热点话题 精深阅读(一) 主题语境:人与社会——锻炼身体,增强体质,提升健康水平 (2020·全国Ⅰ) Race walking shares many fitness benefits with running,research shows,while most likely contributing to fewer injuries.It does,however,have its own problem. Race walkers are conditioned athletes.The longest track and field event at the Summer Olympics is the 50-kilometer race walk,which is about five miles longer than the marathon.But the sport’s rules require that a race walker’s knees stay straight through most of the leg swing and one foot remain in contact(接触) with the ground at all times.It’s this strange form that makes race walking such an attractive activity,however,says Jaclyn Norberg,an assistant professor of exercise science at Salem State University in Salem,Mass. Like running,race walking is physically demanding,she says.According to most calculations,race walkers moving at a pace of six miles per hour would burn about 800 calories(卡路里) per hour,which is approximately twice as many as they would burn walking,although fewer than running,which would probably burn about 1,000 or more calories per hour. However,race walking does not pound the body as much as running does,Dr.Norberg says.According to her research,runners hit the ground with as much as four times their body weight per step,while race walkers,who do not leave the ground,create only about 1.4 times their body weight with each step. As a result,she