Aerobic exercise involves low-to-moderate intensity rhythmic movement of large muscle groups for an extended period of time. It includes activities such as walking and cycling. This is the best form of exercise for improving cardiorespiratory fitness.
Aerobic exercise should be encouraged on most days of the week. When prescribing aerobic exercise, the following should be considered:
- If there is a risk of ischaemia, the intensity and duration of exercise or the physiological demand (i.e., the muscle mass utilised at any given time) should be reduced.
- Maximal HR should be at least 5-10 beats per minute below the ischaemic threshold
- The symptoms that limit an individual’s exercise tolerance may vary according to the modality of exercise. For example, a rowing ergometer, which employs a large volume of muscle mass simultaneously, is likely to cause dyspnoea as the limiting symptom, while a cycle ergometer, which isolates the lower limb musculature, is more likely to induce localised muscle fatigue
- Exercise should be tailored to the individual. Orthopaedic limitations may dictate the type, frequency and duration of exercise in order to prevent exacerbation of symptoms
- Longer duration and more frequent rest periods may be required for those with frailty or severe symptoms
- The chosen mode of aerobic exercise should be one that an individual enjoys and tolerates without pain or residual fatigue. Regularity of physical activity is a significant part of attaining the cardiovascular benefits.
Evidence-based guidelines promote regular moderate physical activity for approximately 30 minutes on most (at least five) days of the week.
Commence with exercise 3-4 days a week (i.e., every second day), progressing to most days (at least 5 days) of the week.
Encourage independent exercise so that individuals have a mix of supervised and unsupervised sessions. Frequency will be guided by the patient's clinical status, motivation and commitment to exercise, and other commitments such as family and work.
Patients with very limited exercise tolerance may require multiple sessions of short-duration exercise (<10 minutes) to achieve the desired activity level.
Exercise prescriptions should begin conservatively. For supervised programs, patients should be closely observed and their recovery reviewed at the next session.
Exercise intensity for patients with HF or CVD is often based on perceived exertion rather than target HRs because cardiac medications can affect HR. Few patients will have had maximal graded exercise testing prior to referral. Exercise should be prescribed at a Borg scale RPE of 11-13, and commence at a short duration (approximately 10 minutes).
Some individuals may be too frail to commence even this volume of exercise. For these patients, low- or moderate-intensity interval training may be more appropriate (e.g., using repeated cycles of 30 seconds of exercise followed by 1 minute of rest).
Exercise intensity may be progressed when the RPE or HR falls at the initial intensity. The new intensity can be adjusted to remain within the RPE and HR bands.
Higher intensities of exercise (up to 80% of VO2 peak) may be conducted in hospitals or in exercise centres with equipment and personnel to manage advanced cardiac life support. Patients aspiring to higher-intensity exercise (up to 80% of VO2 peak or RPE ≥14) should undergo a screening peak exercise test with 12-lead ECG monitoring under medical supervision.
The table below provides guidance on exercise intensity for patients with HF, according to the functional class status.
Table 4: Recommended exercise intensity for heart failure patients
|Patient ‘s NYHA Class
||Guidance on exercise intensity
NYHA Class I-II
RPE 11-14 (moderate intensity as defined on the Rating of Perceived Exertion-Borg scales)
40-75% of HRpeak where HRpeak is predetermined in a symptom-limited graded exercise test
40-70% of HR reserve/VO2 reserve/VO2 peak if a cardiopulmonary exercise test (CPET) has been performed
NYHA Class III-IV
RPE ≤ 13
40-65% of HRpeak where HRpeak is predetermined in a symptom-limited graded exercise test
40-60% of VO2 peak
NB: Exercise intensity is prescribed similarly for HFrEF and HFpEF
High-intensity interval training
High-intensity interval training (HIIT) is a new method of aerobic exercise training currently being trialled in patients with CVD. HIIT involves alternating short bouts (3-4 minutes) of high-intensity (>80-90% of maximum HR) and moderate-intensity (50-70% maximum HR) exercise.
Studies have reported that HIIT is more effective than moderate-intensity continuous exercise in improving aerobic capacity in patients with coronary artery disease[#rognmo-hetland-e-helgerud-j-et-al.-2004] and HF.[#wislff-u-stylen-a-loennechen-jp-et-al.-2007]
Additionally, in patients with HF, HIIT improved left ventricular end-diastolic (18%) and end-systolic volumes (25%), and ejection fraction (35%), whereas these changes are not observed following moderate-intensity training.[#wislff-u-stylen-a-loennechen-jp-et-al.-2007]
A recent meta-analysis also found that HIIT was more effective than moderate-intensity training in improving vascular endothelial function; an important indicator of vascular health.[#ramos-js-dalleck-lc-tjonna-ae-et-al.-2015] However, the rates of adverse cardiovascular responses during and immediately after HIIT training were approximately 5 times higher than in response to moderate-intensity exercise training in cardiac patients.[#rognmo-moholdt-t-bakken-h-et-al.-2012] Accordingly, caution and careful clinical judgement should be taken when considering HIIT prescription to patients with CVD until the safety of HIIT is more clearly determined.
There is no set format for exercise duration progression. The duration of exercise is a function of the intensity that an individual is able to undertake.
Very frail individuals may commence exercising for only 1-10 minutes, accumulating 30 minutes with multiple short sessions and progressing as able. Other individuals may commence at the target intensity for a longer duration (e.g., 10-15 minutes) and progress more rapidly.
Recommendations suggest aiming for approximately 30 minutes on most (at least 5) days per week, although additional benefits accrue from activity of up to 60 minutes. For patients with very limited exercise tolerance, encourage any physical activity.
The aerobic component of an exercise session should consist of a variety of activities targeting a range of large muscle groups. The choice of exercise is at the discretion of the clinician, however, both upper and lower limbs should be included with due consideration to co-morbidities.
Common examples of potentially suitable exercises include:
- Exercise bike
- Rowing machine
- Step ups
- Upper limb ergometry
There is no evidence that one modality of exercise yields a greater benefit than another if patients adhere to the prescribed recommended dose.
Once prolonged exercise is tolerated at a low intensity, the exercise intensity should be gradually intensified to the target level (see table below). After the target level is achieved, the duration may then require increasing. Improved exercise tolerance typically enables higher-intensity exercise at a similar or lower rating of perceived exertion.
Table 5: Example of staging exercise progression
|Up to 10 minutes @ 30 watts
||Up to 10 minutes @ 3.0 km/hr
||10-12 minutes @ 30 watts
||10-12 minutes @ 3.0 km/hr
||12-15 minutes @ 30 watts
||12-15 minutes @ 3.0 km/hr
||15 minutes @ 40 watts
||15 minutes @ 3.5 km/hr
||15 minutes @ 50 watts
||15 minutes @ 4.0 km/hr
||15 minutes @ 60 watts
||15 minutes @ 4.5 km/hr
||20 minutes @ 60 watts
||20 minutes @ 4.5 km/hr
*Very deconditioned patients may need to commence at a duration of less than 10 minutes.