The portion of the hamstrings that extend the hips are a important part of propelling the body forward during locomotion. This extension of the hips is vital to almost every running based sport and it is why most good strength and conditioning coaches and personal trainers use exercises that involve triple extension (extension of hip, knee and ankle). This muscle group is predominately made of slow twitch muscle fibers that again influences the amount of repetitions you should use to train them with. The main aspect of running that improving strength in the hip extensors will benefit is your stride length. It does this in two ways. The first is by increasing the force the hip and the leg applies to the ground each stride. This increase in force gives a larger ground reaction force to the body and results in greater speed and greater distance travelled per stride. As you can reason, improvements in hip extensor strength are vital for acceleration and speed. This aspect of running is not only important for sprinters and other team sports athletes but also long distance runners or marathoners too as they change pace to distance themselves from a competitor or have to outsprint another runner at the finish line.
The second way it increases stride length is that it decreases inhibitory measures the body uses to protect the hamstring during running. If the hip extensor portion of the hamstrings is weak, the brain will send inhibitory signals to the legs preventing them from entering a range that might cause a hamstring pull for their current level of strength. When you become stronger in the hamstrings, the runner can handle greater loads through the hip extensors. This means the brain does not need to send the same inhibitory messages at the same stride length or speed (because now the runner can handle the increased eccentric load). This means an increase in stride length and therefore speed is developed.
The best ways of strengthening the hip extensor part of the hamstrings involves variations of deadlifts, hip extensions and reverse hip extensions. Just like the knee flexor portion of the hamstrings, both open and closed chain exercises will benefit runners. Here are examples of two:
Strengthening the hip extensors will also significantly aid in reduction of hip related injuries and adductor/hamstring pulls. It does this by increasing hip stability during running. Another mechanism that aids injury reduction is that by making sure your hamstrings are strong enough, the hips do not need as much contribution from other muscles that are not prime movers during running. For instance, if the hamstrings as hip extensors are weak, a really common biomechanical issue that develops is that the pelvis has to rely on the posterior portion of the adductors to fully extend the hip. If unattended to for long enough, this can lead to adductor or groin strains and chronic overuse conditions like osteopubis.