Muscle knots in the Flexor Digitorum Longus are typically found deep in the lower leg, along the inner side of the shin bone, and can radiate pain down into the arch of the foot and the underside of the toes. The referred pain often mimics plantar fasciitis or nerve pain, causing aching, burning, or cramping sensations in the arch, toes, or even the inner ankle. You may experience discomfort when walking barefoot on hard surfaces or after long periods of standing or running.