What are Hamstrings? The hamstring is a collection of three large muscles that connect muscles and bones. The location of the hamstring muscles is behind the thigh, precisely along the hip to the bottom of the knee. When standing or walking, the hamstring muscles are not used as much. However, when you do activities that involve bending your knees, such as when running, jumping, and climbing, your hamstring muscles will work very actively. Causes of Hamstring Injury The main cause of hamstring injuries is that the hamstring muscles are stretched beyond their ability to stretch during certain activities, such as running or jumping. These injuries are usually the result of the sudden or slow movement, but with excessive pulling or pressure. The following factors can also increase a person's risk of developing a hamstring injury: Doing sports that involve intense kicking, running, or jumping can cause a hamstring injury. That's why soccer athletes are at high risk for this injury ...