This is a great question that many people ask. It is important to realize that the body has two different fuels it converts to energy: carbohydrates and fats. The body burns these fuels in different proportions depending on your fitness and the intensity of your workout. Your body stores fewer carbohydrates than fat, yet it accesses the carbohydrates more easily. So the goal is to make your body more efficient at burning the stored fat while sparing the carbohydrates. Working out at higher heart rates will burn more carbohydrate calories in the short term, but it is working out in the lower zones that trains your body to become efficient at fat burning. In turn, this improves your endurance and aerobic fitness, eventually leading to a faster metabolic rate during exercise. This means that over time, you can burn as many calories at a low intensity as you were previously burning at a high intensity. With proper training this can happen in as little as three to six months.
Therefore, the best intensity for weight loss is one that seems 'fairly light' to 'somewhat hard'. Often people who cannot lose weight, or who even gain weight despite high intensity exercise and restrictive dieting, find success through a combination of slowing down their exercise, and improving the quality of their diet. This approach is not only more effective, but it's more fun and easier to stick to long-term!
- Emily Cooper, M.D.