Why are my feet and legs so tired?

PTTD, or posterior tibial tendon dysfunction, can be major cause of fatigue in the legs and feet.  PTTD is also known as adult flatfoot deformity.  This condition means that the major tendon in charge of holding up the arch of the foot becomes fatigued and stretched out.  It may be working extra hard to hold up that collapsing arch and this can translate to overall leg fatigue and arch soreness.