Abstract
Physical activity (exercise) is largely thought to be an indispensable part of human wellbeing. The growing prosperity, material/food abundance, sedentary transport and sedentary lifestyles is linked with the growing incidence of lifestyle diseases including CVD. CVD is currently among most common diseases in developed nations. In the UK alone, an estimated 7 million people are living CVD, which accounts for 160,000 deaths annually. Treatment strategies (including physical activity) have been rigorously tested in cohort studies. However, the type, intensity, and duration of physical activity remain in question. This review is seeking to find theoretical and empirical support for different forms of exercise (and of varying degrees) and their beneficial effects in preventing and/or treating CVD.
Literature Review
Cardiovascular Disease (CVD) is a broad term describing all heart and circulation diseases, including heart failure, stroke, arterial fibrillation, cardiomyopathy and coronary heart disease. CVD accounts for upwards of 28% of all deaths occurred in the UK (160,000) in 2012, and an estimated 7 million people were thought have been living with the condition. The disease costs the country an estimated £19 billion annually in lost productivity, premature death, and medication costs (£6.8 billion). Coronary Heart Disease (CHD) is by far the most common and deadly of CVDs, accounting for 16% of male deaths and 10% of female deaths (74,000 deaths) and affecting an estimated 2.4 million people. Other common CVDs include heart attack (175,000 attacks a year), stroke (causes 40,000 deaths annually) and arterial fibrillation. While regular physical activity is known to reduce the risk of onset of, and pace of progression of CVDs, physical exertion may be hurtful . Effectively, it is critical to determining the effectiveness of different types and intensity of physical exertion in relation to CVD outcomes.
The UK Department of Health (2011) and the U.S. Department of Health and Human Services (2009) sets out specific evidence-based physical activity guidelines for people to ensure long-term heath benefits. For children and adolescents, 60 minutes or one hour of physical activity daily is recommended, including at least three days of aerobic, muscle strengthening and bone strengthening activities weekly. Adults must avoid physical inactivity, and while difficulties exist, they should at least have some activity. For substantial health benefits, at least 150 minutes of moderate-intensity physical activity or at least 75 minutes of vigorous intensity physical exercises are recommended. More health benefits may be attained by increased moderate-intensity aerobic activity for up to 300 minutes a week (or 150 minutes of vigorous activity exercises).
While there are specific physical activity guidelines for varied forms of CVD, these do not usually deviate from the general guidelines by the Department of Health (2011) and the U.S. Department of Health and Human Services (2009). For instance, to manage congenital heart disease among adults, the American Heart Association recommends muscle-strengthening activities for at least two days a week and accumulation of 75 minutes of vigorous (or 150 minutes of moderate) activity weekly with every session lasting at least 10 minutes. Children require more than 60 minutes of daily physical activity, coupled with three-day vigorous activity every week. Bone and muscle strengthening activities are advisable at least three days every week, but high-impact aerobic and anaerobic burst exercises are more conducive for this purpose. Sedentary behaviour guidelines include limitation of extended sitting, screen time, sedentary transport, and time spent indoors every day.
The intensity of the exercises has no consequence on the outcomes, as long as the weekly quotas are met. Tjonna AE, et al. (2008) compared moderate-intensity and high-intensity physical activity with respect to outcomes of cardiovascular outcomes and prognosis among patients with metabolic syndrome. A sample of 32 metabolic syndrome patients was randomized to equal volumes of continuous moderate exercise thrice a week for four months, compared to a control group. Oxygen max increased after aerobic interval training compared to continuous moderate training and mitigated more risk factors that comprised the metabolic syndrome. Vigorous exercises had superiour favourable effects on outcomes compared to moderate continuous training and thus exercise intensity is a critical factor in bolstering aerobic capacity and mitigating risk factors of metabolic syndrome. Studies about the intensity of exercise with regard to various CVD outcomes by Haram, et al. (2009), Sari-Sarraf, et al. (2015) and Cheema, et al. (2015) yielded similar results as Tjonna AE, et al. (2008).
According to Gielen, et al. (2010), a non-sedentary lifestyle necessarily reduces the risk factors for developing CVD and/or reduces the pace of progression of the disease after onset. This paper focussed on how physical activity affects the cardiovascular system at a molecular level, including the known and unknown biochemical and physiological mechanisms that mediate exercise-induced cardiovascular effects. Following the arterial vascular tree, the researchers analyzed the effects of exercise in large conduit arteries, the aorta, the microcirculation, resistance vessels, pulmonary and venous circulation. The results indicate that exercise enhances ischemia/reperfusion protection, prevents age-related diastolic dysfunction, reverses left ventricular (LV) remodeling and increases its ejection fraction. Exercise also induces neurohumoral activation and prevents arithmetic, besides preventing diastolic function, valve degeneration and calcification. Vascular effects include reduced aortic stiffness, increased aortic compliance and endothelial vasodilation. It also reduces oxidative stress, increases sensitivity to adenosine, fosters capillary vessel formation, increases venular capillaries and endothelial function. Exercise also has beneficial non-cardiovascular effects, autonomic and neurohumoral outcomes.
Multiple others studies have shown the positive relationship between sedentary lifestyles and CVD, CVD mortality and all-cause mortality. Myers, et al. (2002) found that a negative relationship exists between exercise capacity as measured by a treadmill, and six-year mortality among 3679 CVD subjects and a control group of 2534 normal subjects. This study sought to establish the predictive value of exercise capacity compared to other exercise-test and non-clinical variables. The results showed that 1256 deaths occurred during the follow-up period, comprising an annual mortality rate of 2.6%. The men that passed were older and had comparably lower maximal heart rate, diastolic and systolic blood pressure, as well as exercise capacity than those that survived. The peak exercise capacity was a strong predictor of death among CVD and normal subjects, after adjusting for age. However, Hamer, et al. (2012) insists that the mechanisms through which structured exercise training and other physical exercises reduced the possibility of recurrent cardiac events remain unknown. The prospective study of 1429 subjects with diagnosed CVD (residing in Scotland and England) measured physical activity and multiple risk markers (including body mass index, systolic blood pressure, cholesterol ratio, total-to-HDL and resting heart rate) at baseline.
While there is empirical evidence of the protective effects of physical activity (PA) against CVD mortality and morbidity, less research exists on such effects on some conditions such as stroke, and despite the differences in prevalence rates among males and females, few studies are focused on women. Li & Siegrist (2012) applied internationally recognized quality criteria for conducting a meta-analysis and systematic review, including high quality inclusion. They also had to have a relative risk (RR)/ hazard ratio (HR) and accessible data on confounders. The results indicate that RR of overall heart disease for men in the group with high leisure time PA was 0.76(95% CI, 0.70-0.82, p<0.001) relative to a reference group that had low leisure time PA. Similar effects were observed among female subjects 0.73 (95% CI, 0.68-0.78, p=0.001). A high protective effect of occupational physical activity was clear among both women 83% (95 CI, 0.67-1.03, p=0.001) and men 0.89(95% CI, 0.82-0.97, p=0.001). Effectively, both leisure time and occupational physical activity have beneficial effect of CVD outcomes, including a reduction of the overall risk of stroke and coronary heart disease onset among women and men by 10% to 20% and 20% to 30% respectively.
Nocon et al. (2008) sought to provide an overview of study results on the protective quality of physical activity on all-cause and cardiovascular mortality. Using a systematic search of MEDLINE, which included cohort studies assessing the preventive impact of PA, the results included 883,372 participants, with follow-ups ranging between four and 20 years, the vast majority of studies found a significant reduction in risk of CVD among physically active participants. The CVD mortality rate was markedly reduced (by up 35%) among the physically active subjects.
The heightened risk of CVD among diabetic and obese patients renders them highly critical regard to the effectiveness of physical activity in reducing the risk of onset and/or progression of CVD. The existent literature strongly supports positive lifestyle interventions that involve increased physical activity. Sieverdes et al. (2010) examined the joint and independent associations between self-reported PA and objectively measured cardiorespiratory fitness (CRF) attained from a maximal treadmill exercise test and risk of type 2 diabetes development. Using 24,444 adult subjects and an 18 year follow-up, this study established 589 incidents of diabetes occurred. Upon adjusting for age, response pattern, examination year, fasting glucose, BMI, smoking, family history of CVD and chronic diseases, the sport fitness and running/walking resulted in 28% and 40% less risk of diabetes respectively, relative a sedentary control group.
Karjalainen et al. (2015) also focusses on leisure time PA, but unlike Li & Siegrist (2012), they examined it along with exercise training among type 2 diabetes subjects with coronary artery disease (CAD). While current guidelines for type 2 diabetes and CAD management recommend physical activity, few patients remain regularly active or attend CAD rehabilitative programs (and for those who, dropout rates are high). This study sought to identify the effects of habitual PA on short-term cardiovascular outcomes among CAD patients with or without type 2 diabetes, as well as to determine the benefit of controlled exercise training programs of risk factors associated with heart disease. The results in the two-year follow up study indicate that patients with lower leisure time PA at baseline presented with heightened risk of cardiovascular events. The adjusted HR at 95% confidence interval was 2.1 (1.1 -4.2, p=0.027), 2.0 (1.0-3.9, p=0.044) and 2.3(1.1 -5.1, p=0.033) for regular leisure time PA, 2-3 times weekly leisure time PA and no leisure time PA respesctively. The patients that completed the two-year exercise intervention and training had favorable changes in exercise capacity, both among CAD patients with type 2 diabetes and CAD patients without type 2 diabetes. The control group did not show any statistically significant improvements in key metabolic and autonomic nervous system risk factors.
While Karjalainen, et al. (2015) and Hamer, et al. (2012) tended to dichotomized subjects into physically active and inactive (or used qualitative estimations such as high, low and moderate exercise), more recent studies have sought to group participants into several quantitatively designated classes of physical activity. One such study is Sattelmair et al. (2011). This study makes a decent effort to quantify the amount of physical activity necessary to mitigate the coronary heart disease. The meta-analysis of epidemiological studies investigated primary prevention of CHD and physical activity drawing on cohort studies published in Britain since 1995. The results found that subjects that engaged more than 150 minutes of moderate-intensity leisure time PA had 14% less chance of developing CHD (95% CI, 0.86, 0.77-0.96) compared to the population that reported no leisure time PA. Subjects that engaged in at lest 300 minutes of moderate-intensity leisure time PA were 20% less likely to develop CHD. However, at higher levels of physical activity resulted in proportionately lower relative risk. These findings are in tandem with the guidelines by Department of Health (2011) and U.S. Department of Health and Human Services (2009).
Conclusions and Future Research
The literature included provide an overwhelming support for there being a protective effects of physical exercises of any intensity on varied CVD outcomes (Cardiac Care Network, 2014; Department of Health, 2011; Hamer, et al., 2012). With regard to intensity, it is equally fairly conclusive that high intensity exercise are far more beneficial than moderate and continuous physical activity (Haram, et al., 2009;, Sari-Sarraf, et al., 2015; Cheema, et al., 2015; Tjonna AE, et al., 2008). All forms of physical activity have beneficial effects on CVD outcomes with varying degrees of efficacy, and both the Department of Health (2011) and the US Department of Health and Human Services offer an excellent guide on different exercises and their relative beneficial value. Li & Siegrist (2012)’s findings are in tandem with the recommended prevention and treatment of CVD, which emphasize primary care. The Canadian Cardiac Care Network (2014) for instance, recommends both occupational and leisure time lifestyle changes to ensure greater activity in the management of heart failure, following the onset of different CVD conditions that may lead to heart failure. However, there is little mention of the specific types and intensity of exercise or physical activity can help achieve the outcomes anticipated in the results, or even those that were studied in the parent studies included in this meta-analysis.
Karjalainen et al. (2015) is important because it touches on the behavioral and practical difficulties in the maintenance of active lifestyles among patients, as well as the co-morbidities that often affect the specific disease outcomes. The use of a randomized controlled trials and acceptably large samples makes the methodology robust. Even most importantly, however, the findings indicate the existence of an inverse relationship between short-term cardiovascular outcomes and habitual leisure time PA, but that home-based physical activity training only has limited impact on the cardiovascular risk profile of patients with CAD and type 2 diabetes. However, there is limited literature on occupational, physical activity, and its practical applications in combatting rising CVD and other lifestyle diseases.
The existent evidence on the effects of PA on CVD outcomes is fairly conclusive, but not complete. While evidence abounds that beneficial effects exercise on CVD outcomes, there is still very poor compliance with physical activity recommendations, in possibly because of the perception of the guidelines being unrealistic. These recommendations will come to nought if they are not supported by realistic measures to ensure increased compliance. Effectively, research efforts should be channeled towards the uptake of evidence-based recommendations, health promotion and specific measures to foster exercise compliance.
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