It would seem that if you’re trying to lose weight, the longer you exercise the better. An hour is better than thirty minutes? Right? Intuitively that would make sense. After all, you’ll burn more calories in 60 minutes than 30 if you maintain the same intensity. But recent research calls this idea into question. Some studies show that exercising for longer periods of time is no more beneficial, and may be less so, than doing a 30-minute workout.
Thirty Minutes versus an Hour: Which is Better?
In a study carried out at the University of Copenhagen, researchers divided 61 overweight, non-exercising men into three groups. One group exercised aerobically at a moderate-intensity 30 minute a day by biking or jogging. A second group worked out at a greater intensity for a full hour each day, burning more overall calories than the first group. A third group, the control group, did no exercise during the course of the 13-week study. During the study, the men were asked not to alter their diet or activity level.
The results? Both groups of men lost weight, but there were some surprises. The men who worked out an hour a day at a higher intensity had an average weight loss of 5 pounds, slightly less than expected based on the number of calories they burned each day through exercise. On the other hand, the men who worked out 30 minutes a day lost 7 pounds on average, significantly more than would be expected. Not surprisingly, the sedentary men lost no weight.
Why Did the Men Who Exercised Less Lose More?
The reason for the greater weight loss in the group of men that exercised 30 minutes isn’t entirely clear, but researchers have some possible explanations. You’ve probably heard of the concept of “set point” where your body compensates for calorie restriction and extreme changes in structured physical activity by motivating you to move around more or by altering your appetite. This is a mechanism to compensate for excess energy expenditure. This is all done at an unconscious level to help you maintain your set point weight.
The researchers in this study propose that the men who exercised for an hour and burned more calories may have compensated by eating more and moving around less when they weren’t exercising. On the other hand, the men who exercised for 30 minutes may not have burned enough calories to trigger this type of “set point” adjustment.
Exercise, Set Points, and Compensation
This raises the question – do we have a set point for exercise? Interestingly, there is research to support this idea. A study showed that women who took part in a 13-week walking program unconsciously reduced their activity when they weren’t walking. Another study showed that kids who participated in a physical fitness program at school were less active at home. These studies all support the idea that we compensate for extreme calorie expenditure by making subtle adjustments in food intake and activity level. There may be a threshold level of exercise that triggers compensation if you exceed it.
What Does This Mean?
It’s hard to draw conclusions based on this study since it involved a group of men that were already overweight and had a low fitness level. The results may be different in physically fit individuals of normal weight. Still, it raises the question of whether doing an hour or more of aerobic exercise a day is a good prescription for weight loss. A better approach might be to do a short, intense cardio session followed by strength-training or a circuit-style workout to simultaneously build strength and stamina rather than a long cardiovascular workout.
As research shows, intense workouts that last as little as ten minutes or even less have cardiovascular benefit and increases levels of fat-burning hormones that trim body fat. When you do long cardiovascular workouts of an hour or more, cortisol levels rise more and you run the risk of breaking down lean body mass, especially if you’re carb-deprived. Then there’s the issue of compensation. After an hour or more of cardio, you may be so exhausted that you sit around the rest of the day – or move only enough to get to the refrigerator to replenish your glycogen stores. That’s not a recipe for successful fat loss.
The solution? Cross-train, integrate strength moves into your cardio session circuit-training style and do short, high-intensity cardio rather than running on a treadmill or cycling for an hour or more. You’ll have the added advantage of building more lean body mass this way. That will work in your favor in terms of body composition.
Regulatory, Integrative and Comparative Physiology, 2012; DOI: 10.1152/ajpregu.00141.2012