Estimation of Cardiorespiratory Fitness Without Exercise Testing: Cross-Validation in Midlife and Older Women

Background: Cardiorespiratory fitness (CRF) is associated with important health risk outcomes, including the development of Type 2 diabetes and cardiovascular disease. Measures of maximal or peak oxygen consumption (VO2) are the typical criterion methods for determining CRF; however, in clinical settings, these measures are impractical. Methods: We validated a clinically derived estimate of CRF against predicted maximal VO2 in a sample of healthy, midlife and older adult women (n=188). Women completed a clinic evaluation (including treadmill testing), daily diaries about their physical activity, and additional clinical scales. Two models were tested. The first model calculated estimated cardiorespiratory fitness (eCRF) using assigned weights and regressed eCRF on predicted cardiorespiratory fitness (pCRF). The second model used sample-specific, empirical weights. Both models were tested twice, once with retrospective and once with daily diary physical activity reports. Results: The model accounted for 34% of the variance in pCRF when using assigned weights and 41% of the variance in pCRF when using empirical weights. For age, body mass index, and resting heart rate, assigned and estimated weights were similar, but estimates for physical activity differed. There was little improvement in model fit between retrospective and daily diary measurements of physical activity when either assigned (R-2=0.32) or fitted weights (R-2=0.40) were used. Conclusions: Midlife and older women's CRF can be estimated from routinely collected clinical measures, demonstrating their utility.