Exercise Physiology at Altitude

Vocabulary flashcards covering key altitude-related physiology terms, mechanisms, and adaptations drawn from the lecture notes.

Barometric Pressure

The total air pressure exerted by the atmosphere; falls progressively with increasing altitude.

Partial Pressure of Oxygen (PO₂)

The portion of barometric pressure attributable to oxygen; its decline at altitude limits O₂ availability to tissues.

Hypobaria

Condition of low atmospheric (barometric) pressure experienced at high elevations.

Hypoxia

General term for reduced oxygen availability to tissues, common during altitude exposure.

Hypoxemia

Abnormally low arterial PO₂ (oxygen content) in the blood, triggered by altitude.

Altitude (exercise context)

Elevation above ~1,500 m where reduced PO₂ begins to alter exercise physiology.

Sea-Level Pressure

Standard atmospheric pressure of ~760 mmHg used as baseline for comparison with altitude.

Thermal Lapse Rate

Approximate 10 °C (18 °F) drop in air temperature per 1,500 m ascent, increasing cold stress risk.

Water Vapor Pressure at Altitude

Lower absolute humidity in cold, thin air, enhancing skin and respiratory water loss.

Pulmonary Ventilation

Movement of air into the alveoli; rises within seconds of altitude exposure to compensate for low PO₂.

Chemoreceptors

Sensors in the aortic arch & carotid arteries that detect low arterial PO₂ and stimulate hyperventilation.

Hyperventilation (acute altitude)

Rapid, deep breathing triggered by chemoreceptor stimulation; raises alveolar ventilation but lowers CO₂.

Respiratory Alkalosis

Blood pH elevation due to CO₂ washout from hyperventilation; kidneys excrete bicarbonate to compensate.

Oxyhemoglobin Dissociation Curve Shift Left

Alkalosis-induced increase in hemoglobin’s affinity for O₂, helping maintain arterial saturation despite low PO₂.

Pulmonary Diffusion

Gas exchange between alveoli and blood; not a major limitation at altitude—the problem is low alveolar PO₂.

Oxygen Transport

Process of O₂ binding to hemoglobin; saturation falls from ~97 % at sea level to ~80 % at moderate altitude.

Arterial-Tissue PO₂ Gradient

Driving force for O₂ diffusion to muscles; shrinks from ~60 mmHg at sea level to ~15 mmHg at high altitude.

Plasma Volume Decrease

Up to 25 % reduction within days due to respiratory water loss and diuresis, raising hematocrit temporarily.

Hematocrit

Percentage of blood volume occupied by red cells; initially rises with plasma loss, later rises again via EPO.

Erythropoietin (EPO)

Kidney-derived hormone that stimulates RBC production during prolonged altitude exposure.

Cardiac Output at Altitude

Elevated at rest and sub-max exercise (↑HR) early in exposure, but reduced at maximal effort.

Stroke Volume Changes

Reduced SV from smaller plasma volume; partly offsets the HR-mediated rise in cardiac output.

Sympathetic Stimulation

Altitude-induced increase in epinephrine & norepinephrine, boosting HR, CO, and metabolic rate.

Basal Metabolic Rate (BMR) Increase

Elevation in thyroxine and catecholamines raises energy expenditure at altitude.

Carbohydrate Reliance

Greater dependence on CHO for fuel because glycolysis yields more ATP per liter of O₂ than fat oxidation.

Lactate Response to Altitude

Initial rise in blood lactate at a given workload; after weeks, lactate levels fall despite similar effort.

VO₂ max Reduction

Progressive decline in maximal O₂ uptake beginning around 1,500 m due to limited arterial PO₂ and lower CO.

Acclimatization

Series of physiological adjustments (↑ventilation, ↑RBCs, ↑plasma volume) that partially restore performance over weeks.

Polycythemia

Altitude-induced increase in RBC mass and hematocrit (often 60–65 % in long-term residents).

Capillary Density Increase

Expansion of capillary network in muscles, enhancing O₂ diffusion after weeks at altitude.

Muscle Fiber CSA Decrease

Shrinkage of muscle fiber cross-sectional area with prolonged hypoxia, reducing diffusion distance.

Mitochondrial Function Reduction

Decline in oxidative enzyme activity and ATP production capacity after several weeks in hypoxia.

Glycolytic Enzyme Activity Reduction

Lowered glycolytic potential in muscle with extended altitude exposure, diminishing anaerobic capacity.

Tibetan Chest Adaptation

Genetically larger thoracic circumference giving higher TLC, VC, and TV compared with lowlanders.

Tibetan Hemoglobin Levels

Normal to only slightly elevated hemoglobin despite altitude, reflecting efficient O₂ utilization.

Reduced Pulmonary Vasoconstriction (Tibetans)

Blunted hypoxic pulmonary hypertension, easing right-heart strain at altitude.

Small Muscle Fibers & Glucose Use (Tibetans)

More capillaries, smaller fibers, and greater reliance on glucose oxidation for efficient O₂ use.

Lower Lactate Production (Tibetans)

Genetically lower lactate accumulation during work, indicating superior metabolic adaptation to hypoxia.