Exercise Physiology in Extreme Environments

Vocabulary practice flashcards covering acute and chronic physiological adaptations to extreme heat, cold, high altitude, microgravity, and high-G environments.

Cardiac Drift

The progressive rise in heart rate during prolonged exercise at a constant workload in the heat, driven by reduced stroke volume, decreased blood volume from sweating, and elevated skin blood flow.

Exertional Heat Stroke (EHS)

A life-threatening hyperthermic emergency occurring when core body temperature rises above $40.5^\circ\text{C}$, characterized by central nervous system dysfunction, leaky gut syndrome, systemic inflammation, and multi-organ failure.

Acetylcholine

The neurotransmitter released by sympathetic sudomotor nerves that binds to receptors on eccrine sweat glands to initiate watery sweat secretion for thermoregulation.

Eccrine Sweat Glands

The primary thermoregulatory sweat glands distributed across human skin that secrete a dilute solution of water, sodium, and chloride onto the skin surface to facilitate evaporative cooling.

Leaky Gut Syndrome

Gastrointestinal barrier breakdown caused by severe hyperthermia and reduced gut blood flow, permitting endotoxins to enter the systemic circulation during exertional heat stroke.

Systemic Inflammatory Response Syndrome (SIRS)

An overwhelming systemic inflammatory reaction triggered by circulating endotoxins in heat stroke, leading to blood clotting abnormalities, cell injury, and tissue damage.

Thermoneutral Temperature

An ambient environmental temperature of approximately $26^\circ\text{C}$ ($79^\circ\text{F}$) for humans, at which body temperature is maintained with minimal active thermoregulatory adjustments.

Peripheral Vasoconstriction

An acute physiological reaction to cold stress where cutaneous blood vessels narrow, redistributing warm blood away from skin and extremities toward core organs.

Whole Body Cryostimulation (WBC)

A therapeutic technique exposing the entire body to extremely low temperatures for brief durations, causing profound peripheral vasoconstriction to shield core temperature.

Partial Pressure of Oxygen ($PO_2$)

The portion of total atmospheric pressure contributed by oxygen, calculated by multiplying barometric pressure by oxygen percentage ($21\%$), which drops as altitude increases.

Space Anemia

An acute decrease in red blood cell mass in microgravity, caused by cephalic fluid shifts that induce hemodilution, reducing erythropoietin production and increasing splenic red blood cell destruction.

Orthostatic Intolerance

The inability to maintain blood pressure and cerebral blood flow upon standing in $1\text{G}$ gravity post-spaceflight, resulting in lightheadedness due to plasma volume reduction.

Space Motion Sickness

A neurological condition occurring in early microgravity caused by sensory conflict among visual, vestibular, and proprioceptive signals due to missing gravitational cues.

HiFi M

A compact exercise countermeasure device created by John Pennant and Saint Mary's University, designed to absorb high-impact vibrations in constrained spaceflight environments.

Respiratory Atelectasis

A condition during high acceleration (high G-forces) where blood accumulates at the base of the lungs, restricting effective alveolar gas exchange to a reduced pulmonary zone.

Heat Acclimatization

Physiological enhancements achieved through repeated natural training exposures in hot outdoor weather, resulting in expanded plasma volume and superior sweating efficiency.

Heat Acclimation

Thermoregulatory adaptations induced artificially in indoor or laboratory settings, such as sauna exposure, environmental chambers, or hot water immersion.

Cardiovascular Drift Decay

The loss of heat adaptations after leaving a warm climate, where heart rate response can increase by up to $150\%$ at equivalent workloads after $25\text{ days}$ in temperate conditions.

Wind Chill Effect

The acceleration of body heat loss caused by ambient wind velocity, which significantly decreases perceived temperature and lowers time-to-freezing for exposed skin.

Altitude Hyperventilation

An immediate increase in breathing frequency and depth triggered by hypoxia at high altitude, serving to raise alveolar oxygen pressure while causing hypocapnia and diuresis.

Microgravity Bone Mineral Density Loss

The progressive loss of bone density in weightlessness, averaging $1\text{ to }2\%$ monthly in weight-bearing bones due to elevated osteoclast activity and reduced osteoblast activity.