Physical activity (PA) defined as any bodily movement that is produced by the contraction of skeletal muscle and that substantially increases energy expenditure. PA is also traditionally defined in terms of mode, frequency, duration, and intensity. This article will focus on PA related to aerobic type activities and will explore the benefits mainly related to cardiovascular disease (CVD) risk factors.
Being physically active is one of the most important things that people of all ages can do to improve their health (United States Department of Health & Human Services, 2008). Very strong scientific evidence shows that physically active people have higher levels of health-related fitness, lower risk profiles for developing a number of disabling medical conditions, and lower rates of various chronic diseases than do people who are inactive (Physical Activity Guidelines Advisory Committee, 2008). Disease outcomes inversely related to regular PA in prospective observational studies include CVD, thromboembolic stroke, hypertension, type 2 diabetes mellitus, osteoporosis, obesity, colon cancer, breast cancer, anxiety and depression (Kesaniemi, Danforth, & Jensen, 2001).
The effect of PA on measures of obesity is somewhat controversial. A recent review study (Hansen, Dendale, Berger, van Loon, & Meeusen, 2007)concluded that, in general, an addition of exercise to interventions with a dietary restriction does not induce a greater fat-mass loss than dietary restriction alone. The authors attributed this to a compensatory reduction in daily PA following the implementation of exercise training. In a meta-analysis of pedometer-based walking interventions only a modest amount of weight loss –1.27 kg (95% confidence interval, –1.85 to –0.70 kg) was found (Richardson et al., 2008). However, in a meta-analysis of randomized controlled trials, significant decreases in body weight, BMI, and percent body fat were found (Murphy, Nevill, Murtagh, & Holder, 2007). In addition, in the review by the PAGAC (2008), 24 cross-sectional studies that examined the association between PA and body weight were identified, and of these studies, 23 reported results suggesting an inverse relationship between PA and body weight and/or BMI.
The responses of serum lipoproteins to changes in habitual PA have been well studied. In general, both HDL-C and serum TG reproducibly and favorably respond to changes in habitual PA, with increases in HDL cholesterol and decreases in serum TG (PAGAC (2008). The relationship between PA and the levels of lipoproteins and triglycerides has been studied at length, leading to a large number of meta-analyses in the subject. This has been studied in such great lengths that meta-analyses have been conducted for specific groups. In the study by (G. A. Kelley & Kelley, 2007), the effects of aerobic exercise on lipids and lipoproteins was studied only on adults with type 2 diabetes, and it was found that aerobic exercise lowers LDL-C. In another meta-analysis (G. A. Kelley, Kelley, & Franklin, 2006), chronic aerobic exercise increases HDL-C and decreases TG in adults CVD patients. In addition, more general meta-analyses have been conducted and benefits were also found (G. A. Kelley & Kelley, 2008; G. A. Kelley, Kelley, & Tran, 2004; G. A. Kelley, Kelley, & Tran, 2005).
Impaired fasting glucose
People who regularly engage in at least moderate-intensity aerobic activity have a significantly lower risk of developing type 2 diabetes than do people who are inactive. Lower rates of this condition are seen with 120 to 150 minutes (2 hours to 2 hours and 30 minutes) a week of at least moderate-intensity aerobic activity. As with cardiovascular health, additional levels of PA seem to lower risk even further. In addition, PA helps control blood glucose levels in persons who already have type 2 diabetes (US DHHS, 2008). Large prospective cohort and cross-sectional observational studies that assessed PA through the use of questionnaires all show that increased PA levels are associated with reduced risk for developing type 2 diabetes (PAGAC, 2008). In a study comparing the effects of lifestyle modifications with medication, where the PA prescription portion of the lifestyle portion of the study was 150 min of activity per week, the authors found that the lifestyle component reduced incident diabetes by 58% and had a more powerful effect than the metformin (by 39%) medication (Diabetes Prevention Program Research Group, 2002). In a meta-analysis (D. E. Kelley & Goodpaster, 2001), that analyzed the effects of exercise on glucose homeostasis in type 2 diabetes found that higher levels of PA were clearly associated with a lower incidence of type 2 diabetes, but a dose-response relationship was not evident.
PA can be a potent factor in the reduction of blood pressure. Due to the large number of exercise intervention and prospective studies that measure blood pressure as an outcome, there are a number of meta-analyses investigating the effects of PA and blood pressure (Cornelissen & Fagard, 2005; Hamer, Taylor, & Steptoe, 2006; Murphy, et al., 2007). In the meta-analysis by Cornelissen and Fagard, mean reductions for resting systolic blood pressure (SBP) and diastolic blood pressure (DBP) due to exercise interventions ranged from 2 to 5 mm Hg and 2 to 3 mm Hg respectively. Reductions were greater in hypertensive participants than in prehypertensive and normotensive participants.
In summary, CVD is a major cause of disability and premature death throughout the world, and contributes substantially to the escalating costs of health care. CVD accounts for a large number of deaths and causes a financial burden to Americans. Very strong scientific evidence shows that physically active people have higher levels of health-related fitness, lower risk profiles for developing a number of disabling medical conditions, and lower rates of various chronic diseases than do people who are inactive. More specifically, higher levels of PA and physical fitness are independently associated with lower CVD risk.
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