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Physical Activity Guidelines

December 6 — 7, 2007 Advisory Committee Meeting Minutes

Adverse Events Subcommittee Report

Kenneth Powell, M.D., M.P.H., presented the subcommittee report on adverse events. Adverse events are important because of two particular reasons. One is that they provide a direct counter balance to any possible benefits from physical activity. Additionally, adverse events can significantly influence the level people participate in physical activity. The members of the subcommittee included Julie Gilchrist from CDC, Bruce Jones from the U.S. Army, Carol Macera from San Diego State, Paul Thompson from Hartford Hospital and Susan Carlson was the groups CDC liaison. The subcommittee formulated the following questions:

  1. What are the types of activities that have the lowest risk of musculoskeletal injuries?

  2. How does the amount or dose of physical activity affect these risks?

  3. Are individuals at higher risk of sudden adverse cardiac events when they are being physically active?

  4. What general factors influence the risk of musculoskeletal injury and other adverse events related to physical activity?

Activities can be categorized by non-contact, activities with a fair amount of contact and high-contact activities. As might be expected, the evidence suggests that non-contact activities have the lowest risk of musculoskeletal injuries. There are however, relatively few surveys from which to draw this conclusion.

Dr. Powell introduced Bruce Jones who addressed issues surrounding dose of physical activity. The amount of exercise is determined by several parameters such as duration, frequency, intensity and the total amount of activity is the product of those parameters. It is important to recognize all the potential parameters in determining total activity; otherwise, one may only see a partial picture. Most of the studies pertaining to risk of injury deal with walking as the activity, although there are a few studies that also include other activities such as cycling. Also, many of the studies are older than the date parameters of the CDC database. In reviewing the data the risks and benefits both increase with increasing amounts of activity; however, the benefits plateau at some level. Determining at what level the benefits plateau may be difficult to determine due to individuals varying fitness levels. The more fit one gets from training, the more tolerance one has for the activity without getting injured. In order to minimize the risk while maximizing the benefits one should avoid large increases in the amount of activity. The least active need to be the most careful in initiating a program and sustaining a program.

Dr. Powell next discussed sudden adverse cardiac events. Seven reports in the literature were found that deal directly with this issue. The data from these reports suggest that participation in regular vigorous physical activity results in a little boost in momentary risk; however, by and large, it is a considerably lower risk than others that do very little physical activity. The slight boost in risk occurs at the precise moments the heart is doing heightened work due to vigorous activity.

Other issues surrounding adverse events include the few data sets available that study the effects of moderate intensity activities. The Committee should closely examine the importance of relative intensity. People who are less frequently active and less frequently fit when doing the same thing, their relative intensity is higher compared to individuals that regularly participate in physical activity. Another issue that should be addressed is whether it helps to consult a physician prior to launching into a fitness plan and does it matter what category the individual is in such as, older adult, or what kind of activity the individual plans to do such as moderate activity versus vigorous activity. Body mass index is another important factor but there is too little data to come to strong conclusions on its relationship to adverse events.

 

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