Many of us admire marathon runners - even the idea of running 26 miles is tiring.
But although these athletes may appear to be the epitome of fitness, jogging in small doses, rather than running great distances, may actually be more beneficial for your health, according to a new study.
Scientists tracked the progress of 1,098 healthy joggers and 413 healthy but sedentary non-joggers for 12 years.
They found that heavy-duty joggers were as likely to die as inactive non-joggers, while "light" joggers had the lowest death rates.
Jogging from one to 2.4 hours a week was associated with the lowest mortality and the "optimal" jogging frequency was no more than three times per week.
Overall, significantly lower mortality rates were found in those who adopted a slow or moderate jogging pace. Fast-paced joggers had almost the same likelihood of dying as sedentary non-joggers.
The researchers registered 28 deaths among joggers and 128 among inactive non-joggers.
In general, joggers were younger, had a lower blood pressure and body mass index (BMI), and were less likely to smoke or suffer from diabetes.
Lead scientist Dr Peter Schnohr, from Frederiksberg Hospital in Copenhagen, Denmark, said: "It is important to emphasise that the pace of the slow joggers corresponds to vigorous exercise and strenuous jogging corresponds to very vigorous exercise.
"When performed for decades, this activity level could pose health risks, especially to the cardiovascular system.
"The U-shaped association between jogging and mortality suggests there may be an upper limit for exercise dosing that is optimal for health benefits.
"If your goal is to decrease risk of death and improve life expectancy, jogging a few times a week at a moderate pace is a good strategy. Anything more is not just unnecessary, it may be harmful."
The findings are published in the Journal of the American College of Cardiology.
Maureen Talbot, senior cardiac nurse at the British Heart Foundation, said: "This study shows that you don't have to run marathons to keep your heart healthy.
"Light and moderate jogging was found to be more beneficial than being inactive or undertaking strenuous jogging, possibly adding years to your life.
"National guidelines recommend we do 150 minutes of moderate intensity activity a week. It may sound like a lot, but even brisk walking is good exercise and if you're bit of a couch potato this is a good place to start."