Exercise hyperthermia induces greater changes in gastrointestinal permeability than equivalent passive hyperthermia

Area of Science:

• Exercise Physiology
• Gastrointestinal Physiology
• Environmental Medicine

Background:

• Exertional heat illness and hyperthermia are known to increase gastrointestinal (GI) permeability.
• The precise mechanisms, particularly the role of cardiovascular strain versus core temperature alone, remain unclear.

Purpose of the Study:

• To compare changes in GI permeability between exercise-induced hyperthermia (Ex-Heat) and passive hyperthermia (hot water immersion - HWI).
• To determine if cardiovascular strain during exercise exacerbates heat-induced increases in GI permeability.

Main Methods:

• A pilot study involving six healthy males comparing Ex-Heat and HWI conditions.
• Measurements included heart rate (HR), core temperature (TCORE), rating of perceived exertion (RPE), whole-body sweat loss (WBSL), and GI permeability via the lactulose:rhamnose (L:R) ratio.
• Participants underwent both exercise in heat and passive heating protocols.

Main Results:

• The L:R ratio was significantly higher in Ex-Heat compared to HWI.
• Peak HR, change in HR, and change in RPE were elevated in Ex-Heat.
• No significant differences were observed in trial duration, peak TCORE, or WBSL between conditions.
• L:R ratio strongly correlated with peak HR and change in HR.

Conclusions:

• Exercise-induced hyperthermia leads to greater GI permeability than passive hyperthermia at equivalent core temperatures.
• Increased cardiovascular strain during exercise, not just core temperature, exacerbates heat-induced GI permeability.
• These findings highlight the importance of considering cardiovascular load in managing heat illness and GI distress.