Energy, in either case, must be supplied from one of two sources. Sources of energy during sport come from fat that is stored throughout the body or from carbohydrates that have been recently stored in the muscles.
Energy from Carbohydrates
If you are doing a high intensity workout, or playing a high intensity sport, your body will automatically adjust to burn more carbohydrate as energy. It still burns fat as well, however – it is just that it burns more carbohydrate during this time. If you’ve ever wondered why you tire out faster during a high intensity workout, it is because the source of energy – carbohydrates – is used up rather quickly.
Energy from Fat
Although fat gets burned during high intensity exercise, more fat actually gets burned in relation to the amount of carbohydrate that the body is using during low intensity workouts. Just as high intensity workouts or sports can only be endured for short periods of time, because we have a great deal more fat stored in the body, low intensity workouts and sports can last much longer, and we very seldom run out of this energy source.
How Much Fat and Carbohydrate is being Used During Sport?
Exercise intensity is measured by your heart rate. The higher the heart rate is, the more intense the sport is, and this intensity determines which energy source your body is using. If your heart rate is 65 to 70 the energy being used is about 40 percent carbohydrate and 60 percent fat. If your heart rate is 100, on the other hand, you are burning pure carbohydrate and no fat. The higher the heart rate goes, the more carbohydrate you are burning, and the less fat you are burning.
If you are attempting to burn off fat, as opposed to carbohydrate, it is important to realize this, and to workout or play a sport in such a way that your heart rate remains lower. It is also important to understand that the oxidation rate of either fat or carbohydrate matters a great deal when it comes to your metabolism.
There is a very complex mathematical formula to determine this, but overall, if you pay attention to the heart rate, you can be sure that you are burning the energy source that you most prefer to use.