An increase in air time causes a decrease in stride frequency. However, an increase in hip height reduces ground contact times. So this is my question, can you have an increase in hip height without an increase in airtime? If so, how?
by THEONE
An increase in air time causes a decrease in stride frequency.
I do not think this is necessarily the case. If the hips are too high…then yes, this is the case, however, there is an optimal hip height. Too high, and the foot lands exactly under the centre of gravity resulting in no horizontal motion. Too low, and the foot ground contact time is prolonged.
Wouldnt too much air result in darting of the toes and not enough puss off from the toe. Sprinting is not vertical but horizontal in nature. No wonder there arent 8 ft high jumpers run 9.9.
I don’t think anyone should ever worry about their hips being too high. The higher your hip, the shorter the ground contact and the higher the stride frequency. The increased time in the air is simply due to the reduced time on the ground, since those are the only places you can be. It is during that air time that you’re bringing the foot forward for the next stride, so increasing air time and increasing stride frequncy naturally go hand in hand. You can’t start your next stride if you’re still on the ground finishing the previous one.
Originally posted by Flash
I don’t think anyone should ever worry about their hips being too high. The higher your hip, the shorter the ground contact and the higher the stride frequency. The increased time in the air is simply due to the reduced time on the ground, since those are the only places you can be. It is during that air time that you’re bringing the foot forward for the next stride, so increasing air time and increasing stride frequncy naturally go hand in hand. You can’t start your next stride if you’re still on the ground finishing the previous one.
…“increasing air time and increasing stride frequency naturally go hand in hand.” Flash I don’t agree with that, in fact I think it is the exact opposite. Increase in hip height and a increase in stride frequency go hand in hand. Do not confuse the two.
So again, can you increase hip height without increasing air time?
I disagree. I think hip height and air time go hand in hand. Hip height increases because increased power output is causing the body to rise higher off the ground with each stride, which results in a longer travel path through the air. If you’re travelling higher in the air and your contact time with the ground is concurrently decreasing, you have to be spending more time in the air.
As a practical matter, how would you decrease air time without reducing hip height and increasing ground contact time? In NC Charlie talked about the proper rhythm for plyometric jumps which helps illustrate the point. I’m sure we’ve all seen people doing repetition jumps onto and off of a short block or step. Usually, the person is trying to go back and forth as fast as possible, bam, bam bam. As pointed out by Charlie, the problem with this is that in trying to minimize air time and land as quickly as possible for the next jump, the person ends up increasing contact time with the ground. Instead, the optimal rhythm should be pop. . . pop . . . pop, with the briefest foot contacts. It’s kind of hard to convey in writing but I’m sure you get my point.
Like I said before, either you’re in the air or on the ground. The only way to get to the next step quicker is to reduce the path through the air, which naturally involves reducing hip height and increasing ground contact. In this case, you’re chopping your stride to increase frequency, which will lower your speed. The limiting factor in optimal stride frequency is ground contact, not what happens in the air.
I think this is a great dicussion topic and addresses a central biomechnical issue in sprinting. I wish Charlie would jump in on this.
Flash,
I am with you on that. I am working on finding the notes or audio from the Asheville seminar where Charlie mentioned this. I do recall this topic and what you stated.
Brad, I hope you find your notes and share some more on this topic.
Flash, I get what you are saying, but I am still on the fence. I alway felt you kept the hip heigh by not collapsing on ground contact; which could result from the legs touching down too far infront of the c.o.m. or lack of specific strength in the extensors. Not by trying to push yourself high up in the air. Air time can be too much.
I understand where you’re coming from. You’re right about not collapsing on impact. However, the increased travel through the air is not someting you try to do, it simply happens as power output increases. Charlie discusses this in detail in his seminars when he analyzes the performance of top sprinters (i.e., Ben and Carl). I would strongly recommend buying the seminar videos if you can afford them. I would certainly suggest you invest your money in them before you invest it in anything else (e.g., supplements or training gadgets). I’ll leave the discussion here until Charlie has time to jump in.
THEONE,
You bring up great points. You dont run down the track thinking “I must get max. hip height”, if this was the case we would be bounding coaches 
I believe we are all on the same page. You cannot force this to occur, it will come with proper strength/power gains and training.
Common sense dictates that if you forced air time, you would break even more by the collapse upon ground contact. It is really a culmination of what each of us are saying.
Great topic