Your #1 site for all things sports rehab, sports performance, and orthopedic rehabilitation is: https://www.sportsrehabexpert.com/

Here are the links to the previews videos to Achilles Tendon Injury Rehab

Why You Should Stop Stretching - Part 1: https://youtu.be/_Bc8ncc0uUg

Easiest Achilles Self Treatment - Part 2: https://youtu.be/gLts8rV6aFk

This video is on probably one of the biggest misconceptions that are out there on feet!

Flat feet and Arched Feet are not bad. They are both necessary for everyday tasks! No different from the ability for your head to rotate right and left. Flat feet and arched feet are two extremes that the body should be capable of doing both.

If you put someone in a shoe that gives the "arch support" or limits motion then you are just creating problems by reducing the spectrum of options the foot should be capable of choosing based off the needs of the task.

During gait or walking our foot SHOULD experience supination, to pronation, to re-supination. That is normal and necessary mechanics of walking, gait, running, etc.

Pronation is needed to absorb force (store potential energy) or absorb/attenuate forces.

Supination is necessary to produce force by creating a rigid foot

The body's ability to re-supinate the foot is accomplished through the windlass mechanism. Which is only created by getting great toe extension. 

The only way to get great toe extension during gait is by allowing the foot to pronate and weight bear over the great toe as your center of mass moves forward (horizontally) during gait, walking, running, etc.

If you cannot pronate effectively, you will not create an effective windlass mechanism and thus not experience re-supination.