An injury involving a strain in one or more of the three muscles located at the back of the thigh. The hamstring muscles run between the buttock and the knee, where they are connected to the bones of the lower leg. A hamstring pull often occurs following participation in strenuous sports or other activities involving the heavy use of leg muscles. The symptoms include a sharp pain in the back of the thigh, swelling and weakness in the upper leg, an inability to bend the leg, and discomfort and difficulty walking or sitting down. Treatment is centered on resting the leg as much as possible. In some cases, painkilling medication and physical therapy may be recommended.