If you have knee arthritis, the wearing away of cartilage at the joint, you may think that only long-term, intensive therapy will keep you walking.  But simply increasing light activity may be all it takes to keep you from being sidelined.  A study published in BMJ April 29, 2014, found that more time doing light-intensity physical activity-such as pushing a vacuum cleaner, walking around a room, or strolling through a grocery store-protects against knee arthritis becoming worse and against developing a disability as you age.  How much more activity does it take?  People who spent four hours a day doing light activity had 30% less risk of disability compared with people who spent three hours a day doing the same activities.  Even among people who did almost no moderate activity, the more light activity they did, the less likely they were to develop disability.  "That means that almost any activity you do that is not just sitting will keep you mobile and independent longer, able to walk around the house or go grocery shopping. The more you do each day, the better your knees will support you," says geriatrician Dr. Suzanne Salamon, an instructor at Harvard Medical School.  (Article copied from Harvard Health Letter Volume 39-Number 10| August 2014)