Is it the plantaris or Achilles Tendonitis?

Achilles tendonitis can mimic plantaris tendinopathy!

The plantaris muscle runs from the back of the outside of the knee to insert on the inside of the heel bone. A recent study of 214 elite UK track athletes found 33 had plantaris injuries. Interestingly, a high number were on the right leg of bend runners. In 2011, an anatomical study found the plantaris insertion was near the most common site of pain along the Achilles tendon. In another study, the same researchers concluded that mid portion Achilles tendinopathy may involve the plantaris. Jill Cook, the renowned tendon researcher, recently wrote that ~1 in 5 of long-term unresolved Achilles tendinopathies were found to be the plantaris.

I have found myofascial release (MR) to be effective in treating pain in this area. One recent study, found MR effective in reducing heel pain by working the calf, and another study found MR effective for tennis elbow.

Achilles tendon researchers no longer recommend eccentric exercises over doing traditional calf raises (raise and lower). Eccentric exercises are perfectly fine to do, but slow and heavy is the new recommendation in part because patient compliance is better!

Here is what to do:

Start with this isometric (hold the position) exercises, try it with the heel raised at a few different heights. Progress to calf raises as soon as they are possible with little to no pain.

As of September 2015, tendon researchers now recommend slow and heavy calf raises as the best option for tendon rehabilitation. Eccentric exercises (slowly lower on one leg, and raise back up using two) are no longer considered to be the best option.

https://www.youtube.com/watch?v=KWGR4PeXDpk

Raise (concentric) and lower (eccentric) your body on one leg and gradually add weight with a dumbbell or backpack. Do this with the knee bent as well as straight.