The traditional approach

The traditional approach to a ‘fat burning session’ is to work at relatively low work intensities, normally in the range of  65-75% of maximum heart rate (e.g. In an individual with a max heart rate of 200 it would equate to 130-152bpm). The science behind this recommendation is simple; Fat is mortified by the prospect of high intensity effort! Fats oxidation (burning) rate is fairly low in comparison to carbohydrate, this means it simply can’t be oxidised fast enough to supply the required energy. Think of it as a deficit between supply and demand, whereby fat simply cant keep up with the demand of energy from muscles.  There are numerous scientific studies around to back this up, many quite rightly indicating that the maximum rate of fat oxidation (burning) is achieved at low intensities of exercise, e.g. a brisk walk, or leisurely paced bike ride. As the exercise intensity increases beyond 75% of max heart rate fat takes a back seat, as more and more energy is derived from carbohydrate. So you can begin to see that the recommendation made by many an instructor/friend to train at low intensities (for optimal fat burning) seems to be founded upon on a good body of scientific evidence. Or does it? Lets take a much closer look at the fat loss process!

Energy expenditure and intensity leads the way!

Though science would seem to support the softly softly approach to fat loss, in essence it’s a skewed interpretation of the fat loss process. In reality, you can lose significantly more body fat by exercising at higher than the traditionally excepted ‘fat burning’ intensities (65-75% max heart rate). It seems the most important factor in fat loss orientated exercise is actually the total amount of calories expended rather than the type of calories used. Confused? Have a look at the example below.

The graph above shows that in this example, exercising for 60 min at low intensities used 270kcal. Because it was low intensity exercise, up to 60% fat is used for energy (which equates to 160kcal of fat). In the high intensity option 680kcal was used. Because it was high intensity, a smaller proportion of energy is derived from fat, e.g. only 40% fat used for energy. However, though only 40% of energy came from fat, 40% of 680 still works out at 270 fat kcal’s. This is actually an increase of 110 fat kcal’s over the low intensity option! So you can begin to see that although training at low intensities (65-75% max heart rate) uses proportionately more fat, the total amount of fat used is often low.

The good news about the high intensity exercise option is that the benefits don’t just stop there! First, total energy expenditure is always greater with the high intensity option (in comparison with same time period but at lower intensity). Of course, no body can argue with the basics of energy balance: Energy in vs energy out. Greater energy expenditure can only aid fat loss, not hinder it.

Secondly, when ever you pass from aerobic to anaerobic metabolism (achieved only at high intensities: around 80-85% max heart rate) and sustain anaerobic activity for 10 or more minutes, growth hormone is stimulated to be released. Growth hormone is your friend! Not only does this hormone help to build muscle but it also aids in the mobilisation of fat, meaning fat is more likely to be used for energy during training and also to provide energy for the recovery process. Lastly, placing significant physical exertion on the body causes a change in brain chemistry. Neuropeptides such as endorphins are released, which if released in significant quantities really can leave you on a euphoric high. Experiencing a post exercise high can make you feel more positive about yourself and so making it easier to go for the right dietary choices.  Of course knowing that you can achieve this wonderful high from exercise should motivate you to get going with your next session!

So in summary, the next time you have 60min to spare on cardio go for the higher intensity option, you’ll not only lose more body fat but also finish the session on a high, try it today!

Note: This method of training is contraindicated for those with a pre-existing cardiovascular related medical condition. Always consult with your G.P before embarking on a new training regime.