When it comes to exercise, you really can get too much of a good thing.
That’s the key finding of a new report that suggests prolonged high-intensity workouts — lasting more than an hour each day — do more harm than good and can shorten lifespan.
The health warning, contained in an editorial published online in the journal Heart, advises limiting vigorous exercise to between 30 and 50 minutes per day.
The report’s primary author — Dr. James O’Keefe, of Saint Luke’s Mid America Heart Institute in Kansas City — noted this guideline is especially important for people who regularly engage in high-intensity or vigorous exercise. This includes marathon runners or triathletes who may falsely believe more prolonged and demanding workouts are better for overall health.
In fact, O’Keefe said, the evidence shows that the opposite is true.
“The prevailing logic [has been] that aerobic exercise is clearly good for one’s health and that, if some
is good, more must be better,” he said. “In 1975, Dr. Thomas Bassler, a physician/runner, boldly proclaimed that, if you could run a marathon, you were immune to death from coronary heart disease.

“This urban myth has long since been disproven; indeed an emerging body of evidence suggests the opposite: extreme endurance exercise may exact a toll on cardiovascular health.”

O’Keefe’s recommendations are based on an analysis of studies indicating a daily dose of light- to moderate-intensity exercise — at least 20-30 minutes long — offers the best benefit, in terms of heart health. That doesn’t mean marathon runners or high-intensity exercise buffs are in danger. But he said prolonged, vigorous workouts shouldn’t be done every day.

“The take home message for most is to limit one’s vigorous exercise to 30–50 [minutes per day]. If one really wants to do a marathon or full-distance triathlon, etc., it may be best to do just one or a few and
then proceed to safer and healthier exercise patterns,” he said.

“On the other hand, light or moderate intensity exercise does not present the … risks associated with excessive endurance exercise. A routine of moderate physical activity will add life to your years, as well as years to your life.

"In contrast, running too fast, too far, and for too many years may speed one’s progress towards the finish line of life.”