Over-exercise: Too much of a good thing?

Michelle Tierney
27 October 2014

Above: Participants in the 2009 edition of the Ultra-Trail du Mont Blanc, a 168km race in the Alps (Wikimedia Commons/mako10)

The benefits of regular exercise are well known. So does it make sense that those who exercise the most are healthiest and live the longest? Not necessarily. New evidence suggests that too much high-intensity exercise may increase your risk of health problems, including irregular heartbeat (arrhythmia).

Did you know? Between 2003 and 2013, there was a 40% increase in US marathon finishers.Take the example of Micah True, a famous American ultrarunner who died at the age of 58 while on a training run in New Mexico. Beginning in the 1990s, True lived part of the year with the Tarahumara people of Mexico, who are also known for their distance-running abilities and who gave him the nickname Caballo Blanco (White Horse).

Micah’s death left many people mystified, since they assumed he was not only exceptionally fit but also extremely healthy. In fact, his heart muscle had been slowly weakening over time. This caused his heartbeat to become irregular and the pumping of his heart to become less efficient, ultimately leading to cardiac arrest.

When an incredibly fit person with a hidden health problem dies of a heart attack, it tends to get a lot of attention. And one of the questions that inevitably gets asked is whether, when it comes to exercise, you can get too much of a good thing. Recent scientific research on the impact of intense exercise on your health suggests that the answer may, in fact, be yes.

One study reported that men who exercised intensely for at least five hours a week were more likely to develop an irregular heartbeat by the age of 60 than those who exercised intensely for a maximum of one hour a week. The study also found that those who take part in slightly less-intense exercise for at least an hour a day were less likely to develop an irregular heartbeat than those who did not exercise regularly.

The researchers concluded that moderation is key, and that very high-intensity and prolonged activity can begin to undo some of the benefits of regular exercise. They suggested that there is a “reverse J-shaped association” (Figure 1) between activity levels and heart-related health problems, meaning that both an inactive person and someone with a very intense level of activity would both have a higher risk of cardiovascular problems compared to someone who is moderately active a few times times per week. However, the “inactivity” end of the curve is still higher than the “extreme activity” end, meaning that no exercise is more dangerous than too much.

Figure 1 A graph showing the reverse J-shaped association between level of activity and risk of heart-health problems (Michelle Tierney. Based on the article by Mons, Hahmann & Brenner cited below)

Highly intense exercise may also harm the immune system and make your body vulnerable to sickness. Exercise-induced stress can cause the adrenal glands to produce certain stress hormones that temporarily lower immunity during intense physical exertion. Furthermore, these stress hormones can cause blood pressure and cholesterol levels to rise, leading to further decreased immunity. These effects have been linked to an increased susceptibility to infection observed in endurance athletes after extreme exercise, such as marathon running.

Did you know? Physical activity helps young people develop healthy bones, muscles, joints, hearts, and lungs. The World Health Organization recommends at least 60 minutes a day of moderate-to-vigorous physical activity for those aged 5-17.This emerging research on the risks of extreme exercise in no way questions the clear benefits of exercise in general. In fact, these studies highlight the importance of regular moderate exercise for maximizing good health. They also state very clearly that inactivity is a far bigger health problem than excessive physical activity.

What the latest research findings do suggest is that over-exercising may have harmful effects on your health. In other words, you can get too much of a good thing. So if you want to be healthy and live longer, exercise regularly and moderately. And if you happen to enjoy running ultramarathons, your risk of health problems is likely still lower than someone who does not exercise at all.

Learn more!

Online resources

Autopsy Report: Micah True’s “Manner of Death is Natural” (2012)

Natural Running Center

News report on the death of utlrarunner Micah True.

Is too much high-intensity exercise bad for your heart? (2014)

Marie Ellis, Medical News Today

Article on the dangers of too much high-intensity exercise.

Exercise and Immunity: Can too much exercise decrease your immunity and make you sick? (2014)

Elizabeth Quinn, About Health

Article discussing the negative effects of intense exercise on immunity and health.

2014 Annual Marathon Report (2014)

Running USA

Brief report with statistics on marathons held in the United States in 2013.

Physical Activity and Young People (2011)

World Health Organization

Recommended levels of physical activity for children and the benefits of physical activity for young people, with links to additional information.

Other resources

Mons, U, Hahmann, H., & Brenner, H. (2014). A reverse J-shaped association of leisure time physical activity with prognosis in patients with stable coronary heart disease: evidence from a large cohort with repeated measurements. Heart, heartjnl-2013-305242.

Study showing increased risks for both the least active and most active patients. An abstract is available on the journal’s website, but a subscription is required to view the full text.

Drca, N., Wolk, A., Jensen-Urstad, M., & Larsson, S.C. (2014). Atrial fibrillation is associated with different levels of physical activity levels at different ages in men. Heart, heartjnl-2013-305304.

A Swedish study on the relationship between activity level and health. An abstract is available on the journal’s website, but a subscription is required to view the full text.

O’Keefe, J. H., Lavie, C. J. (2012). Run for your life...at a comfortable speed and not too far, Heart, 99(8), 516-519.

Editorial that addresses both the benefits of running and the dangers of extreme exercise. An extract is available on the journal’s website, but a subscription is required to view the full text.

Michelle Tierney

No bio available. Note biographique non disponible.


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