Relationships of age and weekly running distance to BMI and circumferences in 41,582 physically active women.

OBJECTIVE: To assess in women whether age-related increases in adiposity are dependent on exercise, and, contrariwise, whether exercise-related declines in adiposity are dependent on age. RESEARCH METHODS AND PROCEDURES: Cross-sectional analyses were conducted of 41,582 female runners.
RESULTS: Age affected the relationships between vigorous exercise and adiposity. The decline in BMI per kilometer per week run was linear in 18 to 23 year olds and became increasingly non-linear (convex) with age. Waist, hip, and chest circumferences declined significantly with running distance across all age groups, but the declines were significantly greater in older than younger women, particularly among shorter distance runners. The relationships between body circumferences and running distance became increasingly convex in older women. Conversely, vigorous exercise diminished the apparent increase in adiposity with age. The increase in average BMI with age was greatest in women who ran <8 km/wk, intermediate in women who ran 8 to 15 km/wk or 16 to 31 km/wk, and least in those who averaged over 32 km/wk. Before age 45, waist circumference rose for those who ran 0 to 7 km/wk, showed no significant relationship to age for those who ran 8 to 39 km/wk, and declined in those who ran 40 to 55 and 56 km/wk and more. Age related-increases in hip and chest circumferences before 45 years old were significantly less in women who ran longer weekly distances. DISCUSSION: These cross-sectional associations are consistent with the hypothesis that exercise may mitigate age-related increases in adiposity and that age affects exercise-induced reductions in adiposity (although causality remains to be determined experimentally).