[Silhouette]

Even fit people have trouble in some stations as the escalators can be very steep and very long.

Also, the ambient temperature and other atmospheric properties are far from ideal for physical exertion in many of these stations.

That doesn't matter so much if you're generally fit and completely healthy. If, however, you have something like asthma, the environment potentially exacerbates the condition even if you're otherwise in good shape for that kind of exercise.