The hamstrings, or muscles along the back of the thigh, extend the hip joint and flex the knee joint. They smooth the movement of these joints, but they rebel from performing their duties when an unusual load is placed on them. Then they are torn instead of being normally stretched. This rebellion is most likely to occur when workouts have been prolonged and muscles, because they are tired, have lost their elasticity. In a defiant "No!" the hamstring contracts in a spasm, a natural defense against more strain.
An athlete may feel the hamstring sprain anywhere from the ischial tuberosity of the pelvis (the bones on which he sits) to the attachment at the upper tibia. These sprains happen suddenly and the resultant pain feels like the aftereffects of a swift kick.
The natural contraction resulting from hamstring sprain limits the scope of movement. But range of movement is relative. Such a strain can prevent a person who can usually touch her toes from being able to do it. A gymnast I treated was able to bring her left foot behind her and practically over her head, but I sensed that her hamstring was nonetheless strained. Why? Because when I asked her to perform the same action with her right leg, she was able to take her right foot well over the top of her head. Hamstring strain was limiting what was for her usual scope of movement.
Immediately applying ice anesthetizes the area, and slowly stretching the muscle will help relieve the spasm. Heavy pressure maintained at the focus of the pain is an alternative to stretching. If these methods fail, a muscle relaxant may be required. Aspirin or ibuprofen will help prevent inflammation.
When the initial shock and pain have receded, keep the muscle warm and take pressure off of it by wrapping it in a neoprene pant or an elastic bandage in a figure eight. The torn muscle needs time to recuperate. Though painful, hamstring strains are relatively common, and even if the muscle is seriously ruptured, the necessity of surgical repair is highly unlikely.