C&F Rationale A trend that is increasing in the U.S. is for half and full marathon events to include ‘Clydesdale’ weight divisions for athletes over 90kg (men) and 60kg (women). This has come about because of the desire by athletes, and organisers, in these events to recognise the extraordinary ability of the heavier runners and therefore their true excellence. Clearly big runners have an inherent disadvantage in long distance competition. Remarkable scientific & physiological studies have yielded consistent findings that helps us to understand the astonishing efforts that big people produce to run long distances. Firstly the simple school book formula for kinetic energy (the energy of movement) is E = 1/2mv2 ; where m = mass (weight) and v = velocity (speed). What this means is that for a person to double his or her speed requires four times more energy. So for a 100kg runner to drop from a twelve to a six minute mile to keep up with a 50kg runner, he needs EIGHT TIMES more energy than the 50kg runner requires to run a 12-minute mile - twice as much for the size difference and four times as much for the speed differential. But the real problem is VO2max. This is the rate at which the body utilizes oxygen, which is necessary to convert its stored fuel into energy. As body mass increases, relative VO2max actually decreases. So if you take a highly trained 170cm, 65kg long distance runner and add 12% to his height, he will be just over 190cm tall. If you then configure this new, taller athlete proportionately to the original athlete, he will weigh 90kg. His absolute VO2 max will increase from 5.0 liters/minute to 6.25 liters/minute due to the increased heart volume. This should make a more efficient and therefore faster athlete. But because of the increased body mass, the relative VO2max will actually decrease 9%. So while the athlete is now bigger, has more mass and therefore requires more energy to be competitive, his ability to utilize energy has decreased. It’s as if someone took the pistons out of a couple of cylinders in the engine at the same time they loaded up the trunk. This is why there are very few large, competitive endurance athletes. Just imagine how amazing it would be for a 90kg runner to achieve a 2hr 15 minute marathon! No-one has even been close, and scientists claim it can never happen because such an achievement clearly defies the laws of human performance. Moreover, such achievement defies the laws of physics. Mass is a qualitative measure of a bodys resistance to being accelerated. Force = Mass x Velocity. As such, the heavier runner simply has a larger mass component that must achieve the same velocity component as the smaller or lighter runner. Hence the heavier runner needs to use more force (energy) on his/her bio-mechanical system to cover a given distance. Recent research studies from the National Institute of Fitness and Sports (human performance lab) in the U.S. have asserted that the over-90kg runner’s energy problems are far more acute than their lightweight peers. For example the amount of energy that it takes to move the body during running is directly related to the body weight. Consider this example of estimated energy expenditures: To run one mile in ten minutes: a 55kg athlete burns 78 calories; a 70kg athlete burns 100 calories; a 90kg athlete burns 130 calories and a 110kg athlete burns 160 calories. So, the 110kg athlete who has only just passed the halfway point when the 55kg athlete crosses the finish line has actually worked harder in that athletic achievement! Marathoners in the U.S. are generally disregarding their old prejudices thanks to the encouragement of hundreds of U.S. race directors who include weight divisions in their competitions, so that their heavier athletes can compete on a level playing field – after all isn’t that what competition is about!
Posted on: Fri, 15 Nov 2013 20:09:57 +0000
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