Changes in autonomic nervous system activity upon pool water entry in middle-aged and elderly individuals assessed by heart rate variability analysis

Abstract

Objectives: Aquatic exercise does not put strain on joints and is reported to have beneficial effects such as strengthening muscle and lowering blood pressure in middle-aged and elderly individuals. However, it has been reported that middle-aged and elderly individuals have a risk of arrhythmia during aquatic exercise because their cardiovascular autonomic nervous system (ANS) response on entry into pool water differs from that of younger individuals. This study investigated short-term changes in ANS activity immediately after pool water entry, when marked changes in ANS activity were expected in middle-aged and elderly individuals. [Subjects and methods] Subjects were 24 individuals aged 55 years or older (8 men and 16 women). Heart rate variability analysis was performed to examine resting autonomic activity in a sitting position before pool water entry and in a standing position immediately after pool water entry. [Results] The ratio of high frequency power to total power, an index of parasympathetic activity, was significantly reduced immediately after pool water entry in women. There was a significant negative correlation between age and the ratio of low frequency power to high frequency power, an index of sympathetic activity, before pool water entry. There were no significant differences in other indices. [Conclusion] Parasympathetic activity was suppressed immediately after pool water entry in middle-aged and elderly women, but there was no association between age and ANS activity after pool water entry.