influence of wind...

Track & Field 100m
1

I’ve been wondering recently about the nature of influence that wind has over an athlete. it began with a discussion between myself and a heavy throw specialist. he suggested that a headwind would slow him down more because he presents a wider surface area, while I argued that it would probably slow down a lighter athlete more as it represented a higher percentage of resistance for what a lighter sprinter would have adapted to. I also feel that a lighter athlete would be more likely to improve his time by a larger amount than a heavier athlete if there was a tailwind.

in addition to that, is there some accepted measure of conversion for wind affected times?

X wind = .Ys

thoughts?

2

Assuming a constant wind speed, the force the wind applies to a runner is directly proportional to the surface area of the athlete. (This is a simplified relationship from something very complex.)

Runners will always feel a headwind during a sprint regardless of tailwind/headwind (unless it is about a 40km/h tailwind), since they are running so fast.

The main question then, is about how different body types are blown by the wind.

Suppose we have two athletes of the same weight, and identical running abilities in a no-wind situation (in which they are both fighting against the “wind” while running).

If one of them has a smaller cross-section (which I will just call “smaller”), the smaller athlete will be affected LESS by the wind, since there is less wind force being applied to him/her.

In a race with a headwind, the larger athlete will feel more wind force while running, which leads you to think that the smaller runner will win a race with a headwind, while the larger runner will win the race with a tailwind, but the larger athlete ALWAYS feels more wind force while running, yet can run the same time in a race without wind. You’d have to know the characteristics of individual runners to make the judgment about who would win.

Anyway - if we use the extremes: a very very very small runner will be massively affected by the wind. They will run much faster with tailwind, and much slower with headwind.

A very very very large runner basically won’t be affected by the wind in any form, regardless of its direction.

Related, but not on the same lines, is that a world class sprinter, running into a 2.0 m/s headwind, feels almost exactly twice as much wind resistance as when running with a 2.0m/s tailwind.

3

The law of scale shows that as surface area increases, internal volume increases exponentially. Assuming this is muscle in a fit individual, the bigger (thicker) guy has the advantage in a headwind.

4

It isn’t exponentially - it is to the power of 3/2. If surface area increases by a factor of 2, volume increases by a factor of 2^(1.5).

Charlie, are you speaking from experience or theory about who has the advantage in tailwind/headwind races? I’m a little confused about the theory, since if they are moving at the same speed, the bigger guy will always feel the same multiple of wind force with respect to the smaller guy. He might always feel 20% more wind force, for example, provided they are moving the same speed, regardless if is a headwind or tailwind. If I understand your line or reasoning (which I might not), the thicker guy should win every race since he always has a higher power:windforce ratio.

5

OK, I’m no math genius, but suffice to say there is more internal vol for muscle fibre. Given equal talent, the bigger and thicker guy can handle the addnl resistance better. for the same reason, the bigger and thicker guy can handle colder conditions better as surface heat losses are compensated for by a relatively larger interior vol to generate heat.

6

Thanks. Does the following match what you’ve seen?
The smaller runner should do better with a tailwind (which matches what will happen in theory with someone extremely small), because the larger runner’s advantage of being able to power through a stronger wind is removed, and the smaller runner can get their speed up without being hindered as much by wind?

Which leads me to the question of - in a tailwind - is stride length or stride frequency improved more, and vice versa with a headwind?

7

Let’s leave the power out of it for a while.

As said, the bigger guy will have a larger surface area but also an even larger volume/mass. The wind will decelerate the athlete according to A = F/M, where F is the wind force (which depends on the surface area) and M is the mass of the athlete.

Therefore the wind will always affect the smaller guy more.

As long as we don’t have a tail wind that exceeds the running speed, the wind will have a decelerating effect and the bigger guy will have an advantage. The larger the head wind, the larger the difference between its deceleration on the small guy and the big guy. The smaller guy can only compensate this by producing more acceleration (i.e. more force/body weight) than the bigger guy, and the demand on the compensation increases as the head wind increases.

8

I understand the physics of it Anders, which is why I’m asking Charlie about what his experience has shown. Read the original question and my first post.

9

Well, it was not directed at you. I was only trying to clarify (if only for myself…) the concept of surface area/mass.

Check this http://myweb.lmu.edu/jmureika/track/index.html?viewpapers=Related+Publications

10

In my opinion, there is NO reasonable table possible IMO because wind is only one of many factors and may not have even been taken correctly. It does not account for track surface, temperature, humidity, altitude (beyond a simple over/under rule at 1000m).
All these other factors can be huge.

11

Also, those tables/formulas don’t consider the things discussed above - that is, that the ratio area/mass differs from individual to individual.

My biggest gripe is the wind reading itself. Even if done by the book, it only gives a very rough (at best) estimation of the actual wind experienced by the runner.

12

Ahh, sorry then. Are you (or anyone else) interested in a technical analysis of what is going on? I can provide a fairly thorough mathematical explanation.

13

Sure, but is there a way to look at it from an air molecule level? IE headwind = more air molecules to cut through and tailwind less, higher humidity and colder air = more, altitude and higher temp = less, effect of crosswinds on both headwind and tailwind, etc.

14

There is a way to look at it like that, but it might be a few days before I have the time to go through and write it up (I like doing things like this though). Strangely, higher humidity results in the air density being lower, not higher.

15

if the track was warm (the actual surface not the general area) would it be slightly more elastic and give a bit more spring? or would the effect just be too small to notice?

16

Yes, up to a point. If it’s too hot, the asphalt under the surface may begin to soften too much, unless it’s specially compacted like it was in Atlanta

17

Explains why in part its harder to breath in longer distance races then hey. Air pushed aside for H2Oinstead, less air to breath, less O2 into the blood stream.

Less air molucules, but more H2O in the air creates thicker mass to push through as well?

18

That’s what I always thought too until I eventually learned about it. The number of molecules in air at a given pressure & temperature is basically constant, so air molecules are being replaced by water molecules. Since a water molecule only have about 62% on the mass of an air molecule, the density of the air decreases.