Is it better, we sometimes hear you ask, to walk/swim/jog/cycle more miles at a slower pace or log a shorter distance at a faster clip? Or should you just forget it all and take a nap?

If your main exercise goal is overall good health -- which does not necessarily equate to uber-fitness -- you should focus on two things, says the July issue of the Harvard Heart Letter, a consumer newsletter from Harvard Medical School: burning calories and raising your heart rate. Long, methodical exercise sessions are as good as short, intense bursts provided you choose exercise that boosts your heart rate and your pace of breathing. Brief amounts of an intense activity can burn the same number of calories as do longer or more frequent sessions of a less-intense one.

The Heart Letter cited a 1995 study that followed 17,000 Harvard alumni for 26 years and found that men who burned an extra 700 to 2,000 calories a week through some form of dynamic exercise derived "significant" health benefits.

Harvard Heart Letter editor Patrick Skerrett said: " 'Significant health benefits' means not dying early. Subjects in the study who burned 2,000 calories per week had a death rate [during the study period] about 30 percent lower than those who did zero activity. . . . The positive impact was mostly cardiovascular -- it helped prevent heart disease."

Skerrett recommends that those seeking similar health benefits raise their heart rate for at least 30 minutes per day in periods of no less than 10 minutes. In the study, the likelihood of living longer as a result of exercise increased with the number of calories burned but leveled off at 2,000 calories per week. That equates to walking about three miles per day. A long-term study of women showed similar results.

You can learn roughly how many calories you burn per hour in a given activity at www.caloriesperhour.com. By adjusting intensity, duration and/or frequency of exercise, you can adjust the number of calories you expend. One big caveat: If you want to lose weight, you must burn more calories than you consume.

Activities that burn the most calories in the shortest time include running, swimming and even brisk walking -- anything that forces your heart rate up and keeps it there. Stop-and-go activities like weight lifting and canoeing, while beneficial, will not rip through calories as quickly as will the more-intensive cardio workouts.

If your goal is not simply good health but improved endurance or competition-level fitness, then, alas, you will have to work harder. One way to do this (as always, consult your doctor before undertaking any program involving strenuous exertion): After a warm-up period (five minutes or so), get your heart rate up to 75 to 80 percent of your maximum heart rate and keep it there for 20 to 40 minutes. (The longer the better, generally, but the benefit levels off after about 40 minutes.)

To boost endurance even more, add intervals -- 30- to 60-second spikes in which you elevate your heart rate to between 85 and 95 percent of its maximum. Always try to return to the 70- to 80-percent zone after an interval.

Our Moving Crew chat will cover this and other fitness topics, this Thursday at 11 a.m. at www.washingtonpost.com/wp-dyn/liveonline/health/movingcrew.

-- John Briley