By Mark D. Faries, Ph.D. on Saturday, 21 February 2015
Category: Exercise

Jogging as Deadly as Sitting on Couch?

Some recent headlines have some reconsidering going for their next jog!

"Too much jogging as bad as no exercise at all."

"Fast running is as deadly as sitting on couch, scientists find." 

"Stop that binge jogging! Three times a week is best for you...and too much is as bad as doing nothing."

Could this be true? The media would never sensationalize such a topic, right? Let's clarify.

The Study

These articles were based on a recent research study titled, "Dose of Jogging and Long-Term Mortality: The Copenhagen City Heart Study", published in the Journal of the American College of Cardiology.6

The study followed a group of 1,098 joggers and 413 inactive, nonjoggers (aged 20 to 92 years of age) from 2001 to 2013. In 2001 to 2003 participants were asked about their jogging habits, and were followed until 2013 to determine who had died (i.e. mortality). 

Overall, they support the importance of physical activity – finding that 2.6% of the joggers had died by 2013, while 31% of the inactive, nonjoggers died.

However, when all 4 groups of joggers were looked at, the 'strenuous jogger' and 'moderate jogger' did not differ in a 'hazard ratio' (explained below) for all-cause mortality (dying from anything) than the sedentary nonjoggers.

And it was these results that the media took off with.

Some Key Points of Caution

Despite being a very interesting and intriguing study, there are some key points that help us interpret these results with caution.

Why didn't the media focus on these results!? The headline...

"New study confirms, physical activity is still awesome: To be added to lyrics of popular Lego® Movie song."

Hazard Ratio

So, what is the big deal with these hazard ratios? Well, See the figure below from the actual study.

The red dots represent the 'hazard ratio' of that particular jogging group – which is the probablility that someone in that group, who has not died by 2013, will die by the next measured time point. 

However, if the horizontal line on either side of the red dot (the confidence interval) crosses the vertical dotted line (hazard ratio = 1.0), then those results are considered to be at no higher or lower risk than the reference group of sedentary nonjoggers.

Because the 'strenuous jogger' and 'moderate jogger' lines cross the vertical dotted line, they are not statistically significantly different than the sedentary nonjogger group. The authors conclude,

"Light and moderate joggers have lower mortality than sedentary nonjoggers, whereas strenuous joggers have a mortality rate not statistically different from that of the sedentary group."

Actually, it was only the light joggers (in bottom part of figure) who were found to be at lower risk than the sedentary nonjogger – once some other variables were accounted for (age, sex, smoking, smoking, alcohol use, education level, and who had diabetes).

NOTE: Since hazard ratio results can only be applied within the time frame of the study, and the outcomes should not be broadly inferred – as the popular media is trying to do.

A New Topic?

Despite the recent attention, this not a new topic. Overtraining has long been an area of concern for athletes, including the physiological and psychological consequences. The more recent transition has come in regards to the concern that excessive aerobic exercise can cause overuse damage to the heart and cardiovascular system – which I believe is a legitimate concern, and needed area of research.

A Controversial Topic?

Can we now add exercise to the list of 'too much of a good thing'? The jury is still out, as such findings are seemingly in contrast to years of research that has found a dose-response relationship with mortality and exercise amounts or fitness levels – 'the more the merrier.'

Conclusion

Despite what the media would have us think about this research, we must not lose sight of:

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References

  1. Lee, D. C., Pate, R. R., Lavie, C. J., & Blair, S. N. (2012). Running and all-cause mortality risk - Is more better? Medicine and Science in Sports and Exercise44, 924-924. Annual Conference, San Francisco, CA: S699.
  2. Lee, D. C., Sui, X., Ortega, F. B., Kim, Y. S., Church, T. S., Winett, R. A., ... & Blair, S. N. (2010). Comparisons of leisure-time physical activity and cardiorespiratory fitness as predictors of all-cause mortality in men and women.British Journal of Sports Medicine, bjsports66209.
  3. O'Keefe, J. H., & Lavie, C. J. (2013). Run for your life… at a comfortable speed and not too far. Heart99(8), 516-519.
  4. Schnohr, P. (2012). Assessing prognosis: A glimpse of the future. Jogging healthy or hazard. EuroPRevent. In: Cardiology ESo, Ed. EuroPRevent 2012. Dublin, Ireland: European Heart Journal.
  5. Schnohr, P., Lange, P., Scharling, H., & Jensen, J. S. (2006). Long-term physical activity in leisure time and mortality from coronary heart disease, stroke, respiratory diseases, and cancer. The Copenhagen City Heart Study. European Journal of Cardiovascular Prevention and Rehabilitation13(2), 173-179.
  6. Schnohr, P., O’Keefe, J. H., Marott, J. L., Lange, P., & Jensen, G. B. (2015). Dose of jogging and long-term mortality: the Copenhagen City Heart Study. Journal of the American College of Cardiology65(5), 411-419.
  7. Wen, C. P., Wai, J. P. M., Tsai, M. K., Yang, Y. C., Cheng, T. Y. D., Lee, M. C., ... & Wu, X. (2011). Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. The Lancet378(9798), 1244-1253.

Here is a great in-depth review of the study.

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