¹Health-Related Fitness, NASA/Johnson Space Center, Houston, Texas, USA

²Department of Health and Human Performance, University of Houston, Houston, Texas, USA

³Kelsey Seybold Clinic, NASA/Johnson Space Center, Houston, Texas, USA

⁴University of Missouri at Kansas City, Kansas City, Missouri, USA

⁵Behavioral Medicine Research Center, Baylor College of Medicine, Houston, Texas, USA

Correspondence to: L T Wier, Mail Code AW-9, Health Related Fitness, NASA/Johnson Space Center, Houston, TX 77058, USA. E-mail: larry.t.wier1@jsc.nasa.gov

OBJECTIVE: To evaluate prospectively the influence of habitual physical activity on body weight of men and women and to develop a model that defines the role of physical activity on longitudinal weight change.

DESIGN AND SETTING: Occupational cohort study conducted for a mean of 5.5 y.

SUBJECTS: A total of 496 (341 male and 155 female) NASA/Johnson Space Center employees who completed the 3 month education component of the employee health-related fitness program and remained involved for a minimum of 2 y.

MEASUREMENTS: Body weights were measured at baseline (T1) and follow-up (T2), and habitual physical activity was obtained from the mean of multiple ratings of the 11-point (0-10) NASA Activity Scale (NAS) recorded quarterly between T1 and T2. Other measures included age, gender, VO_{2 max} obtained from maximal treadmill testing, body mass index (BMI), and body fat percentage.

RESULTS: Multiple regression demonstrated that mean NAS, T1 weight, aging and gender all influence long-term T2 weight. T1 age was significant for the men only. Independently, each increase in mean NAS significantly (P<0.01) reduced T2 weight in men (b=-0.91 kg; 95% CI:-1.4 to-0.42 kg) and women (b=-2.14 kg; 95% CI:-2.93 to-1.35 kg). Mean NAS had a greater effect on T2 weight as T1 weight increased, and the relationship was dose-dependent.

CONCLUSIONS: Habitual physical activity is a significant source of long-term weight change. The use of self-reported activity level is helpful in predicting long-term weight changes and may be used by health care professionals when counseling patients about the value of physical activity for weight control.

International Journal of Obesity (2001) 25, 613-621

weight control; body weight; physical activity; aging; gender