The fat burning zone

What does it mean to train in the zone?  Some people getting into the zone is for a long distance run, or maybe a road bike race. Others it may be a after a cup (or three) of coffee and in the office typing away. This zone is more of a mental mindset, but when it comes to the treadmill most people are concerned with the “fat burning zone”.  Anyone that has stepped on a treadmill immediately looks down to check out the chart detailing how hard a person must work to reach the all mighty “fat burning zone” about  60 – 70% of maximum heart rate, consider a moderate work intensity .  Work out at a higher intensity and the individual will go past the fat burning zone and enter the aerobic zone.  The aerobic zone is the intensity that supposedly is best for training the heart.  The higher intensity places a greater challenge on the heart and circulatory system.

 This has led to people training at a moderate intensity for a longer duration to spend more time in the fat burning zone. The science behind this theory is that at moderate work intensity the body releases fat and uses the fat as energy.  So it seems pretty obvious, make my body burn more fat and it will make me lose body fat and look/feel better. However, it is not that easy.

The aerobic zone is classified by 70 – 80% of maximum heart rate; the higher intensity forces the body to start to burn more calories from carbohydrates and less from fat. Although several factors influence this including; sex, diet, and how long you have been training. However, because the body is working at a higher intensity more total energy is being used. If the goal is fat loss the question is, “Should I exercise at an intensity that burns more fat, or at an intensity that makes my heart work harder?”

To test this question researchers at the University of St. Thomas, St Paul , Minnesota tested 36 runners at both intensities. The researchers found that, “If total caloric expenditure is the objective, the upper limits of the aerobic zone will be the most efficient.” Also, it should be noted that the zones overlapped quite a bit. Training at either zone will help to meet the guidelines established by the American College of Sports Medicine for both improved fitness and weight control. Although, if time is an issue, one can work at a higher intensity for a shorter time to burn the same amount of calories. The problem with the “fat loss zone theory” is the body will turn any excess energy; protein, carbohydrates and yes, fat into body fat. The body then must use more energy than  it takes in, regardless the of type of energy. So reducing calories and burning more total calories overall, is the most important issue. The same principle is why low fat diets that don’t reduce total calories won’t work.

An important and usually unrecognized difference between the fat burning zone and the aerobic zone is the energy needed to recover from the higher aerobic exercise intensity. The study,  The body uses energy to repair and recovery, and the more metabolic disturbance the more energy the body uses after the workout.

The take home message is that for most people working at either zone will help met the American College of Sports Medicine guidelines of 2,000 calories of energy expenditure per week. If the goal is fat loss and improved conditioning, it might be beneficial to work at a higher intensity if tolerable.  Regardless, of whether high or moderate intensity it all adds up and all can help improve your health and fitness.  

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