The sources of energy you use when performing exercise varies depending on the intensity it is performed at. At low intensity (easy pace) your body should convert energy or fuel predominantly from fat stores and at high intensity from carbohydrates (stored as glycogen in the body). Your body can convert energy quicker from carbohydrates than from fats. Hence, as intensity increases the continuum of fuel source will switch to carbohydrates to provide the muscles with the fuel they require quickly. When there is a demand for quick energy, carbohydrates are the preferred fuel source.
The fuel continuum is important to understand because at different intensities you will burn more or less fat even if the overall calorie expenditure is greater. The second diagram illustrates this by showing how many grams of fat are ‘burnt’ verses overall calories ‘burnt’ at different intensity levels. At 25 percent VO2max the total calories expended is approximately 250kcal per hour with 24g of fat utilised. Whereas, at 85 percent VO2max with a total calorie expendature of approximately 1,000kcal, only 23g of fat were utilised for fuel. This is a great illustration of how ‘total calories out’ doesn’t necessarily equal fat loss and that the conventional wisdom of ‘eat less vs do more’ is not the total picture for fat loss.
The popularity of HIIT training has developed because it requires less time and can deliver great results. The real benefits of HIIT training are the fact that it releases beneficial fat burning and muscle building hormones. HIIT helps create muscle, ‘burns’ a good amount of calories, continues to burn calories after exercise (through thermoregulation), and elicits beneficial fat burning hormones all in a shorter period of time. Not everyone has one to two hours a day to exercise, so HIIT is the great answer to this because studies have shown that as little as 10 minutes of HIIT can give you great fat burning benefits.
The Right Intensity
SSC needs to be performed at an intensity that meets your goals. Low intensity SSC is great for training your body to be an efficient fat burning machine, and is an important part of a healthy existence. To burn fat you need to train your body to use fat at low intensities. If you always train at high intensities you are training your internal systems to use a high percentage of carbs at rest. In addition, if you consume a lot of starchy carbs and simple sugars you are also training your internal system to predominantly use carbs for fuel. Therefore, your body will not burn optimal amounts of fat even at rest when there is no requirement for quick energy.
The basic truth is that we need to move. Where people go wrong is with the intensity at which they exercise. As you can see from the charts, if you are exercising using SSC you need to choose your intensity wisely. SSC does not produce the beneficial fat burning hormones that HIIT does and you need more time to complete workouts.
My advice is to incorporate both HIIT and LSD into your schedule to maximise health, fitness and weight management. You need to train smarter by matching your intensity to the training goal and eliciting beneficial fat burning hormones.