流水不腐，户枢不蠹liú shuǐ bù fǔ，hù shū bù dù

常流的水不发臭，常转的门轴不遭虫蛀。比喻经常运动，生命力才能持久，才有旺盛的活力。

英Running water is never stale and a door-hinges never get worm-eaten—practice keep one always fit;