Use of Quantile Regression to Investigate the Longitudinal Association between Physical Activity and Body Mass Index

Objective: To examine associations among age, physical activity (PA), and birth cohort on body mass index (BMI) percentiles in men. Methods: Longitudinal analyses using quantile regression were conducted among men with >= two examinations between 1970 and 2006 from the Aerobics Center Longitudinal Study (n = 17,759). Height and weight were measured; men reported their PA and were categorized as inactive, moderately, or highly active at each visit. Analyses allowed for longitudinal changes in PA. Results: BMI was greater in older than younger men and in those born in 1960 than those born in 1940. Inactive men gained weight significantly more rapidly than active men. At the 10(th) percentile, increases in BMI among inactive, moderately active, and highly active men were 0.092, 0.078, and 0.069 kg/m(2) per year of age, respectively. The 10(th) percentile increased by 0.081 kg/m(2) per birth year and by 0.180 kg/m(2) at the 90(th) percentile, controlling for age. Conclusion: Although BMI increased with age, PA reduced the magnitude of the gradient among active compared to inactive men. Regular PA had an important, protective effect against weight gain. This study provides evidence of the utility of quantile regression to examine the specific causes of the obesity epidemic.