问：为什么我发现在跑步机上走会觉得更吃力、更累？

　　Answer: Many people, including me, find a treadmill workout more draining than the same activity on a sidewalk or track. In a 2012 experiment, runners were asked to jog on a track while rating how difficult the exercise felt. Then they hopped on treadmills without speed displays and were told to set the machine to a pace that felt the same as what they had just run. Almost all chose a speed that was much slower. On the treadmill, this gentle pace felt as difficult as swifter running on the track.

　　答：很多人，包括我自己，发现在跑步机上比在人行道或跑道上进行同样的锻炼更累。在2012年的一项实验中，研究者要求跑步者在跑道上慢跑，同时评估这项锻炼的难度感受。然后他们跳到没有速度显示器的跑步机上，把速度设定为刚才慢跑时感觉的速度。几乎所有人选择的速度都慢得多。在跑步机上以较慢速度跑步与在跑道上以较快速度跑步的难度感觉是一样的。

　　为什么在跑步机上锻炼更累人

　　But scientists are unsure why treadmill exercise feels harder. Most people’s biomechanics are the same, whether they are on a treadmill or the ground, studies show. And where there are differences, the advantage would seem to reside with the machine. Treadmill jogging is less jarring than running on the ground, for instance. A 2014 study shows that we strike the ground with about 200 percent of our body weight while running on the track and only 175 percent of our body weight when we are on a treadmill.

　　但是科学家们不确定为什么在跑步机锻炼感觉更吃力。多项研究表明，不管在跑步机上还是在地面上，大多数人的生物力学是一样的。如果说有区别的话，跑步机似乎更有优势。比如，在跑步机上慢跑比在地面上的震动更小。2014年的一项研究表明，我们在跑道上跑步时，撞击地面的力量相当于体重的约200%，而在跑步机上，撞击力量只有体重的175%。

　　So the most likely explanation for any drudgery associated with treadmill exercise is psychological. Treadmills are indoor machines, and many studies show that people generally prefer outdoor workouts. In various experiments, people have reported experiencing less fatigue, more vitality and greater pleasure after walking outside compared with on an indoor treadmill.

　　所以用跑步机锻炼更累人的原因很可能是心理方面的。跑步机是室内机器，而很多研究表明，人们总体来说更喜欢户外锻炼。人们在不同的实验中报告称，与在室内跑步机上锻炼后相比，在户外散步后感觉不那么累，更有活力，更愉悦。

　　Also, treadmills typically provide a walk to nowhere, which may be demoralizing. In a study published last year, volunteers who set out to walk a course that had no clear finish line felt more fatigued afterward than when they covered the same distance with an obvious finish line ahead on which to focus.

　　另外，跑步机通常没有目的地，这可能令人气馁。在去年发表的一项研究中，志愿者们走过两段同样长度的路程，一个没有明确的终点线，另一个有明确的终点线。完成之后，志愿者们发现，如果没有一个明确的终点线可以关注，感觉会更累人。

　　So the lesson may be that, if you can, find a treadmill with a monitor and video programing showing an outdoor walking course with a beginning and, most important, an end.

　　所以，我们可以得出这样的经验：如果可以的话，找一个带监视器和视频节目的跑步机。视频节目可以展示户外行走路程，它有起点，更重要的是，它有终点。