Infant limb kinematics and muscle force variation during kicking is associated with clinical cerebral palsy risk measures.

Early limb motor development progresses from spontaneous to increasingly complex movements. Restricted movement variety in infancy can indicate neuromotor impairment associated with cerebral palsy (CP) risk. The General Movement Optimality Score (GMOS) used in clinic detects abnormal movement patterns, but requires highly trained physiotherapists, limiting accessibility. Objective biomechanical measures may provide quantitative predictors of CP risk, reducing clinical burden while offering novel physiotherapeutic targets. This study investigated whether variation in lower limb kinematics and muscle forces during spontaneous kicking is reduced in infants with lower GMOS scores, indicating higher CP risk. We also examined whether variation correlates with gestational and corrected age, reflecting the transition to more complex movements. Twenty-six Infants aged 0-3 months underwent wired electromagnetic motion capture (Polhemus Liberty System) with musculoskeletal modelling to estimate kinematics and muscle force waveforms, alongside GMOS scoring. Waveform variation was quantified using functional principal component analysis and correlated with GMOS scores and age, while partial least squares discriminant analysis (PLS-DA) identified biomechanical predictors of GMOS indications of 'normal' versus 'poor repertoire' (PR) movements. Variation in knee flexion, hip flexion and abduction kinematics, and rectus femoris, pectineus, biceps femoris and gemelli forces significantly correlated with GMOS scores. Gestational age correlated with hip abduction, ankle dorsiflexion, and gemelli and medial gastrocnemius forces. PLS-DA achieved 85% accuracy distinguishing normal from poor repertoire movements, with knee and hip kinematics and biceps femoris force as key discriminators. These findings demonstrate that lower limb kinematic and neuromuscular variation aligns with clinical motor assessments, supporting their potential as objective biomechanical markers of CP risk.