The effect of cold water immersion on electrocardiogram recordings in healthy male rugby union players

Abstract

Introduction: Although cold water immersion therapy (CWI) is a popular recovery therapy used to accelerate the recovery process in rugby players, the cardiovascular response to cold water immersion places strain on the heart. However, little is known about the cardiac electrical effects due to cold water temperatures. The aim of this study, therefore, was to investigate the effects of cold water immersion therapy at two different water temperatures on cardiac electrical activity in male university rugby players. Methods: A prospective, randomised crossover study design was used to investigate the effects of CWI therapy at two different water temperatures (8ºC and 14ºC) measuring cardiac electrical effects and heart rate variability of male university rugby players. An electrocardiogram (ECG) was used to measure the cardiac electrical effects and a Zephyr™ BioHarness™ was used to measure heart rate variability in the participants. Heart rate variability, blood pressure, and heart rate data were tested for normality. Continuous data were analysed using Statistica 12 and presented as means and standard deviations. Electrocardiogram data was assessed and presented as frequencies and proportions. Significance was set at p<0.05. Results: Significant lower root mean square of successive RR interval differences (RMSDD) (P <0 .00001), and standard deviation of normal-to-normal RR intervals (SDNN) (P<0 .00001) were observed during the cold water immersion period at both 8ºC and 14ºC compared to pre-immersion period. Additionally, the stress index was significantly lower during the cold water immersion period compared to the pre-test values (P=0.000754) at both cold water temperatures. This indicates that there was a greater parasympathetic response during the cold water period. With regards to systolic blood pressure, the initial cold water immersion readings were significantly higher compared to pre-tests for both water temperatures. During the post cold water immersion period (or the post-test period), recorded measurements returned to baseline measures. Importantly, no ECG abnormalities were detected during the cold water immersion tests. Conclusion: These findings showed no cardiac electrical activity abnormalities with cold water immersion therapy in rugby players. Heart rate variability during cold water immersion is significantly higher compared to the non-immersion pre-test period, due to a larger parasympathetic response. This study showed that the parasympathetic system has a predominant effect on the body compared to the sympathetic nervous system during cold water immersion therapy