The hamstrings are probably some of the most well known muscles in the body, or at least the muscle group is. We hear about athletes pulling a hamstring, we feel them to be "tight", or blame them for a lack of flexibility. Often times we may hear the name hamstring and think of negative things such as injury, but when we really look into the muscle group we can gain a better understanding of why they are vital to performance and why strengthening them is crucial!
The hamstrings is a muscle group on the backside of the thigh, and are compromised of three main muscles: the semitendinosus, semimembranosus, and biceps femoris (divided.into a short/long head). While there are technically five muscles that could be classified as hamstrings, these three are the most commonly referred to as the hamstrings and play a crucial role in speed.
Something that is unique to the hamstring is that the muscle group crosses two joints and performs functions at both of them, sometimes in a simultaneous action. Originating from pelvis, the hamstrings run parallel to the femur (thigh bone) and attach at the top of the tibia and fibula just below the knee. This allows the hamstring to perform hip extension (the "flattening at the hip") and knee flexion (the bending of the knee), as well as resist those motions when needed. And when it comes to sports, these actions are very prominent and require hamstring strength in order to execute them.
Sprinting, jumping, landing, kicking (swimming and soccer), throwing, and hitting all move through planes of motion and utilize the act of hip extension or knee flexion. For example, the contraction of the glute and hamstring on a leg will cause the hip to extend and propel the center of mass forward. Done consecutively, we get forward motion such as walking, running, or sprinting. When we sprint, the knee has to flex in order to bring the knee out in front to continue moving forward, and the hamstring gets used to bend the knee. Then when the foot makes contact with the ground, the hamstring has to resist knee extension as too much forced knee extension could cause knee injury.
This example could be recreated in multiple different sports and scenarios. This is where the hamstrings become vital for performance. A weak hamstring cannot resist motion, and it cannot create motion rapidly, therefore leading to low performance and high injury risk. So when a baseball pitcher plants their front leg into the ground and creates torque through the hip, the hamstring prevents the knee from hyper extending, while also extending the hip. When a corner on the football field has to change from a backpedal to sprinting forward, the hamstring prevents the hip from flexing too far, and then acts to propel the body forward through hip extension.
With these things in mind, it is crucial that we learn to train hamstring strength to perform the following functions: knee flexion or anti-extension, and hip extension or anti-flexion. This is done through various movements such as Deadlifts, Glute-Ham Raises, Nordic Hamstring Curls, Romanian Deadlifts, or regular Hamstring Curls. By strength training these movements, we can build higher performing and more resilient hamstrings. In turn, we perform better on the field.