Aerobic exercise burns more calories, so it must be better for fat loss. Right? Not necessarily. Lots of people still think that, which is why you see so many people spending an hour on the treadmill or an elliptical machine. But as a new study suggests, if you’re serious about fat loss, divert more of your workout time into weight training.
According to this study, weight training is MORE effective for fat loss, particularly belly fat loss, than running on a treadmill or working out at a steady pace on an elliptical machine or another piece of cardio equipment. Not to mention, steady-state cardio can be mind-numbingly boring.
What a New Study Shows about Weight Training for Fat Loss
In this study, researchers at Harvard School of Public Health followed more than 10,000 healthy men over the age of 40 for 12 years. The men were part of a larger study called the Health Professionals Follow-Up Study. Over the course of this long-term study, they monitored how much physical activity the participants did and the type along with parameters like their weight and waist size.
As you might expect, guys in the study who were sedentary and spent most of the 12-year period sitting in front of a television or computer screen saw their belly size increase the most. In contrast, those who stepped up their aerobic activity by 20 minutes a day gained significantly less belly fat. However, the real winners were the men who increased their activity by weight training 20 minutes a day. They gained less age-related belly fat than both of the other two groups.
Why might this be? Let’s look at the bigger picture. Although an hour of aerobic exercise, assuming you’re doing it at a moderate intensity, burns more calories than weight training during the time you’re doing it, this doesn’t take into account what happens afterwards.
Assuming you’re pushing against enough resistance when you train, between 60% and 80% of your one-rep max, and doing sufficient volume, you’re turning on fat-burning hormones like growth hormone and testosterone that help you build muscle AND burn belly fat. This means that unless you’re doing high-intensity interval training, you’ll get more of an after-burn effect from weight training in contrast to moderate-intensity aerobics where you get minimal after-burn.
What is the after-burn? It refers to a phenomenon known as excess post-exercise oxygen consumption. After a weight training or HIIT workout, your body has to burn energy to repair itself, replenish fuel stores, and return your body to its baseline, unstressed state. The more you disrupt homeostasis, by stressing your body with weights, the harder your body has to work afterward and the more calories you burn after your workout is over.
More Muscle Tissue Equals More Calories Burned
Another way weight training helps you lose body fat is by the long-term increase in resting metabolism you get when you build more muscle mass. As you know, muscle tissue has higher metabolic requirements than fat, so when you have more of it, you burn more calories throughout the day, regardless of what you’re doing. That’s one of the perks of having more muscle.
You can think of aerobic exercise as a short-term calorie burner and weight training as an investment that pays off with greater calorie burn (and a healthier body composition) over time. Keep in mind, the extra calories you incinerate for each additional pound of extra muscle tissue isn’t large, but it all adds up. There’s a lack of consensus in the literature as to exactly how many calories an extra pound of muscle burns each day. It ranges from 6 calories up to 50, depending on the source you look at.
Improvements in Insulin Sensitivity
Another reason more muscle helps with loss of tummy fat has to do with its effects on insulin sensitivity. Weight training to increase muscle mass causes cells to be more sensitive to insulin, thereby reducing the amount of insulin your pancreas has to produce. When you don’t have as much insulin floating around in your body, you’re less likely to store fat. Bonus: More muscle tissue also lowers your risk for metabolic problems, including metabolic syndrome and type 2 diabetes.
People who have better insulin sensitivity also store less fat around their tummy and waistline. So, more muscle = better insulin sensitivity = less fat storage and lower risk for metabolic issues. As an article on Medscape points out, people who have insulin resistance and type 2 diabetes should focus on weight training to improve insulin sensitivity, not just weight loss. As you age, it’s not enough just to keep fat off, you have to avoid the pitfalls of sarcopenia, age-related loss of muscle tissue that leads to a host of health problems.
How Much of That Weight You’re Losing is Muscle?
Keep in mind, when you use cardio as a weight loss tool, you’re not JUST losing body fat, you’re also losing muscle. That’s why it alone is not an effective tool for long-term weight control. Plus, your body adapts to moderate-intensity cardio fairly quickly. If you enjoy moderate-intensity cardio, don’t give it up, but balance it out with resistance training to help preserve your strength and lean body mass.
You can even work your fast-twitch muscle fibers, the ones you work when you lift heavy weights while getting a cardiovascular workout by doing ballistic movements like plyometrics, kettlebells, or with high-intensity interval training. HIIT training will also give you the after-burn effect that turns your body into a more aggressive calorie burner
The Bottom Line
If you’re doing hours of cardio each week and not seeing results, take a portion of that time and devote it to heavy resistance training. Weight training is what really shapes your body and it also helps with fat loss over time. Make sure your training isn’t too skewed towards aerobics.
Consultant. “Weight Training vs Treadmill: Which Burns More Fat? 1-9-15.
Medscape Family Medicine. “Muscle Mass Linked to Risk for Insulin Resistance”
Am J Clin Nutr. 2006 Sep;84(3):475-82.
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