European Heart Journal Advance Access published online on June 5, 2008
European Heart Journal, doi:10.1093/eurheartj/ehn235
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Intensity of physical exertion and triggering of myocardial infarction: a case-crossover study
1 Institute of Epidemiology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
2 Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA
3 Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA
4 Central Hospital of Augsburg, MONICA/KORA Myocardial Infarction Registry, Augsburg, Germany
5 Institute of Health Economics and Health Care Management, Helmholtz Zentrum München,German Research Center for Environmental Health, Neuherberg, Germany
6 Department of Epidemiology, Ludwig-Maximilians-Universität, Munich, Germany
Received 11 December 2007; revised 11 April 2008; accepted 16 May 2008.
* Corresponding author. Tel: +1 617 384 8751, Fax: +1 617 384 8745, Email: klot{at}helmholtz-muenchen.de
Aims: Acute myocardial infarction (AMI) can be precipitated or triggered by discrete transient exposures including physical exertion. We evaluated whether the risk of having an AMI triggered by physical exertion exhibits an exposure–response relationship, and whether it varies by ambient temperature or by taking place indoors or outdoors.
Methods and results: We conducted a case-crossover study within the Myocardial Infarction Registry in Augsburg, Germany in 1999–2003. One thousand three hundred and one patients reported levels of activity and time spent outdoors on the day of AMI and three preceding days in an interview. The case-crossover analyses showed an association of physical exertion with AMI symptom onset within 2 h, which was strong for strenuous exertion (METs 
6) [relative risk (RR) 5.7, 95% confidence interval (CI) 3.6–9.0), and still significant for moderate exertion (METs = 5) (RR 1.6, 95% CI 1.2–2.1) compared to very light or no exertion. Strenuous exertion outside was associated with a four-fold larger RR of AMI symptom onset than exertion performed indoors, which was not explained by temperature.
Conclusion: This study confirms previous results and shows a graded exposure–response relationship between physical exertion intensity and triggering of AMI onset. These findings may have implications for behavioural guidance of people at risk of AMI.
Key Words: Myocardial infarction • Trigger • Epidemiology • Case-crossover • Strenuous exertion • Onset