SELF-OPTIMIZATION OF WALKING IN NONDISABLED CHILDREN AND CHILDREN WITH SPASTIC HEMIPLEGIC CEREBRAL-PALSY

Children voluntarily adopt a frequency and movement pattern for walkin g. The force-driven harmonic oscillator (FDHO) model was used in this study for accurate prediction of the preferred walking frequency of no ndisabled children and children with spastic hemiplegic cerebral palsy . Four potential optimality criteria with which the preferred walking pattern was forced to comply were examined: minimization of physiologi cal costs, maximization of mechanical energy conservation, minimizatio n of asymmetry in lower limb movements and minimization of variability of interlimb and intralimb coordination. Age and gender-matched nondi sabled children (n = 6) and children with spastic hemiplegic cerebral palsy (n = 6) were tested under six frequency conditions of walking at a constant speed on a treadmill. For the nondisabled children, the re sults indicated that their preferred walking frequency could be accura tely predicted by the FDHO model. They freely adopted a walking patter n that minimized physiological costs, asymmetry, and variability of in ter- and intralimb coordination. For the children with spastic hemiple gic cerebral palsy, the prediction of preferred overground walking fre quency required that the FDHO model be modified to account for muscle mass and leg length discrepancies between limbs and increased stiffnes s. Most of the children achieved the same optimality goals as the nond isabled when walking at the preferred frequency. However, the children were found to use different mechanisms to attain these goals: for exa mple, a steeper increase observed in physiological cost at higher freq uencies; a lowered center of gravity Of the body, which allowed for an gular symmetry; and greater variability of between-joint coordination in the nonaffected limb and less variability in the affected limb.