Fig. 6 Soleus EMG. (A) Nine subject mean (thick curves) + 1 s.d. (thin curves) of soleus normalized linear enveloped (high-pass cutoff frequency 20 Hz and low-pass cutoff frequency 10 Hz) muscle activity over the stride from heel-strike (0%) to heel-strike (100%). Left and right legs are averaged for each subject. Stance phase is 0% to 60% and swing 60% to 100% of the stride. Thick curves are three session average for unpowered walking (black) and powered walking at the beginning of practice session 1 (light gray) and the end of practice session 3 (dark gray). Thin curves are +1 s.d. and follow the same color scheme as means. Curves are normalized to the peak value during unpowered walking at the beginning of each session (unitless). (B) Bars showing the nine subject mean of stance phase r.m.s. average soleus muscle activation (unitless). Error bars are ±1 s.e.m. Practice sessions (1–3) are shown left to right with unpowered walking periods (minutes 7–9 and minutes 12–14 at beginning and end, respectively) in white and powered beginning periods (minutes 3–5) in light gray and powered end periods (minutes 27–29) in dark gray. Percentages listed above bars for powered walking indicate the difference from unpowered beginning in each session. Asterisks indicate a statistically significant difference between powered and unpowered walking (ANOVA, P<0.05).