Most people new to a gym usually make their way over to a treadmill, then immediately look down to check out the chart detailing how hard they must work to reach the “fat burning zone,” about 60 – 70 percent of maximum heart rate, considered a moderate work intensity .
The fat burning zone has kept many people training at a moderate intensity for a long period of time. The science behind this theory is that at a 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 percent 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. If time is an issue, however, 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 must then use more energy than it takes in, regardless of the type of energy consumed, to lose body fat. So reducing calories and burning more total calories overall is an 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 body uses energy to repair and recover, and the more metabolic disturbance at a higher intensity, 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. Although if the goal is fat loss and improved conditioning, it may be beneficial to work at a higher intensity if tolerable.
Regardless of high or moderate intensity, it all adds up and to improve your health and fitness.
Kyler Crouse, BS, CSCS, FMS is a personal trainer and strength coach who trains at Sierra Athletic Club and in the homes of clients in the greater Lake Tahoe area. Crouse specializes in performance enhancement and injury prevention. Visit www.KCstrength.com for more information.