Anthropometric-related percentile curves for muscle size and strength of lower limb muscles of typically developing children

Aims To establish anthropometric-related percentile curves for muscle size and strength in a cohort of typically developing (TD) children and to demonstrate their use through applications in children with cerebral palsy (CP) and Duchenne muscular dystrophy (DMD). Methods Lower limb muscle size and strength were assessed in a large cross-sectional cohort of TD children with 3D freehand ultrasound (four muscles, n=154, male/female=82/72, age range: 0y7mo-17y10mo) and fixed dynamometry (seven muscle groups, n=153, male/female=108/45, age range: 4y6mo-16y1mo), respectively. Generalized additive models for location, scale and shape were used to estimate anthropometric-related, i.e. body mass and height, TD percentile curves and to convert outcomes of individual patients with CP and DMD into z-scores. Results Muscle size and strength, as well as their inter-subject variation, increased with increasing anthropometric values. Individual patients exhibited negative z-scores, indicating muscle size and strength deficits in reference to TD peers. Interpretation The established anthropometric-related percentile curves for muscle size and strength in a cohort of TD children can successfully be used to express patient outcomes in reference to TD. This facilitates the interpretation of muscle size and weakness in children with a motor disability and allows for the evaluation of the disease progression and treatment impact during growth.