I want to run about 20 miles a week to maintain fitness (I'm not training for anything). Is it better for my knees and body in general to run, say, five miles four days a week with three days off, or to run six days a week for three miles each and take one day off? Or what other division of rest and work days would you suggest?

— Linda Lapp, Raleigh, North Carolina

If your objective is to minimize the stress on your body, then opt for the more frequent, shorter runs. The shorter efforts put less repetitive stress on your musculoskeletal system and thus have a reduced risk of injury. There is a bigger issue here though, which is, how do you maintain fitness without getting bored silly doing the same run six days per week? We are, as they say, creatures of habit, and try as we may to find ways to make a three, four, or even five-mile run interesting and creative, we usually end of doing the same ol' route. There is another way: instead of doing the same distance run day after day, mix up the distances each week, have a longer running day, a few shorter ones, and throw in a hike every now and then. Now you've got a lot more "mix" to keep it interesting and to keep the stress on your body manageable. Also, run on soft surfaces with good shoes to further minimize the shock to your joints.

Continue to shake things up by changing the intensity of each run. On the long day, run or walk at a lower intensity (60-70% of your maximum heart rate, or conversation pace). While on one or two of the shorter days do as the Swedes do and fartlek your way around the neighborhood. Fartlek (stop giggling) means speed play, with play being the operative word. Increase the tempo so that you're outside your comfort zone for a few minutes, then ease off and cruise, repeat using parked cars, telephone poles or bad dogs as points to speed up or slow down. Add one to two days of "regular" runs and you've got a plan that will not only maintain your fitness level, it may actually improve it, provided you keep moving faster as your fitness improves. To really take it over the top, mix up your runs with bike rides, Frisbee golf (speed variety), soccer, in-line skating, or snowshoeing every couple of weeks. Don't be afraid to try something new, one of the best ways to stay fit is to find new ways to play outside.