Tibialis Posterior

Posterior tibial tendon is a stabilizer of the foot. Injuries to the tibialis posterior can result in insufficiency of the muscle and a tibialis posterior dysfunction which results in fallen arches (flat feet).

The posterior tibial tendon is slow to heal. Pain in the calf and especially the achilles tendon are often due to overloading of the muscle.

See also:
sportsinjuryclinic.net - Tibialis posterior tendinopathy
runnersconnect.net - Posterior tibial tendonitis