Muscle knots in the Flexor Digitorum Brevis are typically located in the center of the sole of the foot, just above the arch, and beneath the ball of the foot. These muscle knots can refer pain that feels like you’re walking on sharp rocks or glass, radiating from under the toes into the ball of the foot. You may feel a deep, aching discomfort while resting and a sharp, stabbing sensation when walking or standing.