流水不腐，户枢不蠹
running water is never stale and a door-hinge is never worm-eaten;a thing in use never rots
流水不腐，户枢不蠹liú shuǐ bù fǔ,hù shū bù dù
户枢：指门的转轴；蠹：蛀虫，这里指蛀蚀。流动的水不会变质腐臭，经常转动的门轴不会被蛀蚀。比喻经常运动的东西不易被侵蚀，也比喻人经常运动则不易生病。running water is never stale and a door-hinge never gets worm-eaten, practice keeps one fit