Increased afternoon step count increases heart rate variability in patients with cardiovascular risk factors.

AIMS AND OBJECTIVES The present study investigated whether morning or afternoon activity is more effective at increasing the high-frequency (HF) index, a parasympathetic index, in patients with cardiovascular risk factors. BACKGROUND A decreased HF index, a heart rate variability (HRV) parameter, is a well-established marker of poor cardiovascular prognosis. Because blood pressure and sympathetic tone are higher in the morning, physical activity and exercise in the afternoon has been recommended for patients with cardiovascular diseases. However, there have been no reports concerning the superior effects of afternoon exercise on parasympathetic activity and sleep. DESIGN This observational study was a post hoc comparison. METHODS Patients' physical activity was measured for 1 month to determine their habits. Patients' HF index was measured by 24-h Holter electrocardiography. The study enrolled 56 patients. Each patient's morning step count (before lunch) and afternoon step count (between lunch and dinner) were compared. We adhered to the STROBE guidelines in the present study. RESULTS Thirty-one patients took more steps in the morning, and 25 patients took more steps in the afternoon. The present study showed that those who took more steps in the afternoon had a significantly higher HF index during the first hour after sleep onset and during sleep than those who took more steps in the morning (p = .003, .047). CONCLUSIONS The present study showed that those who took more steps in the afternoon had a significantly higher HF index during the first hour after sleep onset and a higher HF index during sleep than those who took more steps in the morning. RELEVANCE TO CLINICAL PRACTICE Exercise in the afternoon may improve the prognosis in patients with cardiovascular disease by not only preventing excessive blood pressure, afterload, and sympathetic tone but also positively influencing the parasympathetic system and sleep.