The myth of the fat burning zone

I’ve been in the fitness industry for more than 15 years, and it amazes me that this topic still exists. But with cardio equipment makers continuing to display low-intensity training as “fat loss” on their monitors and a percentage of personal trainers still prescribing low-intensity cardio as the most effective method for weight loss, it’s no wonder the confusion still exists.

The “fat burning zone” is 50-60 percent of your maximum heart rate. Research has shown that you burn a higher percentage of fat while training at this intensity. People were quick to conclude that this must mean you lose more fat.

The problem with this theory is the most important factor is left out, and that’s the rate of calories being burned. Also, fat is still being used at higher workout intensities and ultimately will result in more fat calories expended overall.

For example, the average exerciser burns about 8 calories a minute while training in the fat burning zone, with about 50 percent of those calories coming from fat.

Compare that with an exerciser working at 70-80 percent of her maximum heart rate (commonly called the cardiovascular zone), where the rate increases to 11 calories a minute on average with about 40 percent of those calories from fat.

The result:

In the fat burning zone (50-60 percent of maximum heart rate):

  • About 50 percent of calories come from fat.
  • About 8 calories per minute are expended.
  • 60 minutes x 8 calories/minute = 480 calories
  • 50 percent x 480 calories = 240 fat calories.

In the cardiovascular zone (70-80 percent of maximum heart rate):

  • About 40 percent of calories come from fat.
  • About 11 calories per minute are expended.
  • 60 minutes x 11 calories/minute = 660 calories
  • 40 percent x 660 calories = 264 fat calories

The cardiovascular zone yields more for both total calories and fat calories burned. And as a bonus, your fitness levels will improve even more. This is key, because the body will begin to burn more fat during and after workouts because the body begins to spare carbohydrates, a process known as “glycogen sparing.” Because carbohydrates are the body’s preferred fuel, and because we have a limited supply, the body naturally begins to use a higher percentage of fat during workouts as our fitness improves.

Also, after intense exercise, the body has to work even harder to restore equilibrium to our body temperature, respiratory rate and hormone levels. This requires high amounts of oxygen, a process known as Excess Post-Exercise Oxygen Consumption (EPOC). With this increased demand for oxygen, more fuel is required from our body during post-workout recovery to achieve homeostasis. And guess what the primary fuel is during this process? FAT!

The take-home message is that there is no magical fat burning zone. For best results, cardiovascular training should include a variety of intensities. While there are countless benefits to training at higher intensities, low-intensity workouts are still important and should be included into your routine, especially if you are just beginning a program. And even an avid exerciser in need of active recovery can benefit from lower intensities a couple of times per week.

TRAINING GUIDELINES FOR OVERALL CARDIOVASCULAR FITNESS

• Structure two to three long and easy-intensity workouts each week. These sessions should be 45 minutes or longer with a target heart rate between 50-70 percent of your maximum.

These workouts should feel comfortable but have you still breaking a sweat. These workouts effectively target your aerobic energy system, which will help develop fat burning enzymes, help maximize recovery, and should be your starting point if you’re just beginning a program.

• Structure one to two moderate-length and -intensity aerobic workouts each week. These sessions should be 30-40 minutes in duration, and the target heart rate should range between 70-80 percent of your maximum. The level of effort in these workouts should be comfortable but challenging.

• Structure one to two short and intense interval workouts into your program each week. These workouts should last between 20–30 minutes with your target heart rate ranging between 80-90 percent of your maximum during work intervals. During these workouts your breathing is heavier and will definitely be above your comfort zone.

CALCULATING TARGET HEART RATE

Step 1: Determine your resting heart rate. This is your heart rate in beats per minute when you are resting. To determine your true resting heart rate, before you get out of bed in the morning, measure your heart rate for one minute. Wait a few minutes after the alarm has gone off, so your heart will recover from being startled. For best accuracy, you should do this three days in a row and take the average.

Step 2: Calculate your heart rate reserve (HRR): 220 – age – resting heart rate (RHR) = HRR

Step 3: Calculate your target heart rate: (HRR x target percentage) + RHR = Target Heart Rate

TARGET ZONES

Zone 1, general health: 50–60 percent of your maximum heart rate.

  •  Lower target heart rate zone = (HRR x 50 percent) + RHR
  •  Upper target heart rate zone = (HRR x 60 percent) + RHR

Zone 2, weight management: 60–70 percent of your maximum heart rate.

  •  Lower target heart rate zone = (HRR x 60 percent) + RHR
  •  Higher target heart rate zone = (HRR x 70 percent) + RHR

Zone 3, aerobic conditioning/weight management: 70–80 percent of your maximum heart rate.

  •  Lower target heart rate zone = (HRR x 70 percent) + RHR
  •  Higher target heart rate zone = (HRR x 80 percent) + RHR

Zone 4, advanced conditioning: 80–90 percent of your maximum heart rate.

  •  Lower target heart rate zone = (HRR x 80 percent) + RHR
  •  Higher target heart rate zone = (HRR x 90 percent) + RHR

Jason Wanlass, the owner of Champion Fitness in Meridian, has more than 15 years’ experience in the fitness industry. Contact him at monsterfit@live.com or www.championfit.net.