Aerobic exercises such as running, walking and cycling are known to elicit a PEH (post-exercise hypotensive) response in both trained and UT (untrained) subjects. However, it is not known whether swim exercise produces a similar effect in normotensive individuals. The complex acute physiological responses to water immersion suggest swimming may affect BP (blood pressure) differently than other forms of aerobic exercises. We tested the hypothesis that an acute bout of swimming would fail to elicit a PEH BP response compared with an equivalent bout of stationary cycling, regardless of training state. We studied 11 UT and ten triathlon-trained young healthy normotensive [SBP/DBP (systolic BP/diastolic BP) <120/80 mmHg)] men and women (age 23±1 years) who underwent 30 min of intensity-matched cycling and swimming sessions to assess changes in BP during a 75-min seated recovery. CO (cardiac output), SV (stroke volume), TPR (total peripheral resistance), HR (heart rate), HRV (HR variability) and core and skin temperature were also assessed. In UT subjects, PEH was similar between cycling (−3.1±1 mmHg) and swimming (−5.8±1 mmHg), with the greater magnitude of PEH following swimming, reflecting a significant fall in SV between modalities (P<0.05). Trained individuals did not exhibit a PEH response following swimming (0.3±1 mmHg), yet had a significant fall in SBP at 50 min post-cycling exercise (−3.7±1 mmHg) (P<0.05). The absence of PEH after swimming in the trained group may reflect a higher cardiac sympathetic outflow [as indicated by the LF (low-frequency) spectral component of HRV) (25 and 50 min) (P<0.05)] and a slower return of vagal tone, consistent with a significant increase in HR between modalities at all time points (P<0.05). These results suggest that training may limit the potential for an effective post-exertional hypotensive response to aerobic swimming.

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