Literature Review
2.1 Introduction
This section presents related literature on the topic under study.
2.2 Physical activity and heart failure
It is well known that lifestyle plays a major role in the way the body functions. It could be
detrimental or of immense benefit to whole body homeostasis. Important lifestyle behaviours
include physical activity, sedentary lifestyle, sleep, and smoking. Physical activity is defined as
any bodily movement produced by the contraction of skeletal muscles that require energy
expenditure above resting level (Pelliccia et al., 2021). Physical activity constitutes most activities
carried out as part of daily routine and is markedly different from exercise. Exercise is a sub-type
of physical activity which is planned and consists of repetitive whole or partial body movements
performed to maintain or improve physical fitness (Pelliccia et al., 2021).
Although chronic HF is characterized by progressive exercise intolerance and exertional dyspnoea
during minimal exercise (Conrad et al. 2018), available data suggests that exercise is beneficial for
HF patients in terms of decreased mortality and morbidity, improved quality of life, functional
capacity and cardiac and vascular function. However, exercise training should be considered as an
adjunct in these groups of patients.
The relative success of an exercise training programme is commonly determined by comparing
changes between baseline and post training fitness markers. Maximal oxygen consumption is the
most commonly reported measure of functional capacity in HF patients but is rarely achieved in
activities of daily living. In carrying out exercise training, it is important to clearly establish the
frequency, type, intensity and length of intervention. This perhaps is the reason why programme
design is the most important and controversial issue regarding the role of exercise training in HF.
Most exercise training programmes have followed the standard prescription of continuous aerobic
exercise used in cardiac rehabilitation (Smart 2010), with resistance exercise sometimes added.
However continuous aerobic exercise may not optimally stress the peripheral muscles, as they are
often atrophied and have fewer fibres, oxidative enzymes, and capillaries in HF patients (Duscha
et al 2008).
Similarly, there has been some controversy on the effect of exercise dose on the efficacy of
training. While Morris et al., (2002) argue that volume of exercise rather than method of delivery
determine improvement in functional capacity, other researchers suggest that programme duration
especially those designed to last 12 weeks and beyond, have more influence on functional capacity
(Støylen et al 2012).
2.2.1 Exercise type and dose
Aerobic training
Aerobic exercise is generally recommended for stable patients on optimal medical treatment, in
New York Heart Association (NYHA) class I - III, reflecting the inclusion criterion commonly
used in previous studies. Study protocols have generally consisted of primarily aerobic exercise,
usually performed on stationary bicycle or treadmill, but have also included aerobic circuit
training, performed for periods of 30–60 min, 3–5 times per week for a duration of 3–6 months.
The exertion level prescribed has been set to 60–80% of maximum aerobic capacity (VO2max)
(Metra et al. 2017). Current guidelines recommend a moderate exercise intensity (40–80% of
VO2max) initially, in stable individuals, as this has been most studied. For patients with more
severe symptoms of NYHA class III, a lower starting intensity of <40% of VO2max is
recommended. After a run-in period, intensity may be gradually progressed to a goal of 85–85%
of maximum (McCoy et al. 2017).
Interestingly, a meta-analysis on the dose-response relationship between PA and risk of heart
failure, showed a higher optimal dose (intensity × frequency), compared to what is recommended
for mortality reduction, while another review could not confirm that “the higher is the better”.
High intensity interval training
High intensity interval training (HIIT) typically involves short intervals of very high intensity
activity (>90% of VO2max) alternating with recovery periods of either complete rest or low
intensity activity. It has been suggested as an alternative approach in low-risk heart failure patients.
A recent meta-analysis did show superior effects of a HIIT protocol with higher increases in
VO2max as compared to a moderate intensity training protocol, although the effect disappeared in
subgroup analysis of isocaloric protocols (Kinno et al. 2017). In addition, the Norwegian-German
SMARTex study showed that HIIT training was not superior to medium intensity aerobic training
for HFrEF. Thus, current guidelines recommend HIIT training, mainly as an alternative strategy
for low-risk patients aiming for return to high intensity activities, or sports participation.
Resistance training
Resistance training has been found to complement aerobic training, as the combination can lead to
greater increases in aerobic capacity when compared to aerobic exercise alone. Furthermore, it
may prevent sarcopenia associated with advanced heart failure. For heart failure patients unable to
perform aerobic exercise, resistance training has been shown to improve muscle strength, aerobic
capacity, as well as measures of quality of life.
Study protocols have typically included a series of 8–10 exercises performed at 40–80% of the 1
repetition maximum (1RM), for 1–3 sets of 10–15 repetitions per exercise. Current guidelines
recommend strength training programs with a frequency of 2–3 days per week in addition to
aerobic training. Resistance training may also be specifically considered in low-risk patients
aiming to return to power-sports, such as weightlifting (Kingsley et al. 2016).
Peripheral muscle training
For patients with severe heart failure symptoms and pronounced reduction in exercise tolerance,
peripheral muscle training may be used in the initial stages of rehabilitation in patients with muscle
wasting and low exercise tolerance (Kingsley et al. 2016). The RPE of these exercises may be
relatively high as the central circulation is engaged to a lesser extent. Techniques may include
endurance training using various weights, pulleys or resistance bands. As adaptation to peripheral
training increases, transition into central circulatory training, including aerobic and strength
training protocols may be introduced.
Aquatic exercise
Water immersion has several immediate physiological effects. Hydrostatic pressure leads to
increased venous return and cardiac preload, resulting in increased stroke volume and cardiac
output via the Frank-Starling mechanism (Kingsley et al. 2017). Total peripheral resistance is
lowered due to vasodilation of periphery as well as abdominal organs. As result, heart rate may be
unchanged or somewhat lower relative to relative perceived exertion of the activity performed.
There has been some concerns that the hemodynamic changes described could be potentially
harmful for certain heart failure patient categories, such as those with mitral regurgitation or severe
systolic impairment. However, recent meta-analyses have shown positive effects of aquatic
training on aerobic capacity, muscle strength and quality of life comparable to that of land based
aerobic exercise. Current guidelines conclude that larger trials are needed to confirm the safety of
aquatic training in heart failure.
Respiratory training
Inspiratory muscle training involves progressive resistance to provide loading to the inspiratory
muscles to achieve a strengthening effect. Typically, training protocols involve a high training
frequency of six or seven times per week, with intensities from 30 to 60% of maximum for 10–12
weeks. Inspiratory muscle training has shown positive effects on maximal inspiratory pressure,
walking distance, and dyspnea in heart failure patients and is recommended as an initial alternative
to aerobic exercise in the most severely deconditioned patients, as a bridge to conventional exercise
training.
2.3 Heart Failure Patients and Barriers to Exercise Adherence and Exercise Uptake
Heart failure (HF) is known to lead to poor health-related quality of life as well as high morbidity
and mortality rates. It is also the most common reason for hospitalization in older adults (Fleg et
al. 2015). Physical activity in HF patients is known to have positive outcomes such as improved
physical capacity and quality of life, and reduced health care utilization. However, adherence to
physical activity is less than 50% in HF patients; it even seems more difficult to achieve than
dietary modification and medication regimes.
Inspite of the fact that published meta-analyses show the positive impact of exercise-based CR,
critically low attendance and adherence rates still constitute a major problem in CR. Predictors of
regular participation in physical activity in healthy adults have been well documented. Lower age
positively correlates with physical activity as well as better self-efficacy, greater social support,
better knowledge of perceived benefits, and a positive attitude toward physical activity (Warraich
et al. 2018). Compared with men, women are less physically active. Engaging in regular physical
activity or having an early history of physical activity has also been described as a predictor of
future physical activity, as have higher education and income level, support from a health care
provider, and support from surrounding people. Being single or having an inactive partner has
been negatively correlated with physical activity levels in older adults. Depression has been
identified as being negatively correlated with physical activity levels.
Barriers and motivations to participation in regular physical activity have been well studied in the
adult population. Barriers to physical activity include internal barriers, such as lack of time, fear
of injury, lack of knowledge, lack of self-discipline or motivation, and ill health or changing health
status (Yang et al., 2018). External barriers to physical activity include environmental
considerations (eg, no facilities nearby), safety, cost, friends/partner not interested, and barriers
related to the weather.
Motivations toward physical activity in adults include advice by health care providers, family
influences, improvement in physical or motor competence, health benefits, and psychosocial
reasons such as enjoying group interaction and meeting with friends. Chronic health conditions
have been identified both as a barrier and as motivations toward physical activity in the older adult
population; individuals may exercise to prevent further physical decline, but their ability to
participate in physical activity could be limited by the same conditions (Pandey, 2019).
Data on rehabilitation in cardiac patients have shown that lower adherence to physical activity is
associated with older age, lower social and economic status, lack of motivation, and financial and
medical concerns. Data on HF-specific barriers to physical activity have shown that experiencing
symptoms and lack of energy is associated with lower adherence to physical activity (Pandey,
2019).
Patients with HF have been described as being less physically active in daily life compared with
healthy adults, but a few studies have described the level of physical activity in HF patients living
at home. To our knowledge, there has been only one study where the amount of physical activity
in 68 HF patients has been examined, using an accelerometer. The authors found that 44% of the
patients were sedentary, 35% were moderately physically active, and 15% were physically active
on a low level (Kitzman et al, 2017). The variance in daily activity in that study could be partly
explained by the patients’ symptoms and self-efficacy. In order to promote physical activity in HF
patients, it is essential to know how physically active they are and to understand the barriers and
motivation they experience for being more physically active. Motivation not only affects exercise
participation, but is also a critical factor in exercise adherence.
There are sex differences in physical activity that could be explained by a number of factors.
Research has indicated that older women’s personal backgrounds are less favorable for physical
activity than those of men (for instance, reported lower levels of education and income, fewer
women were married, and a greater number lived alone) (Yang et al., 2018). In addition, women
perceive their health as poorer, are more likely to experience barriers to physical activity, and
indicate lower self-efficacy for physical activity than men. Motivation and barriers to exercise are
important to consider when promoting physical activity in HF patients.
Among older patients with acute heart failure, physical function is markedly impaired, and frailty
rates and the burden of coexisting conditions are high. Even among older patients with stable and
well-compensated heart failure, severe impairments in physical function are often present owing
to the combined effects of aging, cardiovascular dysfunction, and skeletal-muscle dysfunction. As
patients with chronic heart failure transition to acute decompensated heart failure, physical
function worsens further, and this decline is exacerbated by hospitalization and bed rest. These
deficits often persist. Many patients never recover baseline function, lose independence, and have
high risks of re-hospitalization and death after discharge (sometimes referred to as “post-hospital
syndrome”) (Pandey, et al., 2019).
2.4 Occurrence of Heart Failure In Relation To Physical Inactivity
Previous studies have also yielded conflicting results regarding the benefits of exercise for
patients’ health status. For example, Coats et al., (1990) reported an improvement in patient
reported symptoms after 8 weeks of exercise training among 11 rigorously selected HF patients.
Another randomized trial among 99 HF patients by Belardinelli et al., (1999) revealed
improvements in quality of life as measured using the 21- item Minnesota Living With Heart
Failure Questionnaire (MLHFQ), after 8 weeks of exercise training compared with usual care, and
these improvements were sustained even at 12 months. In contrast, the Exercise Rehabilitation
Trial (EXERT) among 181 patients randomly assigned to 3 months of supervised exercise training
and followed by 9 months of home-based training or usual care showed no differences in MLHFQ
scores (McCoy et al., 2017).
Further emphasizing the confusion surrounding the association of training-induced improvement
in exercise capacity and quality of life is the study by (Metra & Teerlink, 2017) in which 24 weeks
of exercise training improved peak oxygen consumption but not quality of life (MLHFQ) scores.
Most of these studies were conducted prior to current guideline recommendations for
pharmacologic and device therapies, including beta-blockers, biventricular pacemakers,
implantable cardioverter-defibrillators and left ventricular assist devices.
Thus, critical questions remain about whether exercise training can improve patient-reported
health status. However, the ‘HF ACTION’ trial (Flynn et al 2009), which is one of the largest trial
(2331) to examine the effects of exercise training on clinical outcomes in stable HF patients on
optimum medical therapy, showed modest but statistically significant improvements in selfreported health status compared with usual care patients without training. This improvement was
reported to occur early and persisted over time.
2.5 Effects of exercise training in heart failure
Exercise training has similar effects in heart failure patients and healthy individuals, eliciting
positive effects on several of the underlying pathophysiological components, including
improvement of risk factors such as diabetes and hypertension. Peak oxygen consumption has also
been found to increase with exercise training in heart failure (Nordgren et al. 2015). The effect is
thought to be mediated via several pathways, including reversal of concentric remodeling with
subsequent improvements of myocardial contractility and compliance, as well as improved
microvascular circulation, oxygen extraction and metabolic function of large muscle groups.
Furthermore, a combination of aerobic and resistance training has been shown to elicit greater
improvements in aerobic capacity as compared to aerobic exercise alone.
Meta-analyses have shown that exercise protocols have a positive impact on exercise capacity and
quality of life in patients with heart failure. Effects on mortality and re-hospitalization have also
been found, albeit modest. Findings from the recent meta-analysis performed on individual level
data in the EXTRAMATCH II study did show conflicting results, with no significant effect on
mortality or heart failure hospitalization, although the authors conclude that uncertainty around
effect estimates precludes from drawing any definitive conclusions (Lewinter et al. 2015). Overall,
the recent ESC guidelines on Sports Cardiology, gave regular discussion about exercise
participation and provision of an individual exercise prescription for all patients with heart failure,
a class I, level of evidence A recommendation.
Exercise-based cardiac rehabilitation (exCR) has been shown to improve exercise capacity
(commonly estimated by 6-minute walking test or cycle ergometry) and reduce cardiovascular
morbidity and mortality, post-myocardial infarction (Clark et al, 2015). Thus, exCR has a major
role also in patients with heart failure, with the recent ESC-guidelines recommending exCR in all
stable patients with heart failure, to improve exercise capacity, quality of life and to reduce the
frequency of hospital admissions.
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