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

Abstract 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, ♂/♀=82/72, age range: 0y7mo-17y10mo) and fixed dynamometry (seven muscle groups, n=153, ♂/♀=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.