Resistance training builds muscle, but aerobic exercise is the real calorie burner, right? That’s what many people believe. However, a new study finds resistance training burns more calories than expected, and the overall calorie burn may trump the calories you burn during an aerobic workout. However, the calories you burn after a resistance workout aren’t as easy to measure by a Fit Bit. Rather, they’re reflected in the hormonal response to weight training and the additional calories your body expends once the workout is over. That’s the conclusion researchers at Auckland University reached when they compared the calorie expenditure and hormonal responses to aerobic exercise and resistance training.
What the Study Shows about Resistance Training and Calorie Burn
In this study, published in the Journal of Science and Medicine in Sport, researchers looked at the levels of growth hormone in subject subjects after they completed a resistance training workout and after an aerobic session. The participants who resistance trained used lighter weights and high reps similar to a workout that people do in a Body Pump class. In contrast, the other group did a moderate-intensity cardio session on a bicycle. The workouts were adjusted so that each required a similar energy expenditure. Afterward, the researchers measured the growth hormone levels of the participants. The results? The subjects who resistance trained had 56% higher levels of this anabolic hormone. They also had a lactate level that was 80% higher relative to the aerobic group.
Why are the higher growth hormone and lactate important? The resistance training workout, despite using light weights and high reps placed enough stress on the working muscles that they were forced to tap into anaerobic energy pathways to make enough ATP to fuel muscle contractions. The normal energy pathways that use oxygen to make ATP couldn’t fulfill the demand because of the intense nature of the exercise. This also happens when you do high-intensity exercise such as sprinting. Under conditions where aerobic or oxygen requiring pathways can’t supply enough energy, your body converts pyruvate to lactate instead of glucose, as it would when enough oxygen is around. Your muscles can then use lactate as an alternative source of fuel.
Under resting conditions, you have around 2 mmol/L of lactate in your blood, but if you engage an intense workout, your blood lactate level could rise as high as 20 mmol/L. The build-up happens when your body can’t clear lactate from the bloodstream as fast it accumulates during intense exercise. But then there’s the payback. The time during which your muscles make and use lactate creates an oxygen debt that your body must repay once the exercise is over. It’s the oxygen debt that accounts for the extra calories you burn after you put down the weights and recover. To repay that oxygen debt, you breathe harder and your body expends more effort and energy to lower your body temperature back to normal and restore a healthy, resting pH. In fact, you’re familiar with the concept of the afterburn, which is when your body works harder to get back an oxygen debt incurred from generating and using lactate as fuel during intense exercise.
Therefore, the afterburn, corresponding to the oxygen debt, increases the number of calories you burn after a workout. Most calorie monitoring devices, like Fit Bits, don’t take this into account. When you look at your Fit Bit and see you’ve burned 150 calories during a resistance training session, it isn’t the full story. You continue to burn calories for hours after you’ve done your recovery stretches. It also doesn’t take into account the afterburn and hormonal changes that take place after that training session. It’s not just the calories you burn during exercise but the number you burn during and after a workout.
The Power of Growth Hormone
As the study showed, growth hormone levels rose more after the resistance session than after the moderate-intensity cardio workout. Growth hormone is an anabolic hormone that also boosts fat burning. Growth hormone reduces body fat by acting on enzymes that regulate fat storage. So, higher levels of growth hormone can be a boon to fat loss. In addition, resistance training helps build more muscle tissue and muscle is more metabolically active than fat. You burn more total calories per day when you have more muscle on your frame, although the amount is modest.
However, growth hormone might not be as much of a boon for weight loss as it seems at first glance. Brazilian researchers discovered that growth hormone also acts on the brain to help conserve energy during periods of weight loss or starvation. The researchers found that when people lose weight, growth hormone levels rise. Through an action in the brain similar to leptin, the rise in growth hormone in response to calorie restriction increases appetite and the urge to eat. This could work against you if you’re trying to lose weight. Therefore, boosting growth hormone through resistance exercise or high-intensity energy training may not, by itself, lead to fat loss. The key is to control your calorie intake too. Nutrition is 80% of achieving and maintaining ideal body weight.
The Bottom Line
To say that moderate-intensity exercise burns more calories than resistance training only takes into account what happens while you’re working out. Resistance training gives a greater afterburn. The heavier and more intensely you train, the greater the afterburn should be. Plus, it creates a different hormonal environment. For example, growth hormone increases after a resistance workout. These impact your total calorie burn as well and won’t be recorded by your fitness tracker.
The take-home message? Don’t assume aerobic exercise is your best approach to losing weight. A balanced combination of aerobic exercise and resistance training will serve you best. You can even throw some high-intensity interval workouts into the mix as they too should leave you with an afterburn. Keep your workouts varied and balanced. You’ll maximize your benefits that way!
- UCHealth Sports Medicine. “Lactate Profile”
- com. “Growth hormone acts to prevent weight loss”
- com. “When It Comes to Cardio vs Resistance Training New Research Shows, You Can’t Judge the Calorie Burn by Its Number”
- Journal of Science and Medicine in Sport. October 2018Volume 21, Issue 10, Pages 1085–1089.
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