Physiology and Exercise Physiology
This domain checks whether you can predict how a patient's cardiorespiratory and metabolic systems respond to load, and how to turn that into a defensible intensity prescription. Expect calculation items and questions about precautions in cardiac, metabolic and respiratory disease.
Energy systems and fibre types
- Phosphagen (ATP–phosphocreatine): 0–10 s, maximal intensity, no oxygen, fatigues fastest.
- Anaerobic glycolysis: roughly 10 s to 2 min, lactate accumulation, small ATP yield.
- Oxidative phosphorylation: beyond 2 min, mitochondrial, large ATP yield from carbohydrate and fat.
- Type I fibres are slow, oxidative and fatigue-resistant; Type IIa are fast oxidative-glycolytic and highly adaptable; Type IIx are fast glycolytic with high force and rapid fatigue.
Adaptation and detraining
Neural adaptations (recruitment, rate coding, coordination) explain most strength gain in the first 4 weeks; measurable hypertrophy appears from about 6–8 weeks. Significant detraining occurs within 2–4 weeks of unloading, which matters when planning post-operative or bed-rest programmes.
Cardiovascular and respiratory responses
- Fick equation: VO2 = cardiac output × arteriovenous oxygen difference, i.e. HR × stroke volume × (a–vO2 diff).
- Heart rate rises linearly with workload; VO2 plateaus at VO2max; lactate threshold sits near 50–60% of VO2max in untrained people and 70–80% in trained athletes.
- Systolic pressure rises with workload; diastolic should stay stable or fall slightly. A fall in systolic pressure or failure to rise is a warning sign to stop.
- Valsalva raises intrathoracic pressure, reduces venous return, then produces a rebound pressor surge; teach exhalation on effort in cardiac and hypertensive patients.
Worked example
A 40-year-old has resting HR 70 and a measured HRmax of 180. Target at 60% of heart rate reserve (Karvonen): 70 + 0.60 × (180 − 70) = 70 + 66 = 136 bpm. At 70%: 70 + 77 = 147 bpm. Note that using 220 − age would give a different answer, so state your method. If the patient takes a beta-blocker, the heart rate response is blunted and Borg RPE 12–14 should drive intensity instead.
Traps that cost marks
- Treating 220 − age as a measured maximum.
- Mixing percentage of HRmax with percentage of heart rate reserve without naming the formula.
- Confusing delayed-onset muscle soreness (24–72 h, eccentric origin, resolves in 5–7 days) with acute injury.
- Ignoring that isometric, eccentric and concentric training produce different, specific adaptations.