前两年春秋冬曾上过中长跑，对心脏确实很好，但顾忌对关节的损伤还是停了，改成了走:

What I use in Winden is to do indoor exercise bike which does not put much pressure on knees.  Elliptical step machine is another good alternative.  If you are lucky, you may have indoor swimming pool.  I still think swimming overall is the best one.