Mon. Jan 27th, 2020

The Myth of the Fat-Burning Zone

6 min read

By Rachel Cosgrove, USAT Level 1, CSCS

“If you want to lose a few pounds you need to do long, slow, steady-state aerobic exercise in the fat burning zone.”

Heard this advice before? It’s one of the biggest misconceptions in the exercise and weight-loss world. If long, slow, steady-state aerobics was the key to fat loss every person who crosses the finish line of a marathon or Ironman would have very low body fat. This just isn’t the case. Numerous people who train for an endurance event gain weight.

Endurance exercise solely for fat loss does not make sense. Your goal as an endurance athlete is to become efficient and better at running, biking or swimming. A different plan of attack needs to be used to burn fat—a more effective plan.

Reasons Steady-state Aerobic Training is Supposed to Burn Fat

1) It burns calories.
Hard-working muscles demand extra oxygen to help them continue working. However, lots of activities also burn calories by requiring work from the muscles—weight training, sprinting, sleeping—so no extra points for aerobic training.

2) The fat-burning zone.
Yes, it exists, but it has been misinterpreted. The fat-burning zone is a concept that the body burns a greater amount of fat at lower-intensity aerobic exercise than it does at higher intensities. Actually, the body burns a greater percentage of fat at lower intensities than at higher intensities. At lower intensities, the body may burn 50 percent of the calories from fat, while at higher intensities it may only burn 35 percent. But at higher intensities you burn way more total calories—and more fat calories overall—than you do at lower intensities.

3) Aerobic training makes your body an efficient fat-burning machine.
True, but this isn’t a desirable response. Yes, aerobic training does demand work from the muscles, but not as much as other activities, and it doesn’t require the muscle tissue to last, either. Because the only tissue that burns fat in the body is muscle, aerobics are ineffective at building and maintaining your body’s fat-burning tools.

4) Aerobic training raises your metabolism.
This isn’t true. Metabolism is largely a function of how much muscle you carry. Because aerobics do nothing to even maintain muscle, never mind build it, they do not contribute to raising your metabolism while at rest.

The Endurance Athlete’s Adaptation Conundrum

The body adapts to certain circumstances by responding in the reverse manner. Not drinking enough water? Your body tries to retain it. What actually occurs in weight training is a breakdown of muscle tissue, leading the body to adapt by building muscle. When you burn calories doing aerobic training, your body adapts by slowing your metabolism and allowing your body to store more fat. As an endurance athlete, your goal is to become very efficient at aerobic exercise. As it becomes easier for you to perform, you’ll burn fewer calories and lose less weight.

Those who first get into triathlon from, say, a running background often find swimming and biking difficult. They will probably lose some weight initially because their body isn’t used to these activities and is burning greater calories than normal as it exerts more effort. After racing and training for a few years, however, running, biking and swimming will burn much fewer calories then it used to. More calories are burned doing activities the body is not used to.

The work required to run five miles will become less and less as you get fitter. In order to improve, you either go further (do more work for the same amount of calories) or you run those five miles faster. In weight training, as you get better, you add more weight or more reps and there is literally no finish line.

There is an end point, however, with aerobic training. You will eventually reach an intensity that will be the limit of your aerobic zone. Working any harder will send your body into the anaerobic zone, and then you’re no longer doing aerobics.


Your metabolism—or your metabolic rate—is what determines how many calories you burn each day. It is controlled by your thyroid and is largely a factor of muscle mass. Every pound of muscle you put on requires approximately 50 calories per day to maintain. This doesn’t take into account the calories burned developing that muscle, or the calories burned while maintaining that muscle. These 50 calories are the amount needed by that muscle to just sit there.

This equates to 18,250 calories per year, or the equivalent of a little over five pounds of fat. Gaining and maintaining even five pounds of muscle in your training program will assist in burning off over 26 pounds of fat over the course of a year.

Consequently, an athletic physique is not just the result of how many calories burned during exercise, but how many calories the body is forced to burn all the time. Raising your metabolism is the real key to long-term fat loss and body change.

Caloric Expenditure

Fat loss is all about caloric expenditure. You must burn off more calories than you consume to lose body fat. Even among the proliferation of diets—low carb, low fat, high protein—this simple rule remains.

The key to achieving this is not aerobic training, which will burn calories only while you are doing it. It is anaerobic training, which burns calories while you are working out and increases the calories burned for hours afterwards. In the case of weight training, building muscle burns calories, as long as that muscle is retained—even during sleep.

During anaerobic exercise, the body burns a lot of calories. However, the metabolism still remains elevated following a workout. At one time, this was referred to as oxygen debt, but is now known as excess post-exercise oxygen consumption (EPOC). Recovery of the metabolic rate back to pre-exercise levels can require several minutes for light exercise (aerobic training), several hours for very heavy exercise (anaerobic cardio training), and even up to 12 hours or longer for prolonged, exhaustive exercise (interval training or circuit weight training).

The EPOC can add up to a substantial energy expenditure when totaled over the entire period of recovery. If oxygen consumption following exercise remains elevated by an average of only 50 milliliters per minute, and the metabolism remains elevated for five hours, this would amount to an additional expenditure of 75 kilocalories over that time period.

This major source of energy expenditure—which occurs during recovery but is the direct result of exercise—is frequently ignored in most calculations of the energy cost of various activities. Doing the math, if the individual in this example exercised five days a week, he or she would lose the equivalent of approximately 0.1 pounds of fat in one week just from the additional caloric expenditure during the recovery period alone.

Is the effect accumulative? If you trained the next day while your metabolism is still elevated will we have an even higher return? Science has yet to give an answer. However, I have seen amazing results with my clients using this exact protocol.

Interval Training

So, is there a better way of performing cardio workouts to prevent these adaptations and rapidly improve fat loss results? Yes. This is done through interval training.

Interval training refers to a series of intense activity separated by short rest periods. Utilizing interval training will eventually enable you to exercise at a higher overall intensity without getting as tired. This occurs because you alternate periods of high intensity exercise with periods of lower intensity, allowing you to do more work in the same time period than you could before.

The benefits of interval training lie in the fact that as you improve, the work intervals can be made increasingly harder, recovery intervals can be shortened or training can be performed at a higher speed. Like weight training, there is no limit to improvement.

Putting it All Together

In conclusion, endurance athletes to shed a few pounds should substitute the long, slow, steady-state training that is making them more efficient at storing fat with some high-intensity intervals. I recommend starting with five sets of one minute at increased intensity followed by two minutes of recovery. During the one-minute interval, push your limit. In your recovery, take it down to a level where you can carry on a conversation. This workout takes less than 20 minutes and will have your metabolism stoked for burning fat during the rest of the day.

Also include weight training in your schedule to build muscle and keep your metabolism up. Perform a full-body workout twice a week. This should take less than an hour to do and will get your metabolism cranking.

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