Health benefits of physical activity
Physical inactivity is a modifiable risk factor for cardiovascular disease and a widening variety of other chronic diseases, including diabetes mellitus, cancer (colon and breast), obesity, hypertension, bone and joint diseases (osteoporosis and osteoarthritis), and depression.1–14 The prevalence of physical inactivity (among 51% of adult Canadians) is higher than that of all other modifiable risk factors.15 In this article, we review the current evidence relating to physical activity in the primary and secondary prevention of premature death from any cause, cardiovascular disease, diabetes, some cancers, and osteoporosis. We also discuss the evidence relating to physical fitness and musculoskeletal fitness and briefly describe the independent effects of frequency and intensity of physical activity. (A glossary of terms related to the topic appears in Appendix 1).
In a companion paper, to be published in Mar. 28 issue, we will review how to evaluate the health-related physical fitness and activity levels of patients and will provide exercise recommendations for health. Several authors have attempted to summarize the evidence in systematic reviews and meta-analyses. These evaluations are often overlapping (reviewing the same evidence). Some of the most commonly cited cohorts have been described in different studies over time as more data accumulate (see Appendix 2, available online at www.cmaj.ca/cgi/content/full/174/6 /801/DC1). In this review, we searched the literature using the keywords “physical activity,” “health,” “health status,” “fitness,” “exercise,” “chronic disease,” “mortality” and disease-specific yet have other risk factors for cardiovascular disease (see Fig. 1) may be at lower risk of premature death than people who are sedentary with no risk factors for cardiovascular disease.31–33 An increase in physical fitness will reduce the risk of premature death, and a decrease in physical fitness will increase the risk.34–37 The effect appears to be graded,34,35 such that even small improvements in physical fitness are associated with a significant reduction in risk (Fig. 2). In one study,35 participants with the highest levels of physical fitness at baseline and who maintained or improved their physical fitness over a prolonged period had the lowest risk of premature death (Fig. 2). Modest enhancements in physical fitness in previously sedentary people have been associated with large improvements in health status.38 For instance, in another study, people who went from unfit to fit over a 5-year period had a reduction of 44% in the relative risk of death compared with people who remained unfit.36 A recent systematic review of the literature regarding primary prevention in women39 revealed that there was a graded inverse relation between physical activity and the risk of cardiovascular-related death, with the most active women having a relative risk of 0.67 (95% CI 0.52 to 0.85) compared with the least active group.
These protective effects were seen with as little as 1 hour of walking per week. In summary, observational studies provide compelling evidence that regular physical activity and a high fitness level are associated with a reduced risk of premature death from any cause and from cardiovascular disease in particular among asymptomatic men and women. Furthermore, a dose-response relation appears to exist, such that people who have the highest levels of physical activity and fitness are at lowest risk of premature death (as discussed later). Secondary prevention of cardiovascular disease The benefits of physical activity and fitness extend to patients with the established cardiovascular disease.40,41 This is important because, for a long time, rest and physical inactivity had been recommended for patients with heart disease. Unlike studies of primary prevention, many studies of secondary prevention are RCTs (see Appendix 2, available at www.cmaj.ca/cgi /content/full/174/6/801/DC1). Several systematic reviews have clearly shown the importance of engaging in regular exercise to attenuate or reverse the disease process in patients with cardiovascular disease. For instance, a systematic review and meta-analysis of 48 clinical trials5 revealed that, compared with usual care, cardiac rehabilitation significantly reduced the incidence of premature death from any cause and from cardiovascular disease in particular. An energy expenditure of about 1600 kcal (6720 kJ) per week has been found to be effective in halting the progression of coronary artery disease, and an energy expenditure of about 2200 kcal (9240 kJ) per week has been shown to be associated with plaque reduction in patients with heart disease.42,43 Low-intensity exercise training (e.g., exercise at less than 45% of maximum aerobic power) has also been associated with an improvement in health status among patients with cardiovascular disease.44 However, the minimum training intensity recommended for patients with heart disease is generally 45% of heart rate reserve.43 In summary, regular physical activity is clearly effective in the secondary prevention of cardiovascular disease and is effective in attenuating the risk of premature death among men and women.