, whereas the reaction time to relaxation and halfrelaxation time were longer (p < .05) in children with CP. The authors concluded that in children with CP, the capacity for rapid voluntary force production and relaxation is reduced to a greater extent than isometric maximal force.

Muscle contractile properties in children with spastic diplegia.

The aim of the present study was to evaluate contractile properties of the plantarflexor muscles in children with spastic diplegia (SD) in comparison of age-matched healthy children. Twelve prepubertal children with SD aged 11-12 years (6 girls and 6 boys) and 12 age- and gender-matched healthy control children (6 girls and 6 boys) participated in this study. Subjects were seated in a custom-made dynamometric chair with the dominant leg flexed 90 degrees at the knee and ankle joints. Twitch contraction characteristics of the plantarflexor muscles were measured by supramaximal electrical stimulation of posterior tibial nerve in popliteal fossa using square-wave pulses of 1 ms duration at rest and after a brief (5 s) isometric maximal voluntary contraction (MVC), i.e., during post-activation potentiation (PAP). Children with SD had significantly lower (p<0.05) MVC force, twitch contraction peak force (PF), PAP of twitch force, and twitch maximal rates of force development and relaxation compared to control group. Twitch contraction PF:MVC force ratio was higher (p<0.05) in children with SD than in the control group. However, no significant differences in twitch contraction and half-relaxation times were observed between the measured groups. It was concluded that prepubertal children with SD in comparison of normal children are characterized by markedly reduced isometric voluntary and electrically evoked twitch contraction maximal force, capacity for twitch PAP, and rates of twitch force production and relaxation of the plantarflexor muscles. The time-course characteristics of isometric twitch contraction were similar in children with SD and normal children.