High-intensity exercise is growing in popularity. In fact, high-intensity interval training topped the list of fitness trends for 2013. No wonder. It’s more stimulating than moderate-intensity, steady-state exercise. There’s something mind-numbing about hopping on an elliptical machine or treadmill and working out at the same monotonous pace for 45 minutes. According to a study published in the Journal of Sports Sciences, high-intensity exercise was deemed by participants to be more enjoyable. Plus, high-intensity exercise enhances both your aerobic and anaerobic energy systems. Thereby it improves your overall fitness level. But what about fat burning? Is high-intensity exercise more effective for fat loss?
High-Intensity Exercise for Fat Loss
Research published in the Journal of Obesity showed steady-state aerobic exercise has minimal benefits on fat loss compared to high-intensity workouts. Don’t give up steady-state exercise just yet. Not all research supports this idea. Other studies show moderate-intensity exercise is equally effective for fat loss. In fact, two well-conducted studies published in the Journal of the Medical Association and the Women’s Health Initiative study found moderate-intensity exercise was as effective as vigorous exercise for weight loss in previously sedentary women.
From this, you might conclude both forms of exercise are equally effective if you’re trying to lose body fat. Not necessarily. Most studies showing moderate-intensity exercise to be equivalent to high-intensity exercise for fat loss were carried out on previously sedentary overweight or obese subjects. That doesn’t necessarily hold true for people who are already in good shape. If you’re aerobically conditioned, moderate-intensity exercise is less likely to have the same fat-loss benefits as it does for an unfit person. It’s well-known that your body adapts to steady-state exercise over time. This means you expend less energy while you’re doing it.
The Benefits of High-Intensity Exercise for Fat Loss
There are a number of reasons high-intensity exercise may be better for fat loss. When you work out at a vigorous pace, you get a greater release of hormones including catecholamines like norepinephrine and epinephrine that help you burn fat as well as growth hormone, another hormone that boosts fat loss. Moderate-intensity exercise is linked with smaller increases in catecholamines. Why is this important? Norepinephrine and epinephrine (also known as adrenal) help you mobilize fat stores so they can be used for energy. Growth hormone levels also increase more with high-intensity exercise.
High-intensity gives a greater “after-burn” compared to moderate-intensity exercise. After-burn is another term for EPOC (excess post-exercise oxygen consumption). This refers to the fact that unlike moderate-intensity exercise high-intensity exercise taps into your anaerobic energy systems. This creates an oxygen debt that has to be compensated for after you finish your kick-butt workout. As a result, you have to take in more oxygen during the recovery period to bring your system back to equilibrium. Your body also has to work harder to replenish fuel stores it tapped into during your exercise session.
Plus, high-intensity increases core body temperature more and it comes down more slowly than with steady-state exercise. This keeps your metabolism higher during the recovery period. All in all, your body has to work harder to recover from an intense workout and it needs more fuel to do this. It gets this fuel by tapping into fat stores. Steady-state exercise of longer duration may burn more calories and fat while you’re doing it but it doesn’t take into account the greater after-burn benefits of high-intensity exercise. Think about how you feel after doing a high-intensity exercise session versus steady-state exercise. Which overheats you more and for longer?
There’s another way high-intensity exercise primes you for fat loss. In one study, researchers found that seven sessions of high-intensity exercise over a 14 day period enhanced fat-burning capabilities in women who were already moderately active. It seems to increase the activity of enzymes that mobilize and oxidize fat.
High-intensity exercise also improves insulin sensitivity, the ability of your cells to respond to insulin. When your cells are more sensitive to insulin, your pancreas doesn’t have to produce as much of this essential hormone. That’s a good thing since insulin prevents fat breakdown and makes it easier for your body to store fat. That’s not really what you want if you’re trying to get leaner.
Abdominal Fat Loss, Appetite and High-Intensity Exercise
Some research shows high-intensity exercise is superior to moderate-intensity exercise for abdominal fat loss. Reducing belly fat, especially visceral fat is important not just for body composition but for overall health. Visceral fat has been linked with a greater risk for health problems like type 2 diabetes and heart disease.
Finally, at least in rats, vigorous workouts have an appetite-suppressing effect. This also holds true in some human studies, although the effects are shorter term. In rats, high-intensity exercise increases the release of a protein called CRF (corticotropin-releasing factor) that decreases appetite.
The Bottom Line?
Research looking at high-intensity exercise versus moderate-intensity exercise for fat loss is mixed. A number of studies do show high-intensity exercise is more effective, especially for abdominal fat loss. Some of the ones that don’t support this idea were carried out on previously sedentary and overweight individuals. All in all, there’s a place for both high-intensity interval training and moderate-intensity exercise in your fitness plan – and even low-intensity workouts for recovery. Doing varied types of workouts and changing things up regularly makes exercise more interesting and keeps you on your toes! It also can help you avoid reaching a plateau. Regardless of your goals, high-intensity exercise can make your workouts more efficient, effective, challenging and fun.
References:
J. Obes. 2011. “High-Intensity Intermittent Exercise and Fat Loss”
Nutrition, Metabolism and Cardiovascular Diseases. Volume 23, Issue 11, November 2013, Pages 1037-1042.
Medscape Family Medicine. “Moderate Intensity Exercise Effective for Weight Loss”
JAMA. 2003;290:1323-1330, 1377-1379.
Medscape Family Medicine. “Effect of Exercise Training Intensity on Abdominal Visceral Fat and Body Composition”
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