Associations of fitness and physical activity with orthostatic responses of heart rate and blood pressure at midlife

Cardiorespiratory fitness (CRF) and physical activity (PA) are associated with autonomic function, but their associations to orthostatic autonomic responses are unclear in epidemiological setting. We hypothesized that higher CRF and PA would associate with higher immediate vagal responses and lower incidence of adverse findings during orthostatic test. At age of 46, 787 men and 938 women without cardiorespiratory diseases and diabetes underwent an orthostatic test (3‐minutes sitting, 3‐minutes standing) with recording of RR intervals (RRi) and blood pressure (BP) by finger plethysmography. Acute responses of RRi (30:15 ratio) and BP were calculated. CRF was measured by a submaximal step test and daily amount of moderate‐to‐vigorous PA (MVPA) for 2 weeks by wrist‐worn accelerometer. Lifelong PA was based on questionnaires at ages of 14, 31, and 46. High CRF was significantly associated with higher RRi 30:15 ratio (adjusted standardized β = 0.17, P