Preventive Cardiology: The Effects of Exercise

Abstract

Physical adaptations to dynamic exercise (i. e., exercise training) lead to increased aerobic and strength capacities (including cardiovascular reserve, endurance and velocity of movement) (Noakes et al., Clin Sports Med 3(2): 527-543, 1984). These attributes are relevant in vigorous athletes, who in addition to high performance also tend to have better metabolism and health, as well as for older adults who compared to age-matched sedentary adults enjoy better health, greater independence, and better quality of life. Exercise regimens are best tailored to the needs of individual patients, with varying emphasis on strength vs. aerobic, and with different intensities/modes based on clinical contexts. Since the 1950s, an extensive literature has described the benefits and risks of exercise, including reports by the American Heart Association (Fletcher et al., Circulation 86(1): 340-344, 1992) and the International Society and Federation of Cardiology (Bijnen et al., J Int Soc Federation Cardiol 2: 5-6, 1992). The aggregate data conveys a strong case that a sedentary lifestyle is detrimental to health, and creates high a risk for cardiovascular disease. The weight of evidence even led to a Surgeon General's report which made clear and explicit recommendations regarding physical activity (Department of Health and Human Services. Physical activity and health: a report of the Surgeon General. Atlanta: National Center for Chronic Disease Prevention and Health Promotion; 1996). Several major agencies and organizations including the National Institutes of Health, the Centers for Disease Control and Prevention, the American College of Sports Medicine, and the American Heart Association have advanced related recommendations that all adults should exercise with moderate-intensity for at least 30 min on most and preferably all day of the week (Department of Health and Human Services. Physical activity and health: a report of the Surgeon General. Atlanta: National Center for Chronic Disease Prevention and Health Promotion; 1996; Physical activity and cardiovascular health. NIH Consensus Development Panel on Physical Activity and Cardiovascular Health JAMA 276(3): 241-246, 1996; Pate et al., JAMA 273(5): 402-407, 1995; Thompson et al. Circulation 107(24): 3109-3116, 2003). Nonetheless, the majority of adults do not attain the recommended levels of exercise and they are not routinely counseled on the important health benefits of regular physical activity (Prevalence of physical activity, including lifestyle activities among adults - United States, 2000-2001 MMWR Morb Mortal Wkly Rep 52(32): 764-769, 2003; Wee et al., JAMA 282(16): 1583-1588, 1999). This chapter explores the role of occupational and recreational physical activity on morbidity and mortality from coronary heart disease (CHD). The first section will focus on healthy individuals, i. e., primary prevention, and will discuss epidemiologic evidence supporting the practice of regular exercise. The second section will discuss secondary prevention, for patients who already have had some manifestation of CHD such as angina pectoris or myocardial infarction or who have undergone revascularization. Finally, the third section will provide a pathophysiologic framework of the possible mechanisms for the beneficial effects of exercise training. Physical activity, exercise training, and physical fitness have distinct definitions (Thompson et al., Circulation 107(24): 3109-3116, 2003; Caspersen et al., Public Health Rep 100(2): 126-131, 1985). Physical activity is any bodily movement produced by skeletal muscles that results in energy expenditure, including occupational, athletic, and other activities. Exercise training refers more specifically to activity that is planned, structured, and purposeful with the intent of developing or maintaining physical fitness (Caspersen et al., Public Health Rep 100(2): 126-131, 1985). Physical fitness is a set of measurable health-related attributes, including muscle strength, flexibility, body composition, and cardiorespiratory power and endurance. While all are important facets of health, only a minority of adults of any age meet current recommendations for physical activity, exercise training, and/or achieve "optimal" physical fitness (Hansen et al., Med Sci Sports Exerc 44(2): 266-272, 2012). In this chapter, we initially focus on the distinctive health benefits of endurance and strength exercise training. Endurance or "aerobic" exercise includes activities with energy demands that are met primarily by oxidative metabolism. Strength exercise is specialized to increase muscle mass and anaerobic endurance. Strength training also can facilitate aerobic performance as it has the potential to moderate muscle atrophy (sarcopenia) that otherwise occurs with aging, deconditioning, and multimorbidity. Increasing muscle mass with strength training also has benefit of increasing weight loss by raising metabolism and caloric expenditure. Therefore, the combination of aerobic and strength training is often optimal, especially for achieving fitness goals of elderly, obese and/or deconditioned adults who benefit particularly from increased muscle mass as well as aerobic training effects (Brown and Holloszy Aging (Milano) 5(6): 427-434, 1993; McAuley J Behav Med 16(1): 103-113, 1993). While there is conceptually value for exercise regimens that are longer and more intense, this is often not feasible for adults who are frail, deconditioned, or those who may simply be averse to exercise. However, even small amounts of exercise have value; research shows that as little as 15 min of low intensity exercise may be beneficial (Wen et al., Lancet 378(9798): 1244-1253, 2011). Therefore, doing any exercise is better than no exercise, particularly because exercise-induced strength and aerobic capacities often facilitate greater physical activity in addition to exercise.