YES, NO, MAYBEE SO, WHY OR WHY NOT?
I'm not Batman but here are my thoughts on the topic anyhow:
- [*]Increased hip height should increase flight time because increased hip height is associated with toe off occuring close to directly under the location of the center of mass. [*]A toe off from this location would in theory produce greater vertical forces at the moment of toe off which are associated with a higher max velocity. The greater airtime (and also speed) is a result of the increased vertical forces and not directly the cause of it.
Right, so from what Mike has said it sounds like speed will increase hip height, but as we know trying to increase hip height will not make you faster. So more power=more speed=higher hip height or more speed=more power=higher hip height.
I don't think higher hip height=more speed=more power because if you're skipping as high for height you're going to get higher hip height, but obviously not better speed than sprinting
I think you might have misunderstood me, I tried to say the following:
Increased hip height is an indication that toe off is occuring relatively close to being directly under the center of mass (BDC: bottom dead center). When toe off occurs close to BDC vertical force application will be greater due to the fact that force is being applied under the center of mass rather than behind it (which would produce less vertical forces and greater horizontal forces). Increased vertical force application is associated with greater max velocity. Consequently, "high hips" is most likely an indicator of efficient sprint mechanics.
Check out the picture I've drawn to help clarify. These two stickmen and all their segments are of exactly equal size. This demonstrates how toe off position affects hip height as well as the force vectoor. Hopefully, it's true what they say about pictures equalling a thousand words.
You're very very correct on that. The pictures are a little exagerated to get the point across. In the real world, a "high hips" sprinter would probably look more like the "low hips" stickman, with the "high hips" stickman being a near impossibility for a real athlete.
my coach always told me that you wanted to have a higher hip position as so not to waste so much energy trying to raise your center of mass up each step. You use less energy to keep your COM up, and then you can use that energy to counteract the deceleration in the latter stages of your race….
but what do i know? not much…
JJ & Tank,
Good points guys! You guys are not only pointing out the same thing but I think it's a part of the equation I left out. In a spring-mass (or elastic) system, energy in roughly equals energy out and thus less intrinsically created (muscle) force is needed to be produced by the athlete (ala Tank's wasted energy). Consequently, JJ's, "increase the stiffness of the spring" = Tank's "You use less energy to keep your COM up, and then you can use that energy to counteract the deceleration in the latter stages of your race."
I left this part of the equation out because I kind of think it's somewhat a result of the what I posted above but it can indeed become a chicken or egg situation. That is:
[*]The above technical recomendations lead to–> greater vertical force application at toeoff[*]More vertical force application at toe off–> greater vertical displacement of mass (higher flight phase)[*]Greater vertical displacement of mass (higher flight phase)–> greater loading of support leg at touchdown (greater force in) [*]If there is greater force in and IF the spring is stiff, the greater force in = greater force out at less energy expense.[*]Greater force out at less energy expense = less deceleration.
I'd like to add that horizontal force application (and more specifically impulse) cannot be ignored as it is still THE force / impulse that keeps the body moving forward and is what counters the air resistance force and initial braking forces at ground contact.
Increased vertical force / impulse just affords the sprinter enough flight time to keep moving forward fast (time in flight is probably more efficient than time on the ground because initial braking forces are so costly to velocity and cause such marked deceleration) and also helps to reload the leg to a greater magnitude at ground contact because the increased height of the flight phase equals increased vertical ground reaction forces at touchdown.
this is the paradox
what's the trade-off?
1) to train these qualities you need to be going fairly fast, which by it's nature requires long recoveries and allows very few runs… so you almost have to train the power needed for the run seperately and the do what you can to give the athlete some feel (even if it's fake) of what it will be like when they do it right **before they can do it. to me this is one of the values of testing and competetive practices — you get to see what qualities are "stable" under pressure.
2) tempo runs and runs at 90% won;t allow you to achieve certain technical feautres… so even though i don't want tempo runs and speed endurance runs to be sloppy there are certain thing that you have to "let go" per se because the power requirement is too big to survive the workout…
where do you compromise?
I don't have an answer but it brings to mind this great but forgotten thread < https://elitetrack.com/messageboard/viewthread.php?tid=107 >.
Also KT, you mentioned creating a "fake" feel. How do you fake the feeling of doing the technical aspects correctly without the force needed to do it correctly…..assisted runs maybe?
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