www.kaiwheeler.com Personal trainer, Kai Wheeler out of San Diego CA demonstrates a myofascial release technique and stretch to restore proper function and mobility to the hamstrings. The primary function of these muscles is knee flexion and hip extension. Hamstrings can become dysfunctional and tight as a result of a sedentary lifestyle or overuse. The weakening effect of tight hamstrings can cause all sorts of problems by placing burden on other muscles of the upper and lower legs. In some cases the hamstrings may even tear. Hamstring trigger points can refer dull aching behind the knee and pain in the lower back.