Gastrocnemius Muscle Characteristics And Jump Performance In Children With Cerebral Palsy

Cerebral palsy (CP) comprises a group of movement and posture disorders associated with a gastrocnemius that is small, weak, stiff, and highly infiltrated with fat. Jumping is a key developmental milestone in children that is dependent on the gastrocnemius muscle to forcefully plantarflex the ankle and propel the body upwards. Identifying the gastrocnemius muscle properties most related to jumping performance may help guide the treatment of children with CP. PURPOSE: This study aimed to identify gastrocnemius muscle properties most strongly related to the jump performance of children with CP. METHODS: Ambulatory children with spastic CP (n = 19 unilateral and n = 12 bilateral) were age, sex, and race matched with 31 typically developing control children. Stiffness represented by shear-wave elastography, fat infiltration represented by echo intensity, volume, and pennation angle of the gastrocnemius in both limbs were assessed using ultrasound. Jump height (i.e., jump performance) was assessed using a motion capture system. RESULTS: Groups were not significantly different in age, height, body mass, or body mass index. Jump height was 30% lower in children with CP than controls (p < 0.001). Additionally, gastrocnemius volume was 21% and 31% lower in the non-dominant and dominant limbs, respectively, while gastrocnemius stiffness was 15% and 23% higher, and echo intensity was 25% and 38% higher in the non-dominant and dominant limbs, respectively, in children with CP than controls (p < 0.001). There were no differences on pennation angle between groups. Muscle stiffness of the dominant limb was inversely related to jump performance for the whole group of children with CP (r = 0.395, p = 0.027) and more specifically for the subgroup of children with bilateral CP (r = 0.595, p = 0.041). None of the gastrocnemius muscle characteristics were significantly related to jump performance in children with unilateral CP or controls. CONCLUSION: The results suggest that a higher degree of stiffness of the gastrocnemius in the nondominant limb as opposed to the size, architecture, or fat infiltration, is the primary muscle property that limits jump performance in children with CP, especially children with the bilateral subtype. Supported by: This study was funded by the National Institutes of Health (R01HD090126) and the University of Georgia Athletic Association.