Pulling with the hamstrings, or striking in front of the COG is a bad thing for multiple reasons.
Stress on the hamstrings
Contact length, assuming optimal mobility and technique probably shouldnt be an emphasis ever. Teach a person to run this way and they will be injured and slower.
Increase stride length through sprinting and increase specific explosive hip extension. Decrease contact time through sprinting and improved specific reactive ability. Make sure mechanics are proper and optimal mobility. Sitting is bad, sprinting with a tall hip projection is best, as this is an indication that proper mechanics and vertical forces are in place.
I suggest it is a bent knee ahead of cog. Same reason as dorsiflexion and locking the calf-stretch reflex.
I for one cannot get around why – A coach who coaches the fastest athletes will for a few dollars tell others exactly what they are doing. If this was so they would no longer receive top dollars to present at clinics as someone else will have faster athletes. Maybe it is just me.
The idea that athletes try and run as tall as possible means they are trying to/allowing themselves to minimise ground contact and it is commonly thought that if an athlete can minimise ground contact then they will run faster, especially for more elite sprinters. I am however intrigued by this notion in that according to most research you run faster by applying more force in the same or less time (Weyand et al and others). Now this to me is a difficult concept in that as you run faster you generally spend less time on the ground due to improved stiffness qualities, therefore you have less time to apply this “more” force. It is a major challenge for us all to get our athletes to apply more force. The notion that improves strength means more ground force is the answer it seems.
Tying in all this…I am also intrigued by the French methods which from memory I am told “don’t exist” but I am sure Piacenta was onto something when he tried to get his French athletes to try and run with essentially as few strides as possible in the 100m. Christine Arron 44.7 strides and Marie Jose Perec, 42.8 strides! less than Asafa. Le Maitre takes around 43 strides, not many compared to others. What does this have to do with the more force notion discussed above? Well, maybe not much, but maybe a focus on striking slightly further in front of the body to allow greater contact length and therefore more time to apply force. Did these athletes apply more force by increasing contact length and therefore ran faster as a result? Who knows, just some thoughts…
Yohan Blake, does he run tall and upright? Hmm, not from what I’ve seen, slightly piked, a bit like Maurice G at times, does this allow him to increase contact length, maybe so…
As far as your application of force vs time of ground contact question, they are are related but separate components. The application of force happens before ground contact while the runners foot moves towards the ground. The duration of ground contact time is determined by the amount of force created during that foot’s downswing and whether that force is returned as mechanical energy(the spring) or dissipated as heat or sound. If I recall correctly, Charlie mentioned that he used the amount of noise generated by the sprinter’s foot strike as a gauge of slowing down and fatigue.
Generally, you should use caution in trying to change sprinter mechanics. In the case of overstriding or the runner sitting too much, make sure they are adequately recovered and, if so, check core strength and hip flexor mobility.
I think it might be more clear to see that force generation begins before contact, but fcrce application, at least the force reponsible for forward locomotion, only occurs when the foot is in contact with the ground.
The duration of ground contact time is determined by the amount of force created during that foot’s downswing and whether that force is returned as mechanical energy(the spring) or dissipated as heat or sound.
I don’t agree with this. Ground contact time is a function of the COG speed over ground and the mechanics specific to the sprinter.
I don’t know that we are saying separate things. COG speed over ground is a function of the two aforementioned components. Changes in their respective values explains pretty much all locomotion, even most jumping events (Greatly increased forces generated before ground contact in comparison to sprinting, but with that increase in force comes a slightly reduced efficiency in storing the mechanical energy created, increasing ground contact time. But the force occurring before ground contact is increased to greater degree, causing more total force to be stored as mechanical energy, increasing the distance the athlete moves as a result of that action in comparison to sprinting. ) There may be some small force occuring after ground contact, at least outside of a treadmill, but to the extent this is a significant component of sprinting outside of the acceleration phase, where things are more mixed, it is correlated almost entirely with the force generated before footstrike. My understanding is that Weyland would disagree that any force occurs after ground contact, but I have seen studies that differ. Even in studies that suggest that it is occurring, it unlikely to be very significant and shows a significantly smaller EMG. And, again, it is correlated closely enough with pre ground contact force that they should probably be considered as part of the same action. EMG during the two periods show increases during fatigue while EMG during initial ground contact typically shows decreases and an increase in latency. Other factors that cause their individual values to change seem to occur in tandem as well and suggest that any force that occurs after ground contact is a continuation of the pre-ground contact phase of sprinting. They are very interesting studies, I forget the author off hand, but I can probably look them up if you would like.
Mechanics of the sprinter are important, but again, those specific mechanics as they relate to COG speed over ground are inseparable from force generation before ground contact and ground contact time, either increasing or decreasing them. (That there are two interdependent variables is the reason sprinters can show idiosynchrasies in running style and still show similar top speeds.) Let me know if you agree. I don’t think we are saying anything too far apart, but I could be wrong.
Its an important distinction in terms of cause and effect. We train with the idea that we are training a function or process, that if improved, will result in better performance. But if the correlation we see is a passive correlation with no cause and effect, or if it is the effect rather than the cause, training specifically to improve that quality will not improve performance. GCT is one example. Training to improve force generation during GCT will improve velocity and indirectly shorten GCT, but training to shorten GCT specifically will not necessarily improve force generation and will not necessarily improve velocity. Cause and effect are important.
Fair enough. I had meant to explain the questions he had specifically relating to mechanics. I hadn’t meant it (other than the suggestion of checking core strength and hip flexor mobility and the more general point that there can be variance in runner techniques without something being amiss) as a prescriptive training how-to.