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I have heard that the severity of injuries tend to decrease while riding a road bike at high speed. An instance of high speed would be like those in the Tour de France.

The reasoning behind this idea is "enough" speed allows the cyclist to "roll" upon landing thus decreasing the chance of breaking bones for example.

This seems contrary to my basic knowledge of physics and momentum, so, is it true?

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If you can get up to and maintain escape velocity at a bit above sea level (ideally above hill and tree-top height), then if you fall off your bike you won't hit the ground. –  Mike Samuel Jul 30 '12 at 22:32
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@MikeSamuel: yes, leaving the earth's atmosphere lowers the risk of some types of serious injuries but increases the risk of others. :) –  amcnabb Jul 30 '12 at 23:33
    
@amcnabb, I wasn't talking about leaving the atmosphere -- just moving fast enough at a tangent to the Earth's surface that the earth curves away from you at 9.8m every second. But yes, I think there might be other complications with this idea. –  Mike Samuel Jul 30 '12 at 23:59
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I suspect that if this effect exists in TdF riding, it's due more to the circumstances than the speed per se. Higher speeds would be flat or downhill, lower speeds uphill. And likely there's a difference in the likelihood of bikes bumping in the different circumstances. –  Daniel R Hicks Jul 31 '12 at 0:18
    
Is your question solely about race riding, i.e. high speeds and (generally) crashes not due to getting hit by cars? –  Jefromi Jul 31 '12 at 5:18
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In "Epidemiology of bicycle injuries and risk factors for serious injury" by Frederick P Rivara, Diane C Thompson, and Robert S Thompson, the authors gave a questionnaire to 3,390 bicycle riders who had attended a hospital emergency department in the Seattle area.

They found that cyclists involved in a crash at a speed greater than 15 miles per hour were 1.4 times as likely to have a "severe" injury (defined as an injury severity score greater than 8) as cyclists involved in a crash at a speed of 15 miles per hour or less. The 95% confidence interval was 1.0 to 1.9.

(Caveats: 1. It seems strange to me that the authors only reported odds ratios, when they apparently had the data to compute effect sizes too. 2. The fast cyclists differ systematically from the slower cyclists: the odds ratio fell to 1.2 when other factors in the study were controlled for. 3. It's Rivara, Thompson and Thompson.)

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Its good to see an answer with some sort of documental evidence. +1 –  heltonbiker Jul 31 '12 at 11:53
    
They reported odds ratios because the study was a case-control with a non-random sample design so the selection bias makes the population-level effect size impossible to estimate. –  R. Chung Jul 31 '12 at 13:48
    
The effect size that they could have computed was, given that a cyclist was injured in a crash, how much more severe (on average) was their injury if their speed was greater than 15 miles per hour? This would have given some clue as to the practical significance of the observation: are the faster cyclists injured a little bit worse, or a lot worse? –  Gareth Rees Jul 31 '12 at 14:49
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It is totally dependent on the impact. If you run into a wall you want to be going slower. If you hit a bump and are launched off your bike or jump off a cliff you want to be going faster. I don't know physics well enough to explain it that way but I do ride a lot of street (jumping down stairs, off roofs, etc.) so I will explain it how I know you want to land in that sense. Think about the angle of impact jumping off a loading dock, if you drop going at a slow speed you will impact the ground almost at a 90 degree angle, your body will need to absorb almost all the impact (on a non-suspension bike). If you go faster you will impact the ground at say 45 degrees, you will feel a lot less impact on your body.

Taking that to the tour de france (or crashing in general, even on a jump), if you roll rather than slide, your impact on the ground will be a lot less at higher speeds, your chance of twisting a leg or whatever is less because your limb doesn't have time to get planted. It might help to watch some parkour, they will roll out of a jump because they are trying to transfer the impact at an angle against the ground rather than absorbing an impact perpendicular to the ground.

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I don't think the loading dock drop is a good example. Your downwards momentum is the same in both cases. If you also have forwards momentum, that may "feel" better or more controlled, perhaps because you're landing both wheels at once rather than nose-diving? I think you're right regarding rolling your body, however. –  JamesBradbury Feb 7 '13 at 12:57
    
Flat landing with speed is at least better in the sense of having enough speed to keep the bike rolling and thus stable immediately after landing. Landing an almost stopped bike would make very hard to "keep it going". I think, too, that vertical momentum is the same for a flat landing (very different than landing along a slope). –  heltonbiker Feb 15 '13 at 18:13
    
think about it in terms of an airplane crash. Take an airplane going 300 MPH at the time of impact and have it hit the ground in a nose dive, or having it come in on its belly. You will have a better chance of survival on its belly. The angle of the impact has quite a lot to do with the damage done. This is basically creating that "slope" you are talking about. (Notice it was 300 MPH at the time of impact, not faster in the nose dive due to kinetic force). –  BillyNair Feb 23 '13 at 21:51
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As far as I know, in any vehicle, there is a direct relationship between speed and severity, statistically speaking, with "lots" of studies showing that. This also applies to being hit, or front-to-front crashes. There's even the term "high-energy-trauma", applied by health professionals to injuries involving high energies, for example high kinetic energies.

Of course there are confounding factors: are fast riders (professional riders?) more skilled? Are fast racing events the place for a more "focused" riding? Do they fall less, or are someow more prepared to fall?

Anyway, I cannot see how a SLOWER fall could hurt MORE than a fast one. It's a matter of kinetic energy, speed of response of human motor coordination, even common sense.

Although I have not evidence to bring about, I hope this helps someway.

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I can think of one specific case of a slow-fall that regularly injures novice cyclists quite badly: broken collarbone from putting one's arm out too rigidly when tipping over as a result of stopping and not disengaging clipless pedals. –  Angelo Jul 31 '12 at 13:54
    
@Angelo. But it's not the speed that makes the difference to the severity. The speed makes that kind of injury unlikely to happen. If you actually did land on a rigid arm at 15mph+, I'm sure it would hurt even more. –  JamesBradbury Feb 7 '13 at 12:53
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I think there is likely no clear answer. The points go both ways.

Yes at speed there is the ability to roll. But also the risk of trauma with a stationary object. Be it an object or the ground. Humans are soft and squishy with fragile bones compared to concrete and asphalt, rocks or trees.

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