The hip flexors are a group of muscles located at the front of the hip, with the iliopsoas (formed by the psoas and iliacus muscles) being the strongest component. A common belief among athletes is that strengthening these muscles translates directly into faster running speeds, stemming from their role in bringing the leg forward quickly during a stride. This article evaluates that claim, exploring whether raw strength, explosive power, or the absence of restriction is the true factor for speed.
Hip Flexor Function in the Stride Cycle
The primary function of the hip flexors in running occurs during the swing phase, the period when the foot is off the ground. They are responsible for rapidly initiating the knee drive and pulling the recovering leg forward. This action ensures the leg is repositioned efficiently beneath the body for the next ground contact.
Without sufficient hip flexor activity, the leg turnover rate, or cadence, would be severely limited, making high-speed running impossible. At the end of the stance phase, the hip flexors also work eccentrically, meaning they lengthen while contracting, to control and decelerate the backward movement of the leg before the swing phase begins. The combined concentric and eccentric action ensures a rapid and controlled transition from propulsion to recovery.
Strength Versus Explosive Power
For speed, the maximal strength of the hip flexors is less important than their ability to produce force quickly, known as explosive power. Running speed, especially during sprinting, is limited not by the force of the push-off, but by the speed at which the leg can be recovered and repositioned. This recovery speed depends on the rate of force development (RFD) in the hip flexors, allowing for the rapid acceleration of the limb forward.
The ability to generate a high velocity of contraction in the hip flexors is what truly determines a runner’s top-end speed. Training focused on maximal force output, such as heavy lifts, is less effective than training emphasizing high-velocity movements and quick, forceful contractions. Targeted hip flexor resistance training can improve sprint and agility performance, supporting the idea that a power-focused approach directly enhances speed. This power allows the leg to be “cycled” quickly, increasing the step rate.
The hip flexors’ role in the swing phase contrasts with the propulsive role of the glutes and hamstrings, which are responsible for pushing the body forward during the stance phase. Both explosive hip flexion and powerful hip extension are necessary for speed, but the quality of the hip flexor contraction is the limiting factor for achieving maximal leg turnover. Focusing on the velocity of the hip flexor contraction ensures the leg is rapidly prepared for the next powerful extension.
When Tightness Hinders Speed
A common problem limiting speed is not weak hip flexors, but excessively tight or restricted ones. Prolonged sitting often shortens the iliopsoas, reducing its functional range of motion and ability to generate force efficiently. This restriction physically shortens the available stride length because the hip cannot fully extend backward during the push-off phase.
Tight hip flexors contribute to an exaggerated anterior pelvic tilt, where the pelvis tips forward. This altered posture places the antagonistic muscles—the glutes and hamstrings—in a chronically lengthened and mechanically weak position. When the hip flexors are tight, the nervous system can inhibit the opposing gluteal muscles from firing effectively, known as reciprocal inhibition.
This imbalance means that even powerful glutes cannot be fully expressed because the tight hip flexors and inhibited extensors limit the propulsive phase of the stride. Addressing mobility and eliminating restriction often provides a more immediate boost to speed than simply attempting to build more concentric strength. The goal shifts from building raw strength to restoring proper length, function, and balance across the hip joint.