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Intensity of exercise reduces cardiovascular risk

Both the intensity and duration of exercise are important in reducing deaths from coronary heart disease in men, a new study has found (JAMA 2002;288:1994-2000). 
 
Moreover, weight training, long thought to be an inferior type of exercise because it is not aerobic, also yielded discrete cardiovascular benefits. 
 
The researchers, led by Drs Frank Hu, Michael Leitzmann, and Mihaela Tanasescu, from the departments of nutrition and epidemiology at the Harvard School of Public Health, sought to clarify the roles of intensity, duration, and type of exercise in reducing morbidity and mortality from heart disease. They did this by following a cohort of 44 452 professional men enrolled in the health professionals' follow up study. 
 
The men, aged 40-75, answered a detailed questionnaire that assessed their health level through medical history and lifestyle. Additionally, a comprehensive survey of diet and exercise was taken. The main outcome measures were fatal and non-fatal myocardial infarctions and coronary heart disease. Men with a history of stroke, myocardial infarction, revascularisation, angina, and cancer were excluded from the study. 
 
Study participants were followed every two years from 1986 to 1998, and their physical activity levels were assessed each time. Participants were asked about the average time spent walking, hiking, jogging, running, biking, swimming, playing tennis, squash, and racquetball (similar to squash). Later questionnaires added outdoor work and weight training to the activity level section. 
 
The researchers calculated the metabolic equivalents of physical activity by multiplying the time spent in each physical activity by its typical energy expenditure. One metabolic equivalent task (MET) was defined as an expenditure of 1 kcal/kg of body weight an hour or the amount of energy expended by simply sitting quietly and breathing. Vigorous physical activity was defined as an expenditure of 6 METs or more, and activities that met this criteria included jogging, running, rowing, swimming laps, and playing tennis, squash, and racquetball. Less vigorous activities included walking, weight training, and heavy outdoor labour. 
 
The researchers controlled for age, alcohol intake, smoking, and cardiovascular risk factors in their analyses. Over the course of the study 1700 new cases of coronary heart disease were identified among 475 755 person years. 
 
The findings showed that total physical activity, running, rowing, and weight training were each inversely associated with the development of coronary heart disease. Exercise intensity was associated with a reduced coronary heart disease risk independent of the total duration of exercise. 
 
The relative risks associated with moderate (4-6 METS) and high (6-12 METS) activity levels—compared with low activity levels (<4 METS)—were 0.94 (95% confidence interval 0.83 to 1.04) and 0.83 (0.72 to 0.97) respectively. 
 
Men who ran for an hour or more each week at 6 miles per hour (9.7 km/h) had a 42% reduced risk of coronary heart disease than men who did not run (relative risk 0.58; 0.44 to 0.77; P<0.001) . 
 
Those who trained with weights for 30 minutes or more a week had a 23% reduced risk of coronary heart disease compared with those who did not (0.77; 0.61 to 0.98). Rowing for one hour or more a week was associated with a reduced risk of 18% (0.82; 0.68 to 0.99) as was brisk walking (0.82; 0.67 to 1.00). 
 
A half hour or more of brisk walking each day was also associated with an 18% reduction in risk for coronary heart disease, while an increased pace reduced coronary heart disease independent of duration of walking. Low intensity walking failed to produce a significant benefit. 
 
The researchers suggested that "while moderate exercise like brisk walking is associated with reduced risk, greater risk reduction can be obtained with more intense exercise." They further speculated that weight training is beneficial because it increases fat free mass, and raises the basal metabolic rate, and improves glycaemic control. 
 
The study is the first to find a significant reduction in risk of heart attack with weight training. The authors concluded that more research was needed "to address whether inclusion of strength training recommendations for coronary heart disease prevention is warranted."