Associations of Fitness and Physical Activity with Orthostatic Responses of Heart Rate and Blood Pressure at Mid-Life

Abstract

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 < 0.001) and milder acute decrease of systolic BP while standing (β = 0.10, P = 0.001), while MVPA was not (β = 0.04 for RRi 30:15 ratio and β = 0.05 for systolic BP acute response). High lifelong PA was significantly associated with higher RRi 30:15 ratio (β = 0.08, P = 0.002) but not with acute systolic BP response. Those in the lowest tertile of CRF had 9.2‐fold risk (P = 0.002) of having postural orthostatic tachycardia syndrome compared to more fit. Cardiorespiratory fitness and lifelong physical activity, but not current physical activity, were independently associated with higher cardiac vagal response to orthostasis. The present results underscore the importance fitness and lifelong physical activity in prevention of abnormal autonomic function and related cardiovascular risk.