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6. 8. 2012.

Height, weight and body composition of the older athletes

As we age, we tend to lose height and gain weight, as illustrated in the figure below. The reduction in height generally starts at about 35 to 40 years of age and is primarily attributable to compression of the intervertebral disks and poor posture early in aging. At about age 40 to 50 years in women, and 50 to 60 years in men, osteoporosis becomes a factor. Osteoporosis refers to a severe loss of bone mass with deterioration of the microarchitecture of bone, leading to increased risk of bone fracture. Poor diet and exercise habits throughout the life span contribute to the development of osteoporosis in both men and women, while decreased estrogen levels after menopause appear to be responsible for the greater rate of bone loss in women. A gain in weight typically occurs between age 25 and 45 and is attributable to both a decrease in physical activity levels and excess caloric intake. Beyond the age of 45, weight stabilizes for about 10 to 15 years and then decreases as the body loses bone calcium and muscle mass. Many people over 65 to 70 years of age tend to lose their appetite and thus don’t consume sufficient calories to maintain body weight. An active lifestyle, however, tends to help better regulate appetite so that caloric intake more closely approximates caloric expenditure, thereby maintaining weight and preventing frailty in old age.

Beginning at about 20 years of age, as we get older we tend to gain fat. This is largely attributable to three factors: diet, physical inactivity, and reduced ability to mobilize fat stores. As one might anticipate, the body fat content of physically active older people, including older athletes, is significantly lower than that of age-matched sedentary people. However, older athletes have substantially more body fat than younger competitors.
Fat-free mass decreases progressively in both men and women beginning at about the age of 40. This results primarily from decreased muscle and bone mass, with muscle having the greatest effect because it constitutes about 50% of the fat-free mass. Sarcopenia is the term used to describe the loss of muscle mass associated with the aging process. Osteopenia is a companion term used to describe the less severe loss in bone mass with aging than is seen in osteoporosis. Figure below illustrates the changes in muscle mass with aging in a cross-sectional study of 468 men and women, aged 18 to 88 years. There is almost no decline in muscle mass until about age 40, at which time the rate of decline increases, with a greater decline in men than women. Obviously, a decline in activity level is a major cause of this decline in muscle mass with aging, but there are other factors. It is now known that the rate of muscle protein synthesis is reduced as we age while muscle protein breakdown rate is unchanged, leading to negative nitrogen balance and net loss of muscle. Muscle protein synthesis rate in 60-to 80-year-olds is about 30% lower than in a 20-year-old. This reduction in muscle protein synthesis rate in older people is likely associated with declines in growth hormone and insulin-like growth factor-1. Longitudinal data suggest that loss of fat-free mass and gain of fat mass offset each other. As a result, percent fat is increasing while total body mass remains relatively stable.

There is also a significant decrease in bone mineral, starting at about age 30 to 35 in women and at age 45 to 50 in men. Throughout the life cycle, bone in constantly being formed by osteoblasts and resorbed by osteoclasts. Early in life, resorption occurs at a slower rate than synthesis, and bone mass increases. With aging, resorption exceeds synthesis, resulting in a net loss of bone. The loss of both muscle and bone mass is at least partially attributable to decreased physical activity, especially a lack of weight-bearing exercise. Since bone mineral accounts for less than 4% of total body mass in young adults, the contribution of osteopenia to the loss of total fat-free mass is small compared to that of sarcopenia.
These differences in weight, relative(%) body fat, fat mass, and fat-free mass with aging are demonstrated in figure below. These data are from a study of young(18-31 years) and older(58-72 years) men and women who either were sedentary or were endurance-trained athletes. Body weight, relative body fat, and fat mass were higher in older sedentary groups, whereas fat-free mass was lower. Similar trends, except for body weight, were noted for the endurance-trained athletes. However, the young and older endurance-trained athletes had much lower total body weight, relative body fat, and fat mass values and similar fat-free mass values compared to their sedentary age-matched counter-parts.

With training, older men and women can reduce weight, percent body fat, and fat-free mass; but as in younger individuals, this is more likely with resistance training than with aerobic training. Men appear to experience greater changes in body composition than women, but the reasons for this have not been clearly established.
The most significant changes in body composition result from a combination of diet and exercise, with a modest reduction in caloric intake(500-1000 kcal/day) being the preffered approach. A more substantial reduction in caloric intake(>1000 kcal/day) is likely to result in a loss of fat-free mass as well as fat mass. This is not desirable, as a loss in fat-free mass is associated with a reduction in resting metabolic rate, thus decreasing the rate of weight and fat loss. Exercise that increases fat-free mass will likely increase resting metabolic rate, which would increase the rate of weight loss. It appears that older adults experience changes in body composition due to exercise training similar to those for younger adults.

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