Author + information
- Peter Schnohr, MD, DMSc∗ (, )
- Jacob L. Marott, MSc and
- James H. O’Keefe, MD
- ↵∗Frederiksberg Hospital, Copenhagen City Heart Study & Epidemiological Research Unit, Nordre Fasanvej 57, Copenhagen DK-2000, Denmark
We thank Dr. Andersen, Drs. Burtscher and Pesta, Drs. Charansonney and Cohen-Solal, Mr. Maessen and colleagues, and Dr. Sanchis-Gomar and colleagues for the interest in our paper and their many insightful comments (1).
The 1986 paper by Paffenbarger et al. was the first of many studies to report a U-shaped association between leisure-time physical activity and mortality. In the short interim since our study was published in the Journal, 2 more large prospective observational studies have reported similar U-shaped or reverse J-shaped associations. The recurring theme is that moderate doses of exercise markedly reduce risks for long-term mortality (both all-cause and cardiovascular deaths), but the subgroups that perform very high doses of exercise appear to lose some of the mortality benefit conferred by moderate exercise. The Million Women Study (2) found that regular physical activity was associated with dramatically lower risks of coronary heart disease (CHD); however, the women who did not take at least 1 day/week off of strenuous exercise appeared to lose some of the cardioprotection (Figure 1A). Another large study recently reported that exercise dramatically reduced the risk of death during follow-up (3); however, again, the maximal benefits were noted in the moderate range, with the familiar reverse J-curve suggesting an attenuation of benefit at the highest level of exercise (Figure 1B). In 2013, we published a study of a random sample of 1,878 joggers who were followed for up to 35 years and compared with 16,827 nonjoggers. The increase in survival among joggers was similar between the sexes (6.2 years in men and 5.6 years in women), but surprisingly those who jogged for the longest time (>4 h/week), at a fast pace, and >3 times/week appeared to lose much of the longevity benefit that was noted with less strenuous jogging (4).
We analyzed the association between mortality and quantity, pace, and frequency of jogging, both individually and combined, in 1,098 healthy joggers and 3,950 healthy nonjoggers; the reference group was the 413 nonjoggers who reported being sedentary during leisure time. The analyses of pace and frequency of jogging suggested a U-shape. In the combined analysis, we found that light joggers had the lowest hazard ratio compared with sedentary nonjoggers. We also found that moderate joggers had a significantly higher hazard ratio compared with light joggers. This finding suggested a U-shape between jogging dose and mortality. The strenuous joggers also had a significantly higher hazard ratio compared with light joggers. In addition, we reported that the hazard ratio for strenuous joggers compared with sedentary nonjoggers was insignificant. We acknowledge that the power to detect a difference was low.
We found that a relative scale of pace (intensity) is more appropriate than an absolute scale (miles/h) when the age span is wide (20 to 95 years) and when the participants have wide differences in levels of physical fitness. Thus, we simply estimated the speed by using the subject’s own perception of pace (slow, average, fast). This technique for assessing relative intensity of exercise was proven effective for assessing the effects of training.
It is correct that we analyzed the impact of intensity and duration of walking and cycling on mortality in previous studies and found that the relative intensity was of more importance than the duration. Nevertheless, this finding is not contradictory to our new findings, because even fast walking and leisurely cycling are not as intense as slow jogging, which qualifies as vigorous exercise (6 metabolic equivalents).
The most important take-away message from all of these studies is that exercise, such as running or jogging, confers powerful benefits for health and longevity (1–3). A less certain corollary emerging from these data suggests that some of the benefits of regular physical activity may be attenuated at very high doses of long-term intense exercise. More than 50% of the U.S. adult population performs insufficient physical activity, whereas the subgroup of Americans who may be overdoing exercise is perhaps 2% to 3% (5). The small size of the cohort of over-exercisers makes the upturn at the end of the reverse J- and U-curves less statistically significant. However, in studies with large numbers, such as the 1.1 million women from the United Kingdom (2), the 35,000 women (3.2%) who exercised strenuously 7 days/week experienced a statistically significant loss of most or all of the protection against CHD, stroke, and venous thromboembolism that was noted among the moderate exercise groups. Furthermore, focusing on higher risk groups, such as those with previous CHD, also improved the statistical power and made the loss of benefit among the high-dose exercise cohort statistically significant.
All 3 of the co-authors of this response strongly advocate for the benefits of exercise, including jogging, to our patients and our own family and friends. The first jogging race, to our knowledge in Europe (the Eremitage Race), took place in Copenhagen in 1969, and was initiated and is still controlled by Peter Schnohr. Still, we also emphasize that if one is exercising to improve long-term cardiovascular health and longevity, it may be best to aim for moderate rather than extreme efforts, or at least take 1 day a week off of strenuous exercise.
Please note: The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation
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