The effects of hydration status on post-exercise hypotension in healthy normotensive recreationally active adults : a thesis presented in partial fulfilment of the requirements for the degree of Master of Health Science, Massey University, Wellington, New Zealand

Abstract

Post-exercise hypotension (PEH), the acute reduction in blood pressure (BP) following a single exercise bout, contributes to long-term BP reductions associated with regular exercise. The magnitude and duration of PEH are modified by individual and exercise characteristics, yet the effect of hydration status has rarely been examined. Hypohydration may amplify PEH by reducing plasma volume and venous return. This study determined the effect of hydration status on PEH following moderate-intensity cycling in healthy, normotensive, recreationally active adults. Nine participants completed two 30-minute cycling bouts at 80% of functional threshold power under euhydration and hypohydration conditions. Hypohydration was induced through 18 hours of fluid restriction, with no subsequent rehydration. Heart rate (HR) was recorded every two minutes and rating of perceived exertion (RPE) every five minutes during exercise, and BP was measured every five minutes during a 30-minute standing recovery. Urine specific gravity was greater in the hypohydration vs. euhydration condition (1.023 ± 0.002 vs. 1.009 ± 0.007, t-test – P = 0.004). Despite matched power output between conditions, a main effect of hydration was present for HR during exercise (P = 0.014) and recovery (P = 0.019). Post-hoc comparisons identified higher RPE with hypohydration at minute 25 (7 ± 1 vs 6 ± 2, P = 0.009) and 30 (8 ± 1 vs 6 ± 2, P < 0.001). The maximum reduction from baseline in systolic BP (SBP) was greater in the hypohydrated condition (-12 ± 3 vs -6 ± 5 mm Hg, t-test – P = 0.002), with no difference for diastolic BP (-8 ± 6 vs -8 ± 6 mm Hg, t-test – P = 0.965) or mean arterial pressure (MAP) (-8 ± 3 vs -5 ± 5 mm Hg, t-test – P = 0.138). Analysed as the change from baseline at each recovery time point, a main effect of hydration was present for SBP (P < 0.001) and MAP (P = 0.050) with greater reductions following hypohydration. Hypohydration produced PEH sufficient, in some cases, to induce orthostatic intolerance and syncope. As hypohydration is common in recreationally active adults and athletes, these findings carry practical relevance for safe management of post-exercise recovery.