By Michael Ormsbee, PhD, Florida State University
Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Research on high-intensity interval training (HIIT) shows that individuals can exercise for a shorter duration, but still lose more fat, gain more muscle, and improve body composition to a greater degree than with a traditional aerobic program. Photo By Syda Productions / Shutterstock
Exercise and RMR
Much research has shown that the combination of high exercise energy expenditure and high energy intake in endurance-trained people can elevate RMR for a short period of time from a few hours all the way up to about 24 hours, but not permanently.
However, there doesn’t seem to be substantial evidence that this elevated resting metabolic rate will occur at all with regular, recreationally active people, though some research has shown benefits in the elderly. The effect of weight training on RMR is complicated.
Weight training may play a large role in total daily energy expenditure—but with one caveat. It is estimated that one pound (lb) of muscle burns between 5–10 calories at rest per day. Thus, if you are thinking of gaining muscle to increase your total daily energy expenditure, you would have to add quite a bit of muscle in order to have any real effect.
Keep in mind, though, the difference between dieting alone versus dieting and exercise. Although it is less common to see someone recreationally lift weights and gain 10 lbs of muscle, it is not uncommon for someone to diet and lose that amount of muscle mass, especially if exercise is not included in their fat-loss plans.
In a scenario like this, with a loss of 10 lbs of muscle, then muscle mass would play a significant role in total daily energy expenditure. If we take an average of seven calories per lbs, this would add up to 700 calories per week. Can you see how easily this would change your energy balance equation?
HIIT Versus Aerobic Exercise
Ultimately, while exercise of almost any intensity and duration certainly carries many health benefits along with it, the effect of recreational endurance exercise or weight lifting is not likely to play a large role in increasing RMR outside of the exercise time itself. Unfortunately, a lot of the magazine and media claims that it will increase RMR don’t hold any water.
Thus, although weight training may play a large role in your total daily energy calorie expenditure, it’s not likely to increase your resting metabolic rate dramatically. What about other forms of exercise—for example, High-Intensity Interval Training, or HIIT?
For those of you who try to lose weight and improve body composition through exercise, it’s likely that you have been told to do aerobic exercise because it’s thought to increase both cardiorespiratory fitness and to help lose weight and fat. Most aerobic exercise interventions consist of moderate-intensity, steady-state exercise, for about 30 to 40 min for three to four days per week, over four to six months of time.
Unfortunately research on these kinds of exercise programs—more often than not—have shown only a minimal fat loss. In contrast, a lot of the research shows that HIIT exercise actually results in significant fat loss.
Now, this may sound counterintuitive because higher intensity exercise burns more carbohydrates—while lower intensity exercise burns more fat. However, the key to body fat manipulation is all about the total amount of calories burned. Luckily, some research has directly compared traditional aerobic exercise to HIIT.
HIIT Exercise Results
Researchers split young women into two groups. One did three, 20-minute HIIT workouts per week on a bike for 15 weeks. The exercise consisted of an eight-second sprint followed by 12 seconds of low-intensity cycling—this continued for 20 minutes.
The other group did aerobic exercise at a moderate pace, three times per week working from just 10 minutes up to 40 minutes over the 15-week study. The most interesting part was that the women in the HIIT group lost 2.5 kg, or 5.5 lbs, of subcutaneous fat, the kind directly underneath your skin, whereas no change in fat occurred with steady state aerobic exercise.
Thus, this study shows that higher intensity exercise may be much more time efficient for weight loss and improvement in body composition. In fact, much of the research regarding HIIT is showing that individuals can exercise for a shorter duration but still lose more fat, gain more muscle, and thus improve body composition and health to a greater degree than they can with a traditional aerobic program.
Peter M. Vishton is Associate Professor of Psychology at William & Mary. He earned his PhD in Psychology and Cognitive Science from Cornell University. Before joining the faculty of William & Mary, he taught at Northwestern University and served as the program director for developmental and learning sciences at the National Science Foundation.