ReviewThe effects of resistance training on muscle strength, quality of life and aerobic capacity in patients with chronic heart failure — A meta-analysis
Introduction
Chronic Heart Failure (CHF) is a dynamic and progressive syndrome, which develops secondary to structural or functional abnormalities of cardiac tissue. It leads to the inability of the heart to supply enough blood to meet the body's metabolic needs and causes breathlessness, fatigue and reduced exercise tolerance [1]. Life expectancy in patients with CHF is increasing however, many of these recovered years are spent with debilitating burden of symptoms [2], high incidence of hospitalisations [3], [4] and a poor ultimate prognosis [4].
Treatment for patients with CHF is alike other terminal illnesses and is primarily focussed on managing symptoms and maintaining quality of life (QoL). Exercise training is an integral component of this paradigm [5], [6], [7] due to its capacity to ameliorate symptoms [8], reduce hospital admissions [9] and improve functional capacity, which translate into improved QoL [8], [10], [11], [12]. Traditional approaches to exercise rehabilitation have largely focussed on aerobic-based training given its ability to increase aerobic capacity (VO2peak) [13], [14], [15]. However, it is now accepted that exercise intolerance in CHF is not exclusively due to central cardiovascular factors and consequently, clinicians are moving beyond a centrally focussed treatment approach. Specifically, the “muscle hypothesis” argues that abnormalities in peripheral muscle tissue initiate deleterious feedback loops and become drivers for disease progression [16]. Adding to the fact that muscle mass is strongly correlated with VO2peak [17], [18] it has been argued that targeting muscle dysfunction may interrupt these maladaptive feedback loops and improve exercise tolerance [19].
Resistance training (RT) is normally employed for conditioning skeletal muscle tissue however, it was largely overlooked for patients with CHF prior to 1990’s due to concerns that high cardiac afterload may adversely affect left ventricular remodelling [8], [20]. More recently, modern methods of hemodynamic measurement have allayed these concerns by confirming the integrity of the left ventricle during RT [12], [21]. With confirmation of safety and acknowledgment of the wider health and fitness benefits, RT is now supported in clinical practice guidelines for people with cardiovascular disease [22]. There are however, several unresolved limitations to these guidelines, which continue to impact on clinical decision making.
Firstly is the question of applicability of current best practice guidelines to patients with CHF. The joint council Scientific Statement from the American Heart Association recommends RT for individuals with and without cardiovascular disease [22]. The guideline presents a consensus of evidence supporting the safety and efficacy of RT through large randomised controlled trials and meta-analyses. However, these data are largely derived from patients with cardiovascular diseases other than CHF, or in patients with few comorbidities or risk factors. In specific reference to CHF, the guidelines are based on only a small number of individual studies [23], [24]. The precision of estimates of effects derived from such studies is limited and authors acknowledged the need for further evidence. The consequences of overly generalised guidelines for cardiovascular disease is particularly problematic in CHF, since it is the end stage of other cardiovascular conditions and as such, patients often suffer from multi-organ and co-morbid disease which can further challenge management. For instance, Havranek et al. [25]. reported an incidence of diabetes and chronic obstructive pulmonary disease of 40% and 33%, respectively, in elderly patients with CHF.
Secondly, patients with CHF are generally older than those with other cardiovascular conditions, yet this age discrepancy is largely unaddressed in these guidelines. The Framingham Heart study reported a mean age of diagnosis of 76.4 years for CHF [26], compared to 56 or 65 years for the median age of first myocardial infarction, for men and women respectively [27]. Patients with CHF, particularly those who are elderly, are a heterogeneous group and differ significantly from patients with other cardiovascular diseases. The complexity of the illness merits exclusive exercise recommendations for treatment. It is for this reason, that explicit medical guidelines exist for patients with CHF which pay specific attention to the management of co-morbidities, as well as issues related to older age [28].
Finally, the focus for cardiac rehabilitation remains heavily on aerobic or centrally focussed training and limited evidence exists to support RT as an effective standalone therapy. It was previously reported that RT has a smaller effect compared to aerobic training in increasing peak VO2 in patients with CHF [29], however RT produces greater improvements in skeletal muscle strength and endurance [30]. The American Heart Association acknowledges the potential benefits of RT for cardiovascular health, weight management and prevention of disability and falls, however, given the extensive benefits of aerobic training, RT was not recommended to be used as its substitute [22]. Some clinicians and researchers have argued that many patients have insufficient capacity to tolerate aerobic exercise, such as those who are elderly or have more advanced CHF and that RT may be a suitable alternative for these patients [31], [32], [33].
Systematic reviews and meta-analysis are the reference standard for developing clinical practice guidelines because of their methodological rigour and assessment of potential bias. To our knowledge only one meta-analysis has analysed the effects of RT versus usual care in patients with CHF [34], however this study did not analyse muscular strength. Therefore, the purpose of this meta-analysis was to systematically review randomised controlled trials (including quasi-randomised designs) and meta-analyse the effects of RT, as a single intervention, on muscle strength, aerobic capacity and QoL in patients with CHF.
Section snippets
Search strategy
With the support from a clinical librarian, we developed search strategies to identify controlled trials of RT in patients with CHF. Specifically, we focussed on the effect of RT on muscle strength (1 repetition maximum, 1RM, and/or peak isokinetic torque), aerobic capacity (measured by VO2 peak and/or 6 min walk distance [6MWD]), and QoL measured using the Minnesota Living with Heart Failure questionnaire. We searched CINAHL, Medline, EMBASE, and Cochrane databases up to 10th July, 2016. In
Study selection
The search strategy identified 10,424 citations. After removal of duplicates, 7650 were broadly screened by title and abstract and 7596 articles were excluded. Fifty-five articles were included for full text review. Of these, a further 45 were excluded leaving 10 articles for inclusion in the meta-analysis. The reasons for excluding articles are shown in Fig. 2; 19 papers did not report on the outcome(s) of interest. One additional study was identified incidentally while confirming inclusion
Discussion
The main findings of the current meta-analysis are that RT as a single intervention can increase muscle strength, aerobic capacity, and QoL in patients with CHF. However the effect of RT on muscle strength is mainly during slow controlled movements (1RM) and not during rapid movements. Older adults, who are the vast majority of patients with CHF, are underrepresented across studies and there are no RT studies in patients with severe CHF (NYHA IV).
To our knowledge, only one previous
Conflict of interest
The authors report no relationships that could be construed as a conflict of interest.
Acknowledgements
Associate Professor Levinger is supported by Future Leader Fellowship (ID: 100040) from the National Heart Foundation of Australia. We would like to thank Evelyn Hutcheon and Steven Chang from Western Health library service for their help with the literature search.
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