流水不腐，户枢不蠹

liúshuǐ bù fǔ, hù shū bù dù

[Running water is never stale and a door-hinges never get worm-eaten-practice keep one always fit] 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