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Research Article

Adverse Metabolic Response to Regular Exercise: Is It a Rare or Common Occurrence?

  • Claude Bouchard mail,

    claude.bouchard@pbrc.edu

    Affiliation: Human Genomics Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America

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  • Steven N. Blair,

    Affiliation: Departments of Exercise Science and Epidemiology/Biostatistics, University of South Carolina, Columbia, South Carolina, United States of America

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  • Timothy S. Church,

    Affiliation: Preventive Medicine Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America

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  • Conrad P. Earnest,

    Affiliation: Preventive Medicine Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America

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  • James M. Hagberg,

    Affiliation: Department of Kinesiology, University of Maryland, College Park, Maryland, United States of America

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  • Keijo Häkkinen,

    Affiliation: Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland

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  • Nathan T. Jenkins,

    Affiliation: Department of Kinesiology, University of Maryland, College Park, Maryland, United States of America

    Current address: Department of Biomedical Sciences, University of Missouri, Columbia, Missouri, United States of America

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  • Laura Karavirta,

    Affiliation: Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland

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  • William E. Kraus,

    Affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina, United States of America

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  • Arthur S. Leon,

    Affiliation: School of Kinesiology, University of Minnesota, Minneapolis, Minnesota, United States of America

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  • D. C. Rao,

    Affiliation: Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri, United States of America

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  • Mark A. Sarzynski,

    Affiliation: Human Genomics Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America

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  • James S. Skinner,

    Affiliation: Professor Emeritus of Kinesiology, Indiana University, Bloomington, Indiana, United States of America

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  • Cris A. Slentz,

    Affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina, United States of America

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  • Tuomo Rankinen

    Affiliation: Human Genomics Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America

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  • Published: May 30, 2012
  • DOI: 10.1371/journal.pone.0037887

Reader Comments (13)

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Regression to the mean

Posted by trobc on 04 Jun 2012 at 20:16 GMT

The technical error (TE) defined as the within-subject standard deviation derived from these measurements was computed. An adverse response for a given risk factor was defined as a change that was at least two TEs away from no change but in an adverse direction.
http://plosone.org/article/info:doi/10.1371/journal.pone.0037887#article1.front1.article-meta1.abstract1.sec2.p1

I commend Bouchard and his colleagues on undertaking and reporting their study of the potential for actual harm in a subset of individuals who are induced to undertake rigorous exercise. Such a finding has implications for the universal recommendation to exercise for those whose current physical condition does not contraindicate it. They report that about 8-13% of the study population experience worsening in four biomarkers of cardiac risk after a course of exercise.
Unfortunately, there is a simple competing explanation for the observed phenomenon: regression to the mean. Assuming no beneficial effect of exercise and that technical error is equal to the standard deviation in the population (as for systolic blood pressure), a simple simulation shows that using the authors’ criterion the fraction of apparent negative changes would be approximately 8%, not far from the 12.2% observed for systolic blood pressure by the authors. However, since there is a well established beneficial effect, it should work against this and so the 8% expected by regression to the mean has to be adjusted for the average beneficial effect.
The upshot is that the authors should provide an additional analysis that takes regression to the mean into account explicitly, as it could considerably lower the estimate of the fraction with truly adverse effects. It would also be interesting to see what the percentage of “harmful changes” take place in the control groups of the randomized studies, for comparison.

No competing interests declared.