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The champions

发布时间:2019-03-07 01:07:01来源:未知点击:

By Robert Adler HORSES are the most efficient running machines on Earth, say researchers in Italy. Their secret could be the ability to store energy in their tendons and muscles. Surprisingly, many animals can cover the same distance faster without using more metabolic energy. Scientists have speculated that this is because, as animals walk, run or hop, they store energy in three ways: through the pendulum-like movements of their limbs, in tendons that stretch like rubber bands and—some believe—in tensed muscles. The second half of each stride releases the stored energy, propelling the animal forward at little cost. But scientists continue to debate how much each of these mechanisms contributes. Researchers at the Institute of Advanced Biomedical Technology in Milan filmed horses on on a treadmill while measuring their oxygen consumption. They found that walking was slightly more economical than the other gaits. But the 500-kilogram horses expended no more metabolic energy galloping at 7 metres per second than they did trotting the same distance at half that speed—although, of course, they expended the energy faster and had to breathe harder. As the researchers report in the Journal of Experimental Biology (vol 202, p 2329), motion analysis showed that the running horses performed 10 per cent more work than their oxygen consumption could account for, giving an “apparent efficiency” of 110 per cent—the highest ever found for a land animal. Humans reach about 75 per cent efficiency when they run. Horses need not violate the laws of physics to achieve more than 100 per cent apparent efficiency. This value is the ratio of the mechanical work done—which includes the work involved in moving forward as well as springing in the air during the gallop— divided by the energy obtained from oxygen. It excludes the energy stored in elastic muscles and tendons during each stride. That elasticity allows the animals to do vastly more mechanical work while consuming the same amount of oxygen per metre, says Alberto Minetti, the physiologist who led the study. Horses store and release up to 6 joules per kilogram during each stride, he says: “Like a sports car, the horse’s efficiency is not just in its engine. It’s in the transmission and suspension too.” Minetti’s team found that a galloping horse stores energy in three ways—by stretching its long, elastic tendons, by bending its spine like a bow, and by the forces that muscles exert on tendons without contracting. Finding that muscles may contribute to efficient locomotion without changing length corroborates recent studies on smaller animals, says Peter Weyand,