Alterations in body weight and composition consequent to 20 wk of endurance training: the HERITAGE Family Study

Background: Obesity is a major public health problem in the United States. The role of physical activity and formal exercise in controlling body weigh t has not been clearly determined. Objective: This study determined the magnitude of change in body weight and composition across sex, race, and age in response to 20 wk of endurance tr aining. Design: Men and women (n = 557) of various ages (16-65 y) and 2 races (blac k and white) exercised on cycle ergometers 3 d/wk for a total of 60 exercis e sessions starting at 55% of maximal oxygen consumption (VO(2)max) for 30 min/session and building to 75% of VO(2)max for 50 min/session, where it wa s maintatined during the last 6 wk. Skinfold-thickness measurements, circum ferences, body composition (by hydrostatic weighing), and body fat distribu tion (by computed tomography scan at IA-LS and the waist-hip ratio) were de termined before and after training. Results: All skinfold-thickness and circumference measures, waist-hip ratio , body mass index, total body mass, fat mass, percentage body fat, and comp uted tomography scan measures of total, subcutaneous, and visceral abdomina l fat decreased with training, whereas total body density and fat-free mass increased. These changes were significant, but small. There were several d ifferences in training response by sex and race, but not by age. Conclusions: A short-term exercise intervention can induce favorable change s in body composition, but the magnitude of these changes is of limited bio logical significance. Increasing physical activity likely has a major effec t on body-composition and fat distribution characteristics only when it is of a greater magnitude and sustained for much longer periods.