Introduction Exercise training

Introduction
Exercise training (ET) is believed to increase aerobic capacity, prognosis, health-related quality of life (QOL) in patients with heart failure(HF). The purpose of this study is to determine the effect of exercise on Exercise Capacity in HF. The following four studies discuss the effectiveness of exercise training on functional status, all-cause mortality, hospital admission rate and health-related QOL of patients with HF.

Main body
A study by Corvera-Tindel et al (2004) evaluate the effectiveness of a 12 weeks of low-intensity home walking exercise program(HWE) on clinical outcomes for HF patient. The primary oucome included exercise capacity and functional performance. The secondary outcome included dyspnea and fatigue. All patients (n=79) were randomized into the training group (n =42) underwent low intensity (40%-65%) HWE training, and the no-exercise control group (n = 37). There were improvement shown in 6-minute walk test with 45% of training group patients improved their 6-MWT distances . The post global rating of symptoms also improve when compared with a usual activity control group. The limitation of this study included that research assistants conducted the 6-MWT were not blinded to the subgroups. To reduce possible bias in conducting outcome measures, they should be blinded to the allocation groups. Time and distance walked were recorded by a pedometer given to the patients. The pedometers were not sealed, patients could read the daily distances travelled . There were also minor clinical events such as flu, comorbidities interrupted the 51.4% patients in the training program. The compliance rates slowly decreased from 81% in the 5th week to 65% to 71% in the last 6 weeks. Low compliance rate may have affected the training effects on peak Vo2.

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With strengthening exercises prescribed in addition, Dracup et al (2007) aim to evaluate the effects of a home-based exercise program on clinical outcomes in patients with HF. The exercise program consisted both aerobic and resistance exercises. The combined clinical outcomes consisted of all-cause hospitalisation, mortality, hospital admission rate, QOL, hostility , functional performance, and the psychological states of anxiety, depression. A total of 173 patients were randomized to control(n=87)or home-based exercise (n=86). The functional performance was assessed by cardiopulmonary exercise testing and the 6-MWT. The current study demonstrated no improvement in all-cause mortality in participants in home-based exercise group. However, the exercise group(12.8%) has reduced number of multiple (2 or more) hospitalizations than control group (26.6%) with P = .018. The limitation was patients randomized to the experimental group have low compliance to exercise as only 44% of them had complete pedometer and daily diary data. Underdosage of exercise intensity and duration may have result in insignificant change in exercising group. A physiological benefit is unlikely without patients in exercise group performed the correct amount of exercise. It is a legitimate concern that exercise group of patients may not have achieved an ideal amount of exercise.

In a larger cohort, O’Connor et al (2009) conducted a Controlled Trial Investigating Outcomes of Exercise Training (HF-ACTION) to evaluate the issue of efficacy and safety of exercise training among HF patients. A total of 2331 patients were randomized from 82 centers from various countries to aerobic exercise with usual training group or usual care control group. The intervention included 36 supervised, moderate-intensity training of 60% to 70% heart rate reserve. After 18 supervised sessions , patients transited to home-based training for a median follow-up of 30 months. The primary end point consisted of all-cause mortality or hospitalisation. The key secondary clinical end point was health-related QOL. The HF-ACTION authors presented no evidence of significant difference in the intervention effects in both groups. This less-than-expected training effect reflected a low compliance rate to exercise in the training group with only 30% of subjects achieved the targeted exercise dosage. After adjusting the highly prognostic predictors of mortality, significant reductions for both clinical end points was seen in training group. One of the limitation in this study was cross over effect. A large percentage of patients (55%) in the usual care alone group were not satisfied. Although control group were not told to follow an exercise regimen during this period, some of the control patients exercised regularly. Thereby diminishing this study’s ability to determine a significant effect of ET on the clinical outcomes.

Finally, a study by Belardinelli et al ( 2012) aim to investigate the effects of a 10-year supervised moderate ET program on sustained improvement in functional capacity and QOL in chronic HF patients. A study of 123 patients were randomized into a supervised trained group (T group, n =63) and a nontrained group (NT group, n= 60). The T group underwent a supervised ET at 60% of peak oxygen consumption (VO2), 2 times weekly for 10 years. In general, sustained improvement in functional capacity were reported by those patients who undergo a 10-year supervised ET program of moderate intensity. Hospital readmission ( p < 0.001) and cardiac mortality (p < 0.001) than was lower in the T group and QOL score (p < 0.05), was significantly better in the T group versus the NT group. Hence, the clinical benefits of exercise training in systolic CHF can be expected to be long lasting. Supervision seems to be an important factor to decrease dropouts and increase adherence to long-term exercise scheme. Overall, the drop-out rate was low and participation in training was adequate due to supervision. However, potential of bias may exist as for NT group, they were free to do aerobic activities such as walking and swimming.

Discussion
Based on the four articles, exercises were beneficial on improving heart capacity. The study by Corvera-Tindel et al (2004) suggested that 12 weeks of low intensity home walking exercise program is suitable for patients with HF. Both walking distance and global rating of symptoms were improved in HF patients from training group. However the focused of this article was upon the immediate physical responses of the exercise training program rather than evaluating physical benefits, in terms of mortality and morbidity in long term. A reduction in hospital re-admission rates, improved morbidity, and a decline in mortality are the key indicators of the advantages of exercises for patients with HF. As such, they are the important outcome measures for investigating the efficacy of exercise training on patients with HF. Other three articles did address these outcome measures.

All four studies have been conducted in the generation of contemporary medical treatment for HF. In HF-ACTION trial, 45% had an implanted pacemaker or implantable cardioverter defibrillator and 94% of HF patients were receiving medication such as ?-blockers, angiotensin-receptor blocker or ACE inhibitor. Similarly, medications were distributed in the 2 groups of patients in 10 year exercise training . 100% of patients were given angiotensin receptor blockers or angiotensin- converting enzyme inhibitors.Given the proven survival benefits of these medical therapy, it might be expected that any cumulative all-cause mortality benefit with exercise is likely to be limited.

No survival advantage with exercise training seen in Dracup et al are in accordance with HF-ACTION trial but not with that of Belardinelli et al. The10 year supervised exercise training did improve the health-related QOL of patients with HF in ET compared with usual care. One major concern is the reporting of compliance to exercise prescription. While the reports included the intended exercise intervention dose, it is impossible to regulate patients’ adherence and fidelity. Without proper self-reported exercise training protocol compliance, the exercise dose received cannot be quantified. This may have a significant impact on intervention effectiveness and the results. Compared to other three studies, the10 year exercise training was supervised and the adherence rate was excellent (88%). Supervision ensured good compliance and confirm exercise intensity and period at the levels prescribed. The ability for patients to follow an exercise program on their own was ideally with support from community-based health professionals and other participants from the cardiac rehabilitation program. A practical, safe, longstanding, supervised maintenance standard has yet to be developed. A home exercise program would reduce the time and constraints on ease of accessibility to participate in exercise program in hospital or coronary club.

Conclusion
In conclusion, the four articles presented that exercises for patients with HF is safe. Improvements in exercise capacity and health-related QOL, reduced in hospitalization with exercise training can be attained, despite differences in training duration, presence of supervision of training and outcome measures. The exercises may also reduce mortality in the longer term. Future clinical research of exercise training in HF need to take into account the interventions to reinforce the long-term benefits of exercise training which can be applicable in a home-based environment.

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