The age-old workout question; which is better, lower or higher intensity levels? First of all, it depends on your definition of what's better? The word "better" is contingent on what kind of exercise you are doing, what are your goals, how's your health, what's your fitness level, your personal exercise schedule, etc.
If you can run or walk vigorously for 30 minutes, will it provide greater health benefits than walking more slowly for 30 minutes? "But what if, the moderate exercise is done for longer time so that it burns as many calories as the shorter intense workout, without all the huffing and puffing. Could it be just as good or maybe even better?"
Calorie for calorie, research supports that vigorous exercise is almost always better for heart health, calorie burning and weight loss, building of the HDL ("Good") cholesterol and may be more beneficial in improving insulin sensitivity and other metabolic factors. "Regular higher intensity exercise requires physiologic capacities that cannot be developed by walking slowly, no matter how much slow walking is done." (Annual Review of Public Health, 2011)
"Being able to do strenuous exercise is a marker for good health. So it's not surprising that observational studies find that vigorous exercisers are at lower risk for chronic disease and tend to live longer than those who do moderate and low exercise." (Berkeley Wellness Letter, Winter Issue 13-14)
Supporters of moderate exercise suggest that it's all about the "moderation factor." Those who practice moderation in their exercise are also most likely to practice moderation in all other aspects of their lives, health habits and diet.
If 30 minutes at a low intensity of exercise burns 200 calories, about 100 of those come from fat. If you exercise for 30 minutes at twice the intensity, you may burn 400 calories, with 160 of them coming from fat. You still burn fat when working out at a higher intensity and during the hours after your high-intensity workout, you continue to burn calories at a higher rate because your metabolic rate continues to stay elevated.(UCB, Wellness Letter)
Exercise can be measured in calories, minutes, or miles per week. A study that followed Harvard alumni for decades, suggests that the key to heart health and decreased mortality rates is to "burn a fair number of calories." This research supports burning 1,500 calories per week regardless of its intensity.
Training 15 hours a week for a marathon won't keep you "healthier" than five hours of aerobic exercise a week. Exercise with greater intensity has a greater opportunity for wear and tear on a person's joints, overuse injuries, injuries and other problems; therefore it's not the best option for many people.
The best guidelines come from the American College of Sports Medicine and the American Heart Association. Their advice is that healthy people do moderate-intensity aerobic exercise for at least 150 minutes a week (30 minutes, 5 days a week); or you can do vigorous aerobic exercise for at least 75-minutes a week; or a combination of moderate and vigorous activities.
On average, one minute of vigorous activity is considered equivalent to two minutes of moderate activity. "Up to a point, the more exercise you do each week, the greater the benefits, especially for weight loss."
Moderate exercise means working hard enough that you raise your heart rate, break a sweat, yet you are still able to carry on a conversation. Vigorous exercise increases the heart rate and sweating even more and it would be hard to hold a continuous conversation.
Lower-intensity exercise does have its advantages. People are often more willing and able to do it and stick with it. There's less chance of injury. It does promote weight loss, given that you do the exercise for longer amounts of time.
The bottom line is that you should exercise most or all days of the week and work up to more strenuous activities, if possible. Any exercise is good and consistency is the overall key to long term function and health. If you have a choice and want to do the best with your exercise time then "increased intensity" is the better way to lose weight and affect your health.