Resistance training increases 6-minute walk distance in people with chronic heart failure: a systematic review Academic research paper on "Basic medicine"

Resistance training increases 6-minute walk distance in people with chronic heart failure: a systematic review

Chueh-Lung Hwang, Chen-Lin Chien and Ying-Tai Wu

National Taiwan University, Taiwan

Question: Does resistance training, either alone or as an adjunct to aerobic training, improve cardiac function, exercise capacity and quality of life in people with chronic heart failure? Design: Systematic review with meta-analysis of randomised trials. Participants: Adults with stable chronic heart failure. Intervention: Progressive resistance exercise training, alone or as an adjunct to aerobic training. Outcome measures: Cardiac function, exercise capacity and quality of life. Results: 241 participants from eight trials performed 2 to 6 months of moderate-intensity resistance training (50-75% of 1RM). Most programs consisted of 5 to 6 exercises for large limb and trunk muscles with two sets of 8 to 12 repetitions, three times a week. Resistance training significantly increased 6-minute walk distance (WMD 52 m, 95% CI 19 to 85) but not peak oxygen consumption (WMD 1.4 ml/kg/min, 95% CI -0.3 to 3.1). When used as an adjunct to aerobic training, resistance training did not significantly alter left ventricular ejection fraction (WMD -0.5%, 95% CI -4.3 to 3.3), peak oxygen consumption (WMD -0.7 ml/kg/min, 95% CI -2.3 to 1.0), or Minnesota Living with Heart Failure Questionnaire scores (WMD -0.9, 95% CI -5.4 to 3.7), compared with aerobic training alone. Conclusion: Resistance training increased 6-minute walk distance compared to no training, but had no other benefits on cardiac function, exercise capacity, or quality of life if used alone or as an adjunct to aerobic training in people with chronic heart failure. However, further high quality, large scale, randomised trials are needed. [Hwang CL, Chien CL, Wu YT (2010) Resistance training increases 6-minute walk distance in patients with chronic heart failure: a systematic review, Journal of Physiotherapy 56: 87-96]

Key words: Resistance training, Exercise capacity, Quality of life, Chronic heart failure

Introduction_

Both the prevalence and incidence of chronic heart failure have increased due to the improved survival of coronary heart disease patients and to the aging of populations worldwide (Bleumink et al 2004). The major symptoms of chronic heart failure include exertional dyspnoea, fatigue, exercise intolerance, and functional limitations, which may result in poor quality of life. Previous studies suggested that both central and peripheral impairments limit exercise capacity in chronic heart failure patients (Mueller et al 2007, van Toi et al 2006, Volaklis and Tokmakidis 2005). Aerobic exercise training has been considered a safe and effective strategy to improve clinical symptoms (Flynn et al 2009, Mueller et al 2007, O'Connor et al 2009). Consistent results in meta-analyses provide further evidence that aerobic training is an effective treatment strategy (Chien et al 2008, Rees et al 2004, van Toi et al 2006).

Chronic heart failure is characterised by skeletal myopathy with reduced muscle mass, decreased vascular density and conductance, and impaired muscle oxidative capacity. This results in a shift toward type-II muscle fibres (Duscha et al 1999, Harrington and Coats 1997, Hulsmann et al 2004, Sunnerhagen et al 1998). These abnormalities may lead to disuse atrophy, further inactivity, and even cachexia. This progressive weakness has been noted in people with chronic heart failure and correlated with the severity of disease and exercise capacity (Hulsmann et al 2004, Toth et al 1997), suggesting that resistance training may help to ameliorate

peripheral muscle weakness in chronic heart failure. Moreover, muscular strength is reported as a predictor of long-term survival in chronic heart failure (Hulsmann et al 2004).

Resistance training has been considered in people with chronic heart failure recently because it imposes less cardiac demand than aerobic exercise (King et al 2000, McKelvie et al 1995, Meyer et al 1999). Several studies have established the safety of resistance exercise (Braith and Beck 2008, Braith et al 2005, Cheetham et al 2002, Jennings and Esler 1990, Magnusson et al 1996, Meyer 2006, Volaklis and Tokmakidis 2005, Williams et al 2007a, Williams et al 2007b). The American College of Sports Medicine has recommended that people with cardiac disease should add resistance training to their exercise program (Thompson et al 2010). However, the use of resistance training by people with chronic heart failure is controversial and its use in clinics remains limited because of uncertainty about its benefits and risks (Elkayam et al 1985).

In the past decade, resistance training has been proven to improve both muscle strength and functional capacity in individuals with chronic heart failure. It can improve static as well as dynamic muscular strength by increasing the cross-sectional area of local muscle (Magnusson et al 1996). Furthermore, skeletal muscle adapts metabolically to resistance training in people with chronic heart failure (Minotti et al 1990). Some studies showed definite improvement in muscle strength, peak oxygen consumption

and quality of life after resistance training, although there were no beneficial effects on left ventricular function (Levinger et al 2005a, Levinger et al 2005b). One study of 14 high-risk chronic heart failure patients demonstrated an average of 26% improvement in muscle strength after adding an 8-week resistance training regimen to aerobic training (Barnard et al 2000). There is even some evidence in chronic heart failure patients that resistance training added to aerobic training can improve heart function, exercise tolerance and quality of life more than aerobic training alone (Degache et al 2007, Maiorana et al 2000a). A recent systematic review of the effect of resistance training on these outcomes included non-randomised trials (Spruit et al 2009), introducing important potential for bias in the results. Therefore, the effects of resistance training, either alone or in combination with aerobic training, in people with chronic heart failure remain unclear. Therefore the following research questions for this study focused on people with heart failure:

1. Does resistance training improve heart function, exercise capacity and quality of life in people with chronic heart failure more than no intervention or usual care?

2. If combined with aerobic training, does it show a greater improvement in these measures than aerobic training alone?

Methods_

Identification and selection of studies

Six electronic databases (PubMed, MEDLINE, EMBASE, Chinese Electronic Periodical Service [CEPS], CINAHL, and Cochrane Library Register of Controlled Trials) were searched from the earliest available date until September 2009. We hand-searched reference lists of all identified original articles, previous meta-analyses and reviews. Experts were asked to identify any other relevant trials known to them. The following keywords and Medical Subject Heading (MeSH) terms were used in our searches: heart failure, heart dysfunction, ventricular dysfunction, resistance training, strength exercise, strength training, weight-lifting, and weight training (see Appendix 1 on the eAddenda for the full search strategy).

Box 1 Inclusion criteria.

Design

• Randomised trial

Participants

• Adults with chronic heart failure

• Diagnosis based on clinical signs or left ventricular ejection fraction <40%

Intervention

• Progressive resistance exercise training, with training defined as a structured, hospital- or home-based program with a target exercise type, intensity, duration and frequency, and with regular measurement of whether these were achieved

Outcome measures

• Cardiac function

• Exercise capacity

• Quality of life

Comparisons

• Progressive resistance exercise training versus no training or usual care or sham exercise

• Progressive resistance exercise training plus aerobic exercise training versus aerobic exercise training only

Published randomised trials limited to human subjects were considered. Articles written in languages other than English or Chinese were excluded. Two reviewers (CLH and CLC) reviewed the trials using predetermined criteria independently (Box 1). Reviewers were not blinded to authors, place of publication, or results.

Assessment of characteristics of studies

Quality: All trials were critically appraised for methodological quality using the PEDro Scale (0 to 10, Maher et al 2003, de Morton 2009) by two reviewers (CLH and CLC). Any disagreements were resolved by discussion with another reviewer (YTW).

Participants: Age, gender, and cause and severity of chronic heart failure were recorded to determine the similarity of participants between groups and between trials.

Intervention: The target intensity, duration, and frequency of exercise and the length of the intervention period were recorded. For the study question assessing the effect of resistance training alone, the control was categorised as no intervention, usual activity or sham exercise. For the study question assessing the effect of combined training versus aerobic training alone, the target intensity, duration, and frequency of aerobic exercise were also recorded.

Outcome measures: We recorded cardiac function (measured by the left ventricular ejection fraction), exercise capacity (measured at the impairment level by peak oxygen consumption and at the activity level by the 6-min walk test), and quality of life (measured by disease-specific scales).

Data analysis

The reviewers extracted post-intervention sample sizes, means, and standard deviations (SD) for the experimental and control groups. The authors were contacted to provide additional information if necessary.

The analyses were performed using RevMan 5. In each study, the effect size for the intervention was calculated by the difference between the means of the experimental and control groups at the end of the intervention. If the outcome was measured on the same scale, the weighted mean difference (WMD) and 95% confidence interval (CI) were calculated. Otherwise, the standardised mean difference (SMD) and 95% CI were calculated. Data were pooled using a fixed effect model and heterogeneity was calculated using a Chi-square test (%2). A random effect model was used to re-analyse data when significant heterogeneity was noted. Publication bias was investigated by using the funnel plot (Leandro 2005).

Results_

Flow of studies through the review

The search was performed on October 1, 2009. After screening the titles and abstracts, ten studies met the inclusion criteria (Beckers et al 2008, Cider et al 1997, Delagardelle et al 2002, Feiereisen et al 2007, Haykowsky et al 2005, Mandic et al 2009, Pu et al 2001, Selig et al 2004, Tyni-Lenne et al 2001, Williams et al 2007a). Two studies (Selig et al 2004, Williams et al 2007a) had overlapping subjects, and the one with larger sample size was included (Selig et al 2004). Two other studies were excluded because of incomplete data (Delagardelle et al 2002, Haykowsky et al 2005). The study by Feiereisen and colleagues also

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consisted of resistance training and control groups that were excluded due to lack of control group randomisation (Feiereisen et al 2007). We included one study (Barnard et al 2000) through searching reference lists of one review article (Volaklis and Tokmakidis 2005) (Figure 1).

Characteristics of included studies

Tables 1 and 2 summarise the characteristics of the included studies.

Quality: The methodological quality of the eight included trials ranged from 4 (Barnard et al 2000) to 7 (Beckers et al 2008, Mandic et al 2009, Pu et al 2001) on the PEDro scale (Table 1), with a mean of 5.7 out of 10 (SD 1.2). No trials blinded participants or therapists, while four trials blinded assessors, seven had 85% or greater retention rates, and all reported between-group differences with point estimates and measures of variability.

Participants: Most of the included studieshad predominantly male participants with stable chronic heart failure and mean ages ranging from 55 to 65 years. Only one study recruited only women (Pu et al 2001), with participants aged a mean of 77 years. New York Heart Association classifications ranged from I to III and left ventricular ejection fraction was approximately 40% in most studies. One study included participants with left ventricular

Table 2. Summary of included studies (n = 8).

Participants

Interventions

Outcome measures

Resistance exercise versus control

Cider et al (1997)

HF (21 IHD, 1 CMP, 2 VD) NYHA II-III

n = 12 Exp (9 males, aged 62 yrs) 12 Con (7 males, aged 65 yrs)

Exp = PRE at 60% of 1RM, 1 min/set x 2 sets x 6 exercises, 60 min x 2 /wk x5mo Con = usual activity

Peak VO2 QOL (QOL-HF) QOL (NHP) Adverse events

Pu et al (2001) HF (12 IHD, 1 VD, 3 idiopathic)

NYHA I-III

n = 9 Exp (all females, aged 77 yrs, LVEF 36%)

7 Con (all females, aged 77 yrs, LVEF 36%)

Exp = Supervised PRE at 80% of 1RM, 8 reps x 3 sets x 5 exercises, 60 min x

3/wk x10wk Con = sham (low-intensity stretching exercise, 2/wk)

Peak VO2 6-min walk test LVEF

Adverse events

Selig et al (2004)

HF (23 IHD, 16 DCM) NYHA II-III

n = 19 Exp (15 males, aged 65 yrs, LVEF 27%)

20 Con (18 males, aged 64 yrs, LVEF 28%)

Exp = PRE at moderate intensity, 30-120 sec x1 setx6 exercises,

3/wk x3mo Con = usual care

Peak VO2 Adverse events

Tyni-Lenné et al (2001)

HF (15 CAD, 9 IDCM) NYHA II-III

n = 16 Exp (8 males, aged 63 yrs, LVEF 30%)

8 Con (5 males, aged 62 yrs, LVEF 30%)

Exp = Supervised PRE at 13-16/20 on Borg scale, 25 reps x 2 sets/exercise, 60 min x 3/wk x8wk

Con = usual activity

Peak VO2 6-min walk test QOL(MLHF-Q) Adverse events

Combined resistance and aerobic exercise versus aerobic exercise

Barnard et al (2000)

HF (14 CAD, 6 CMP, 1 VD) n = 14 Exp (all males, aged 55 yrs) 7 Con (all males, aged 60 yrs)

Exp = Aerobic exercise training at 60 to 80% of peak HR, 30 min x 3/wk

PRE with intensity at 60 to 80% of 1RM, 8 to 12 reps x 2 sets/exercise x 2/wk Con = Aerobic exercise training at 60 to 80% of peak HR, 30 min x 3/wk Both groups = Supervised exercise x8wk

Adverse events

Beckers et al 2008)

HF (34 IHD, 24 DCM) NYHA II-III

n = 28 Exp (18 males, aged 58 yrs, LVEF 26%),

30 Con (24 males, aged 59 yrs, LVEF 23%)

Exp = Interval aerobic exercise training at 90% of maxHR, 8 to 15 min/exercise x 10 to 45 min

PRE at 50 to 60% of 1RM, 10to 15 reps x1to2 sets x 9 exercises (including respiratory muscle)

Con = Interval aerobic exercise training at 90% of maxHR, 8 to 15 min/exercise x 60 min

Both groups = Supervised, 60 min x 3/wk x6mo (70 sessions)

Peak VO2 LVEF

QOL (HCS) Adverse events

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ejection fraction of approximately 45% (Pu et al 2001) and two studies did not report these characteristics of disease severity (Barnard et al 2000, Cider et al 1997). Four studies reported compliance of at least 80% (Barnard et al 2000, Feiereisen et al 2007, Pu et al 2001, Tyni-Lenné et al 2001), and one study reported 'excellent' compliance (Beckers et al 2008). Two studies reported compliance with means of 75% and 78% respectively (Cider et al 1997, Mandic et al 2009) and one study did not report compliance (Selig et al 2004). Among all of the studies, only one sudden death was reported, which occurred at home three days after the most recent resistance training session. One drop-out was reported in the resistance training group due to noncompliance (Table 3). One study reported that four patients had intermittent mild musculoskeletal symptoms during resistance training with minor modification of their training protocol afterwards (Pu et al 2001). No safety issues were reported by either the resistance training alone or combined aerobic training studies.

Interventions: Four studies (Cider et al 1997, Pu et al 2001, Selig et al 2004, Tyni-Lenné et al 2001) compared resistance training alone with usual activity, usual care, or sham exercise. The other four studies (Barnard et al 2000, Beckers et al 2008, Feiereisen et al 2007, Mandic et al 2009) studied combined (resistance and aerobic) training versus aerobic training groups.

All the training programs were supervised. The length of training ranged from 2 to 6 months. The intensity for resistance training was moderate or about 50-75% of one repetition maximum (1RM), while aerobic training on a treadmill or cycle ergometer was moderate to vigorous intensity. Two studies used high intensity exercise at 80% of 1RM, with no exercise-induced cardiac events reported (Barnard et al 2000, Pu et al 2001). The resistance training usually consisted of 2 sets of 8-12 repetitions for 5-6 exercises targeting the large muscle groups of upper limbs, trunk, and lower limbs. The exercise duration was around 30-60 minutes and exercise frequency was 2-3 times per week. One study included respiratory muscle training as one of the nine exercises (Beckers et al 2008). This was the largest number of exercises among the eight studies.

Effect of resistance training

We examined by separate analyses the effect of resistance training alone or in combination with aerobic training. Four studies reported cardiac function, seven reported exercise capacity, and five reported quality of life. All reported whether there were adverse events.

Cardiac function: The effect of resistance training alone on cardiac function was examined in one trial (Pu et al 2001), with no significant difference in left ventricular ejection fraction compared to control (MD 1.8%, 95% CI -5.7 to 9.3). Three studies with 115 participants provided postintervention data for pooling with a fixed model to examine the effect of resistance training as an adjunct to aerobic training on cardiac function. The overall improvement in left ventricular ejection fraction was comparable to that obtained with aerobic training only (WMD -0.5%, 95% CI -4.3 to 3.3) (Figure 2, see also Figure 3 on the eAddenda for detailed forest plot).

Exercise capacity : The effect of resistance training alone on peak oxygen consumption was calculated using the pooled post-intervention data of four studies with 96 participants.

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Beckers 2008 Feiereisen 2007 Mandic 2009

-20 -10 0 10 20

Favours aerobic Favours combined

Figure 2. Weighted mean difference (95% CI) of effect of combined resistance and aerobic training versus aerobic training only on left ventricular ejection fraction by pooling data from 3 studies (n = 115).

A Cider 1997 Pu 2007 Selig 2004 Tyni-Lenne 2001

-20 -10 0 10 20 ml/kg/min

Favours control Favours resistance

B Beckers 2008 Feiereisen 2007 Mandic 2009

ml/kg/min

Favours aerobic Favours combined

Figure 4. Weighted mean difference (95% CI) of effect of resistance training on peak VO2. (A) resistance training compared with non-training by pooling data from four studies (n = 96); (B) combined resistance and aerobic training compared with aerobic training alone by pooling data from three studies (n = 115).

Resistance training alone showed a favourable trend only on peak oxygen consumption (WMD 1.4 ml/kg/min, 95% CI -0.3 to 3.1) (Figure 4a, see also Figure 5a on the eAddenda for detailed forest plot). The effect of resistance training as an adjunct to aerobic training was derived from three studies with 115 participants. The addition of resistance

Pu 2001

Tyni-Lenne 2001

Favours control

Favours resistance

Figure 6. Weighted mean difference (95% CI) of effect of resistance training versus control on the 6-minute walk distance by pooling data from 2 studies (n = 40).

Feiereisen 2007 Mandic 2009

-50 -25 0 25 50 Favours combined Favours aerobic

Figure 8. Weighted mean difference (95% CI) of effect of combined resistance and aerobic training versus aerobic training only on quality of life as measured by Minnesota Living with Heart Failure Questionnaire by pooling data from two studies (n = 57).

training to aerobic training did not significantly affect peak oxygen consumption (WMD -0.7 ml/kg/min, 95% CI -2.3 to 1.0) (Figure 4b, see also Figure 5b on the eAddenda for detailed forest plot).

Two studies with 40 participants examined the effect of resistance training alone on the 6-minute walk test. The post-intervention data were pooled using a fixed effect model. Resistance training increased the 6-minute walk distance significantly, by 52 m (95% CI 19 to 85) more than non-training (Figure 6, see also Figure 7 on the eAddenda for detailed forest plot). No studies of resistance training as an adjunct to aerobic exercise measured the 6-minute walk distance.

Quality of life: Two studies examining the effect of resistance training alone measured quality of life. Cider and colleagues (1997) used the Quality of Life Questionnaire - Heart Failure, which measures somatic and emotional aspects, life satisfaction, and physical limitations. They reported unchanged quality of life in the training group. Tyni-Lenne and colleagues (2001) used the Minnesota Living with Heart Failure Questionnaire as the measurement tool, on which lower scores indicate better quality of life. They reported a beneficial effect of resistance training on quality of life after 8 weeks, with median scores of 19 (range 0 to 61) in the resistance training group and 44 (range 3 to 103) in the control group (p < 0.001).

Two studies with 57 participants examined the effect of resistance exercise as an adjunct to aerobic training. Both used the Minnesota Living with Heart Failure Questionnaire. Their data were pooled using a fixed effect model. Adding resistance training to aerobic training programs did not significantly change Minnesota Living with Heart Failure Questionnaire scores compared to those obtained with aerobic exercise alone, WMD 0.9 (95% CI -5.4 to 3.7) (Figure 8, see also Figure 9 on the eAddenda for detailed forest plot). A third study (Beckers et al 2008) used the Health Complaints Scale, which primarily measures somatic symptoms. Combined resistance and aerobic training was significantly more beneficial than aerobic training, with 12 (60%) of the 20 combined-training participants reporting a marked decrease in cardiac symptoms, compared with 7 (28%) of the 25 aerobic-training participants (OR 3.86, 95% CI 1.11 to 12.46).

Funnel plots were constructed for the five meta-analyses performed. Although they demonstrated no evidence of publication bias, each plot contained four data points or fewer. This makes the power of the tests too low to distinguish change from real asymmetry (Higgins and Green 2008). Therefore, the funnel plots are not presented.

Discussion_

This systematic review provides some firm evidence about the effects of resistance training on cardiac function, exercise capacity, and quality of life in people with chronic heart failure. The search for evidence was systematic and thorough. The included studies had PEDro scores of 4 to 7 (out of 10). Meta-analysis of the results was performed where possible. When compared to usual or low-intensity activity, a significant beneficial effect of resistance training on 6-minute walk distance was demonstrated based on the results of two studies. However, further research is required to determine whether this is considered clinically worthwhile by people with chronic heart failure.

The results did not indicate a beneficial effect of resistance training on cardiac function. People with chronic heart failure have reduced cardiac output because of impaired ventricular systolic or diastolic function, or both. Chronic heart failure patients primarily have elevated heart rates rather than stroke volume. This allows them to meet metabolic demands accompanied by possible high work load on the heart resulting from increased exercise intensity (Cheetham et al 2002). A study of one bout of isotonic exercise with different intensities found minimal changes in central haemodynamics, which were well tolerated by the chronic heart failure patients (King et al 2000). Significant improvements in muscular strength as well as reduction in peripheral resistance, resulting in improved afterload to the heart, were demonstrated after long-term resistance training (Maiorana et al 2000b, Selig et al 2004, Tyni-Lenne et al 2001). Two studies found that exercise training did not alter left ventricular function regardless of exercise mode (Mandic et al 2009, Pu et al 2001), while other studies reported favourable but non-significant effects on left ventricular function (Beckers et al 2008, Feiereisen et al 2007). Notably, the participants in the former two studies had a slightly higher left ventricular ejection fraction (at 30% and 36%) at baseline than in the latter two studies (at 23% and 26%). Further study is required to examine if there was a ceiling effect or if cardiac function could adapt after exercise training.

This review partially supports the belief that resistance training could elevate maximally tolerable exercise workload without changing peak oxygen consumption (Magnusson et al 1996), given the effect on 6-minute walk distance. The mechanisms that may contribute to the peripheral adaptation of the muscle, such as the increased cross-sectional area, capillarisation, and oxidative capacity, were proposed by Magnusson (1996). Previous studies found that skeletal myopathy, including impaired muscle metabolic capacity and muscle fibre transformation, may be the primary limiting factors of exercise capacity (Okita et al 1998, Vescovo et al 1998). Other studies correlated the improvement of muscle strength, aerobic, and anaerobic performance with increases in muscle fibre cross-sectional area as well as in citrate synthase activity, and lactate dehydrogenase and muscle mitochondrial ATP production rates (Pu et al 2001, Williams et al 2007a). In addition to the muscular level, an improvement of neurovascular level could also contribute to the improvement in 6-minute walk distance. Chronic heart failure in patients with skeletal myopathy may induce sympathetic nerve activation with resultant peripheral vasoconstriction (Clark et al 1996). Plasma norepinephrine levels at rest and submaximal exercise may decrease after high repetitions and moderate resistance training (Tyni-Lenne et al 2001) and thus increase blood flow in response to submaximal activity, such as the 6-minute walk test (Selig et al 2004).

The results of this review suggest that resistance training alone does not significantly improve peak oxygen consumption. Two studies we reviewed (Selig et al 2004, Tyni-Lenne et al 2001) reported increments of 8% and 10%, respectively. Combining resistance with aerobic training failed to demonstrate a greater increase in peak oxygen consumption than aerobic training alone. Similar effects on peak oxygen consumption among three types of exercise training were noted by Feiereisen and colleagues (2007), with gains of 17%, 11%, and 14% for groups undertaking resistance, aerobic, and combined exercise training respectively. Resistance training can have a direct effect on blood flow and metabolism of skeletal muscles independent of any central adaptation due to the specificity of exercise training (Pu et al 2001, Selig et al 2004). If peripheral muscle weakness plays a role in exercise limitation, resistance training may be helpful to improve exercise capacity even though the peak oxygen consumption may not change after training (Delagardelle et al 2002, Feiereisen et al 2007, Hulsmann et al 2004). Delagardelle and colleagues (2002) found combined training was superior to endurance training alone in terms of left ventricular function, peak oxygen consumption, and strength. The inconsistent finding may result from differences in training mode, intensity, or volume of exercise. Further investigation is needed.

Two meta-analyses have reported that exercise training significantly improves quality of life in people with chronic heart failure (Flynn et al 2009, van Tol et al 2006). Nevertheless, there remain disagreements about the effect of resistance exercise alone on quality of life (Cider et al 1997, Tyni-Lenne et al 2001). In this review, quality of life as measured by the Minnesota Living with Heart Failure Questionnaire showed a favourable but non-significant trend with resistance training. A study demonstrated that the improvementin muscle strength after training correlated with the improvement of quality of life (Jankowska et al 2008). Since resistance training ameliorates muscle strength more effectively than aerobic training alone, adding resistance

exercise may strengthen the effect of exercise on quality of life. Beckers and colleagues reported that resistance exercise combined with aerobic training had a significant greater benefit on quality of life, as measured by the Health Complaints Scale, than aerobic training alone (Beckers et al 2008). Furthermore, low compliance was noted in the study that reported no improvement in QOL (Cider et al 1997). There is a need for further studies on resistance training on quality of life, especially with strategies to optimise adherence to the training regimen (Mandic et al 2009).

This review had some limitations. The numbers of included studies and sample sizes were relatively small. The outcome variable measures were often different between studies, limiting the potential for meta-analysis. The likelihood of publication bias can not be assessed. Data for females were very limited. A previous study indicated that female patients had less improvement in cardiopulmonary function than males after combined resistance and aerobic training (Miche et al 2008). Thus the conclusion of this review may not be applicable to female populations. The gender differences in aetiology and pathophysiology of chronic heart failure (Regitz-Zagrosek et al 2004) and responses to resistance training deserve further investigation.

In conclusion, resistance training alone increases 6-minute walking distance but has no additional benefits on heart function, maximal exercise capacity, or quality of life. Furthermore, it does not improve any of these outcomes in people with chronic heart failure who already perform aerobic exercise training. However, further prospective controlled trials of high-quality and large scale are needed to confirm the conclusion of this systematic review. ■

eAddenda: Appendix 1, Figures 3, 5, 7, 9 available at jop.

physiotherapy.asn.au

Competing interests: None declared.

Correspondence: Assoc Prof Ying-Tai Wu, School and

Graduate Institute of Physical Therapy, Floor 3, No.17,

Xuzhou Rd., Zhongzheng District, Taipei City 100, Taiwan.

Email: ytw@ntu.edu.tw

References_

Barnard KL, Adams KJ, Swank AM, Kaelin M, Kushnik AR, Denny DM (2000) Combined high-intensity strength and aerobic training in patients with congestive heart failure. Journal of Strength and Conditioning Research 14: 383388.

Beckers PJ, Denollet J, Possemiers NM, Wuyts FL, Vrints CJ, Conraads VM (2008) Combined endurance-resistance training vs. endurance training in patients with chronic heart failure: a prospective randomized study. European Heart Journal 29: 1858-1866.

Bleumink GS, Knetsch AM, Sturkenboom MC, Straus SM, Hofman A, Deckers JW, et al (2004) Quantifying the heart failure epidemic: prevalence, incidence rate, lifetime risk and prognosis of heart failure The Rotterdam Study. European Heart Journal 25: 1614-1619.

Braith RW, Beck DT (2008) Resistance exercise: training adaptations and developing a safe exercise prescription. Heart Faiurel Reviews 13: 69-79.

Braith RW, Magyari PM, Pierce GL, Edwards DG, Hill JA, White LJ, et al (2005) Effect of resistance exercise on skeletal muscle myopathy in heart transplant recipients. American Journal of Cardiology 95: 1192-1198.

Cheetham C, Green D, Collis J, Dembo L, O'Driscoll G (2002) Effect of aerobic and resistance exercise on central hemodynamic responses in severe chronic heart failure. Journal of Applied Physiology 93: 175-180.

Chien CL, Lee CM, Wu YW, Chen TA, Wu YT (2008) Home-based exercise increases exercise capacity but not quality of life in people with chronic heart failure: a systematic review. Australian Journal of Physiotherapy 54: 87-93.

Cider A, Tygesson H, Hedberg M, Seligman L, Wennerblom B, Sunnerhagen KS (1997) Peripheral muscle training in patients with clinical signs of heart failure. Scandinavian Journal of Rehabilitation Medicine 29: 121-127.

Clark AL, Poole-Wilson PA, Coats AJ (1996) Exercise limitation in chronic heart failure: central role of the periphery. Journal of the American College of Cardiology 28: 1092-1102.

de Morton NA (2009) The PEDro scale is a valid measure of the methodological quality of clinical trials: a demographic study. Australian Journal of Physiotherapy 55: 129-133.

Degache F, Garet M, Calmels P, Costes F, Bathelemy JC, Roche F (2007) Enhancement of isokinetic muscle strength with a combined training programme in chronic heart failure. Clinical Physiology and Functional Imaging 27: 225-230.

Delagardelle C, Feiereisen P, Autier P, Shita R, Krecke R, Beissel J (2002) Strength/endurance training versus endurance training in congestive heart failure. Medicine and Science in Sports and Exercise 34: 1868-1872.

Duscha BD, Kraus WE, Keteyian SJ, Sullivan MJ, Green HJ, Schachat FH, et al (1999) Capillary density of skeletal muscle: a contributing mechanism for exercise intolerance in class II-III chronic heart failure independent of other peripheral alterations. Journal of the American College of Cardiology 33: 1956-1963.

Elkayam U, Roth A, Weber L, Hsueh W, Nanna M, Freidenberger L, et al (1985) Isometric exercise in patients with chronic advanced heart failure: hemodynamic and neurohumoral evaluation. Circulation 72: 975-981.

Feiereisen P, Delagardelle C, Vaillant M, Lasar Y, Beissel J (2007) Is strength training the more efficient training modality in chronic heart failure? Medicine and Science in Sports and Exercise 39: 1910-1917.

Flynn KE, Pina IL, Whellan DJ, Lin L, Blumenthal JA, Ellis SJ, et al (2009) Effects of exercise training on health status in patients with chronic heart failure: HF-ACTION randomized controlled trial. JAMA 301: 1451-1459.

Harrington D, Coats AJ (1997) Skeletal muscle abnormalities and evidence for their role in symptom generation in chronic heart failure. European Heart Journal 18: 1865-1872.

Haykowsky M, Vonder Muhll I, Ezekowitz J, Armstrong P (2005) Supervised exercise training improves aerobic capacity and muscle strength in older women with heart failure. Canadian Journal of Cardiology 21: 1277-1280.

Higgins JPT, Green S (2008) Cochrane Handbook for Systematic Review of Interventions. Version 5.0.2. The Cochrane Collaboration. Available at www.cochrane-handbook.org.

Hulsmann M, Quittan M, Berger R, Crevenna R, Springer C, Nuhr M, et al (2004) Muscle strength as a predictor of long-term survival in severe congestive heart failure. European Journal of Heart Failure 6: 101-107.

Jankowska EA, Wegrzynowska K, Superlak M, Nowakowska K, Lazorczyk M, Biel B, et al (2008) The 12-week progressive quadriceps resistance training improves muscle strength, exercise capacity and quality of life in patients with stable chronic heart failure. International Journal of Cardiology 130: 36-43.

Jennings GL, Esler MD (1990) Circulatory regulation at rest and exercise and the functional assessment of patients with congestive heart failure. Circulation 81: II5-13.

King ML, Dracup KA, Fonarow GC, Woo MA (2000) The hemodynamic effects of isotonic exercise using hand-held

weights in patients with heart failure. Journal of Heart and Lung Transplantation 19: 1209-1218.

Leandro G (2005) Meta-analysis in medical research: the handbook for the understanding and practice of meta-analysis(2nd edn). Malden: Blackwell Publishing.

Levinger I, Bronks R, Cody DV, Linton I, Davie A (2005a) The effect of resistance training on left ventricular function and structure of patients with chronic heart failure. International Journal of Cardiology 105: 159-163.

Levinger I, Bronks R, Cody DV, Linton I, Davie A (2005b) Resistance training for chronic heart failure patients on beta blocker medications. International Journal of Cardiology 102: 493-499.

Magnusson G, Gordon A, Kaijser L, Sylven C, Isberg B, Karpakka J, et al (1996) High intensity knee extensor training, in patients with chronic heart failure. Major skeletal muscle improvement. European Heart Journal 17: 1048-1055.

Maher CG, Sherrington C, Herbert RD, Moseley AM, Elkins M (2003) Reliability of the PEDro scale for rating quality of randomized controlled trials. Physical Therapy 83: 713-712.

Maiorana A, O'Driscoll G, Cheetham C, Collis J, Goodman C, Rankin S, et al (2000a) Combined aerobic and resistance exercise training improves functional capacity and strength in CHF. Journal of Applied Physiology 88: 1565-1570.

Maiorana A, O'Driscoll G, Dembo L, Cheetham C, Goodman

C, Taylor R, et al (2000b) Effect of aerobic and resistance exercise training on vascular function in heart failure. American Journal of Physiology. Heart Circulation and Physiology 279: H1999-2005.

Mandic S, Tymchak W, Kim D, Daub B, Quinney HA, Taylor

D, et al (2009) Effects of aerobic or aerobic and resistance training on cardiorespiratory and skeletal muscle function in heart failure: a randomized controlled pilot trial. Clinical Rehabilitation 23: 207-216.

McKelvie RS, McCartney N, Tomlinson C, Bauer R, MacDougall JD (1995) Comparison of hemodynamic responses to cycling and resistance exercise in congestive heart failure secondary to ischemic cardiomyopathy. American Journal of Cardiology 76: 977-979.

Meyer K (2006) Resistance exercise in chronic heart failure-landmark studies and implications for practice. Clinical and Investigative Medicine 29: 166-169.

Meyer K, Hajric R, Westbrook S, Haag-Wildi S, Holtkamp R, Leyk D, et al (1999) Hemodynamic responses during leg press exercise in patients with chronic congestive heart failure. American Journal of Cardiology 83: 1537-1543.

Miche E, Roelleke E, Wirtz U, Zoller B, Tietz M, Huerst M, et al (2008) Combined endurance and muscle strength training in female and male patients with chronic heart failure. Clinical Research in Cardiology 97: 615-622.

Minotti JR, Johnson EC, Hudson TL, Zuroske G, Murata G, Fukushima E, et al (1990) Skeletal muscle response to exercise training in congestive heart failure. Journal of Clinical Investigation 86: 751-758.

Mueller L, Myers J, Kottman W, Oswald U, Boesch C, Arbrol N, et al (2007) Exercise capacity, physical activity patterns and outcomes six years after cardiac rehabilitation in patients with heart failure. Clinical Rehabilitation 21: 923-931.

O'Connor CM, Whellan DJ, Lee KL, Keteyian SJ, Cooper LS, Ellis SJ, et al (2009) Efficacy and safety of exercise training in patients with chronic heart failure: HF-ACTION randomized controlled trial. JAMA 301: 1439-1450.

Okita K, Yonezawa K, Nishijima H, Hanada A, Ohtsubo M, Kohya T, et al (1998) Skeletal muscle metabolism limits exercise capacity in patients with chronic heart failure. Circulation 98: 1886-1891.

Pu CT, Johnson MT, Forman DE, Hausdorff JM, Roubenoff R, Foldvari M, et al (2001) Randomized trial of progressive resistance training to counteract the myopathy of chronic

heart failure. Journal of Applied Physiology 90: 2341-2350.

Rees K, Taylor RS, Singh S, Coats AJ, Ebrahim S (2004) Exercise based rehabilitation for heart failure. Cochrane Database of Systematic Reviews: CD003331.

Regitz-Zagrosek V, Lehmkuhl E, Lehmkuhl HB, Hetzer R (2004) Gender aspects in heart failure. Pathophysiology and medical therapy. Archives des maladies du coeur et des vaisseaux 97: 899-908.

Selig SE, Carey MF, Menzies DG, Patterson J, Geerling RH, Williams AD, et al (2004) Moderate-intensity resistance exercise training in patients with chronic heart failure improves strength, endurance, heart rate variability, and forearm blood flow. Journal of Cardiac Failure 10: 21-30.

Spruit MA, Eterman R-MA, Hellwig VACV, Janssen PP, Wouters EFM, Uszko-Lencer NH (2009) Effects of moderate-to-high intensity resistance training in patients with chronic heart failure. Heart 95: 1399-1408.

Sunnerhagen KS, Cider A, Schaufelberger M, Hedberg M, Grimby G (1998) Muscular performance in heart failure. Journal of Cardiac Failure 4: 97-104.

Thompson WR, Gordon NF, Pescatello LS (2010) ACSM's guidelines for exercise testing and prescription (8th edn). Philadelphia: Lippincott Williams & Wilkins.

Toth MJ, Gottlieb SS, Fisher ML, Poehlman ET (1997) Skeletal muscle atrophy and peak oxygen consumption in heart failure. American Journal of Cardiology 79: 1267-1269.

Tyni-Lenne R, Dencker K, Gordon A, Jansson E, Sylven C

(2001) Comprehensive local muscle training increases aerobic working capacity and quality of life and decreases neurohormonal activation in patients with chronic heart failure. European Journal of Heart Failure 3: 47-52.

van Tol BA, Huijsmans RJ, Kroon DW, Schothorst M, Kwakkel G (2006) Effects of exercise training on cardiac performance, exercise capacity and quality of life in patients with heart failure: a meta-analysis. European Journal of Heart Failure 8: 841-850.

Vescovo G, Serafini F, Dalla Libera L, Leprotti C, Facchin L, Tenderini P, et al (1998) Skeletal muscle myosin heavy chains in heart failure: correlation between magnitude of the isozyme shift, exercise capacity, and gas exchange measurements. American Heart Journal 135: 130-137.

Volaklis KA, Tokmakidis SP (2005) Resistance exercise training in patients with heart failure. Sports Medicine 35: 1085-1103.

Williams AD, Carey MF, Selig S, Hayes A, Krum H, Patterson J, et al (2007a) Circuit resistance training in chronic heart failure improves skeletal muscle mitochondrial ATP production rate-a randomized controlled trial. Journal of Cardiac Failure 13: 79-85.

Williams MA, Haskell WL, Ades PA, Amsterdam EA, Bittner V, Franklin BA, et al (2007b) Resistance exercise in individuals with and without cardiovascular disease: 2007 update: a scientific statement from the American Heart Association Council on Clinical Cardiology and Council on Nutrition, Physical Activity, and Metabolism. Circulation 116: 572-584.