Effects of Hydrostatic Weight on Heart Rate During Water Immersion

The aim of this study was to analyze the influence of hydrostatic weight on the changes in heart rate (HR) observed during water immersion (WI). Ten men underwent the following experimental situations: HRR—recumbent position, outside the water; HRS—standing position, outside the water; HRU—standing position, immersed up to the umbilical scar region; HRUW—standing position, immersed up to the umbilical scar region with the addition of weight to equal force weight reached in the situation standing outside the water, and HREND—standing position outside the water again. The HR was measured at the final 15 seconds of each experimental situation. ANOVA for repeated measures with posthoc Tukey tests were used. No statistically significant difference was found between HRU (60.6 ± 7.7 bpm) and HRUW (64.9 ± 7.7 bpm); however, in the comparison of these two situations with HRS (75.7±7.7 bpm), HRU presented a statistically significant difference, while HRUW did not produce a significant bradycardia. Thus, the decrease in hydrostatic weight, during WI, does not influence the behavior of HR. Humans use water immersion (WI) for relaxation (Oda, Matsumoto, Nagakawa, & Moriya, 1999), physical activity (Alberton, Olkoski, Pinto, Becker, & Kruel, 2007; Silvers, Rutledge, & Dolny, 2007), and as a means for providing medical therapy (Suomi & Collier, 2003; Tovin, Wolf, Greenfield, Crouse, & Woodfin, 1994). Moreover, WI has been used to study human cardiovascular physiology. WI induces various changes in the cardiovascular system including a