Any parent that takes their kid out for a walk knows that children tire more quickly than adults, but why is that? Do kids and small adults walk differently from taller people or do they tire faster for some other reason? Peter Weyand from Southern Methodist University, USA, is fascinated by the effect that body size has on physiological function. 'This goes back to Max Kleiber's work on resting metabolic rates for different sized animals. He found that the bigger you are the slower each gram of tissue uses energy,' explains Weyand, who adds, 'It's interesting to know how and why metabolism is regulated that way.' Intrigued by the question of why smaller people use more energy per kilogram body mass than larger individuals when walking, Weyand teamed up with Maurice Puyau and Nancy Butte, from the USDA/ARS Children's Nutrition Research Center at Baylor College of Medicine, and undergraduate Bethany Smith. Together they decided to measure the metabolic rates of children and adults, ranging from 5 to 32 years old, weighing between 15.9kg and 88.7kg and ranging in height from 1.07m to 1.83m, to try to find out why larger people are more economical walkers than smaller people. Weyand and his colleagues publish their discovery that walkers of all heights use the same amount of energy per stride, making short people less economical because they take more steps. They also derive a fundamental equation to calculate exactly how much energy walkers use with direct applications in all walks of life. The team publishes its discovery on 12 November 2010 in The Journal of Experimental Biology at http://jeb.biologists.org/cgi/content/abstract/213/23/3972.
First Weyand and colleagues filmed male and female volunteers as they walked on a treadmill at speeds ranging from a slow 0.4m/s up to 1.9m/s. Meanwhile, they simultaneously measured the walkers' oxygen consumption and carbon dioxide pro
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The Company of Biologists