Fluid & Electrolytes in Exercise Physiology

Comprehensive vocabulary flashcards covering thermoregulation, fluid balance, dehydration mechanisms, acclimatization, and sports beverage composition from the Fluid & Electrolytes lecture.

Hypothalamus (Thermoregulation)

The thermoregulatory center in the brain that detects elevations in core body temperature via venous blood returning to the heart and coordinates effector responses to increase skin blood flow and trigger sweating.

Radiation (Heat Transfer)

The transfer of heat energy between the body and the environment through electromagnetic emission by one object and absorption by another via skin capillaries.

Convection (Heat Transfer)

The exchange of thermal energy between a solid surface (such as the human body) and a moving fluid or gas (such as air currents or water).

Conduction (Heat Transfer)

The direct transfer of heat energy between two physical objects that are in direct physical contact with one another (e.g., warm human skin and an applied ice pack).

Evaporative Cooling

The primary avenue of heat dissipation during exercise where the vaporization of $1\,\text{L}$ ($0.3\,\text{gal}$) of sweat from the skin removes approximately $573\,\text{kcal}$ of heat from the body.

Insulative Hypothermia

A cold-acclimatization adaptation observed in Australian aborigines sleeping in the cold desert, characterized by lowered skin and core body temperatures that decrease the thermal gradient with the environment to minimize heat loss and conserve energy.

Heat Acclimatization

Physiological adaptations induced by training in the heat for at least $60\,\text{min/day}$ (peaking around $7$ days and maximal after $14$ days), causing an earlier onset of sweating, sweat gland hypertrophy without increasing gland count, a higher sweat rate, and expanded blood volume.

Dehydration Performance Threshold

A fluid deficit equivalent to as little as $2\%$ of body weight, which is sufficient to reduce aerobic capacity, impair non-body-weight dependent performance, and decrease upper and lower muscle strength by $5.5\%$.

Glycerol Hyperhydration

The pre-exercise consumption of a 3-carbon alcohol with osmotic properties ingested with large volumes of fluid to draw water intracellularly and expand plasma volume; formerly prohibited by WADA between 2010 and 2018.

Sensible Water Loss

Measurable and regulated daily fluid losses from the body, primarily consisting of urine excretion ($800\text{--}1600\,\text{mL/day}$) and fecal output ($\sim 100\,\text{mL/day}$).

Insensible Water Loss

Continuous, largely unregulated fluid loss occurring via passive skin evaporation and respiratory tract exhalation, which varies from $200\,\text{mL/day}$ in warm, moist air to $1500\,\text{mL/day}$ during high-altitude cold, dry conditions.

Metabolic Water

Water synthesized internally as an end product of aerobic cellular respiration ($\text{Glucose} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{ATP}$), providing roughly $300\,\text{mL/day}$ ($0.3\,\text{L/day}$) of daily fluid input.

Antidiuretic Hormone (ADH)

A peptide hormone synthesized by the hypothalamus and secreted by the posterior pituitary gland during dehydration to stimulate renal water reabsorption and decrease urine output.

Exercise-Associated Hyponatremia

A dilutional state where plasma sodium drops to $\le 130\,\text{mmol/L}$ (critical at $\le 120\,\text{mmol/L}$) due to excessive plain water intake during prolonged events ($> 4$ hours), leading to cerebral edema (dilutional encephalopathy) and pulmonary edema.

Weight-Urine-Thirst (WUT) Principle

The IOC-recommended triad for evaluating pre-exercise hydration: day-to-day body weight fluctuations kept under $1\text{--}2\%$, urine specific gravity below $1.020$ (or $< 900\,\text{mOsmol/kg}$) with pale yellow color, and the absence of thirst.

Isotonic Sports Drink

A beverage with an osmolality matching human body fluids that rapidly replenishes water lost in sweat while providing a carbohydrate fuel boost; preferred for team sports and middle- to long-distance running.

Hypertonic Sports Drink

A high-osmolality beverage containing higher carbohydrate and salt concentrations than body fluids, used post-workout to restore glycogen stores or during ultra-endurance events when co-ingested with isotonic fluids.

Hypotonic Sports Drink

A beverage with lower carbohydrate and electrolyte osmolarity than body fluids, designed for rapid fluid replacement without an unneeded carbohydrate load (e.g., for gymnasts).

Post-Exercise Sodium Rehydration

The addition of sodium ($\sim 77\,\text{mmol/L}$ of $\text{NaCl}$) to recovery fluids to prevent a rapid drop in plasma osmolality, sustain the osmotic drive to drink, and minimize excess urinary water loss.

Exercise-Associated Muscle Cramping

A neuromuscular syndrome resulting from localized muscular fatigue and altered nervous system reflex control rather than an acute whole-body sodium deficit, though potentially aggravated by excessive plain water ingestion.