11.2 Aerobic Exercise Prescription: FITT-VP, Intensity Monitoring & Progression

11.2 Aerobic Exercise Prescription: FITT-VP, Intensity Monitoring & Progression

Core Clinical Mandate: An aerobic prescription is as specific as an ultrasound prescription. "Do some cardio" is not a treatment plan. The FITT-VP framework forces every variable to be stated, documented, and progressed.

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The FITT-VP Framework

General population targets: at least 150 minutes per week of moderate-intensity aerobic activity, or 75 minutes per week of vigorous-intensity activity, or an equivalent combination — commonly spread across at least three days, with additional benefit up to roughly 300 minutes per week.

Bout structure: total accumulated volume is what matters most. Three 10-minute walks deliver meaningful benefit for a patient who cannot tolerate a continuous 30-minute session, and starting with accumulated bouts is a legitimate and well-supported strategy.

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Three Ways to Set Intensity

1. Percentage of Heart Rate Reserve — the Karvonen Method

$THR = \left[(HR_{max} - HR_{rest}) \times \%\text{intensity}\right] + HR_{rest}$

Worked example. A 50-year-old with a resting heart rate of 70 bpm, prescribed 60% intensity:

• Estimated HRmax = 220 − 50 = 170 bpm
• Heart rate reserve = 170 − 70 = 100 bpm
• 60% of reserve = 60 bpm
• Target heart rate = 60 + 70 = 130 bpm

Karvonen is preferred over a plain percentage of maximal heart rate because it anchors to the individual's resting heart rate and therefore tracks fitness. Note that the plain percentage-of-maximum method would have given 0.60 × 170 = 102 bpm — a substantially lighter and less appropriate stimulus for the same nominal "60%."

2. Rating of Perceived Exertion

The original Borg RPE scale runs from 6 to 20, designed so that multiplying the rating by ten approximates heart rate in a healthy young adult (RPE 13 ≈ 130 bpm). Landmarks: 6 = no exertion at all, 9 = very light, 11 = light, 13 = somewhat hard, 15 = hard, 17 = very hard, 20 = maximal exertion. A separate Borg CR10 category-ratio scale runs 0 to 10 and is used more often for dyspnoea and pain.

RPE is the intensity tool of choice whenever heart rate is unreliable: beta-blockers and other rate-limiting medications, pacemakers, atrial fibrillation, autonomic neuropathy, and transplanted hearts.

3. The Talk Test

• Moderate intensity: the patient can talk in full sentences but cannot sing.
• Vigorous intensity: the patient can only manage a few words before needing a breath.

Crude but remarkably robust, free, and immediately teachable for home programs.

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Session Structure

1. Warm-up — 5 to 10 minutes of light aerobic activity. This is not optional. Warm-up raises muscle temperature and enzyme activity, increases tissue extensibility, and, critically, allows coronary blood flow to increase in step with myocardial demand. Abrupt high-intensity onset without warm-up is associated with ischaemic ST-segment changes even in asymptomatic individuals.
2. Conditioning phase at the prescribed intensity and duration.
3. Cool-down — 5 to 10 minutes of gradually decreasing activity. During exercise the skeletal muscle pump is a major contributor to venous return. Stopping abruptly removes that pump while peripheral vasodilation persists, causing venous pooling, a fall in venous return, and post-exercise hypotension or syncope. A gradual cool-down is also the period of greatest arrhythmia risk in cardiac patients, so it is supervised rather than skipped.
4. Flexibility work is best placed after the cool-down, when tissue temperature is elevated.

The Cool-Down Rule: Never let a patient go straight from vigorous exercise to a hot shower or to standing still. Peripheral vasodilation plus a lost muscle pump is the classic setup for exertional syncope.

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Continuous vs. Interval Training

For a severely deconditioned patient, interval formats are often the easier option, not the harder one: two minutes of walking alternating with one minute of rest accumulates far more total work than a failed attempt at continuous walking.

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Progression Rules

• Change one variable at a time, so that any adverse response is attributable.
• Extend duration before increasing intensity. Increase total weekly time by roughly 5 to 10% per week in the initial conditioning stage.
• Three stages: initial conditioning (roughly the first 4 to 6 weeks, emphasising tolerance and technique), improvement (progressive increases over several months), and maintenance (holding the achieved dose indefinitely).
• Older and deconditioned adults progress more slowly and benefit from longer warm-ups, lower starting intensity, and non-weight-bearing or aquatic modes where joint pain limits walking.
• Stop or reduce for: chest discomfort, unusual dyspnoea, dizziness or light-headedness, palpitations or an irregular pulse, unusual fatigue, claudication beyond the prescribed threshold, or a fall in systolic blood pressure during increasing workload.

Mode Selection in Musculoskeletal Practice

Integrate, Do Not Bolt On: In a musculoskeletal plan of care, the aerobic prescription should be chosen so that it does not aggravate the presenting complaint and preferably assists it. Prescribing treadmill walking to a patient with irritable neurogenic claudication will fail; prescribing a flexed-posture stationary cycle will not.