Fat Burning Zone

Many athletes and regular exercisers would love to lose body fat and improve their overall body composition. If we could identify the exercise intensity that evokes the highest rate of fat oxidation, then we could selectively carry out workouts at this intensity and make dramatic improvements to our bodies.

Low intensity sessions to burn off fat

There are two key variables that we need to know:

  1. Fatmax - the exercise intensity at which the highest rate of fat oxidation occurs
  2. Fatmax zone - the range of exercise intensities in which the fat oxidation rates remain within 10% of Fatmax

Research

Researchers from Birmingham University's Human Performance Laboratory attempted to pinpoint the exercise intensities at which fat metabolism is maximised in a study of 18 male endurance cyclists with a training background of at least three years. Their work found that the Fatmax Zone is between 68% and 79% MHR

Alternative research has suggested that when you cycle, swim, row or run at a modest intensity of only 50% VO2max (about 69% MHR), fat provides about 50% of the calories you need to keep going for the first hour or so. If you keep going after that, fat becomes even more generous, providing around 70% of the total energy after two hours and 80% or more if your work duration exceeds three hours. If you increase the intensity then the Fat contribution decreases - at 75% VO2max fat provides 33% of the energy.

High Intensity sessions - just as good!

The implication from all this research is that if you wish to burn maximum amounts of fat then you should train in the 68 to 79% MHR window. The reality is that if you train at higher intensities you can burn just as much fat - you cannot be serious - read on

If you cycled along at 50% VO2max, fat would provide about 50%, on average, of the energy you needed to keep going. If you cycle along at 75% VO2max, fat would provide 33% of the required calories. Thus, the slower workout sounds better from the fat breakdown perspective - or does it?

A moderately fit athlete exercising at 50% VO2max generally consumes about 220 Calories during a 30 minute workout. If the same athlete works out at 75% VO2max, 330 Calories are burned during the same period. Of course, 50% of 220 Calories and 33% of 330 Calories yield an identical number of calories coming from fat - 110 Calories.

Interval work may be the solution

Australian Researchers at the University of New South Wales and the Garvan Institute studied 45 overweight women over a period of 15 weeks. Three times a week the ladies cycled for 20 minutes, sprinting in bursts of 8 seconds followed by 12 seconds of easy cycling.

Professor Steve Boutcher, leader of the team, stated that the women lost 3 times more weight as other women who exercised regularly at a continuous pace for 40 minutes. The women in the study were said to have lost weight mainly from their legs and buttocks.

It is not clear as to how it works but interval training is far more response in getting the body to yield its fat.

Fat provides all your energy

If fat alone was meeting all your energy needs, you would not be breaking down carbohydrate during your workouts and as a result your leg muscles would be amply and permanently stocked with glycogen (assuming, of course, that your diet contained a normal carbohydrate content). Each time you ate, the carbohydrate from your meal would be processed and transported to your muscles. Your muscle cells would say, 'No thanks, I do not need more carbohydrate, I am already full.' The surplus carbohydrate from your meal would be converted to fat. Looks like a no win situation - as fast as you burn fat off it is replaced.

Effective way to lose fat

Most exercisers are time constrained to some degree and do not have hours to spend on low intensity sessions. When time is limited, there is little reason to train in your Fatmax Zone. If your overall goal is to get leaner, the bottom line is that calorie burning is the best way to achieve it.

The most effective way to lose body fat is to burn slightly more calories than you take in, and to continue this negative energy balance over an extended period.

Medium-chain triglycerides (MCT)

MCTs are a class of fatty acids occurring normally in oily foods which require less energy for uptake and storage in the body and are easier to digest and absorb than ordinary fats. Research indicates that the consumption of MCT oil (14-20grm/day - 112-160 calories) could be a useful addition to the diet for athletes trying to loose or maintain body fat. MCT oil is commercially available.

Coconut oil and Palm oil are naturally rich in MCT but they also contain long-chain triglycerides (LCT). Studies have demonstrated a weight loss effect with a MCT/LCT mix - 14grm with a 12% MCT content [Asia Pacific Journal Clinical Nutrition 2003;12(2):151-160].

Related Research Papers

  • Med Sci Sports Exerc 2002; 34(1):92-97
  • Asia Pacific Journal Clinical Nutrition 2003;12(2):151-160

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Associated Pages

The following Sports Coach pages should be read in conjunction with this page:

Associated Books

The following books provide more information related to this topic:

  • Principles of Anatomy and Physiology, G.J. Tortora et al., ISBN 0 06 046704 5
  • Strength Training Anatomy, F. Delavier, ISBN 0 7360 4185 0
  • Atlas of Skeletal Muscles, R.J. Stone et al., ISBN 0 697 13790 2
  • The Muscle Book, P. Blakey, ISBN 1 873017 00 6
  • Advanced Studies in Physical Education and Sport, P Beashel et al., ISBN 0 17 4482345
  • Physical Education and the Study of Sport, B. Davis et al., ISBN 0 7234 31752
  • Essentials of Exercise Physiology, W.D. McArdle et al., ISBN 0 683 30507 7
  • Physical Education and Sport Studies, D. Roscoe et al., ISBN 1 901424 20 0
  • The World of Sport Examined, P. Beashel et al., ISBN 0 17 438719 9
  • Advanced PE for Edexcel, F. Galligan et al., ISBN 0 435 50643 9
  • Examining Physical Education, K. Bizley, ISBN 0 435 50660 9
  • Sport and PE, K Wesson et al., ISBN 0 340 683821
  • PE for you, J. Honeybourne, ISBN 0 7487 3277 2