Fig. 5. Ankle muscle root mean square electromyography (EMG) for soleus (Sol.; top), medial gastrocnemius (MG), lateral gastrocnemius (LG) and tibialis anterior (TA; bottom). Values are mean stance phase root mean square (r.m.s.) average muscle activation for nine subjects (error bars are ± 1 s.e.m.). Surface gradients increase from left (0%-level) to right (15%-uphill) with unpowered walking (minutes 4–6) in white and powered walking (minutes 4–6) in gray. All r.m.s. values (unitless) are normalized to the unpowered 15% grade condition. Values above bars indicate percentage difference in powered versus unpowered condition. Asterisks indicate a statistically significant difference between powered and unpowered walking (ANOVA, P<0.05).