Immediate Re-Hydration Post-Exercise is Not Coincident with Raised Mean Arterial Pressure Over A 30-Minute...

Area of Science:

• Exercise Physiology
• Cardiovascular Regulation
• Fluid Balance

Background:

• Post-exercise hypotension is a significant physiological response.
• Plasma volume expansion is a key aspect of rehydration.
• The timing of fluid intake post-exercise may influence physiological recovery.

Purpose of the Study:

• To investigate the impact of immediate versus delayed rehydration on mean arterial blood pressure (MAP) and plasma volume (PV) expansion post-exercise.
• To test the hypothesis that fluid ingestion would increase MAP and reduce PV expansion.
• To determine if exercise intensity and dehydration level were sufficient to elicit measurable PV changes.

Main Methods:

• Eight male participants cycled in heat (35°C, 50% RH) until 1.0kg body mass was lost.
• Fluid intake (1L water) was administered either immediately or 2 hours post-exercise, in a randomized crossover design.
• Mean arterial blood pressure was measured every 5 minutes for 30 minutes post-exercise; plasma volume changes were assessed 24 hours post-exercise.

Main Results:

• No significant plasma volume expansion was observed 24 hours post-exercise, irrespective of rehydration timing.
• Repeated measures ANOVA indicated a significant time effect (p=0.006) but not a treatment effect (p=0.655) on MAP.
• MAP tended to be lower when fluid was consumed, with a 92% probability of the inverse effect compared to the initial hypothesis.

Conclusions:

• The exercise protocol was insufficient to induce significant plasma volume expansion, preventing definitive conclusions on rehydration timing's effect on PV.
• The hypothesis that fluid ingestion would attenuate post-exercise hypotension was not supported.
• Evidence suggests a potential inverse relationship, where drinking water post-exercise may lead to lowered blood pressure rather than increased MAP.