Stress fractures, or tiny cracks in the surface of a bone, are serious running injuries that requires immediate treatment.
应力性骨折，或者在骨头表面上的微小裂缝，是严重的跑步受伤，并且需要立即治疗。
2
Avoid concrete as much as possible: It's about 10 times as hard as asphalt, and is a terrible surface for running.
尽量避免水泥路面：其硬度是沥青路面的十倍，是非常不适合跑步的路面。
3
Thin wooden slats circle the unit to provide a smooth runningsurface to roll it and openings on the side and slated Windows let light into the interior.