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My top three secrets for sprinters are muscle reactivity & elasticity, hip mobility & flexion, and pelvic stability.
In plain English, that is specific application of force during ground contact. Because we know there is nothing you can do in the air to apply more force and cover ground (i.e. move forward) faster.
Biomechanically speaking, you must put your body into the best possible position to apply forces (horizontal and vertical) from a motionless crouch position, to acceleration, then to max velocity. The vectors change with every step until MaxV!
So what am I leading to?
Hip Height and Vertical displacement!
You’ve heard the expression “STAY TALL” by so many coaches, but there is so much more than this vague statement.
We’ll reference the image below, created by Derek Hansen for Charlie Francis’ material. The red runner has the lower hip height, whereas the yellow runner has a higher and better hip height.
Increased hip height has 6 good reasons:
- Increased hip height means shorter ground contact times. I’ve covered the topic of ground contact in several past articles.
- Increasing hip height increases flight time and more distance covered because the increased hip height provides a “toe off” occurring closer to the center of mass location. See Jon Goodwin article and video on Why Usain Bolt Run So Fast.
- A better positioning in toe off means greater forces applied, which means a greater max velocity.
- Increased hip height means less energy is required to stay above the center of mass.
- Using assisted devices for overspeed training (i.e. harness and bungee cord, or training partner) will actually reduce hip height as the artificial forward force will pull your COM into the ground, thus reducing hip height.
- A high hip height allows for the follow through of the back leg and foot to pass under the hips, and drive the knee in a powerful position to drive down and back. Some coaches like Latif Thomas recommend punching the ground in a powerful yet forceful way to increase speed.Remember the pendulum in the Grandfather clock? It’s not the weight that affects the oscillation, it’s the length of the string. Shorter strings produced faster frequencies.
For more information, see the 30 minute video from Derek on Hip Height & Running Mechanics as he discusses more about Hip height and its implications for running speed, running economy, movement velocity and injury prevention.
Below is a chart that speaks a 1000 words.
Cut and paste the text directly from the chart, we see the weaker sprinter’s center of gravity (COG) almost drops immediately during the flight phase and must be raised excessively during the next support phase or ground contact.
Whereas Elite sprinters COG continues to rise in ta ballistic arc well into the flight phase, resulting in a much higher hip height at the start of the next ground contact.
image credits: Derek Hansen, Twitter @DerekMHansen
Lashawn Merritt Video demonstrating Hip Height and Vertical Displacement
In this video On YouTube, we have a super slo-mo of Lashawn Merritt. What is good about the video is the chain fence in the background as a reference point. Watch the video, and with my above 6 points, you can clearly see he is doing a lot of things right.
Of course, the obvious thing is his positive vertical displacement of his hips relative to the fence.
Do you see a positive vertical displacement as in the chart above?
Watch his dorsiflexion of the ankle joint just prior to ground contact.
Watch carefully the ground contact, and how he applies force to the ground, from the landing of the foreplate, right up to the toes. (Shon Grosse and I discussed this in our webinar on spikes and why shoe companies are trying to maximize this for the sprinters and middle distance runners)
Note how the action of sprinting involves more of a pushing action against the ground. (You may argue it’s a pulling action)
We can learn a lot from this video. I like it.