Thermoregulation and Exercise Physiology

Vocabulary flashcards covering mechanisms of heat transfer, physiological control of body temperature, and exercise responses in hot environments.

Normal Core Temperature Fluctuation

Body temperature normally varies only about 1.0–1.8 °F (≈0.6–1 °C) under resting conditions.

Metabolic Heat Production Efficiency

Only about 25 % of ATP is used for physiological work; the remaining 75 % is released as heat.

Conduction (k)

Transfer of heat between two solid objects in direct contact, e.g., sitting on a cold bleacher.

Convection (C)

Heat transfer via motion of gas or liquid across a surface; faster air or water flow increases heat exchange.

Radiation (R)

Emission of infrared rays; at room temperature ~60 % of resting heat loss occurs via radiation.

Evaporation (E)

Primary avenue of heat dissipation during exercise; liquid sweat absorbs heat and vaporizes, removing ~80 % of exercise‐generated heat.

Dry Heat Exchange

Combined heat transfer through conduction, convection, and radiation (excludes evaporation).

Insulation

Resistance to dry heat exchange; still air trapped in clothing is an ideal insulator.

Humidity

Amount of water vapor in the air; high humidity decreases the vapor-pressure gradient and limits evaporative cooling.

Preoptic-Anterior Hypothalamus (POAH)

Brain region acting as the body’s thermostat, integrating thermal information and initiating responses.

Peripheral Thermoreceptors

Temperature sensors in the skin that send information to the POAH and cerebral cortex, providing early warning of environmental changes.

Central Thermoreceptors

Receptors in the brain and spinal cord that monitor blood temperature; sensitive to changes as small as 0.01 °C.

Skin Arterioles

Blood vessels regulated by SNS signals from POAH; vasodilate to lose heat, constrict to conserve heat.

Eccrine Sweat Glands

Widely distributed glands activated by sympathetic cholinergic fibers (acetylcholine) to secrete sweat for cooling.

Skeletal Muscle Shivering

Involuntary rhythmic contractions that increase metabolic heat production when cold.

Thyroxine

Thyroid hormone that can double metabolic rate, increasing heat production.

Catecholamines

Epinephrine and norepinephrine released by adrenal medulla; elevate metabolic rate and heat production.

Heat Stress

Any environmental condition that elevates body temperature and challenges homeostasis.

Cardiovascular Drift in Heat

During prolonged exercise in heat, stroke volume falls and heart rate rises to maintain cardiac output.

Critical Temperature Theory

Exercise stops when brain temperature reaches about 40–41 °C (104–105.8 °F) regardless of muscle temperature.

Hyperventilation in Heat

Elevated pulmonary ventilation proportional to increased core temperature, independent of dehydration.

Dehydration Effects

Reduces sweat rate and skin blood flow, elevates HR and peripheral resistance, lowering stroke volume and cardiac output.

Oral Rehydration

Consumption of fluids and electrolytes to prevent heat-related performance decline and cardiovascular strain.

Pre-cooling

Intentional lowering of core temperature before activity (cold water immersion, cooling garments) to extend heat storage capacity.

Eccrine vs. Apocrine Glands

Eccrine glands aid thermoregulation; apocrine glands (axilla, face, genital) mainly respond to emotional stimuli and add little to heat loss.

Sweat Composition

Sweat starts isotonic to plasma in the gland but becomes hypotonic as Na⁺ and Cl⁻ are reabsorbed in the duct.

Training Adaptation: Sweat Rate

Well-trained and acclimated athletes produce larger volumes of sweat at lower core temperatures, enhancing evaporative cooling.

Aldosterone

Adrenal hormone that promotes renal Na⁺ reabsorption (and water retention) to conserve electrolytes lost in sweat.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that increases water reabsorption in kidneys, reducing urine output during dehydration.

Sex Differences in Sweating

On average, women sweat less than men; differences largely reflect conditioning and heat acclimation status rather than sex alone.