Fat burning zone – marvel or myth?
In recent years there has been a lot of discussion about the fat burning zone, the subject of this blog. As most personal trainers will be working with clients who want to lose weight or stabilise their weight, it’s helpful for fitness professionals to have a good understanding of the concept of the fat burning zone – and the critiques.
Fat burning and maximum heart rate
As every personal trainer will know, the body breaks down fat, carbohydrate or protein into glucose for energy, depending on the intensity of the client’s work out and the type/amount of food they have been eating.
When you look on a treadmill, it will often list the fat burning zone at an intensity of anything around 50-75% of maximum heart rate. This is based on the idea that within this zone your body is burning the optimum amount of fat and that if you work any harder than this, you don’t burn any more fat to generate the extra energy, you burn carbohydrate instead, as your body will move to a more efficient source of energy at a higher intensity.
Some fitness trainers will therefore recommend that a client wanting to lose weight should train within this fat burning zone.
Why some personal trainers take issue with the fat burning zone
However, many fitness professionals have questioned the idea of a fat burning zone. The reason is simply that if you work at a higher intensity, you will burn more calories. This is the basis for interval training- also known as metabolic conditioning.
For example, a client running at 65% for one minute may burn around 10 calories, while at 85% it would go up to around 13 calories (see our blog on Using METS to calculate calories burned). There are also arguments that slower training increases appetite while high intensity training depresses appetite, and studies that suggest that subjects can burn more calories in less time with interval training than by remaining in the so-called fat burning zone for the full work out.
For this reason, personal trainers will often devise training programmes that require clients to spend some time working at 50-75% and some time at 80-90%, with recovery periods built in, in order to get the best overall results (see our blogs on How a personal trainer can use interval training and Interval training to motivate a client and progress fitness).
Either way, it can be useful for a client to have their heart rate measured with a heart monitor, so that the personal trainer can get a clear idea of how hard the client is working during any given exercise.
Fitness testing and goals for fat burning
When a personal trainer takes on a new client, they should start by carrying out a fitness and lifestyle test (see our blog on The importance of fitness testing). This will usually include weighing the client, taking some key measurements and running a body fat percentage test (see our blog on Body fat analysis). The fitness trainer may also complete a nutritional analysis.
The personal trainer will also talk to the client about their goals, which may include weight loss. However, they could also discuss body composition: by working out regularly, a client should see an increase in their muscle mass and a decrease in their body fat. Whether or not this is reflected by weight loss seen on the scales, it can lead to a more muscular body and bring benefits such as an increase in strength and improvements to heart and lung performance.
Metabolic training over fat burning
In summary, many personal trainers today will encourage clients to follow high intensity training programmes and complete some metabolic conditioning, rather than focusing on the fat burning zone. This may include interval training and hypertrophy training. High intensity training is recognised as an efficient way of increasing all-round fitness and improving body composition.