I had trouble with the presentation (could be my settings) but I think I saw something that made me think. Did you state that flight time was more or less the same across a range of speeds? In other words, for elite sprinters at Max V, flight time is more or less equal? If so, doesn’t this mean that vertical displacement, and therefore relative vertical force, is the same? In other words, an object, including a sprinter, once projected into the air vertically, stays in the air (flight time) soley based on the vertical component of force that launched him/her into the air. If flight times are the same, relative displacement must also be the same (all objects respond to gravity equally) so the relative force (bodyweight must be compensated for) is the same. I would bet that one difference would be that, limb length etc. accounted for, faster sprinters cover more distance during that flight time. Wouldn’t this mean that horizontal forces were greater, not vertical forces? If vertical forces were in fact greater at higher speeds, why is flight time not increasing with speed, as flight time is dependent solely on vertical displacment and is totally independent of horizontal displacement?
I will take a stab at this, and my answer is no. Here’s why.
-Flight time is same across all speeds, but
-Stride frequency increases as speeds get faster because
-Ground contact times get smaller. Also
-Increased force production isn’t most important to increase vertical displacement
-Vertical force production is most important because it allows athletes to overcome bodyweight faster.
-Thus vertical force allows faster strides via decreased ground contact time
I hope that makes sense. I think you are right in that if flight times are the same then vertical displacement should be too. That might be an error on Mike’s part. Also, I don’t think stride length changes have much to do with the role horizontal force plays. It’s kind of the nature of running faster.