📌 Professor’s Notes: Quick Revision
High-yield revision notes for rapid review before university examinations.
- Exercise physiology explains how the body supplies energy and maintains homeostasis during physical activity. Regular exercise improves oxygen utilization, metabolic efficiency, insulin sensitivity, and cardiovascular fitness.
- Types of exercise:
- Isotonic or dynamic exercise involves a change in muscle length with joint movement, such as walking, running and cycling.
- Isometric or static exercise produces tension without significant change in muscle length, such as pushing against a wall.
- Muscle work depends on muscle size, strength, fibre type, motor-unit recruitment, type of contraction, training, fatigue resistance and environmental conditions. Contractions may be concentric, in which the muscle shortens, or eccentric, in which it lengthens while resisting a load.
- Type I fibres are slow, oxidative and fatigue-resistant, making them suitable for endurance activity. Type II fibres contract rapidly, produce greater force and fatigue more quickly. According to the size principle, small motor units are recruited first, followed progressively by larger units as force requirements increase.
- The immediate energy source for muscle contraction is adenosine triphosphate. Stored adenosine triphosphate supports maximal activity for only about 2–3 seconds, while phosphocreatine rapidly regenerates it and supports intense activity for approximately 5–10 seconds.
- Aerobic metabolism uses oxygen to oxidize carbohydrates and fats and supports prolonged exercise. During high-intensity exercise, anaerobic glycolysis provides rapid energy, with lactate formation when oxygen availability is insufficient.
- VO₂max is the maximum rate of oxygen consumption during maximal exercise and is an important measure of aerobic fitness and endurance. It depends mainly on maximum cardiac output, along with pulmonary function, muscle blood flow, capillary density and oxygen extraction.
- During exercise, ventilation increases through greater tidal volume and respiratory rate. Above the lactate threshold, lactate and hydrogen ion production increase, causing a disproportionate rise in ventilation to help maintain acid–base balance.
- Cardiovascular changes include increased heart rate, stroke volume and cardiac output. Cardiac output may rise from about 5 litres/minute at rest to 20–25 litres/minute during strenuous exercise. Skeletal muscle blood flow increases markedly because of local metabolic vasodilation.
- During dynamic exercise, systolic blood pressure rises, whereas diastolic pressure remains unchanged or may fall slightly. During static exercise, both systolic and diastolic pressures rise substantially because contracting muscles compress blood vessels.
- Exercise increases catecholamines, glucagon, antidiuretic hormone and cortisol. These hormones help mobilize glucose and fat, maintain plasma volume and provide energy substrates.
- Aerobic training increases stroke volume, plasma volume, capillary density, mitochondrial activity and oxygen extraction. Resting and submaximal heart rates decrease, while maximum cardiac output and VO₂max improve.
- Regular exercise improves glucose control, helps maintain healthy body weight, strengthens bones and muscles, improves cardiovascular health and supports psychological well-being.
📝 Practice MCQs
🎙️ Frequently Asked Viva Questions
High-yield viva questions with concise answers for rapid university examination preparation.
Q1. Why is VO₂max considered the best indicator of aerobic fitness?
Answer: VO₂max is the highest rate of oxygen utilization during maximal exercise. It reflects the combined efficiency of the cardiovascular, respiratory, and muscular systems.
Q2. What limits VO₂max in healthy individuals?
Answer: The major limiting factor is maximum cardiac output. Muscle capillary density, mitochondrial content, and oxygen extraction also influence VO₂max.
Q3. What is the physiological significance of the lactate threshold?
Answer: It is the exercise intensity at which lactate begins to accumulate rapidly. A higher lactate threshold allows sustained exercise with less fatigue.
Q4. Why does ventilation increase disproportionately after the lactate threshold?
Answer: Lactic acid increases hydrogen ion concentration. Buffering produces extra CO₂, which strongly stimulates chemoreceptors and increases ventilation.
Q5. Why does fatigue develop earlier during isometric exercise than isotonic exercise?
Answer: Sustained contraction compresses blood vessels, reducing muscle blood flow and oxygen supply while accelerating metabolite accumulation.
Q6. What is the size principle of motor unit recruitment?
Answer: Small, fatigue-resistant motor units are recruited first. Larger fast-twitch motor units are added only when greater force is required.
Q7. Why are Type I muscle fibers more resistant to fatigue?
Answer: They contain abundant mitochondria, myoglobin, and oxidative enzymes, allowing efficient aerobic ATP production during prolonged exercise.
Q8. Why does cardiac output increase during exercise?
Answer: It increases to deliver more oxygen and nutrients to active muscles and remove carbon dioxide and metabolic waste.
Q9. How do trained athletes achieve a higher cardiac output?
Answer: Mainly by increasing stroke volume, with a relatively lower heart rate during rest and exercise.
Q10. Why does skeletal muscle blood flow increase during exercise despite sympathetic activity?
Answer: Local metabolic vasodilators override sympathetic vasoconstriction, producing functional vasodilation in active muscles.
Q11. Why does diastolic blood pressure remain unchanged or fall slightly during dynamic exercise?
Answer: Widespread vasodilation in active muscles lowers total peripheral resistance, offsetting the rise in cardiac output.
Q12. Why is isometric exercise not recommended for uncontrolled hypertension?
Answer: It causes a marked rise in both systolic and diastolic blood pressure, increasing myocardial workload.
Q13. Why does carbohydrate loading improve endurance performance?
Answer: It increases muscle glycogen stores, delays glycogen depletion, and postpones fatigue during prolonged exercise.
Q14. Why is water containing salt better than plain water after prolonged exercise?
Answer: Sodium improves water retention, restores plasma volume faster, and supports thermoregulation during recovery.
Q15. What are the most important physiological adaptations produced by aerobic training?
Answer: Increased VO₂max, stroke volume, capillary density, mitochondrial enzymes, insulin sensitivity, and fatigue resistance improve exercise performance.
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