Tired child

If you've ever had to pick up and carry a tired child through the mall, you know that walking sometimes tuckers out the 1. Now 2 think they know why. The results appear in the Journal of 3 Biology.Larger animals tend to use less energy per gram of body mass than smaller ones do, even at rest. But what happens when they're in motion? 4 recruited walkers of different ages and sizes, from a three-foot-tall kindergartner to a six-foot adult. While the subjects logged miles on the treadmill, the scientists 5 their stride and metabolism.And they found that people pretty much walk the same way, egardless of their stature. If you scaled a five-year-old up to be six-and-a-half feet tall, the giant child would lope along just like a similarly sized adult. What's more, walkers of all heights use the same amount of energy per step. That means that big people don't 6 energy by strolling in a more economical style. They expend less energy because—just as you may have always 7 —they simply need fewer strides to cover the same ground. Which means that for some people a walk in the park ain't necessarily a walk in the park.