[quote author="Isaiah Miller" date="1326005315"]Sorry if you misunderstood me, but try this for me. Video yourself jogging with and exaggerated bouncing motion then video yourself jogging with that same bouncing but try your best to keep the hips higher with less knee flexion. Whenever we sprint our body collapses during ground contact and the only way to lessen that effect is to apply significant vertical force down into the ground to keep the hips from dropping. If a runner does not apply enough vertical force you will see significantly longer ground contacts, low hips, and/or a longer amortization phase. Just push up and stay up/don’t collapse. I think I will post a video because explaining this is a little difficult.
A video might help, but if I do understand you right, we should use a term other than vertical displacement. Vertical displacement implies that there is actual movement in the vertical component, not a vertical resistance that, if lacking, might lead to collapse….it actually means the body is moving up and down with every stride. I don’t see that happening in that particular video and it wasn’t what I expected.[/quote]That is a very good point maybe we do need some other terminology. Try this think about vertical displacement as being positive and negative/positive=good and negative equals bad. Now that this has been stated, imagine jumping on a trampoline with loose springs that greatly descends as you make contact with it…The higher you want to bounce the greater it descends, so as you spring into the air viewers will notice that you have a lot of vertical displacement because of the depth you started from at the bottom of the jump. Now imagine have a trampoline with hard springs that barely descends when you jump on it so when you jump you are getting displacement but it doesn’t “appear” to be as much as the soft trampoline. Now lets say the total descent of the soft spring trampoline is 25 inches and the total ascent is 30 inches. Now lets also say the total descent of the hard spring trampoline is 10 inches and the total ascent is 20 inches. The jump on the 1st trampoline would look as though you had more positive displacement, but that is only because of the depth of the descent. I hope this helps to makes things a little clearer if not I tried :-)…I will post a video soon.