Stretch out those hamstrings so you can move easier and reduces chances of common knee injuries from running. In the modern world most people sit for long hours resulting in a tight hamstring which restricts proper movement. Hamstrings are group of three muscles that sit on the back of the thigh. They cross two joints, the hip and the knee…and their function is to bend the knee and extend the hip.  Chronic hamstring pain can increase risk of injury and impairs optimal performance for athletes.