Fig. 1.

Electrodes placed on the skin of the subject's leg recorded electromyographic (EMG) signals from the soleus muscle, a plantar flexor. A computer processed the soleus EMG to control air pressure sent to an artificial pneumatic muscle so that there was a proportional relationship between EMG amplitude and air pressure. As air pressure increased, it caused the artificial muscle to develop tension by shortening in length. The exoskeleton effectively created a cocontraction about the ankle joint proportional to soleus muscle activation. White arrows about the ankle joint show the direction of torque created by the exoskeleton and user's soleus muscle. Thus, when the soleus muscle was activated, the exoskeleton produced a dorsiflexor torque limiting the ability of the soleus to produce plantar flexor torque.