Exercise Physiology Foundations
The Exercise Physiology Foundations domain tests how the body meets the energy demand of movement and how cardiovascular, respiratory, neuromuscular, and endocrine systems integrate. Questions often ask you to interpret acute responses, distinguish energy systems, or apply a physiological equation rather than recall a label.
Core rules and concepts
- ATP is the immediate energy currency. The phosphagen system (ATP-PCr) supports brief, high-power efforts; glycolysis supports short-to-moderate efforts and produces lactate; oxidative phosphorylation supports sustained work and yields roughly 30–32 ATP per glucose in modern estimates.
- The Fick equation is central: VO2 = cardiac output (Q) × arterial–venous O2 difference. Q = HR × stroke volume.
- During progressive exercise, HR and Q rise, blood flow is redistributed to active muscle, and a–vO2 difference widens. Stroke volume plateaus near 40–60% of VO2max in many people.
- Lactate is both a fuel and a signaling molecule; it is not the sole cause of fatigue. Fatigue is multifactorial (Pi, H+, Ca2+ handling, substrate depletion, heat, central factors).
- EPOC is the excess post-exercise O2 consumption; it reflects replenishment of phosphagens, lactate clearance, restored O2 stores, and elevated temperature/ventilation, but its calorie cost is often overstated.
- The size principle describes orderly motor-unit recruitment from small, fatigue-resistant units to large, powerful units.
Worked example
A 70 kg cyclist has Q = 20 L/min and a–vO2 difference = 150 mL O2 per liter of blood. VO2 = 20 × 150 = 3,000 mL/min = 3.0 L/min. Relative VO2 = 3,000 ÷ 70 = 42.9 mL/kg/min. Using approximately 5 kcal per liter of O2, energy expenditure is 3.0 × 5 = 15 kcal/min, or 450 kcal in 30 minutes. The reasoning chain matters: Fick equation first, then relative scaling, then caloric conversion.
Traps that cost marks
- Mixing absolute (L/min) and relative (mL/kg/min) VO2; relative values allow comparisons across body sizes.
- Treating 220 − age as a measured maximum; it is a population estimate with large individual error.
- Claiming lactate causes acidosis or fatigue directly; lactate production is associated with, not identical to, H+ accumulation.
- Confusing oxygen deficit at exercise onset with EPOC after exercise.
- Ignoring that substrate use shifts with intensity and training status; “fat burning” is not confined to low intensity.
- Assuming HR is always a valid intensity marker; beta-blockers, pacemakers, heat, and anxiety alter the HR–VO2 relationship.