Exercise physiology and prescription: METs, energy systems, intensity, training

1The MET (3 marks in W22, S24, S25)

One metabolic equivalent (MET) is the energy used at rest, sitting quietly: about 3.5 mL of oxygen per kg of body weight per minute (roughly 1 kcal per kg per hour). An activity of 4 METs uses four times the resting energy.

Uses: grading activity intensity (light below 3 METs, moderate 3–5.9, vigorous 6 or more); Phase I cardiac rehab goes up to about 3 METs; a good functional capacity is 7 METs or more; sexual activity is reasonable when 3–5 METs are tolerated.

2Energy systems (7 marks in S24)

Muscles run on ATP, but they store only enough for a few seconds. Three systems remake it, overlapping all the time; which one leads depends on how hard and how long the effort is.

Fuel mix: fat dominates at rest and low intensity; carbohydrate takes over as intensity rises. The respiratory quotient (CO₂ produced ÷ O₂ used) is about 1.0 for carbohydrate and 0.7 for fat.

3Aerobic and anaerobic exercise (3 marks in W22)

4Methods of measuring exercise intensity (7 marks in S23)

1. Heart-rate reserve (Karvonen) method (W25): target HR = resting HR + intensity × (maximum HR − resting HR). Maximum HR is estimated as 220 − age (or 208 − 0.7 × age, Tanaka). Example: age 60, resting HR 70: maximum 160, reserve 90; 50% = 70 + 45 = 115.
2. Percentage of maximum heart rate: simple but less precise.
3. Oxygen uptake: % of VO₂max or VO₂ reserve, from a cardiopulmonary exercise test (the gold standard).
4. METs: choose activities by their MET value; on a treadmill or cycle, set the workload in METs or watts.
5. Rating of perceived exertion: Borg 6–20 (moderate 12–13) or CR10 breathlessness (moderate to strong, 3–5 in pulmonary rehab).
6. Talk test: moderate if the patient can talk but not sing; vigorous if only a few words.
7. Field-test speed: walking at about 80% of the speed reached on the 6MWT or shuttle test.
8. Thresholds: ventilatory or lactate threshold; ischaemic threshold (train at least 10 beats below the heart rate where angina or ST change appears).
9. Strength training: % of one-repetition maximum (1RM) or the number of repetitions possible.

Use RPE and the talk test when heart rate is unreliable: beta-blockers, atrial fibrillation, pacemakers, heart transplant.

5Principles of training and adaptations

• FITT-VP: Frequency, Intensity, Time, Type, Volume, Progression.
• Principles: overload (work above usual levels), specificity (you improve what you train), progression, individuality, reversibility (gains fade within weeks of stopping), warm-up and cool-down.

6Cardio-respiratory changes with ageing and a fitness programme (7 marks in S16)

Fitness programme for older adults (WHO 2020): 150–300 minutes a week of moderate aerobic activity (or 75–150 minutes vigorous); muscle-strengthening on 2 or more days; varied activity that emphasises balance and strength on 3 or more days a week to prevent falls; start low and progress slowly; longer warm-up and cool-down; check medicines and heart conditions first. Regular exercise slows the loss of fitness, strength and independence with age.

7Exam corner

Past questions (MUHS, 2016–2026)

• 7-mark questionsCardio-respiratory changes with ageing and a fitness programme (S16). Methods of measuring exercise intensity (S23). Types of energy systems with examples (S24).
• 3-mark questionsDefine one MET and state its value (W22). Three differences between aerobic and anaerobic exercise (W22). Define MET and give the METs of two daily activities (S24). Metabolic equivalent (S25). Karvonen's formula in cardiac rehabilitation (W25; worked on the IHD page).