IB SEHS Complete Review: Physiological Systems, Homeostasis, Fatigue, Training, and Adaptation

Comprehensive vocabulary flashcards covering the IB Sports, Exercise, and Health Science (SEHS) curriculum, including inter-system communication, cardiovascular and respiratory transport, homeostatic feedback mechanisms, acute and chronic environmental adaptations, muscle fatigue pathways, post-exercise recovery modalities, and scientific training qualities.

Homeostasis

The maintenance of a stable internal environment (regulating variables such as temperature, glucose, blood pressure, pH, hydration, and $\text{O}_2/\text{CO}_2$) using sensory receptors, a control center, and effectors to maintain cellular and enzyme function, athletic performance, and survival.

Negative Feedback Loop

The most common homeostatic control mechanism that detects a deviation from a physiological set point and triggers responses that reverse the change to restore normal conditions through a sequence of stimulus, receptor, control center, effector, and response.

Positive Feedback Loop

A biological feedback mechanism that amplifies a disturbance, driving physiological variables further away from baseline balance; it is non-stabilizing but essential for specific isolated processes.

Blood Glucose Regulation

A homeostatic dual-hormone negative feedback loop that maintains circulating blood sugar within the normal resting range of $4.0\text{--}7.8\,\text{mmol/L}$ by releasing insulin from pancreatic $\beta$-cells when levels rise or glucagon from pancreatic $\alpha$-cells when levels fall.

Insulin

A peptide hormone secreted by the $\beta$-cells of the pancreas that decreases blood glucose by stimulating cellular glucose uptake, promoting glycogenesis in muscle and liver tissue, and inhibiting gluconeogenesis.

Glucagon

A peptide hormone secreted by the $\alpha$-cells of the pancreas that elevates blood glucose by stimulating hepatic glycogenolysis (glycogen breakdown) and gluconeogenesis.

Intrinsic Cardiac Regulation

Pacemaker and conduction control originating entirely inside the heart, where the Sinoatrial (SA) node sets the baseline heart rate, the Atrioventricular (AV) node delays the impulse to allow ventricular filling, and the Bundle of His and Purkinje fibers distribute the electrical depolarisation for coordinated ventricular systole.

Extrinsic Cardiac Regulation

Cardiovascular regulation mediated outside the heart via the autonomic nervous system (sympathetic stimulation increasing heart rate and contractility; parasympathetic vagal stimulation decreasing heart rate) and circulating endocrine hormones (adrenaline, noradrenaline, and thyroid hormones).

Acute Responses to Heat

Immediate thermoregulatory adjustments upon heat exposure, including increased sweat secretion for evaporative cooling, cutaneous vasodilation to transfer heat to the environment, elevated heart rate and cardiac output to sustain blood pressure, redistribution of blood away from the GI tract to the skin and working muscles, and elevated ventilation.

Long-Term Heat Adaptations

Acclimatization adjustments developing over $7\text{--}14\,\text{days}$ of thermal exposure, characterized by an earlier and faster onset of sweating, more dilute sweat to conserve $\text{Na}^+$ and $\text{Cl}^-$, plasma volume expansion, decreased resting and submaximal heart rate, and reduced core body temperature at equal workloads.

Acute Responses to Humidity

Physiological strain occurring in vapour-saturated air where sweat cannot evaporate effectively, leading to rapid core body temperature escalation, excessive dripping fluid loss without cooling, marked cardiovascular load, and premature fatigue.

Acute Mountain Sickness

A condition caused by acute altitude exposure and hypoxia (reduced ambient oxygen partial pressure and arterial oxygen saturation), clinically presenting with headaches, nausea, dizziness, hyperventilation, and reduced aerobic endurance capacity.

Fatigue

An exercise-induced, reversible decline in skeletal muscle force generation, power output, and physical endurance originating anywhere along the motor or energy-producing pathways.

Central Fatigue

Neuromuscular fatigue localized in the central nervous system (brain and spinal cord) that restricts efferent motor drive as a protective mechanism against physiological trauma, resulting in slowed reaction times and impaired motor coordination.

Peripheral Fatigue

Fatigue occurring downstream of the central nervous system at the neuromuscular junction (NMJ) or within the working muscle fibres due to metabolite accumulation, fuel depletion, or excitation-contraction uncoupling.

Muscle Acidosis

The excessive buildup of hydrogen ions ($\text{H}^+$) from high-intensity anaerobic glycolysis that drops intramuscular pH from $7.1$ down to approximately $6.5$, inhibiting rate-limiting enzymes and hindering calcium ($\text{Ca}^{2+}$) binding to troponin during cross-bridge cycling.

Cori Cycle

A metabolic recovery pathway in which lactate generated by anaerobic glycolysis in contracting muscles is transported through the bloodstream to the liver to be reconverted into glucose and returned to circulation.

Electrolytes in Muscle Contraction

Essential charged minerals governing cellular excitability and contraction: $\text{Na}^+$ regulates fluid balance and action potential generation, $\text{K}^+$ mediates repolarization, $\text{Ca}^{2+}$ enables actin-myosin cross-bridge binding, and $\text{Mg}^{2+}$ supports ATP resynthesis and muscle relaxation.

Delayed Onset Muscle Soreness (DOMS)

Symptomatic post-exercise muscle pain, tenderness, and structural inflammation resulting from unaccustomed eccentric contractions; its resolution signals physiological tissue restoration.

Slow-Wave Sleep (Stage 3 NREM)

The deepest non-rapid eye movement sleep phase, during which the majority of physical recovery takes place through heightened growth hormone (GH) release, protein synthesis, and cellular repair.

Placebo Effect in Recovery

A psycho-neurobiological phenomenon wherein an athlete's psychological belief in a recovery modality triggers central dopamine and endogenous opioid release, reducing pain and perceived fatigue without accelerating physiological tissue repair.

Sarcopenia

The involuntary, age-related degeneration of skeletal muscle mass, strength, and function, which is mitigated and delayed by ongoing resistance and balance training.

Energy Balance

The thermodynamic relationship between total energy intake from food and drink versus total energy expenditure (basal metabolic rate, thermic effect of food, and physical activity), governing changes in body weight.

Muscular Hypertrophy

The enlargement of total muscle cross-sectional area and individual skeletal muscle fiber diameters resulting from chronic resistance training overload.

J-Shaped Curve of Immune Function

A model illustrating that sedentary behaviour provides low immune protection, moderate exercise maximizes immune circulation (T-cells, B-cells, macrophages) and lowers infection risk, while excessive overtraining elevates cortisol and causes immunosuppression.

Atherosclerosis

A vascular disease characterized by the deposition of fatty plaques inside arterial lumens, reducing vessel elasticity and lumen diameter, and increasing the risk of myocardial infarction and stroke.

Visceral Fat

Adipose tissue stored intra-abdominally around vital organs that markedly raises the risk of metabolic syndromes and type 2 diabetes, which is reduced by physical activity.

Osteopenia

A clinical condition marked by an early, moderate reduction in bone mineral density (BMD) below normal thresholds, predisposing individuals to osteoporosis if mechanical loading is absent.

Osteoporosis

A progressive skeletal disease characterized by severe bone demineralization, structural microarchitectural deterioration, and high fracture susceptibility, preventable through regular weight-bearing exercise.

Leptin

A hormone produced by adipose tissue that acts on the hypothalamus to suppress appetite when fat stores are sufficient; physical activity improves leptin sensitivity, whereas obesity induces leptin resistance.

Lactate Inflection Point (LIP)

The highest exercise workload or oxygen uptake where blood lactate production equals clearance, occurring at approximately $50\text{--}60\%\,\text{VO}_2\,\text{max}$ in untrained individuals and shifting to $80\text{--}90\%\,\text{VO}_2\,\text{max}$ in endurance-trained athletes.

Principle of Specificity

The training principle asserting that physiological, metabolic, biomechanical, and neuromuscular adaptations occur exclusively in the energy systems, movement patterns, and muscle groups stressed during training.

Progressive Overload

The systematic and gradual escalation of training stress (manipulating session frequency, intensity, or duration) over time to continually drive structural adaptation and prevent performance plateaus.

Principle of Reversibility

The training principle stating that physiological fitness adaptations are lost when training stimulus ceases or drastically declines, resulting in strength losses of approximately $10\%$ per week and $\text{VO}_2\,\text{max}$ reductions up to $15\%$ in $2\text{--}3\,\text{weeks}$.

Periodization

The structured planning and division of an athletic training program into progressive phases (macrocycles, mesocycles, and microcycles) that include planned tapering, peaking, and recovery to optimize performance while preventing burnout.

Macrocycle

The largest training periodization block, typically spanning an entire competitive season or annual cycle, comprised of preparatory, competitive, and transition phases.

Mesocycle

A medium-duration training division typically lasting $4\text{--}12\,\text{weeks}$, focusing on the progressive development of specific athletic capacities such as endurance, hypertrophy, or maximum strength.

Microcycle

A short-term training block typically spanning $5\text{--}10\,\text{days}$ (commonly a single week) outlining individual daily training sessions, intensity variations, and recovery days.

Overreaching

A short-term accumulation of excess training load that causes temporary performance decrements and acute fatigue, from which full recovery and supercompensation occur within days following rest.

Overtraining

A chronic maladaptation state triggered by persistent excessive training volumes, insufficient recovery, poor nutrition, or life stress, resulting in prolonged performance collapse, elevated resting heart rate, insomnia, mood disturbances, and immune suppression.

Prehabilitation

Targeted proactive exercise interventions designed to strengthen vulnerable kinetic links, enhance joint stability, and improve mobility to reduce the risk of sports-related injuries.

RAMP Protocol

A four-phase structured warm-up sequence: Raise body temperature, heart rate, and respiration; Activate key musculature; Mobilize relevant joint ranges of motion; and Potentiate the neuromuscular system using sport-specific drills.

Stroke Volume (SV)

The volume of blood ejected from the left ventricle into circulation during a single systole, averaging $60\text{--}70\,\text{mL/beat}$ in untrained individuals at rest and $100\text{--}120\,\text{mL/beat}$ in endurance-trained athletes, governed by end-diastolic preload, contractility, and afterload.

Cardiac Output (CO or Q)

The total volume of blood pumped by the ventricles per minute, calculated by multiplying heart rate by stroke volume ($CO = HR \times SV$), which increases from $\sim 5\,\text{L/min}$ at rest up to $20\text{--}40\,\text{L/min}$ during maximal exercise.

Blood Redistribution (Vascular Shunt)

The sympathetic-mediated diversion of cardiac output during physical exertion that causes vasoconstriction in the kidneys and GI tract alongside marked vasodilation in working skeletal muscles, the heart, lungs, and skin.

Diastole

The cardiac cycle phase during which the ventricular myocardium relaxes, allowing the ventricles to fill with blood entering from the atria.

Systole

The cardiac cycle phase characterized by forceful ventricular myocardial contraction that propels pressurized blood out of the heart into systemic and pulmonary circulations.

Alveoli

Microscopic terminal air sacs in the respiratory tract possessing thin walls, vast surface areas, and extensive surrounding capillary networks that serve as the primary site of external gas exchange.

Bicarbonate Ion Transport

The predominant mechanism of blood carbon dioxide transport in which $70\%$ of circulating $\text{CO}_2$ is converted and transported in the blood as bicarbonate ions ($\text{HCO}_3^-$).

Minute Ventilation (VE)

The total volume of air inspired or expired per minute, defined mathematically as tidal volume multiplied by respiratory rate ($VE = TV \times RR$), rising from approximately $6\,\text{L/min}$ at rest up to $100\text{--}150\,\text{L/min}$ during maximal exertion in endurance athletes.

Tidal Volume (TV)

The volume of air inspired or expired during a normal respiratory cycle, averaging approximately $0.5\,\text{L}$ ($500\,\text{mL}$) at rest and increasing to $2\text{--}3\,\text{L}$ during vigorous exercise.

Vital Capacity (VC)

The maximum volume of air that can be voluntarily exhaled after completing a full, maximal inhalation, typically measuring between $4\text{--}6\,\text{L}$.

Residual Volume (RV)

The volume of air remaining inside the pulmonary alveoli and airways following a maximal forced exhalation, measuring approximately $1.2\,\text{L}$.

Total Lung Capacity (TLC)

The total volume of air contained within the lungs following maximal inspiration, calculated as vital capacity plus residual volume ($\text{TLC} = \text{VC} + \text{RV}$).

Afferent Neurons

Sensory nerve fibers of the peripheral nervous system that conduct impulses from peripheral sensory receptors (sensing pressure, temperature, chemical concentrations, and limb position) inward to the central nervous system.

Efferent Neurons

Motor nerve fibers of the peripheral nervous system that carry regulatory signals outward from the central nervous system to target effectors, split into somatic (skeletal muscle) and autonomic (cardiac muscle, smooth muscle, and glands) branches.

Somatic Nervous System

The voluntary motor subdivision of the peripheral nervous system that innervates skeletal muscle via single motor neurons to execute voluntary movements as well as involuntary shivering contractions.

Autonomic Nervous System (ANS)

The involuntary division of the peripheral efferent nervous system comprising the sympathetic branch (accelerating cardiac output, mobilizing fuels, and causing bronchodilation) and the parasympathetic branch (slowing heart rate and supporting digestion and recovery).

Baroreceptor Reflex

An autonomic homeostatic blood pressure reflex mediated by stretch receptors in the carotid sinus and aortic arch; when arterial pressure increases, baroreceptor afferent firing increases to stimulate vagal activity and suppress sympathetic tone, decreasing heart rate.

Proprioceptors

Sensory mechanoreceptors (specifically muscle spindles and Golgi tendon organs) located in muscles, tendons, and joint capsules that monitor kinesthetic position, muscle stretch, and tension, which also stimulate the rapid initial increase in ventilation at exercise onset.

Chemoreceptors

Specialized sensory receptors located centrally in the medulla oblongata and peripherally in the carotid and aortic bodies that detect changes in blood and cerebrospinal fluid $\text{CO}_2$, $\text{H}^+$ (pH), and $\text{O}_2$ concentrations to modulate ventilation depth and rate.

Antidiuretic Hormone (ADH / Vasopressin)

A peptide hormone synthesized in the hypothalamus and released from the posterior pituitary during dehydration or intense sweating (in response to increased plasma osmolarity), which promotes renal water reabsorption, minimizes urine output, and preserves plasma volume and blood pressure.

Catecholamines (Epinephrine and Norepinephrine)

Sympathetic adrenal hormones released under acute physical stress that increase myocardial contractility and heart rate, cause bronchodilation, stimulate glycogenolysis and lipolysis for rapid fuel availability, and redistribute systemic blood flow to active skeletal muscles.