Ankle Plantar-flexor Power in Human Gait

In human gait the majority of mechanical work is generated by the ankle joint. It is commonly thought that concentric contraction of the ankle plantar flexors is the mechanism behind A2 power generation. This study investigated the relationship between the EMG activity of the ankle plantar flexor muscles and A2 power generation. The gait patterns of six healthy adults were recorded. The following gait measures were extracted with respect to stance time: point of A2 power generation and A2 peak power, EMG activity of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SOL) and peroneus longus (PL) muscles. On average, peak A2 power generation occurred 14% (as a percentage of stance time) post EMG peak activity of the plantar flexor muscles. At the point of A2 peak power generation, respective EMG activity of the SOL and PL muscles were 62% and 74% of the maximum activity recorded during stance. These results show that A2 ankle power is partly produced by concentric action of the ankle plantar flexor muscles. It also shows that passive return of elastic energy stored in these muscles (previous to the heel-off event) may play a major role in producing A2 power.