Muscles and Metabolism

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.