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 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 .
The UK Department of Health (2011) and the U.S. Department of Health and Human Services (2009) set 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). These guidelines are drawn from the latest research evidence and give specific recommendation for different population groups, but are limited for the lack of evidence on the actual adoption of these prescriptions.
Tjonna 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 that received Continuous Moderate Exercice (CME). Oxygen maximal uptake increased after aerobic interval training (AIT) compared to CME and mitigated more risk factors that comprised the metabolic syndrome. AIT enhanced endothelial function by 9% against CME’s 5% (p<0.001), besides increasing insuling dignaling, excitation-contraction coupling, skeletal muscle biogenenesis and lower blood glucose. 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. However, the study suffers from the small sample size, while injury risk and safety of the training protocol used in the study is not known.
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 systematically analyzed published scientific evidence on the effects of exercise in large conduit arteries, the aorta, the microcirculation, resistance vessels, pulmonary and venous circulation. The results indicate that exercise has benefitial effects on CVD outcomes, including ischemia/reperfusion protection, prevention of age-related diastolic dysfunction, reverses left ventricular remodeling and increases its ejection fraction. This study’s findings are overly dependent on animal experiements, and certain areas of the venous system and microcirculation relain largely unknown. Reviewing literature also presents selection bias, reconcilliation of different methods and contexts among others. However, the use of randomized controlled trials in the studies included Gielen, et al. (2010) make for sound finds, such that the residual molecular understanding incompleteness should not hinder the result’s clinical application.
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. The study uses widely accepted and reproducible measures for variables such as the treadmill speed and grade and the cohort design with such a large sample is should be robust in identifying the temporal cause-effect sequence, but the applicability of these results to women is questionnable especially since the prevalence of CVD varies among men and women.
Li & Siegrist (2012) applied internationally recognized quality criteria for conducting a meta-analysis and systematic review, including high quality inclusion criteria. 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. The design was fairly rigourous in minimizing selection, and the studies included were equally compelling, but it remains difficult to explain the specific effect of PA that produces positive CVD outcomes. Further, the accurate evaluation of PA in the questionnaire due to the lack of uniformity in all the studies used in the studies included.
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 study included 33 research reports with follow up of between 4-20 years, with the majority showing positive cause-effect relationship between PA and CVD outcomes. The risk of adverse events reduced by 35%(at 95% CI) and all-cause mortality fell by 33 percent (95 percent CI). Goel, et al. (2011) conducted a retrospective analysis of data gathered from a registry of 2395 consecutive patients that had undergone percutaneous coronary intervention, and came to similar conclusions as Nocon et al. (2008). Thus, the results are in line with the majority of studies in this field, and even though random effect models were applied in the mata-analysis, which helps achieve uniformity in the interpretation of the studies, but difficutlies with meta-analysis hold. These included selection bias and lack of reliability due to the subjectivity in the interpretation of studies included.
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 through mail back surveys and Cox regression analysis (in the estimation of hazard ratios). 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. This study excels because of the inclusion of extensive baseline examinations, large cohort size, long follow-up period and standardized measurement of variables. However, it is limited by by possible bias in the classification of PA groups.
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. The randomized controlled trial and the large sample are among this study’s strengths, increasing reliability and validity (Chapman, 2005; Gratton & Jones, 2010).
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), other 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).
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. The literature included provide an overwhelming support for there being a protective effects of physical exercises of any intensity on varied CVD outcomes (Department of Health, 2011). With regard to intensity, all forms of exercise are beneficial and it is equally fairly conclusive that high intensity exercise are far more beneficial than moderate and continuous physical activity (Tjonna AE, et al., 2008). 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. 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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