The Hip Flexors & Knee Drive in Sprinting
Compared to a distance runner, a sprinter spends more time in the air. In addition to a vigorous arm swing, you need a powerful leg thrust and a higher knee lift. Research has revealed that world-class sprinters have higher stride rates than good sprinters even though their stride lengths are about the same, according to Stanley Brown’s “Exercise Science.” Powerful hip flexors and greater knee flexion help to bring your recovery leg forward sooner and increase speed.
The Hip Flexion
When you first accelerate, your hip flexion should be just below parallel to the ground. Your forward thrust, or hip extension, should be explosive. When you reach maximum speed, your hip flexion will approach a 90-degree angle to the ground. If your hip flexors are weak, you won’t be able to generate enough force to accelerate. Your knees won’t lift high enough, which shortens your stride. If your hip flexors are tight, you’ll overextend your lower back while sprinting. Strong hips enable your thighs to quickly accelerate as well as propel you forward against gravity.
The Knee Lift
When you accelerate, your knee should be fully extended, which allows for the greatest degree of hip extension. As you recover, the knee flexes as your hips flex, which sends your foot toward your buttocks. A high knee lift also forces you to push harder on your rear foot. As your hip starts to extend again, your knee swings open and forms a 90-degree angle with your shin. Your knee then extends again as your foot lands on the ground. As you reach maximum speed, your body angle will become more perpendicular.
Rotation of Hips and High Stride Rate
If you want more and faster strides as well as a long stride length, you have to quickly rotate your upper legs around the hip joints. Hip extension is key in the movement of your leg and foot to the ground. Hip flexion helps in the recovery of your upper legs after landing. This flexion motion starts just before the foot rises from the ground and continues through to the high knee lift. The swing time of the leg depends on how fast this motion takes.
Degree of Knee Flexion and Sprint Performance
To speed the time from takeoff until your foot hits the ground, your knee should be bent at an extreme angle. This knee position should be held during most of your stride. The movement of your heel toward your buttocks shortens your leg lever. This allows your hips to quickly swing your leg forward and back into a high knee lift. Your leg swing takes a lot less time and you sprint faster. When you don't bend your knee enough or extend your knee too soon, it's often the sign of fatigue or incorrect sprinting form.
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Kay Tang is a journalist who has been writing since 1990. She previously covered developments in theater for the "Dramatists Guild Quarterly." Tang graduated with a Bachelor of Arts in economics and political science from Yale University and completed a Master of Professional Studies in interactive telecommunications at New York University.