I recently attended the annual track and field summit that included sessions on sprints, hurdles, throws and jumps. I especially enjoyed the seminars by Dr. Ralph Mann on sprint mechanics. Here are some of the main points that I picked up.
Ralph emphasizes “front side” mechanics rather than “back side” mechanics. It is a mistake to think that you should push vigorously behind you to make you go fast forward once you are at full speed; rather you should concentrate on popping your feet of the ground as fast as you can in front of you and pop them back down also as quickly as you can. There is not enough time or benefit in thinking about pushing behind you.
Ground time is the key to speedy sprinting, the shorter the better. According to Ralph’s model the best male sprinters spend no more than about .087 seconds on the ground on each step. Lesser sprinters spend more time on the ground. Time in the air on the other hand is much the same for the full range of sprint abilities. So a major distinguishing factor is how quickly you can punch off the ground on every step.
It turns out that the back leg doesn’t (or shouldn’t) push off the ground to full extension; it should be slightly bent at the knee, with the ankle actively attempting to dorsi-flex. This is counter intuitive since you would think that you should push off as hard as you can, and extend off the ground, to get the most push. But it turn out that the amount of time it takes to push that last little bit into full extension is better spent quickly pulling the knee forward and upward in recovery ready for the next step.
Also the “recovery leg” doesn’t bend at the knee so much that your heel kicks your butt, i.e. full knee flexion shouldn’t occur. In the past the theory was that the more you bend the knee the faster you could bring it through since it has a lower moment of inertial and can hence rotate through quicker. Well this is probably true but it is not needed; there is time enough for the leg to swing through correctly even when it is only partially bent. In fact poor sprinters recover too quickly and reach full thigh flexion too early after rear foot toe off. Full flexion of the thigh (i.e. highest knee lift at the front) should occur more than a quarter of the way into the air phase (about .033 seconds after toe off) and not earlier. Ralph believes this is the best overall single descriptor of good sprint mechanics. It allows the foot to come straight down touching the ground just slightly in front of the center of gravity. If the knee comes through too fast it will either hit the ground from an “up to down” path (not good) or the knee will cast out the shin causing the sprinter to over stride. Over striding is bad because your touchdown point is too far in front of your center of gravity, causing you to slow down. High heels at the back is a sign of poor technique, whereas high knees and an upright posture is a sign of good technique. Remember we are after front side mechanics not back side mechanics.
Good touch down position is reached with the swing through knee even with the knee of the leg touching down. If the swing knee is behind the lead knee at touch down this is a sign of poor technique, back side mechanics and over striding.
Here are some critical values from Ralph Mann’s elite sprinter model for male sprinters.
- Horizontal Velocity 12.55 m/s
- Stride Rate 4.63 steps/second (will alter with leg length)
- Stride Length 2.7 m (will alter with leg length)
- Ground Time 0.087 sec (will alter with leg length)
- Air Time 0.123 sec
- Upper Leg Recovery Time 0.033 sec
Ralph summarizes:
“Success in the short sprint is determined by the ability of the athlete to generate great amounts of explosive strength at the proper time. Generally the proper mechanical application of this strength results in an elite performance that is characterized by a high stride rate and moderate stride length.”
For an in deeper insight, I recommend you buy his book
The Mechanics of Sprinting and Hurdling
Dr. Ralph V. Mann
2011 Edition
This work can be purchased at https://www.createspace.com/3604805