7.3 Aerobic Conditioning and Cardiorespiratory Fitness

Aerobic Conditioning and Cardiorespiratory Fitness

Aerobic conditioning builds the capacity to sustain activities such as walking and stair climbing. Match the exercise to the patient’s baseline function, goals and safety requirements. In rehabilitation, symptoms and the response to workload help guide the prescription.

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The FITT-VP Exercise Prescription Framework

Use FITT-VP to record the dose and decide what to change when the patient’s capacity improves.

Saudi physical activity guidance for healthy adults recommends 150–300 minutes a week of moderate aerobic activity, 75–150 minutes of vigorous activity, or a combination of equivalent intensity and duration. Activity can accumulate across the week. A person entering supervised rehabilitation may begin with much shorter bouts and a different intensity, depending on medical stability and functional capacity.

Volume example: An activity estimated at 4 METs for 30 minutes on five days gives 150 minutes and an estimated $4 \times 30 \times 5 = 600$ MET-minutes per week. This is a workload estimate. Record symptoms and effort separately because the same absolute workload can be easy for one person and difficult for another.

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Target Heart Rate Calculations and Mathematical Models

Estimating peak heart rate

Age equations such as $220 - \text{age}$ and the Gellish equation, $207 - 0.7 \times \text{age}$, estimate maximal heart rate in beats per minute (bpm) at a population level. An individual’s result can differ substantially. When a suitable symptom-limited exercise test is available, use the measured peak and the response to workload on the patient’s current medications to guide the prescription.

Heart Rate Reserve Method

1. Calculate HRR as peak heart rate minus resting heart rate.
2. Multiply HRR by the intended intensity fraction and add resting heart rate.

$$\mathrm{Target\ HR} = \mathrm{Resting\ HR} + f \times (\mathrm{Peak\ HR} - \mathrm{Resting\ HR})$$

In graded exercise studies, a percentage of HRR corresponds more closely to the same percentage of oxygen uptake reserve than to the percentage of maximal oxygen uptake. Use workload, symptoms and clinical restrictions alongside heart rate.

Worked estimate: For an adult aged 60 with resting HR 75 bpm, the Gellish equation gives $207 - 0.7 \times 60 = 165$ bpm. Estimated HRR is $165 - 75 = 90$ bpm. At a hypothetical 60% HRR, the estimate is $75 + 0.60 \times 90 = 129$ bpm. Select the clinical starting intensity using the patient’s assessed response and program limits.

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Subjective Exertion and Metabolic Equivalents

Borg Perceived Exertion Scales

On the Borg 6–20 scale, 6 denotes no exertion, 13 somewhat hard, 15 hard and 20 maximal exertion. Teach the scale before exercise and ask the patient to rate their current effort. The rating can supplement measured workload and vital signs, including when medications affect heart rate. Measure the patient’s pulse separately when the heart-rate response is needed.

A category-ratio scale commonly uses ratings from 0 to 10. Identify what the patient is rating, for example whole-body effort or breathlessness. Follow the scale and instructions specified for the test or program. Ratings from the two scales have different anchors.

Metabolic Equivalents (METs)

One standard MET represents approximately 3.5 mL oxygen per kilogram per minute. This is a reference value. Actual resting oxygen uptake varies with individual characteristics. Moderate absolute intensity in adults is commonly 3.0–5.9 METs and vigorous absolute intensity starts at 6.0 METs. Relative intensity depends on capacity. For example, an estimated 4-MET walk may be a demanding workload for a patient early in rehabilitation.

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AHA Diagnostic Exercise Testing Safety

Screen Before Testing

The AHA diagnostic exercise testing statement identifies acute MI within two days, ongoing unstable angina, uncontrolled arrhythmia with hemodynamic compromise, active endocarditis, symptomatic severe aortic stenosis, decompensated heart failure, acute pulmonary embolism, pulmonary infarction or DVT, acute myocarditis or pericarditis, acute aortic dissection, and a physical limitation that prevents safe adequate testing as absolute contraindications.

Examples of relative contraindications include known obstructive left main coronary stenosis, moderate-to-severe aortic stenosis with uncertain symptom relationship, uncontrolled ventricular rate with tachyarrhythmia, acquired advanced or complete AV block, severe resting outflow gradient with hypertrophic obstructive cardiomyopathy, recent stroke or TIA, limited ability to cooperate, resting SBP above 200 mmHg or DBP above 110 mmHg, and significant uncorrected anemia, electrolyte imbalance or hyperthyroidism. The responsible testing team weighs the clinical benefit and risk, including whether to defer or change the protocol.

Terminate a Diagnostic Test When Indicated

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Warm-Up and Recovery

Begin at an easy workload and increase gradually toward the intended effort. The warm-up lets the patient rehearse the movement and gives the clinician time to observe the early symptom and hemodynamic response.

After planned exercise in a stable patient, light rhythmic movement can ease the transition to rest. Muscle contractions help propel venous blood toward the heart while vasodilation can persist. This can support venous return and attenuate the early pressure fall. Continue the monitoring specified for the program. After a diagnostic test, follow its recovery position and ECG and pressure monitoring protocol.

If dizziness, near-syncope, chest discomfort or another concerning symptom develops, stop the activity, assist the person into a safe position and assess promptly according to the clinical protocol.

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Bed Rest and Deconditioning

During prolonged recumbency, reduced upright loading and changes in fluid distribution can lower plasma volume. With return to standing, gravity shifts blood toward the legs and abdomen. Lower circulating volume and altered cardiovascular responses to standing can reduce venous return and contribute to orthostatic symptoms. Bed-rest studies also show reduced stroke volume and aerobic capacity. The rate and extent of these changes depend on the duration and conditions of unloading and the patient’s health.

Reduced muscle loading can decrease strength and lean tissue, particularly in the lower limbs. Longer periods of unloading can increase bone loss. Check mobility precautions and function before progressing activity.

Bedside example: After clearance to mobilize following an inpatient stay, a patient becomes pale and lightheaded within one minute of standing. BP drops from 122/80 to 94/56 mmHg, a decrease of 28 mmHg systolic and 24 mmHg diastolic. Help the patient into a safe position, reassess and alert the team as indicated. Deconditioning can contribute, and the team must also evaluate other causes, such as bleeding, volume loss or medication effects.

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Aerobic Progression in Clinical Populations