Physiological Response to Cold Water Swimming Among Members of a Swimming Club in Lagos, South West Nigeria

Background: Cold water immersion elicits acute cardiovascular, thermoregulatory, and hormonal responses including peripheral vasoconstriction, tachycardia, and noradrenaline surges. Recreational cold water swimming has gained popularity in Nigeria's coastal cities for its purported health benefits, yet the acute physiological responses in tropical-acclimatised Nigerians have not been characterised. Objectives: This study aims to measure changes in core temperature, heart rate, blood pressure, and perceived exertion before, during, and after a standardised cold water swim session among club members at a Lagos swimming facility. Methods: Thirty adult swimmers will participate. Tympanic temperature, heart rate, and blood pressure will be measured at pre-immersion, five minutes into swimming, on exiting the water, and 15 minutes post-swim. Water temperature will be recorded. The Borg Rating of Perceived Exertion will assess subjective effort. Repeated measures ANOVA with Bonferroni correction will compare time-point values. Expected Outcomes: Significant transient increases in heart rate and blood pressure are anticipated during cold immersion, with gradual normalisation post-swim, and core temperature declining slightly before rebounding during active swimming. Conclusion: Findings will contribute baseline cold water immersion physiology data relevant to recreational safety guidelines for Nigerian swimmers. Keywords: cold water swimming, cardiovascular response, thermoregulation, core temperature, Lagos.