Fuel For Exercise We use both fat and carbohydrates for energy while exercise. During exercise at a very low intensity (e.g., walking or jogging), fat accounts for most of the energy expenditure. As exercise intensity increases up to the lactate threshold (the exercise intensity that marks the transition between exercise that is almost purely aerobic and exercise that includes a significant anaerobic contribution; also considered the highest sustainable aerobic intensity), the contribution from fat decreases while the contribution from carbohydrates increases. When exercising just below the lactate threshold, you are using mostly carbohydrates. Once the intensity of exercise has risen above the lactate threshold, carbohydrates become the only fuel source. If you exercise long enough (2 hours), your muscle carbohydrate (glycogen) content and blood glucose concentration become low. This metabolic state presents a threat to the muscles’ survival, since carbohydrates are muscles’ preferred fuel. When carbohydrates are not available, the muscles are forced to rely on fat as fuel. Since more fat is used at low exercise intensities, people often assume that low-intensity exercise is best for burning fat. However, while only a small amount of fat is used when exercising just below the lactate threshold, the rate of caloric expenditure and the total number of calories expended are much greater than they are when exercising at a lower intensity, so the total amount of fat used is also greater.
Posted on: Sat, 07 Sep 2013 01:22:37 +0000
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