The hamstring muscle group, located at the back of the thigh, is composed of three distinct muscles: the semitendinosus, the semimembranosus, and the biceps femoris. These muscles cross both the hip and knee joints, giving them a dual role in lower-body movement. Their combined functions include flexing the knee and extending the hip, making them central to movements like walking, jumping, and running. The strength and resilience of this muscle group are directly related to running performance and increased speed.
Hamstring Function in Speed Generation
The hamstrings perform a complex, dual action during the running gait cycle that is coordinated to maximize speed. The first action occurs during the stance phase, where the muscles work with the glutes to extend the hip, providing the propulsive force that drives the body forward. This concentric contraction generates the necessary horizontal force against the ground to accelerate the runner.
The second, more demanding role occurs during the swing phase, specifically the terminal swing. As the forward-swinging leg straightens rapidly before foot contact, the hamstrings must eccentrically contract (lengthen under tension) to decelerate the knee extension. This braking action controls the limb and prepares the foot for an efficient ground strike. The forces experienced during this high-speed eccentric contraction require the hamstrings to absorb energy quickly.
As running speed increases toward a maximum sprint, the time available for deceleration drastically shortens. This reduction means the muscles must generate a significantly higher amount of force at a faster rate. Weakness in this phase compromises the ability to control the limb, limiting the rate at which the legs can cycle and directly capping top-end velocity.
Strength and Power Translation to Velocity
Increased hamstring strength and power translate directly into faster running speed by influencing stride mechanics. The ability to generate maximum force enables a runner to apply greater power during the propulsive phase, contributing to a longer stride length. Stronger hip extension allows the foot to push off the ground with more authority, covering more distance with each step.
The concept of power, the rate at which force can be generated, is also important. In sprinting, power is represented by the ability to quickly absorb and then generate force, particularly during the brief ground contact time (GCT). Elite runners achieve faster speeds by reducing the GCT to under 0.10 seconds. Eccentric hamstring strength allows for a more rapid and stable transition from the deceleration of the swing phase to the powerful extension of the stance phase.
A high eccentric strength capability allows the hamstrings to withstand the extreme forces of the late swing phase, enabling the leg to swing through faster. This quicker limb turnover directly increases stride frequency, or the number of steps taken per second. A combination of powerful hip extension for stride length and resilient eccentric action for stride rate are the primary mechanisms linking hamstring strength to running velocity.
Key Training Principles for Speed-Specific Strength
Training the hamstrings for speed requires moving beyond traditional isolation exercises to focus on movements that mimic the demands of high-velocity running. The primary principle is to emphasize eccentric loading, the muscle’s ability to resist lengthening, as this action is most utilized during a maximal sprint. Exercises that achieve this include the Nordic Hamstring Curl, where the body is slowly lowered from a kneeling position, and the Romanian Deadlift (RDL).
The RDL is effective because it trains the hamstrings in a hip-dominant pattern under substantial load, working them in a lengthened state that correlates to their function during the swing phase. Incorporating explosive movements is also necessary to improve the rate of force development. Kettlebell swings and light, high-velocity deadlifts help train the hamstrings for the rapid, powerful concentric contraction needed for hip extension and propulsion.
For the most specific training stimulus, the inclusion of actual sprinting is necessary, as it generates the highest hamstring activation of any exercise. Hill sprints or resisted sprints, such as those performed with a sled, are beneficial because they safely overload the muscles. This method lowers the high-risk eccentric demand while maintaining a high force output. A comprehensive program balances high-tension, slower eccentric work with high-velocity, explosive movements to produce speed-specific adaptation.
The Role in Injury Mitigation
Strong hamstrings play a protective role, which indirectly supports sustained speed by preventing injuries. Hamstring strains are common in sports requiring explosive speed, with the majority occurring during the terminal swing phase when the muscle is at its longest and under peak eccentric tension. Insufficient eccentric strength means the muscle fibers cannot handle the rapid rate of force absorption, leading to tears.
Eccentric-focused training, such as the Nordic Hamstring Curl, has been shown to significantly reduce the risk of hamstring strain injuries, with reported reductions reaching as high as 85%. This protective effect is partly due to the training-induced increase in muscle fascicle length, which makes the muscle more resilient to being overstretched under high load. A stronger, more robust hamstring can absorb more energy before reaching its failure point.
Maintaining strength balance between the hamstrings and the opposing quadriceps muscles is important, as an imbalance can increase the strain placed on the posterior chain. By mitigating the risk of injury, strong hamstrings ensure that an athlete can consistently participate in high-speed training and competition. Injury prevention is an essential component of maximizing long-term velocity.