A new study helps resolve an apparent contradiction highlighted by the recent death of runner-author Jim Fixx while jogging: Regular exercise, which has a healthy long-term effect against coronary artery disease, can also raise the risk of cardiac arrest during the exercise itself.

The study, reported in the New England Journal of Medicine, included 133 male victims of cardiac arrest in the Seattle area. It found that the risk of cardiac arrest during exercise was higher than at other times. The increased risk during exercise was largest for those not in the habit of exercising, smallest for those who average at least 20 minutes a day of vigorous workout.

But the overall risk of cardiac arrest (during exercise or not) was much lower for habitually vigorous men than for sedentary men.

As an accompanying editorial notes, these findings suggest that "any short-term risk of exercise is outweighed by the long-term beneficial effects of physicial activity."

Death from cardiac arrest during exercise is a rare event, despite the heavy publicity of Fixx's death. Still, experts caution all persons with a history of heart problems to consult a doctor before starting an exercise program. Those unaccustomed to strenuous exercise should be careful not to overdo early workouts. Like all exercisers they should warm up slowly, pace themselves and cool off gradually.