Step-length asymmetry drivers in unilateral cerebral palsy: Exploring the interplay between neuromotor constraints and energy optimization

Introduction Step-length asymmetry is a prevalent, energy-inefficient gait deviation in children with unilateral cerebral palsy (CP). While neuromotor impairments and energy efficiency factors are implicated in gait deviations, their combined predictive power on step-length asymmetry remains poorly understood.Objective This study aimed to quantify the independent and synergistic predictive roles of specific neuromotor constraints and energetic efficiency variables in explaining step-length asymmetry in this population.Methods Fifty-two children with unilateral CP (aged 8–18 years; Gross Motor Function Classification System levels I – II) participated. Step-length asymmetry was defined as the absolute percentage difference between affected and less-affected limb step lengths, normalized to their mean. Neuromotor function was assessed through dorsiflexor strength, plantarflexor dynamic spasticity slope, passive dorsiflexion range, and ankle proprioceptive acuity. Energetic efficiency was evaluated using the metabolic cost of walking and self-selected walking speed.Results Hierarchical multiple linear regression demonstrated that the final model, incorporating neuromotor impairments and energy efficiency factors, accounted for 70% of the total variance in step-length asymmetry (R2 = 0.70, p < .001). Neuromotor impairments were primary drivers, explaining 58.8% of the variance (R2 = 0.588, p < .001), but adding energy efficiency factors provided a unique, statistically significant predictive contribution of 11.2% (ΔR2 = 0.112, p = .0008). The strongest individual predictors of step-length asymmetry were dorsiflexor weakness, dynamic spasticity slope, metabolic cost of walking, and self-selected walking speed.Conclusion Step-length asymmetry in unilateral CP is a multifactorial phenomenon significantly predicted by specific neuromotor and energy efficiency factors. Importantly, the statistical dominance of dorsiflexor strength in our specific model should not be misconstrued as a clinical directive to deprioritize plantarflexor strengthening, given the undeniable biomechanical role of the plantarflexors in forward propulsion and contralateral step length. Nonetheless, these findings underscore the need for integrated rehabilitation strategies that simultaneously target dorsiflexor strength, dynamic spasticity, and gait efficiency (including walking speed and metabolic economy) to optimize gait symmetry and function in this population.