In general, the larger and taller runners had faster optimum speeds. Much of the gender difference may be due to variations in body size and leg length, which have been shown to affect running mechanics, Steudel says. The most efficient running speed determined in the study varied between individuals but averaged about 8.3 miles per hour for males and 6.5 miles per hour for females in a group of nine experienced amateur runners. Metabolic energy costs increased at both fast and slow speeds and revealed an intermediate pace of maximal efficiency. Peak efficiency was determined by measuring runners' metabolic rates at a range of speeds enforced by a motorized treadmill. 'What that means is that there is an optimal speed that will get you there the cheapest,' metabolically speaking, Steudel says. However, Steudel and Cara Wall-Scheffler of Seattle Pacific University have now shown that the energetic demands of running change at different speeds. Though sprinting feels more demanding in the short term, the longer time and continued exertion required to cover a set distance at a slower pace were thought to balance out the difference in metabolic cost, says Karen Steudel, a zoology professor at the University of Wisconsin-Madison. The result debunks the long-standing view that running has the same metabolic cost per unit of time no matter the speed - in other words, that the energy needed to run a given distance is the same whether sprinting or jogging.

A new study, published online March 18 in the Journal of Human Evolution, shows that the efficiency of human running varies with speed and that each individual has an optimal pace at which he or she can cover the greatest distance with the least effort.

The long dark sprinting