Diete - Physical exercise

Diete - Physical exercise

Physical exercise is an important complement to dieting in securing weight loss. Aerobic exercise is also an important part of maintaining normal good health, especially the muscular strength of the heart. To be useful, aerobic exercise requires maintaining a target heart rate of above 50 percent of one's resting heart rate for 30 minutes, at least 3 times a week. Brisk walking can accomplish this.

The ability of a few hours a week of exercise to contribute to weight loss can be somewhat overestimated. To illustrate, consider a 100-kilogram (220 lb) man who wants to lose 10 kilograms (22 lb) and assume that he eats just enough to maintain his weight (at rest), so that weight loss can only come from exercise. Those 10 kilograms (22 lb) converted to work are equivalent to about 350 megajoules (84,000 calories). (We use an approximation of the standard 37 kilojoules or 9 calories per gram of fat.) Now assume that his chosen exercise is stairclimbing and that he is 20 percent efficient at converting chemical energy into mechanical work (this is within measured ranges). To lose the weight, he must ascend 70 kilometers. A man of normal fitness (like him) will be tired after 500 meters of climbing (about 150 flights of stairs), so he needs to exercise every day for 140 days (to reach his target). However, exercise (both aerobic and anaerobic) would increase the Basal Metabolic Rate (BMR) for some time after the workout. This ensures more calorific loss than otherwise estimated.

The minimum safe dietary energy intake (without medical supervision) is 75 percent of that needed to maintain basal metabolism. For our hypothetical 100-kilogram man, that minimum is about 5,700 kilojoules (1,300 calories) per day. By combining daily aerobic exercise with a weight-loss diet, he would be able to lose 10 kilograms in half the time (70 days). Of course, the described regime is more rigorous than would be desirable or advisable for many persons. Therefore, under an effective but more manageable weight-loss program, losing 10 kilograms (about 20 pounds) may take as long as 6 months.

There are also some easy ways for people to exercise, such as walking rather than driving, climbing stairs instead of taking elevators, doing more housework with fewer power tools, or parking their cars farther and walking to school or the office.