A hamstring injury occurs when you strain or pull one of your hamstring muscles — the group of three muscles that run along the back of your thigh.
The hamstring muscles are a group of three muscles that run along the back of your thigh from your hip to just below your knee. These muscles make it possible to extend your leg straight behind your body and to bend your knee. When any one of these muscles stretches beyond its limit during physical activity, injury can result.
A hamstring injury typically causes a sudden, sharp pain in the back of your thigh. You might also feel a popping or tearing sensation. Swelling and tenderness usually develop within a few hours. You may also experience bruising or discoloration along the back of your leg, as well as muscle weakness or an inability to put weight on your injured leg.
Most hamstring strains will improve on their own overtime without interventional procedures. Some athletes and their physicians are experimenting with platelet-rich plasma injections into the site of torn muscle, but there are no large scale studies to prove efficacy for these injections for this particular problem.