Many athletes and exercisers strive to reduce their body fat and improve their body composition. By identifying the intensity of exercise that elicits the highest fat burning, we can selectively choose activities and create dramatic changes and improvements in our bodies.
Long-duration high-intensity training
There are two key figures we need to keep an eye on:
- Fatmax – Exercise intensity at which fat burning is at its highest
- Fatmax zone – The frequency of exercise intensity where fat burning remains within 10% of Fatmax
Researchers from Birmingham attempted, with the help of a study of 18 endurance cyclists with at least 1 year of training experience, to determine the exact exercise intensity at which fat burning is maximized. The results showed that the Fatmax zone is between 68-79% of maximum heart rate.
Other research has shown that when cycling, swimming, rowing, or running at a moderate intensity of just 50% VO2max (about 69% of maximum heart rate), fat provides you with about half of the calories you need to continue for the first hour. After two hours at the same intensity, fat provides you with around 70% of your total energy after 80% or more if the activity lasts closer to three hours. If you then increase the intensity to 75% VO2max, the fat supply decreases to 33% of your energy consumption.
High-intensity training – just as good!
The conclusion of all this research is that if you want to burn the maximum amount of fat, you should train in the zone between 68-79% of your maximum heart rate. The truth is that if you train at a higher intensity, you can burn just as much. If you cycle at 50% VO2max, fat contributes an average of 50% of the energy you need to continue. If you cycle at 75% VO2max, fat contributes 33% of the calories required. So slower training sounds better from a fat burning perspective – right? An average athlete training at 50% VO2max generally consumes about 220 calories during a 30-minute training session. If the same athlete trains at 75% VO2max, they will burn
330 calories during the same period. This means that 50% of 220 calories and 33% of 330 calories provide exactly the same proportion of calories from fat – 110 calories.
Fat as the sole source of energy
Let's consider one of the extremes. If fat alone accounted for your entire energy needs, you would not break down carbohydrates during exercise. The result of this would be that your leg muscles would be constantly stuffed with glycogen (assuming your diet contains a normal amount of carbohydrates).
Every time you eat, the carbohydrates you consume are processed and transported to your muscles. Your muscle cells would say, "No thanks, I don't need any more carbohydrates, I'm already full." The excess carbohydrates from your target food would then be converted into fat. A win-lose situation – as fast as you burn fat, it is replaced with new fat.
Effective ways to lose fat
Most exercises and training sessions are somewhat time-limited, and we rarely have time to spend hours on low-intensity training. When time is limited, there is little or no reason to train in your Fatmax Zone. If your overall goal is to become slimmer, calorie burning is the key to success. The most effective way to lose body fat is to burn slightly more calories than you eat and to maintain this negative energy balance over a longer period of time.