Age-related changes in co-contraction during heel and toe walking. Age-related changes in co-contraction across the ankle joint in late swing (A–C) and early stance (D–F) in typically-developed children during heel (A and D) and Toe walking (B and E) and in cerebral palsy children (C and F). Each symbol indicates data from one child. Full lines indicate regression lines calculated for the populations of children. Dashed lines indicate 95% confidence intervals. Correlation coefficients and level of statistical significance are given in the upper left corner of each graph. CP = cerebral palsy; Sol = soleus muscle; TA = tibialis anterior muscle; TD = typically-developing.