October 23rd, 2014

The Survival Benefits of Physical Activity: Moderate vs. Vigorous Intensity

CardioExchange’s Harlan M. Krumholz interviews Eric J. Shiroma about his research group’s study of the relative survival benefits of moderate- versus vigorous-intensity physical activity. The study is published in the Journal of the American Heart Association.

Krumholz: Please summarize your findings for our readers.

Shiroma: We found that physical activity is inversely associated with both all-cause mortality and cardiovascular disease mortality in both men and women. This supports the current U.S. federal guidelines recommending at least 150 minutes of moderate-, 75 minutes of vigorous-intensity physical activity, or an equivalent combination. In examining the relative benefits of moderate- compared with vigorous-intensity physical activity, we found that men (but not women) experienced a slight additional all-cause mortality benefit when a greater proportion of their activity was vigorous in intensity. However, for cardiovascular disease mortality, moderate-intensity and vigorous-intensity activity conferred similar benefits in both men and women.

Krumholz: Some studies have suggested that more exercise above a certain level is not better, but in your study, more exercise conferred lower risk. How do you reconcile your findings with those that suggest a plateau?

Shiroma: With respect to the dose-response curve of physical-activity volume (at any intensity above moderate) and mortality, there is a leveling off at the highest volumes. Notably, this leveling off does not mean a lack of reduced risk compared with being sedentary; it just means little additional benefit compared with other high levels. In our study, we observed a similar trend among men but did not see a leveling off among women, possibly because not as many women as men in our study engaged in the highest level of physical-activity volume (>10 hours per week). Therefore, low statistical power (and even some selection bias) may have been factors.

Krumholz: We are limited by observational studies in this field, with their limitations. Are you concerned by confounding in these types of studies? 

Shiroma: Residual confounding is always a concern in observational studies, but we were able to control for many of the usual confounders, such as age, diet, smoking status, and alcohol consumption. In addition, when comparing the unadjusted or age-only estimates with the fully adjusted models, we did not observe large differences in the estimates, suggesting that confounding did not account for the observed effect. It is possible, however, that questionnaire use resulted in misclassification of what is moderate- versus vigorous-intensity physical activity. A more objective assessment of intensity may provide further insight into this relationship.

Krumholz: Should we be making recommendations about exercise as strongly and precisely as we recommend drugs that have been tested in randomized controlled trials?

Shiroma: A plethora of data supports the value of physical activity in maintaining good health. Questions remain about the optimum intensity and patterning of physical activity, but consistent evidence shows the overall benefits of increasing the volume of physical activity. However, any medical recommendation should be tailored to the individual patient’s fitness levels and injury risk. Randomized controlled trials may help to define some of the nuances of physical activity as a “prescription,” but that should not detract from the overall message about its value.

Krumholz: What are your recommendations about exercise for longevity?

Shiroma: The guidelines recommend regular physical activity (150 minutes moderate, 75 vigorous, or a combination) to reduce the risk for premature mortality. Our study supports those recommendations, and we conclude specifically that moderate-intensity physical activity, which may be more appropriate and easier to promote in a more sedentary population, confers benefits similar to those of a more vigorous-intensity program.

Given the findings from Dr. Shiroma’s study, share your thoughts about the relative benefits of moderate- versus vigorous-intensity exercise.

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