Right foot flexion and straightening inside tendon pain may be caused by trauma, plantar fasciitis, lumbar disc herniation, overwork and other reasons. 1. Trauma: the right foot suffers from sprains, impacts, falls and other external violent factors, injury to the foot ligaments, muscles and bone tissue, etc., which may cause the right foot flexion and extension of the inner tendon pain performance. 2. Plantar fasciitis: plantar fasciitis is a chronic injury caused by sports, plantar fasciitis is mostly single-foot onset, in addition to the plantar near the heel of the pain, there are some patients will feel the foot bending straight inside tendon pain. 3. Lumbar disc herniation: Lumbar disc herniation compresses the central canal spinal cord or nerve roots causing numbness, weakness and radiating pain in the lower limbs, which may also cause tendon pain inside the right foot flexion and extension. 4. Overwork: Excessive exercise or sudden strenuous exercise can also lead to bending and straightening tendon pain. In normal life, pay attention to rest, avoid strenuous exercise, overwork and so on. If necessary, you should go to the regular hospital in a timely manner, to clarify the cause of the disease, under the guidance of professional doctors to take targeted treatment.