Physical Activity of Weight Loss
According to the ACSM, the optimal approach to weight loss combines mild caloric restriction with regular physical activity. Together these two strategies should provide a caloric deficit not to exceed 500 to 1000 calories per day. The physical activity component should manipulate exercise intensity and duration to burn from 300 to 500 calories per session and 1000 to 2000 calories per week.
Use of CaloriesOne of the obvious benefits of physical activity is that it burns calories. Calories are consumed according to body weight, so heavier people burn more calories per minute than lighter people for the same activity. To use it, multiply your body weight by the coefficient in the calories/min/lb column and then multiply this value by the number of minutes spent participating in the activity. For example, to determine the calories expended by a 170-pound person who walks at 4.5 mph for 30 minutes, do the following: Body fat contains about 3500 calories per pound. Fat storage, however, which includes some lean support tissue muscle, connective tissues, blood supply, and other body components-represents approximately 2700 calories per pound. If this person performs this exercise daily, 1 pound will be lost in approximately 11 days or 33 pounds in 1 year, provided caloric intake is unchanged. Aerobic exercises, such as walking and cycling, contribute significantly to weight loss. Minimal guidelines for maintaining fitness and losing weight require 300 calories per exercise session performed at least three times per week or 200 calories per session performed at least four times per week. Added weight loss can be accomplished by increasing the length of each exercise session and/or the number of sessions per week. High-intensity activities burn extra calories, but low-intensity exercises are recommended to prevent injury. Complete to determine the number of minutes that you should participate in your favorite activities to burn a minimum of 300 calories. Deconditioned people should start slowly and gradually progress to using 300 to 500 calories per exercise session. For many people, low-intensity, long-duration physical activity, such as walking, is optimal. For weight loss, all calories do not have to be expended in one exercise session. Three 15 Â minute walks in a day result in a substantial expenditure of energy. Any physical activity above the amount normally done in a day is a bonus for weight control. The cumulative effect of activities such as walking upstairs, mowing the lawn, and mopping floors can be combined with a structured exercise program to produce steady, safe weight loss.
Exercise Stimulates MetabolismBasal metabolic rate (BMR) is the energy required to sustain life when the body is in a rested and fasted state. BMR is measured in calories and represents the energy needed to keep the heart, lungs, liver, kidneys, and all other organs functioning. More calories are used to maintain BMR than to perform any other function. Approximately 70% of the energy liberated from food is expended to support BMR. Metabolism is affected by age, gender, nervous system activity, secretions from endocrine glands, nutritional status, sleep, fever, climate, body surface area, and amount of muscle tissue. Because men have more muscle tissue than women, their BMRs average 5% to 10% higher. BMR declines with age, primarily because of the physical inactivity and muscle loss that often accompany aging. The annual decrease in BMR beginning at 25 or 30 years of age, though imperceptible, has serious ramifications for weight management and accounts for a significant amount of the weight gained with age. Authorities estimate that the loss of muscle tissue is equal to 3 % to 5 % every decade after age 25 to 30 years. The subsequent decline in BMR produces changes in body composition . Exercise and physical activities are the keys to weight management because they increase and/or sustain muscle tissue, thus accelerating metabolism and using calories.
The Key to Weight ControlAlthough scientifically controlled studies have not yet proven that physical activity is instrumental in losing weight, they provide compelling evidence as to its importance in weight control and weight loss maintenance. People who lose weight and keep it off almost always exercise daily. Studies that attempt to identify predictors of successful weight maintenance point to physical activity as one of the best markers for long-term success. Researchers at the University of California at Davis found that 90% of the women who had lost 20 pounds and kept it off for at least 2 years were avid exercisers; of the women who had regained the weight, only 35% were physically active. At the Baylor College of medicine in Houston, another group of researchers put 160 obese adults on one of three year-long weight loss programs: diet only, exercise only, or exercise and diet. Everyone lost weight. (The exercise and diet group lost the most). But 2 years later, the exercise-only participants were the only ones to keep the weight off. Other large-scale studies that follow men and women in weight-loss programs for 10 years consistently show that major weight gain is much more likely to occur in people who are sedentary than those who are physically active. Thus although physical activity as a singular strategy has modest effects on weight loss, it is the key strategy for lifelong weight control. More importantly, moderate exercise improves health and reduces risk factors associated with morbidity and mortality for the obese just as it does for normal-weight people.
Combining Dietary Modification and ExerciseBecause caloric consumption and expenditure are involved in weight management, both should be manipulated to be effective. Combining sensible exercise and sensible changes in eating habits that can be maintained for life is the most effective approach to permanent weight management. Dieting alone can promote significant weight loss, but a substantial component of the weight loss may be lean tissue. Physical activity alone results in modest fat loss and an increase in lean body mass. Combination strategies involving both food restriction and physical activity meet the goals of weight management most effectively: it improves body composition by promoting weight loss, fat loss, and lean-tissue gain.
BeHavioral EffectsSome evidence suggests that obese people are more likely than normal-weight people to eat in response to external cues. A clock that says it is suppertime; media messages advertising food and beverages; and the sight, sound, and aroma of food are more apt to elicit eating behavior in the obese. This is the basis of the "externality" hypothesis: if people can learn to eat in response to external cues, they can also learn to recognize cues that stimulate eating behavior, substitute other behaviors for eating, and use techniques that decrease the amount of food eaten. As a result of this training the response to external cues should be reduced and replaced by attention to internal hunger signals. Many techniques have been developed over the past 20 years that may assist people in resisting the tendency to eat indiscriminately or to overeat. Generally these techniques employ one or more of the following approaches:
- Self-monitoring: a journal or daily log is kept, recording food consumption, physical activities, and circumstances related to eating.
- Control of precursors to eating: the events and circumstances that elicit eating and overeating are identified.
- Control of eating: behavioral modification techniques are used to control, change, or modify specific eating behaviors.
- Reinforcement through the use of rewards: rewards tied to the achievement of behavioral goals are identified and used.
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