Acute increase in arterial stiffness after swimming in cooler water

Cold stimuli increase arterial stiffness, but it has not been explored whether arterial stiffness increases after swimming in cooler water. To investigate the effects of water temperature on changes in arterial stiffness after swimming, 13 men participated in three trials of 20-min swimming in 25 and 30°C water (S25 and S30, respectively) and sitting at poolside (CON) in random order. There were no significant differences between the S25 and S30 trials in mean swimming distance (719 vs. 722 m) and heart rate reserve during swimming (63% vs. 63%). Sublingual temperature was lower after swimming in 25°C water versus before swimming. Aortic pulse wave velocity (aortic PWV, an index of central arterial stiffness based on applanation tonometry) and brachial-ankle pulse wave velocity (baPWV, an index of systemic arterial stiffness based on air plethysmography) were higher 30 min after versus before swimming in 25°C water. Aortic PWV recovered to pre-swimming levels by 60 min after swimming in 25°C water, but baPWV was higher even at 60 min after swimming. PWVs did not change in the CON and S30 trials. Systemic vascular resistance based on Doppler ultrasonography did not change, but forearm vascular resistance based on strain-gauge plethysmography was higher 30 and 60 min after swimming in 25°C water. Heart rate was higher, but stroke volume was lower 30 min after swimming in 25°C water, resulting in no detectable change in cardiac output. In conclusion, arterial stiffness increases acutely after moderate-intensity swimming in cooler water.