You’d think that spending an hour a day sweating at the gym would be enough to guarantee good health. But a 2010 study in the American Journal of Epidemiology added to growing evidence that what you do during the rest of the day also makes a difference. The researchers followed 123,000 people for 13 years and found that men and women who spent more than six hours per day sitting down were 18 and 37 percent, respectively, more likely to die during the study than those who sat fewer than three hours per day. What’s most surprising is that these risks were completely unrelated to how much exercise the subjects reported getting.

            Scientists aren’t yet sure why spending long periods of time sitting down should cause health problems, but they view it as a sign that the low-intensity activity associated with simply walking around and doing everyday chores makes an important contribution to health. Research a the University of Massachusetts Amherst suggests that it can also make a key contribution to weight loss, since it’s low-key enough that it doesn’t spark hunger to compensate for the calories burned. A forthcoming Amherst study compared a group of volunteers who sat all day (they even used wheelchairs to visit the bathroom) with a group that didn’t sit down at all. Preliminary results show that the difference in energy expenditure was hundreds of calories – but the level of expenditure was hundreds of calories – but the level of appetite hormones and reported hunger in the two groups remained identical.

            Of course, for people who work in office settings, walking around all day isn’t really an option. Some experts recommend scheduling regular “micro-breaks” every 30 to 60 minutes, in which you stand up, stretch, and walk away from your desk for a few minutes (preferably not to the fridge). Free downloadable programs like Workrave (www.workrave.org) provide periodic warnings to remind you when to take these breaks.

            Another low-intensity calorie-burning option is to replace your desk chair and use an exercise ball instead or even switch to a standing desk. A 2008 study by researchers at the University of Buffalo found that either sitting on an exercise ball or standing resulted in an extra 4.1 calories burned per hour compared to sitting ina regular office hair. Best of all, the typing rate of the subjects in the study was the same in all three cases. If you try either or these options, don’t go “cold turkey” – start with no more than a few hours a day. Also, be alert for signs of lower-back pain when sitting on the exercise ball, since the lack of support could expose existing weaknesses in stabilizing muscles.

            None of this suggests that more vigorous exercise isn’t also important. For example, a 2010 University of Western Ontario study that compared low-and high-intensity activity found that easier exercise acts primarily on your heart, while harder exercise acts on your muscles. You need both your heart and muscles to be healthy, so don’t try to get away with just one of the options. In fact, -- and this is a message that applies in almost every aspect of fitness, diet, and health – the very best approach you can take to choosing your exercise intensity is to avoid doing the same thing every day.