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Aerobic Exercise Prescription

Definition / Explanation

Aerobic exercise prescription in cardiac rehabilitation is the process of quantifying the correct intensity, duration, frequency, and progression rate for a patient's cardiovascular training. Unlike general fitness prescriptions, CR prescriptions must account for medication effects (beta-blocker chronotropic blunting), cardiac risk stratification, and the need for physician-signed Individualized Treatment Plans (ITPs) updated every 30 days. ^[raw/cardiac-recovery-fitness-protocol-deep-research.md]

Intensity Targets

Graded Exercise Test (GXT) — Preferred Method

When a GXT is available, prescription is calculated from measured maximal functional capacity and peak heart rate. Target intensity is 40–80% of Heart Rate Reserve (HRR) or Oxygen Consumption Reserve (VO₂R). ^[raw/Exercise_Progression_and_GXT_Standards.md]

Karvonen Formula (target heart rate calculation):

Target Heart Rate = (HR_max − HR_rest) × %Intensity + HR_rest

Where HR_max is measured directly from GXT, and HR_rest is measured after 5 minutes of quiet seated rest. ^[raw/cardiac-recovery-fitness-protocol-deep-research.md]

Limitation: Only ~30% of CR clinics actually perform intake stress testing. ^[raw/Exercise_Progression_and_GXT_Standards.md]

Without GXT — Estimation Method

In the absence of GXT data, initial targets must be estimated using: - Resting heart rate + 20–30 bpm as a starting point - Borg Rating of Perceived Exertion (RPE) ceiling of 11–14 (6–20 scale, "light" to "somewhat hard")

This subjective ceiling becomes the primary safety guard when objective cardiac data is unavailable. ^[raw/Exercise_Progression_and_GXT_Standards.md]

Borg RPE Scale Reference

RPE (6–20) Descriptor Clinical Interpretation
6 No exertion Resting
7–8 Extremely light Warm-up territory
9–10 Very light Very easy activity
11–12 Light Target zone lower bound for Phase II
13–14 Somewhat hard Target zone upper bound for Phase II
15–16 Hard Phase III+ only, with telemetry clearance
17–18 Very hard Reserved for high-risk screened athletes
19–20 Extremely hard Contraindicated in CR

^[raw/cardiac-recovery-fitness-protocol-deep-research.md]

Duration and Frequency

  • Initial Phase II target: 20–30 minutes of continuous exercise, 3 days/week ^[raw/cardiac-recovery-fitness-protocol-deep-research.md]
  • Minimum for general health: 150 minutes/week moderate-intensity (≈1000 kcal/wk) ^[raw/Optimizing_Exercise_Volume_for_Secondary_Prevention.md]
  • Progression: Increase duration by 1–5 min/week until 40–60 min is comfortably tolerated, then begin titrating intensity ^[raw/Exercise_Progression_and_GXT_Standards.md]

Duration-First Progression Rule

Progression must prioritize increasing session duration before adjusting speed or resistance load. Among real-world CR clinics, 60 out of 77 explicitly follow "duration first" sequencing. Only 10 adjust intensity before duration. Attempting to increase intensity first causes sudden spikes in rate-pressure product, raising myocardial oxygen demand before the coronary vasculature has adapted. ^[raw/Exercise_Progression_and_GXT_Standards.md]

Ranked Progression Indicators (clinical decision framework)

  1. Sustained subjective RPE — patient finds current workload comfortable for 2+ consecutive sessions
  2. Stable hemodynamic response — blood pressure and ECG remain within normal ranges during and after exercise
  3. Predetermined session count — typically 6–12 sessions at a given level before progression

Documentation of progression adjustments must be systematic: 59 out of 73 surveyed clinics document per session; 13 do so weekly. ^[raw/Exercise_Progression_and_GXT_Standards.md]

MET-Minute Calculation

Volume is quantified as MET-minutes per week, calculated as: ^[raw/Optimizing_Exercise_Volume_for_Secondary_Prevention.md]

Volume (MET-min/wk) = Frequency (days/wk) × Intensity (METs) × Time (min/day)

Where 1 MET = 3.5 mL·kg⁻¹·min⁻¹ (resting oxygen consumption). An increase in functional capacity of just 1 mL·kg⁻¹·min⁻¹ is associated with a 10% reduction in cardiac mortality. ^[raw/Optimizing_Exercise_Volume_for_Secondary_Prevention.md]