Fig. 7. Tuning coefficients. The mean values, over all participants and trials, of the normalized tuning coefficients are plotted for three spatial directions. The tuning coefficients correspond to the PCs shown in Fig. 6. Here the normalized tuning coefficients were computed using Eqn 17, and were obtained as gait percentage averages over all participants and walking trials. To provide information on the variability of each normalized tuning coefficient, a variability number B_i(j) is assigned to each curve, where j=1...3 (spatial directions) and i=1...N (model segments or PCs). Each number was computed by first estimating the area between plus and minus one standard deviation about the tuning coefficient mean, and then dividing by the total area beneath the tuning coefficient mean – from 0% to 100% gait cycle.