Quantile Differences in the Age-Related Decline in Cardiorespiratory Fitness Between Sexes in Adults Without Type 2 Diabetes Mellitus in the United States.

Objective: To comprehensively assess the extent to which the decline in cardiorespiratory fitness (CRF) with age differs between sexes. Participants and Methods: This study used data from the Aerobics Center Longitudinal Study, conducted between September 1974 and August 2006, consisting primarily of White adults from middle-to-upper socioeconomic strata restricted to adults without type 2 diabetes mellitus (33,742 men and 9,415 women). Quantile regression models were used to estimate the differences in age-associated changes in CRF between the sexes, estimated using a maximal treadmill test. Results: For adults aged up to 45 years, significant differences in slopes relating to age and CRF between men and women were observed for all adjusted percentiles of CRF other than the 90th percentile; women reported significantly greater declines in CRF per year. For those aged 45-60 years and those older than 60 years, no significant differences in age-related declines in CRF were observed between the sexes. Conclusion: This study found that compared with men, the onset of decline in CRF was found to occur earlier and at lower CRF percentiles in women. This is of particular concern, given that compared with men, women already tend to have lower CRF levels. These findings suggest that maintaining the levels of physical activity sufficient to maintain moderate-to-high levels of fitness is particularly important for women earlier during adulthood.