Subgroup Interactions and Changes in Cardiorespiratory Fitness among Postmenopausal Women

Abstract

Approximately 38% of women in the U.S. are postmenopausal and the majority of these 25 million women obtain less than optimal amounts of physical activity. Physical inactivity, coupled with atherogenic risk factors associated with menopause, places them at elevated risk for CVD and all-cause mortality. In order to provide this group with targeted public health messages, it is beneficial to examine whether subsets of this population significantly differ in their physiological response to the exercise treatments. PURPOSE: To examine changes in fitness across different doses of aerobic exercise in subgroups of post-menopausal women in the DREW study. METHODS: We obtained baseline and 6-month follow-up fitness measures for 424 postmenopausal women randomly assigned to a non-exercise control group (n = 94), or 1 of 3 exercise treatments of 4 kcal/kg/wk (n = 145), 8 kcal/kg/wk (n = 89) or 12 kcal/kg/wk (n = 96). The intervention period was six months in duration. Subgroups analyzed included age (≤55y vs >55y), BMI (<30 vs BMI ≥30), baseline fitness (<1.3 L/min vs ≥1.3 L/min), self-identified race (Caucasian vs. non-Caucasian) and self-reported HRT usage. We used the least squares mean change by sub-group and treatment condition versus controls adjusted for baseline VO2, age, ethnicity, weight, and peak heart rates to examine treatment effects. P-values are for treatment-by-subgroup interactions. RESULTS: A significant increase in mean VO2 max was seen in all exercise groups compared to the control group with a significant trend across increasing exercise doses (p <0.0001). In subgroup analyses, similar results were observed with a greater change in VO2 max with increasing weekly energy expenditure. Subgroup interactions for age (p=0.10), BMI (p=0.23), baseline fitness (p=0.79), ethnicity (p=0.23) and HRT use (p=0.70) did not reach statistical significance indicating that in this population, the benefits of improved fitness were similar for all subgroups. CONCLUSIONS: Among post-menopausal women in the DREW study, changes in VO2 max were positively associated with increasing weekly energy expenditure. The benefits of increased fitness did not significantly differ by age, BMI, baseline fitness, ethnicity or HRT use.