Theoretically, weight loss simply involves eating fewer calories than you are expending. However, the number of calories you burn remains affected by the intensity of exercise -- or how hard you are working -- and the duration of the activity. Although higher-intensity exercise burns more calories per minute than lower-intensity exercise, it does not necessarily mean that exercising at a high intensity will make you lose weight faster.
The Research
Several studies have examined the effect of exercise intensity on weight loss. A 2003 study published in the "Journal of the American Medical Association" divided 184 sedentary women into four groups of varying intensity and duration. All four groups experienced significant weight loss, but there was no significant difference between groups despite the different intensities.
Another study published in 2004 in the "Archives of Internal Medicine" compared the weight loss of 120 sedentary men and women divided into three groups of varying intensities and one control group. This time, the people in the high-intensity and long-duration group experienced significant weight loss while the other groups did not. Since the high-intensity, short-duration group did not share the weight loss of the high-intensity, long-duration group, it appears that duration is more important than intensity in degree of weight loss.
An Inverse Relationship
Exercise intensity and duration have an inverse relationship. The harder you exercise, the shorter the amount of time you can sustain that intensity, while exercising at an easier intensity allows you to exercise for a much longer duration. Since increasing intensity results in a decrease in duration and since the 2004 "Archives of Internal Medicine" study found that duration is more important than intensity for weight loss, it is probably better to focus on exercising for a longer period of time than at a high intensity.
Adherence
Another reason that exercising at high intensity may not assist you in losing weight faster is that exercising hard is, plain and simple, no fun. It can be difficult and even painful, and you may find yourself dreading your workouts. Adhering to a regular exercise program at a moderate intensity will help you reach your weight-loss goals much faster than a gut-busting workout once a week.
Safety Concerns
There are safety concerns involved with exercise at a high intensity. The harder you work out, the higher your heart rate and blood pressure become. If you are overweight and/or sedentary, you are already at an increased risk for heart disease. Unless your doctor has examined you and cleared you for vigorous-intensity exercise, you should not exercise at higher than a moderate intensity for safety reasons.
References
- "Archives of Internal Medicine"; Effects of the Amount of Exercise on Body Weight, Body Composition, and Measures of Central Obesity; Chris A Slentz; Jan. 2004
- "Journal of the American Medical Association"; Effect of Exercise Duration and Intensity on Weight Loss in Overweight, Sedentary Women; John M Jakicic; 2003
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