Peripheral vascular tone during heat load is modified by exercise intensity

Area of Science:

• Exercise Physiology
• Human Thermoregulation
• Environmental Physiology

Background:

• Understanding how the body dissipates heat during exercise is crucial for performance and safety.
• Non-evaporative heat loss (radiation and convection) and evaporative heat loss (evaporation) are key thermoregulatory mechanisms.
• The influence of exercise intensity on peripheral heat exchange, particularly in the extremities, requires further investigation.

Purpose of the Study:

• To quantify non-evaporative and evaporative heat loss from the hand during graded leg exercise.
• To determine the relationship between esophageal temperature, skin temperature, and hand heat loss at different exercise intensities.
• To assess the impact of increasing exercise intensity on hand thermal conductance and the underlying thermoregulatory responses.

Main Methods:

• Four healthy men performed cycling exercise at 20%, 35%, and 45% of VO2max in a controlled 20°C environment.
• A direct hand calorimeter was used to measure radiative, convective, and evaporative heat loss from the hand.
• Esophageal and mean skin temperatures were continuously monitored throughout the exercise protocol.

Main Results:

• Leg exercise initially caused a decrease, then an increase in hand radiative and convective heat loss.
• Hand non-evaporative heat loss and thermal conductance (k) were significantly lower at higher exercise intensities for a given esophageal temperature.
• The relationship between hand heat loss and esophageal temperature, as well as thermal conductance and esophageal temperature, showed a decreasing slope with increasing exercise intensity.

Conclusions:

• Increasing exercise intensity reduces hand heat loss and thermal conductance, despite rising core body temperature.
• This reduction is attributed to increased reflex vasoconstrictor tone, a non-thermal factor, overriding thermoregulatory vasodilation.
• These findings highlight the complex interplay between central and peripheral thermoregulation during exercise.