F or many years, cardiac physicians were strongly influenced by Thomas Hilton's "Rest and Pain" and advocated prolonged rest for the majority of their patients. However, the past 3 decades have seen a complete revolution in this thinking, and moderate to vigorous exercise is now prescribed not only for the prevention of ischemic heart disease 1 but also as a major component of treatment after myocardial infarction, 2 angioplasty and coronary bypass surgery, and heart transplantation 3 and in congenital heart disease 4 and stable congestive heart failure. 5,6 This report defines exercise and physical activity, considering their impact on susceptibility to cardiovascular disease. It also examines the physiological effects of regular exercise, suggesting how exercise-induced changes might improve cardiac performance. It discusses the influence of the type, intensity, frequency, duration, and volume of exercise and their respective contributions to the development of a rational exercise prescription, commenting on problems of sustaining compliance and the potential dangers of excessive exercise. A final section of the article suggests possible avenues for future research.
Physical Activity, Exercise, and FitnessTo understand how physical activity and exercise fit into the model of modern cardiovascular health, it is important to understand specific terms and concepts. Physical activity has been defined as any bodily movement produced by skeletal muscles that results in energy expenditure. Exercise can be defined as a subset of physical activity that is planned, structured, repetitive, and purposeful in the sense that improvement or maintenance of physical fitness is the objective. Physical fitness includes cardiorespiratory fitness, muscle strength, body composition, and flexibility, composing a set of attributes that people have or achieve that relates to the ability to perform physical activity. 7 Physical fitness is best assessed by measures of maximal (or peak) oxygen intake (V O 2 ). Many studies estimate fitness levels by measurement of either the peak work rate or MET level (where 1 METϭan energy expenditure of 14.6 kJ ⅐ kg) achieved during graded exercise tests. 8 When defining the amount of physical activity or exercise, an important interrelation exists between the total dose of activity and the intensity at which the activity is performed. Dose refers to the total amount of energy expended in physical activities that require repetitive muscular movement (usually expressed in kilojoules or kilocalories). Intensity can be defined in absolute or relative terms. Absolute intensity reflects the rate of energy expenditure during exercise and is usually expressed in METS, kJ ⅐ min Ϫ1 or kcal ⅐ min
Ϫ1. Relative intensity refers to the relative percentage of maximal aerobic power that is maintained during exercise and is expressed as a percentage of maximal heart rate or a percentage of maximal oxygen intake. For example, brisk walking at 4.8 km/h, 3 mph, has an absolute intensity of approximately 4 METs. In relat...