Team Blog

The end of my Bolt trilogy

Henry Hagnas

It appears that my guide to the 100 m has turned into a trilogy. My last two postings covered some stats about sprinting 100 m in 9.58 s and the what the limits of 100 m performance may be based on historical models.

The science of elite sprinting

What do we know about the biomechanics of elite sprinting? When I refer to elite sprinting I’m talking about running at speeds of 10 m/s plus i.e. below 10s for 100m. At these speeds the answer is very little. Because sprinters hit top speed from the 60 m mark and are more likely to run at top speeds in competition we need to look at sprinting in competition. So what do we know about that? There is a wealth of data about split times etc (similar to my first post) which provides interesting information about velocity profiles of the race and the stride characteristics but an understanding of the biomechanics of elite sprinters in competition is sparse.

So what did we do?

After Bolt’s world recorded run in Berlin in 2009 myself and Prof Beneke (Marburg University) decided to try and understand the mechanics of sprinting of the three fastest men in history (Bolt, Gay and Powell). We took these split data from Berlin and then run a mathematical model – using methods and equations from past work on sprinting – to estimate a number of parameters to try and explain why Bolt is so fast.

I suppose the first question – why study Bolt in 2009 and not other world record holders? Well Bolt has knocked off 0.14s over the 100m in 2 years – previously this has taken at least 15 years. Bolt is also tall – 6’5’’ – abnormally tall for a sprinter. As mentioned in my last post, his height should be a disadvantage at the start and the acceleration phase – at Berlin it wasn’t (this is the part of the race that if Bolt doesn’t get right in London his competitors have a chance to beat him). From 50m plus his height and therefore his huge step length is an advantage. Ok, so nothing new here.

One of the parameters we calculated was stance time – how long the foot is on the ground for. Throughout the whole race Bolt’s stance time was greater than his competitors. Why is stance time important? Past research has shown that an increase in the vertical force is important for sprinting. By having his foot on the ground for longer Bolt is able to apply this force over a longer (optimal) time frame. Cheetahs do a similar thing by developing gait mechanics that prolong their periods of ground force application by increasing ground contact time. Vertical stiffness is also important for sprinting. This is the spring mass model for you closet biomechanists out there. Think of a spring (your leg) and then you body mass as one lump of mass located atop of the spring – this is the spring mass model. The faster you run the stiffer the spring. The stiffness for Bolt, Gay and Powell were between 3.8 – 5.7 times greater than us mere mortals who can only sprint at about 12 s pace for 100 m. The interesting thing is that Bolt’s stiffness was significantly less than his competitors – this was due to the increased stance time. This is fairly surprising – but it may allow Bolt to store and release energy more efficiently than his competitors.

But it’s all theory…

The thing is, even though these are the first studies to attempt to explain sprinting at the speeds of Bolt et al. in competition these are estimates. We haven’t collected data from these sprinters. What needs to happen is to develop miniaturised kit to go in the spikes…and then put Bolt in the spikes…easy as pie. I don’t suppose anyone knows the Jamaican team!

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