A muscle strain (muscle pull or tear) is a common injury, particularly among people who participate in sports.

The thigh has three sets of strong muscles: the hamstring muscles in the back of the thigh, the quadriceps muscles in the front, and the adductor muscles on the inside. The quadriceps muscles and hamstring muscles work together to straighten (extend) and bend (flex) the leg. The adductor muscles pull the legs together.

The hamstring and quadriceps muscle groups are particularly at risk for muscle strains because they cross both the hip and knee joints. They are also used for high-speed activities, such as track and field events (running, hurdles, long jump), football, basketball, and soccer.