Background: Previous studies have suggested that higher levels of regular physical activity and cardiorespiratory fitness are associated with a reduced risk of coronary heart disease. We investigated the independent associations of physical activity during leisure time and maximal oxygen uptake (a measure of cardiorespiratory fitness) with the risk of acute myocardial infarction.

Methods: During the period 1984 to 1989, we performed base-line examinations in 1453 men 42 to 60 years old who did not report having cardiovascular disease or cancer. Physical activity was assessed quantitatively with a detailed questionnaire, and maximal oxygen uptake was measured directly by exercise testing. During an average follow-up of 4.9 years, 42 of the 1166 men with normal electrocardiograms at base line had a first acute myocardial infarction.

Results: After adjustment for age and the year of examination, the relative hazard (risk) of myocardial infarction in the third of subjects with the highest level of physical activity (> 2.2 hours per week) was 0.31 (95 percent confidence interval, 0.12 to 0.85; P = 0.02), as compared with the third with the lowest level (P = 0.04 for linear trend over all three groups). The relative hazard in the third with the highest maximal oxygen uptake (> 2.7 liters per minute) was 0.26 (95 percent confidence interval, 0.10 to 0.68; P = 0.006) (P = 0.006 for linear trend), after adjustment for age, the year and season when the examination was performed, weight, height, and the type of respiratory-gas analyzer used. After up to 17 confounding variables were controlled for, the relative hazards for the third of subjects with the highest level of physical activity (0.34; 95 percent confidence interval, 0.12 to 0.94; P = 0.04) and maximal oxygen uptake (0.35; 95 percent confidence interval, 0.13 to 0.92; P = 0.03), as compared with the values in the lowest third, were significantly (P < 0.05) less than 1.0.

Conclusions: Higher levels of both leisure-time physical activity and cardiorespiratory fitness had a strong, graded, inverse association with the risk of acute myocardial infarction, supporting the idea that lower levels of physical activity and cardiorespiratory fitness are independent risk factors for coronary heart disease.