A pulled hamstring occurs when one or more of the three muscles at the back of the thigh are stretched too much or develop tears in their muscle fiber or tissues. Pulled hamstrings, also called a hamstring strains, can vary in severity and are usually classified into three grades depending on the amount of damage to the area. Grade one strains have small tears within the muscle group resulting from over stretching. Grade two and three are more acute and involve significant to severe damage up to the point of a total rupture.
Hamstring muscles are composed of the semitendinosus, semimembranosus, and biceps femoris, collectively called the "hamstrings." They extend from the lower buttocks to the back of the knee. The hamstring's primary functions are to bend the knee and move the thigh rearward.
The hamstrings are used a great deal in running and jumping, so a hamstring injury is a common occurrence among athletes. Sudden explosive movements are the most common cause of tears in the muscles resulting in hamstring strains or pulled muscles. Hamstring injury symptoms include swelling, bruising, pain, and spasms. Often, at the moment the injury occurs, a snap can be felt in the muscle.
Additional causes that increase the risk of a pulled hamstring include lack of flexibility or hamstring strength, excessive body weight, and loss of muscle control from strenuous exercise or fatigue. Hamstring injuries most often occur when the muscle is being elongated. It is less common for a hamstring injury to occur when the muscle is contracting or from a blow.
Treatment for a pulled hamstring usually includes icing the affected area and compressing the thigh by wrapping it with sports tape, bandages, or compression sportswear. As soon as the muscle pain subsides to a manageable level, the athlete should begin stretching the muscles and moving them through the non-painful range of motion to reduce the build up of scar tissue and to reduce swelling. Rehabilitating the muscle does not mean returning to the activity too soon; the muscle must be gradually strengthened to reduce the risk of reinjury or of permanent damage.
While it is impossible to completely prevent a hamstring injury, participants in competitive sports that require abrupt movements, such as track and field, football, or tennis, must have well-conditioned legs to prevent muscle strain. This involves strength training for both the hamstrings and the front of the thigh, or quadriceps, for muscular balance, which helps reduce the risk of a pulled hamstring. Also, stretching and warming up before physical activities should be done to increase flexibility and reduce the chance of injury.