The dynamic balance of the children with cerebral palsy and typical developing during gait Part II: Instantaneous velocity and acceleration of COM and COP and their relationship.

As a companion research subsequent to analyzing displacement of center of mass (COM) and center of pressure (COP) in Part I, the purposes of this study were to quantify dynamic stability using magnitudes and patterns of instantaneous velocity and acceleration of COM and COP of the children with cerebral palsy (CP) during walking, and compare the data with those of the typically developing (TD) children. The instantaneous velocity and acceleration of COM and COP were acquired by calculating the first and second derivatives of displacement data presented in Part I. Velocity and acceleration of COM and COP were normalized by each participant's leg length to eliminate the influence of individual's stature. The results indicate that the preferred walking speed is significantly higher in TD groups than hemiplegic group (Hemi) and diplegic group (Di). The peak values of instantaneous velocity and acceleration of COM in vertical, medio-lateral (ML) and antero-posterior (AP) directions and velocity and acceleration of COP in ML direction were significantly higher in Di group than TD group. Both CP groups showed great variability in COM and COP parameters. Therefore, although Di group demonstrated higher peak values than Hemi group, the only significant difference between two groups was instantaneous COP velocity in ML direction. The findings of this study suggest that this assessment may be of value for research or clinical evaluation of dynamic balance dysfunction during walking and provide comparisons and insights for specific treatments or surgical interventions for the children with CP.