[kentlyons]

I went looking at the published paper (https://www.sciencedirect.com/science/article/pii/S258900422...) and it says on pg3: "this specific type of plantarflexion because the relatively high soleus electromyography (EMG) on-time (i.e., soleus activation) coincided with upward angular motion of the ankle". The supplementary materials show EMG and range of motion graphs.

A bit of googling says plantar flexion is the same muscle movement needed for pushing the accelerator pedal while driving or ballet dancers standing on their toes.

My guess (not my field of expertise) is the muscle is activated strongly in isolation (the toe pushing down motion) and inducing a large range of motion. So it's not raising the heel so much as pushing the toe down.