Obesity and Sports

Physical activity decreases in direct relationship to the degree of obesity. Obesity has been defined as being 20 percent or more overweight, using the concept of relative weight. Obesity in younger individuals [Page 539]is generally characterized by elevated levels of fat mass and fat-free mass, whereas obesity in the older adults is reflective of high levels of body fat, but low quantiles of fat-free mass. There is positive energy imbalance between energy intake and energy expenditure in obese individuals and the most variable component of the daily energy expenditure is the physical activity.

Although the etiology is multifactorial, it is readily accepted that low levels of physical activity are one of the leading risk factors for the development of obesity and its attendant comorbidities. Many obese individuals are sedentary, have little training or skills in physical activity, and are difficult to motivate toward increasing their activity. Young children who have a family history of obesity and also have low levels of physical activity are at increased risk for development of childhood obesity The loss of fat-free mass and gain in body fatness—preferentially stored in central regions of the body—in the adults are at least partially attributable to physical inactivity. The decline in physical activity may accelerate the accumulation of central body fat in women during the menopause transition.

Exercise and sports can be described as a subcategory of physical activity defined as any voluntary movement produced by the skeletal muscles that results in increased energy expenditure. Although the line between sports and exercise is certainly not clear, exercise is planned, structured, and repetitive movements and sport is a physical activity or skill carried out by a set of rules and engaged in recreatively or competitively.

Physical activity, regardless of what kind, expends energy. The average sedentary person usually expends only 300–800 calories a day in physical activity, most of this from informal, unplanned types of movement. On the other hand, athletes usually match their resting metabolic rate energy expenditure through hard, intense exercise. Increased levels of physical activity are associated with decreased risks for obesity. Those engaging in vigorous exercise that causes heavy sweating or large increases in breathing or heart rate, one to three hours a week, or walking for more than four hours a week, are better able to ward off weight gain than their more sedentary counterparts.

Physical activity can reduce the risk for obesity for several reasons. First, it can vary widely from person to person, and thus when it is increased or decreased, it can have large influences on total energy expenditure, and consequently, energy balance. Second, physical activity can increase the amount of fat free mass FFM (or lean muscle mass) that one has. FFM is the primary determinant of resting metabolic rate, and has long-term consequences for energy balance. Third, exercise training can influence substrate (nutrient) utilization, thereby playing a role in how ingested nutrients are partitioned into fat and FFM. Finally, there is some suggestion that exercise can increase endorphins and mood, and reduce feelings of hunger in the short term, so an increase in exercise might lead to reduced energy intake.

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