A Better Way to Burn Fat

If your weight-loss efforts seem stalled or stymied, heart-rate-based interval training may provide just the metabolic boost you need.

It’s not fair, you say: You’re eating right and you’re working out for hours every week, yet your unwanted fat is barely fazed – in fact, it’s just plain ignoring you. What gives?

Well, it could be that you haven’t yet trained your body to burn fat efficiently. Or it could be that you’ve adapted to your current program and, as a result, you’re burning fewer calories than you were a few months ago. Either way, stalled weight loss can be frustrating, but here’s the good news: Using strategic heart-rate training, you can drop those stubborn pounds.

Heart-rate training is a personalized form of cardiovascular training that serves more than weight-loss goals. It establishes optimal exercise intensities – or zones (see right) – based on your unique metabolism, heart rate, current level of fitness, and health or fitness goals.

By strategically working out within these parameters, you encourage your cardiorespiratory system to become stronger and more efficient. This leads to improved athletic performance and a tendency for your body to use stored fat rather than its circulating and stored sugar (glucose and glycogen) for energetic fuel.

The bottom line? Regardless of why you undertake heart-rate training, you’ll probably wind up burning more fat, more easily. And if you’re trying to lose weight, that’s probably especially sweet music to your ears.

Gauge Your Intensity

Whether you run, swim or do step aerobics, you can use your heart rate to personalize your weight-loss program. The idea is to train at the right intensity for the right amount of time. All you need is a heart-rate monitor or a keen sense of your exertion levels. (See “Master Your Monitor” in the October 2005 archives for a guide to heart-rate monitors.)

This approach removes some of the traditional focus on “per-session caloric burn” and instead places it squarely on metabolic fitness. “Heart-rate training changes your physiological structure,” says Kevin Steele, PhD, vice president of research and development at Life Time Fitness. “The goal is to improve cardiorespiratory strength, increase lean body mass and elevate metabolism in the process.”

You’ll first need to determine your anaerobic threshold (AT), the heart rate at which your body transitions from burning primarily fat to using primarily carbohydrates (sugars) for energy. When your body kicks into sugar-burning gear, lactic acid begins to accumulate in the bloodstream faster than you can use it. While this intensity produces a high rate of caloric burn and significant fitness gains, it’s difficult to maintain for long. Happily, you don’t have to.

By simply cycling your intensity up and down (interval training) so that your heart rate repeatedly approaches, crosses and then drops below your AT, you can achieve dramatic fat-burning results, both during exercise and while you’re going about your daily business.

Find Your Happy Place

You can calculate your AT by taking a Metabolic Assessment Profile (MAP) test at your health club, or you can get a general sense of it by referencing the heart-rate-training chart at lifetimefitness.com/heart_rate. (For more on cardio-testing methods, see “Cardio Capacity” in the May 2006 archives.)

The heart-rate training zones are based on your individual AT and form the backbone of your weight-loss program.

Zone 1. Use this warm-up and active recovery zone to begin and end your workout, and when you’re fatigued, sore or overtrained. Your heart rate is 60 to 70 percent of your AT, and you generally burn more fat calories than carbohydrates.

Zone 2. In the aerobic development zone (70 to 90 percent of your AT), you build your aerobic base and efficiency, which improves your overall conditioning and endurance. In this zone, you are typically still burning more calories from fat than carbohydrates.

Zone 3. Just below or at your AT (90 to 100 percent), the aerobic endurance zone is where your body begins to use an equal combination of fat and carbs as a fuel source and creates a higher caloric burn rate. This “hard” zone challenges your cardiovascular system and results in improved endurance and cardio efficiency.

Zone 4. The anaerobic endurance zone (100 to 110 percent of AT) raises your AT and increases your tolerance to lactic acid, training the body to reuse it as an energy source. In this zone, your body primarily uses carbs for energy.

Zone 5. In this zone – the most difficult of all – you pour on effort and intensity for short intervals that challenge your body to reach its full athletic potential. Carbs are nearly the sole fuel source. This level of exertion is extremely difficult to maintain for more than a few minutes (or for the untrained, seconds).

If your primary goal is weight loss, you can apply heart-rate training to your program by initially spending a significant portion of your workout in zones 2 and 3, which help you develop a solid aerobic base. Concentrating your efforts there allows you to exercise harder and longer while burning fat as the primary source of energy.

Once you’ve developed an aerobic base, you’ll begin to exercise at intensities closer to your AT (the boundary which separates zones 3 and 4). You’ll burn a greater number of calories, but more important, you’ll teach your body how to shift between the aerobic and anaerobic energy systems, building your metabolic rate and encouraging your body to burn fat at increasing levels of intensity, thus improving your exercise endurance. (You’ll recognize that you’ve built a solid aerobic base when you can spend time doing cardio exercise without experiencing the high fatigue level you felt when you first started the program.)

From Stalled to Stellar

Caroline Connor, of Shelby Township, Mich., had just about given up on trying to lose weight when she learned about heart-rate training. Connor’s fitness had stalled so much that she started to wonder if her body was actually immune to exercise. As a last resort, she decided to give Life Time Fitness’s O2 heart-rate-training program a try.

Twice a week with a trainer, Connor did group workouts based on her unique AT, exercising primarily in zones 1, 2 and 3. She also did similar workouts on her own twice a week. By the end of the six-week program, the 48-year-old nurse had dropped her body fat from 20 to 18 percent, and lowered her four-mile running time by more than four minutes.

Most people embarking on a heart-rate-training program for the first time see changes in as little as three to four weeks – provided they exercise three to four times per week in the zones appropriate for their current level of fitness. The following changes will be evident in both your cardiovascular and musculature systems:

Cardio. By introducing training stimuli, the heart becomes more efficient at working above its resting heart rate. Translation: It becomes easier to work out harder for longer – thus you burn more calories with greater ease, and in less time. Your resting heart rate also decreases, meaning your heart is capable of pumping the same amount of blood with fewer beats. Ultimately, your cardiac output and efficiency improve.

The key to metabolic-training success, says Steele, is consistency and variety. Working in different zones helps boost your overall fitness level, increasing the range in which your body uses fat for fuel. It also helps maximize the number of calories you burn postworkout and encourages your body to store carbs as quicker-burning glycogen instead of fat.

Musculature. Mitochondria, often referred to as “cellular power plants,” are responsible for burning fat. Regular exercise increases the number of mitochondria in your cells. Thus, increasing mitochondria through exercise helps you burn more fat calories – not only when you’re exercising, but also when you’re at rest. By strategically working out in zones 2, 3 and 4, you can increase your mitochondrial count, build lean muscle mass and increase your metabolic rate, resulting in fat burning that extends hours beyond your workout.

Breaking Through

Running 30 minutes at the same pace every day is great for general health, but over time, this type of repetitive workout is likely to lead to a fitness – and weight-loss – plateau. Heart-rate training helps you cleverly avoid this trap by empowering you to work out at an appropriate and constantly varying level of challenge – one that your unwanted fat can’t possibly ignore.

Fueling Up

If you’re intent on losing weight, there’s one simple fact you can’t ignore, regardless of how effective your training system is: You need to burn more calories than you consume in order to shed pounds. “It’s the opposite of your checkbook,” quips Kevin Steele, PhD, vice president of research and development at Life Time Fitness. “You need to create a deficit every day to lose weight.” But calories should not be your only concern. Choosing a wide variety of whole foods — complex carbs from vegetables, fruits and whole grains; healthy fats from nuts, seeds, fish and olive oil; and high-quality sources of protein — can enhance your body’s utilization of nutrients while minimizing the toxic load many refined and processed foods put on your body. “Good, high-quality fuel is more efficient and effective at everything it does, including supporting exercise,” Steele says. “The cleaner it comes in, the more efficient the digestive process will be, and the faster it will get into the working tissue.” Eating several smaller meals throughout the day (especially breakfast), and having a snack or small meal 30 to 45 minutes postworkout, will also ensure your body receives the nutrition it needs to continue making fitness and weigh-loss strides. —SME

Sheila Mulrooney Eldred is a Minneapolis-based freelance writer.