Unable to recruit during COVID-19 crisis

Cardiovascular disease (CVD) is the leading cause of death worldwide. Hypertension is a well-established risk factor for the development of CVD. Lifestyle modifications, including exercise, remain the cornerstone of blood pressure (BP)-lowering strategy. Swimming has long been a popular recreational activity for exercise, and is recently gaining widespread recognition as an effective option in maintaining and improving cardiovascular health. Previous studies that involved pool swimming as an intervention (versus no pool swimming) demonstrated favorable benefits of the former on BP reduction. However, no studies to date have specifically investigated the effect of cold-water sea swimming on BP. Indeed, the naturally lower water temperature in the sea may engender a 'cold water immersion' experience in sea swimmers with subsequent stress physiology, which have been shown to exert unique effects on cardiovascular hemodynamics. This study primarily aims to determine the impact of cold-water sea swimming on BP in a group of habitual sea swimmers in Galway who will be randomly assigned to either continue or stop swimming for 4-6 weeks. Other objective and subjective health benefits to sea swimming will also be explored in this study. Given the ubiquitous nature of this activity in the Irish general public, particularly in Galway, this study has potential from a public health perspective, and would add to the literature base pertaining to the benefits of sea swimming on cardiovascular health.

Consenting participants will be randomly assigned, 1:1, to either continuation of sea swimming or discontinuation of sea swimming for 4-6 weeks, stratified by the type of swimmer (those who purely immerse in the water for a brief period of time versus those who actually swim [i.e., exercise] in the water) and use of blood pressure medication at the time of study commencement (yes or no), using a block size of four to maintain balance between intervention arms. In line with previous studies that assessed the impact of swimming intervention on BP, participants randomized to the swimming arm should pursue sea swimming 2 or more days/week.

Inclusion Criteria:

• habitual swimmers (i.e., sea swimming at least 2 times/week for the past year)
• 18 years of age or older
• able to provide informed consent

Exclusion Criteria:

• underlying cardiac (e.g., self-reported heart failure) or pulmonary diseases (e.g., self-reported chronic obstructive pulmonary disease)
• recent orthopedic procedures (e.g., joint replacement therapy)
• severe disabling comorbidity
• recent arm (both arms) or chest wall injury
• pregnant or breast feeding