Exercise Physiology, Prescription, and Diagnostic Exercise Testing
Physiology to own
The Fick equation, VO2 equals cardiac output times arteriovenous oxygen difference, explains why maximal oxygen uptake is centrally limited in most healthy people. Stroke volume plateaus at roughly 40-60% of VO2max while heart rate keeps rising, and peripheral training widens the arteriovenous difference. Maximal heart rate is best measured; 220 minus age has a standard deviation near 10-12 beats per minute and overestimates in young athletes while underestimating in older adults.
Thresholds and prescription
The lactate threshold sits near 50-60% of VO2max in untrained people and 70-80% in trained endurance athletes. One MET equals 3.5 mL/kg/min. Prescriptions follow FITT: frequency, intensity using heart rate reserve by the Karvonen formula, percentage of VO2max, or rating of perceived exertion, then time and type, with progressive overload and specificity.
Diagnostic testing
Indications include chest pain evaluation, known or suspected coronary disease, arrhythmia provocation, and functional capacity assessment. Absolute contraindications include acute myocardial infarction, unstable angina, and uncontrolled symptomatic arrhythmia. The Duke treadmill score combines exercise duration, ST-segment deviation, and angina index. Chronotropic incompetence and a blunted heart rate response carry prognostic weight, and beta-blockers blunt peak heart rate and reduce test sensitivity.
Traps
- Confusing the Borg 6-20 scale (roughly heart rate divided by ten) with the 0-10 category-ratio scale.
- Treating a normal resting ECG as excluding disease.
- Quoting an age-predicted maximum as measured.
Rule of thumb: if peak heart rate falls below 85% of age-predicted without a rate-limiting drug, call the study submaximal and interpret a negative result cautiously.