A new study finds that exercise that is extreme in either volume or intensity may be associated with high levels of atherosclerosis in the coronary arteries.

The study, presented in August at a meeting of the European Society of Cardiology, studied 169 veteran competitive endurance athletes against a control group of 171 relatively sedentary subjects. Compared with the control group, the study found lower levels of coronary artery calcium in athletes who ran fewer than 35 miles a week or cycled fewer than 150 kilometers...