Sprinting seems like a simple exercise on the surface, but when you dig a little deeper, you find that it's the little things that separate the fastest runners in the world from the competition. Something as seemingly small as dorsiflexing your foot throughout its path in each stride will shave seconds off your finishing time, improving speed and overall sprint efficiency.
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Dorsiflexion involves bringing the top part of your foot, which is also known as the dorsum, up toward your shin. This shortens the distance between your toes and your ankle and contracts the muscles of your shin, primarily the tibialis anterior muscle. This motion is emphasized among speed athletes and during plyometrics. The opposite motion of dorsiflexion is known as plantarflexion, and involves pointing your toes away from your shin. (Ref. 1)
Shorten the Lever
The primary function of emphasizing dorsiflexion during a sprint is to shorten the lever represented by your leg below the knee. As you push off your rear foot and it rises off the ground, you should dorsiflex it as you bring it forward, keeping it tight under your hips. The shorter lever length between the knee and the toes creates a faster pendulum swing before you make contact with the ground for your next stride. (Ref. 2)
Load the Spring
Creating a shorter and more efficient pendulum swing for your legs is only the first step to creating a more efficient sprinting stride. Dorsiflexing as you run also puts your foot in an ideal position to absorb the shock of the landing and tenses your muscles to spring forward into the next stride. Think of it as loading a spring prior to exploding forward. Sprinters run primarily on the balls or toes of the feet, so landing in this dorsiflexed position puts you right where you want to be to attain maximum speed. (Ref. 2)
Making the Change
It's difficult to make the necessary adjustments to your running form during a full-out sprint, so training exercises can help you make those changes before you hit the track at full speed. Sprinters often perform high knee exercises, running in place as they emphasize the dorsiflexed position of their feet. Running with your feet landing directly under your center of gravity encourages a natural dorsiflexed position, unlike under or over-striding. Maintaining a rigid, upright body posture during your maximum speed phase will encourage proper foot position relative to your hips.