Mechanisms contributing to gait speed and metabolic cost in children with unilateral cerebral palsy

BACKGROUND: Gait speed and metabolic cost are indicators of functional capacity in children with cerebral palsy. Uncovering their mechanisms helps guide therapeutic actions. OBJECTIVES: To investigate the contributions of energy-generating and energy-conserving mechanisms to gait speed and metabolic cost of children with unilateral cerebral palsy. METHODS: Data on eccentric and concentric muscle work, co-contraction, elastic torque and vertical stiffness of the affected-limb, forcing torque of the non-affected limb, gait speed and metabolic cost were collected from 14 children with unilateral cerebral palsy, aged 6–12 years. Analyses included two groups of multiple regression models. The first group of models tested the association between each dependent variable (i.e., speed and metabolic cost) and the independent variables that met the input criteria. The second group verified the contribution of the non-selected biomechanical variables on the predictors of the first model. RESULTS: Gait speed (R(2) = 0.80) was predicted by elastic torque (β = 0.62; 95%CI: 0.60, 0.63), vertical stiffness (β = −0.477; 95%CI: −0.479, −0.474) and knee co-contraction (β = 0.27; 95%CI: −1.96, 2.49). The production of eccentric work by the affected limb proved relevant in adjusting the vertical stiffness (R(2) = 0.42; β = −0.64; 95%CI: 0.86, −0.42); elastic torque of the affected-leg was associated with impulsive torque of the non-affected leg (R(2) = 0.31; β = 0.55; 95%CI: 0.46, 0.64). Metabolic cost of gait (R(2) = 0.48) was partially predicted by knee co-contraction (β = 0.69; 95%CI: 0.685, 0.694). CONCLUSIONS: The chain of associations revealed by the two steps models helped uncover the mechanisms involved in the locomotion of children with unilateral cerebral palsy. Intervention that changes specific energy conserving and generating mechanisms may improve gait of these children.