When Ellen Zwiefel started putting on weight after the birth of her second child, she did what a lot of people do: She tried to run it off. Four or five times a week, she laced up her running shoes and ran five miles, nonstop. But the scale refused to budge. Figuring she wasn’t doing enough, Zwiefel, 44, started attending regular cycling classes and doing additional workouts on cardio machines. Months of heroic effort, however, did little to reshape her body. “Nothing was working,” she says. “I thought my metabolism had just slowed down and that I’d never be able to lose the weight.”
But rather than give up, Zwiefel sought help. Under the guidance of Jason Stella, NASM-PES, CES, head of training at Life Time Fitness in Chanhassen, Minn., Zwiefel took up a strength-building program. Instead of low-intensity, repetitive exercise sessions on treadmills and ellipticals, she began doing shorter, more intense workouts with weights that were never the same from one day to the next.
Four months later, Zwiefel’s shoulders, arms and abs had the sculpted, athletic look she’d always wanted. Better yet, 15 pounds had melted off, and her body fat percentage was 7.5 points lower. Friends started asking her how she’d pulled it off. “Strength training made all the difference in the world,” she says.
Many gym-goers — and even some health and fitness professionals — still believe that strength training is only for people who want to gain weight in the form of shirt-stretching muscles, and that long-duration exercise like running and cycling is the fastest way to lose fat. In-the-know trainers like Stella, however, believe otherwise.
Both their real-life experience and the latest fitness research suggest that low- to moderate-intensity aerobic exercise, while beneficial, is not the fastest route to leanness and overall health that many people believe it is. The real key to fat loss is high-intensity exercise, especially strength training — with real weights, real sweat and real effort.
The results may have little to do with what the scale tells you. Your weight may go down, stay the same, or even go up a bit. Your shape, however, will change dramatically, says Stella. “I always ask my clients, ‘Do you want to hit a number on the scale, or do you want to be leaner, more athletic, and able to fit into your clothes better, even if you weigh a little more?’ For most people, it’s no contest.”
Muscles and Metabolism
Aerobic activity is great for your heart and lungs. For many, it can be a meditative way to clear the mind, blow off stress and get in touch with nature. For others, it’s a challenging and invigorating competitive sport. But as a tool for getting leaner, aerobic exercise by itself is a mediocre strategy.
Here’s the problem: To lose weight, you must burn more calories than you eat. Stay in a calorie-deprived state long enough, and your body begins to burn through its own tissues for fuel. Presto! The number on the scale goes down. You can make that number drop through aerobic exercise and calorie restriction. But what most bathroom scales won’t tell you is how much of the weight you lose is in the form of fat, and how much of it is muscle. And losing muscle mass can sabotage your weight-loss efforts.
Muscle contraction is a primary engine of fat loss, explains Stella: The more muscle mass you have to contract, the more calories you can burn. In addition, strength-training workouts that take large muscle groups to a state of burn will increase the release of hormones that aid in reducing body fat. So anyone who wants to lose fat should make every effort to hang on to, and even gain, as much lean muscle mass as possible.
The best way to do that is resistance training, which will help you hold on to your muscle tissue while you lose fat. You might even gain some muscle while you’re restricting your calories, as long as you’re getting enough protein. (Stella recommends a gram of protein per pound of lean body weight per day, which requires an individual to know his or her body fat percentage.) In turn, this extra muscle keeps your metabolism humming, even as restricted food intake threatens to slow it down.
The Fat-Burning Machine
Numerous studies have demonstrated conclusively that strength training, in conjunction with good nutrition, burns fat much more effectively than dieting alone and dieting in conjunction with aerobic exercise. What no study has shown yet is exactly how.
This much is known: Aerobic activity burns fat while you’re exercising, but anaerobic (meaning without oxygen) activity burns fat in the minutes, hours and days following exercise, as your body recovers from your workout. Compare the energy costs of the two activities during a workout session, as many studies have done in the past, and aerobic activity appears to burn more fat, which may explain why many health and fitness professionals still recommend it.
But if you add up the fat burned by the two activities during and after exercise — including what’s burned between sets during the workout itself — anaerobic activity comes out ahead. Way ahead.
Several factors contribute to this. An exerciser consumes additional oxygen in the hours and days following a strength-training session (a phenomenon known as excess post-exercise oxygen consumption, or EPOC), and that accounts for some of the difference. Simply put, you burn more calories and keep your metabolism elevated when you use more oxygen. The muscles of a strength-trained athlete also remain slightly contracted (meaning they’re still firing) for several hours after working out, which adds fuel to the metabolic furnace. And it’s likely that the fat-burning effect of an anaerobic workout is cumulative, so that with each successive set, you burn incrementally more fat, leading to a kind of fat-burning jackpot at the end of your workout.
But, as with many questions in the relatively young field of exercise science, a complete answer remains elusive. “The truth,” says Christopher Scott, PhD, associate professor at the University of Southern Maine and an expert in metabolism, “is that we don’t have a valid way of measuring anaerobic energy expenditure.”
Absent a full explanation, experts like Alwyn Cosgrove, MS, CSCS, posit that intense anaerobic exercise causes an unusual amount of metabolic perturbation — breakdown in muscle and other tissues — from which the body must scramble to recover.
Cosgrove, co-owner of Results Fitness in Newhall, Calif., and coauthor of The New Rules of Lifting for Life (Avery, 2012), explains that this systemwide disturbance results in a temporary but significant spike in resting metabolic rate. This spike, combined with the large amounts of fat and calories burned by the activity itself, probably accounts for the remarkably high energy expenditure of these types of activity.
You can’t see all the benefits of strength training in the mirror, but you’ll definitely feel them. One reason: Regular, intense resistance training can have a dramatic effect on your endocrine (or hormonal) system, which manages energy, mood and other components of well-being.
Hormones also regulate your body’s immediate and long-term responses to strength training, so they not only help you burn fat and build muscle directly after a workout, but they also make you a more efficient fat-burning, muscle-building machine, 24/7.
Strength training affects dozens of hormones directly or indirectly, but here are a few of the key players:
- Before you even begin your strength-training session, your adrenal glands secrete epinephrine and norepinephrine, which aid in producing more force, blood flow, and the metabolism of sugar and fat. This helps explain why you might start to feel charged up as soon as you lace up your lifting shoes or stroll up to the front desk at the gym: Your adrenals are revving up.
- Heavy strength training stimulates your anabolic (tissue-building) growth hormone and testosterone. Growth hormone boosts your immune system, increases fat metabolism, and promotes growth in your muscles, tendons and ligaments. Testosterone — abundant in men but present in small amounts in women as well — supports muscle growth while boosting mood and energy. Strength training may thus be an effective, natural way to counteract the drop in testosterone (and resulting loss of muscle mass and energy) that tends to occur in men as they age.
- Peptide YY, a digestive hormone stimulated by anaerobic training, can also aid in fat loss by counteracting the effects of ghrelin, a “diet-sabotaging” hormone that can make you hungrier and more likely to store fat when you cut calories.
- Over time, strength training has been shown to lower insulin resistance, a condition associated with type 2 diabetes that limits your ability to access and burn fat cells. The upshot? Your newly insulin-sensitive metabolism burns fat more efficiently.
Different approaches to strength training, from high reps to low reps, heavy weights to light weights, and everything in between, all elicit slightly different responses from your endocrine system. This has led some zealous exercisers to “chase” different hormones with overly rigid workout programs or to seek out sketchy “hormone-boosting” supplements.
But Jonathan Mike, PhD(c), USAW, CSCS, NSCA-CPT, an expert on the hormonal effects of exercise at the University of New Mexico, advises against such strategies. “The actions of the various hormones are interrelated,” he explains. “You can’t raise one without affecting the others, negatively or positively.”
Mike advises clients to stick with a general resistance-training program. (For more on an especially effective fat-burning method, see “Training Tips,” below and the “Rev Up Your Metabolism!” workout.)
The Power of Inefficiency
In addition to biochemical benefits, a progressive strength-training program also keeps you operating at maximal inefficiency. And that’s better than it sounds.
The problem with many repetitive exercise programs is that they require progressively less energy the more you do them. That’s partly because repetition of any activity makes you more efficient: Your body gets better at performing that task. This is especially true if you’ve lost a significant amount of weight. Your body will naturally use less energy to move your new, lower weight. You’ll also expend less energy during low- to moderate-intensity exercise. This enhanced efficiency can be a major impediment if you’re trying to lose weight.
Your best bet, then, is to find ways to make your exercise program more inefficient. With aerobic exercise, you can mix it up: Alternate longer runs, rides or swims with some intermittent training — intervals in which you go hard for a short burst (30 to 60 seconds), then slow down to an easy pace for a minute or two. But it’s even simpler with strength training: Slap some extra weight on the bar, or take some off. Do sets for time instead of stopping at a predetermined number of reps. Adjust your rest time between sets, do your exercises in a different order, or do different exercises altogether, and you have a new set of challenges to which your body has to adapt. Tweak your program regularly, and you can continue improving for as long as you keep up your strength-training efforts.
“Changing things up guarantees inefficiency,” says Lou Schuler, CSCS, coauthor of The New Rules of Lifting for Life. “And that’s what you want when you’re trying to create a metabolic stimulus for fat loss.”
Many people find that the variety and progression inherent in strength training keeps the activity engaging, which is an advantage in itself. But Cosgrove believes that higher-intensity activities may actually burn large amounts of fat in part because they require so much focus and attention, and don’t allow you to simply go through the motions. After all, it’s pretty tough to zone out when you’re holding a loaded barbell over your head. “There may be a cognitive element to effective fat-loss programming that we don’t yet fully understand,” he says.
At some point, says Cosgrove, health and fitness professionals may find out exactly what’s going on cognitively and metabolically, allowing them to devise programs that burn fat even faster. But for now, they aren’t sweating the details — and neither should you. “We’ve been wrong in the past about the mechanism behind it,” he admits. “For all I know, strength training simply summons the gods of fat loss. But we’re not wrong about the fact that it works.”