All forms of exercise, whether they're low intensity or high intensity, force your muscles to work. In order to contract your muscles and keep yourself moving, you need an energy source, which is provided in the form of calories from fat and carbohydrates stores in your body. Low-intensity exercises burn fat and carbs, but high-intensity exercises will burn more of both.
Heart Rate Zones
How hard you work during exercise has an effect on your heart rate. The harder you work and the more intense your workout, the faster your heart will beat. A faster heart rate will contribute to an increased metabolism, which translates to more calories burned. Low-intensity exercises, such as jogging, put you in the aerobic heart zone, which is between 50 and 70 percent of your maximum heart rate. You can find your maximum heart rate by subtracting your age from 220. The American Heart Association cautions that this is a general system of measurement. Individual heart rates will vary.
Fat vs. Carbs
Although you burn calories from fat and carbs during exercise of any intensity, how much you burn of each will change based on your effort. At low intensity, you burn more fat relative to carbohydrates, while high-intensity workouts consume more carbs relative to fat. Still, the total number of calories you burn is the only factor in determining weight loss, not the percentage of calories that come from body fat.
Fat Burn Zone Myth
A pervading myth in the fitness industry suggests that, since you burn more fat relative to carbs at lower intensities, these types of exercises are preferable to intense workouts for fat loss. In fact, you burn more calories from both fat and carbs working at a high intensity. To reach this high-intensity calorie burn, you need to jack your heart rate above 80 percent of its maximum. This puts you in the anaerobic zone.
Advantages and Disadvantages
Low-intensity exercises are generally less stressful on your heart and muscles than intense workouts, but there are disadvantages. Not only will you burn more calories during a hard workout than a lighter one, but anaerobic workouts also benefit from an afterburn effect, as your body continues to consume calories at a higher rate post-exercise due to hormones that are released during intense exertion.
- Brian Mac Sports Coach: Heart Rate Training Zones
- Built Lean: The Fat Burning Zone Myth -- Don’t Be Fooled
- National Council on Strength and Fitness: Benefits of Sprint Training vs. Traditional Aerobic Training
- Sydney Morning Herald: Forget the Jog Slog and Fit in a Sprint for Maximum Weight Loss Results
- American Heart Association: Target Heart Rates
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