Picture from West Family Chiro
If I have excess pronation or flat feet (pes planus) can I do anything to help build up my arch?
3 primary exercises that you can do are strengthening the posterior tibialis and the intrinsic muscles of the feet.
To strengthen the posterior tibialis muscle to help build up the arch of the foot you use a moderate strength band and perform inversion (turning foot in) and pushing down (dorsiflexion) 3 sets of 10 x slowly. See picture below.
The next way to strengthen this muscle is to stand do a calf raise (is strengthens the posterior tibialis as well). You do 3 sets of 10 slowly up and down.
Scrunch your feet up 30 x. This strengthens the intrinsic muscles to build up the arch as well.