Exercise thermoregulation with bed rest, confinement, and immersion deconditioning

Area of Science:

• Human physiology
• Exercise physiology
• Thermoregulation

Background:

• Prolonged inactivity, such as bed rest or confinement, significantly impacts human physiological regulation.
• Altered thermoregulation is a known consequence of deconditioning, affecting core temperature (Tcore) responses during physical exertion.

Purpose of the Study:

• To investigate the mechanisms behind excessive Tcore increase during exercise after deconditioning in humans and dogs.
• To explore the role of hypovolemia, heat loss, and vasodilation in post-deconditioning hyperthermia.

Main Methods:

• Human subjects underwent bed rest and head-down water immersion, followed by exercise testing.
• Canine subjects experienced cage confinement and treadmill exercise.
• Core temperature, sweating, and forearm vascular responses were measured.
• Interventions included estrogen supplementation, exercise training, and glucose administration.

Main Results:

• Deconditioning led to excessive Tcore rise during exercise, independent of exercise mode.
• Hypovolemia in men correlated with hyperthermia; estrogen restored plasma volume in women.
• Decreased tissue heat conductance and increased forearm venoconstriction were observed post-deconditioning.
• Exercise training in dogs attenuated Tcore rise; glucose administration showed protective effects in both species.

Conclusions:

• Reduced core-to-periphery heat conduction, primarily due to decreased peripheral vasodilation, is a major cause of hyperthermia after deconditioning.
• Glucose metabolism may play a role in modulating these thermoregulatory responses.