Running does wonders for the muscles involved in plantar flexion — pointing your toes toward the floor — but leaves a host of other small muscles throughout the foot and ankle weak. (sweatscience.com)
Therefore, it appears that during dynamic plantarflexion with an extended knee position preferentially targets the gastrocnemius, while performing plantar flexion with a flexed knee preferentially targets the soleus muscle. (strengthandconditioningresearch.com)
Another point here is to work through the opposite of plantar flexion — the heel - down, toes - up action called dorsiflexion. (sonima.com)