Effect of upright exercise on threshold for cutaneous vasodilation and sweating

Area of Science:

• Human Physiology
• Thermoregulation
• Exercise Physiology

Background:

• Understanding the body's thermoregulatory responses to environmental and physical stressors is crucial for maintaining homeostasis.
• Cutaneous vasodilation and sweating are key mechanisms for heat loss, influenced by core and skin temperatures.
• The interplay between posture, exercise, and thermoregulatory thresholds requires further investigation.

Purpose of the Study:

• To determine if exercise or upright posture alters the internal temperature threshold for cutaneous vasodilation.
• To investigate the effect of exercise and posture on the relationship between skin blood flow (SkBF) and sweat rate (SR).
• To quantify the individual and combined contributions of posture and exercise to changes in thermoregulatory thresholds.

Main Methods:

• Measurements of esophageal temperature (Tes), forearm SkBF, and SR were conducted in four conditions: supine rest, upright rest, supine exercise, and upright exercise.
• All trials were performed under conditions of elevated skin temperature (38-38.5°C).
• Analysis focused on the internal temperature threshold for vasodilation and sweating, and the relationships between Tes, SkBF, and SR.

Main Results:

• Upright exercise significantly increased the internal temperature threshold for cutaneous vasodilation by 0.39°C compared to supine rest (P<0.01).
• Neither the onset threshold for sweating nor the slopes of SkBF-Tes and SR-Tes relationships were significantly altered by upright exercise.
• Both upright posture (0.11°C shift) and exercise (0.28°C shift) independently contributed to the elevated vasodilation threshold.

Conclusions:

• Upright posture and exercise independently elevate the internal temperature threshold for cutaneous vasodilation.
• This shift reduces skin blood flow at a given core temperature during exercise and increases the threshold difference between vasodilation and sweating.
• These findings highlight altered thermoregulatory control during combined upright posture and exercise, potentially impacting heat dissipation capacity.