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 people can train less, but still lose more fat, build more muscle and improve body composition more than with a conventional aerobics program. Photo by Syda Productions / Shutterstock
Exercise and RMR
Many studies have shown that the combination of high kinetic energy consumption and high energy consumption in endurance trained people can increase the RMR for a short period of a few hours up to about 24 hours, but not permanently.
However, there does not appear to be any substantial evidence that this increased resting metabolic rate will even occur in normal, recreational people, although some research has shown that the elderly have benefits. The effect of strength training on RMR is complicated.
Strength training can play a big role in total daily energy expenditure – but with one limitation. It is estimated that one pound (lb) of muscle burns between 5 and 10 calories a day at rest. So if you were thinking of building muscle to increase your total daily energy expenditure, you would need to add quite a bit of muscle to get any real effect.
However, be aware of the difference between dieting alone and diet and exercise. While it is less common for someone to lift weights and gain 10 pounds of muscle in their free time, it is not uncommon for someone to diet and lose that amount of muscle, especially if exercise is not part of their fat loss plans.
In such a scenario, with a 10 pound muscle loss, muscle mass would play a significant role in total daily energy expenditure. If we ate an average of seven calories per pound, that adds up to 700 calories per week. Can you see how easily this would change your energy balance equation?
HIIT versus aerobics
While exercise of almost any intensity and duration is sure to have many health benefits, the effects of recreational endurance training or weightlifting outside of exercise time itself are unlikely to play a major role in increasing your RMR. Unfortunately, many magazines and media outlets claim it will increase the RMR if they hold no water.
While weight training plays a huge role in your daily calorie expenditure, it is unlikely that your resting metabolism will increase dramatically. What about other forms of exercise, such as high-intensity interval training or HIIT?
For those of you trying to lose weight and improve body composition through exercise, you have likely been told to do aerobic exercise as it is designed to improve cardiorespiratory fitness as well as help with weight loss and fat. Most aerobic exercise consists of steady-state, moderate-intensity exercise for about 30 to 40 minutes, three to four days per week for four to six months.
Unfortunately, research on such exercise programs has shown – for the most part – only minimal fat loss. In contrast, a lot of research shows that HIIT training actually leads to significant fat loss.
This may sound counterintuitive because higher-intensity exercises burn more carbohydrates – lower-intensity exercises burn more fat. However, the key to manipulating body fat lies in the total amount of calories burned. Fortunately, some research has compared traditional aerobic exercise directly to HIIT.
HIIT exercise results
The researchers divided young women into two groups. One did three 20-minute HIIT workouts a week on a bike for 15 weeks. The exercise consisted of an eight-second sprint followed by 12 seconds of low-intensity cycling – this lasted 20 minutes.
The other group did aerobic exercise at a moderate pace and worked from just 10 minutes to 40 minutes three times a week during the 15-week study. The most interesting part was that the women in the HIIT group lost 2.5 kg of subcutaneous fat, the kind just under your skin, while there was no fat change when doing aerobic exercise at steady state.
Thus, this study shows that higher intensity training can be much more time efficient to lose weight and improve body composition. In fact, much of the research related to HIIT shows that individuals can exercise for shorter periods of time, but still lose more fat, build more muscle, and thus improve body composition and health to a greater extent than with a traditional aerobic program.
Peter M. Vishton is Associate Professor of Psychology with William & Mary. He holds a PhD in psychology and cognitive science from Cornell University. Prior to joining the faculty at William & Mary, he taught at Northwestern University and was program director for development and learning sciences at the National Science Foundation.