Exercise Guidelines: One Trial Does Not Fit All

Deciphering how much and which exercises to do.

Sheri Colberg-Ochs By Sheri Colberg-Ochs, PhD

You've already heard some about the differences between the types of exercise (aerobic vs. resistance) in the last article posted, but do we really know as much as we think we do about how much and which exercise is most beneficial to your health and diabetes control? Actually, the answer is no. There are numerous reasons why our knowledge is lacking in these areas. Let me start by explaining how we "know" what we think we do about exercise and the effects of physical training.

Exercise Trials and Results

As a researcher, you come up with a testable hypothesis about the effects of training. Then you get people to volunteer to participate, conduct the exercise training, write up the results, and publish them in a reputable research journal. (Well, it's never quite that simple, but you get the idea.)

Let me give you an example of how "mythical" our exercise recommendations have become. Although a panel of experts extensively reviewed all of the published research on exercise training when the federal government came up with its latest physical activity recommendations for Americans in 2008 (i.e., 150 minutes of moderate or 75 minutes of vigorous aerobic exercise per week, found online at www.health.gov/paguidelines/guidelines), no one has ever actually designed a study to test whether the recommendations work and are optimal for everyone. The guidelines also say that aerobic activities should minimally be done for 10 minutes at a time, although you can add up all the time during the day. Do we know beyond a shadow of a doubt if this would be appropriate training for everyone? Absolutely not.

The Problem With Trials

The problems with interpretation and applicability arise both from how you design the study and who participates. For example, with aerobic training, most studies involve doing 8 to 12 weeks of moderate training at least three days per week. Why this amount? A lot of studies are done at universities where academic quarters last 10 weeks and semesters for 15, and it's easier to finish a study within the limits imposed by the academic schedule. Does that mean that's an optimal length to train? We don't actually know—yet anyway. Who participates in the studies is also a confounder because if you study only college-aged students, the results of the study really cannot be applied to other groups, like older individuals or people with certain chronic diseases. You can see how it can easily become overwhelming to make new exercise recommendations that would have been adequately tested in kids, various ethnic groups, pregnant women, aging athletes, people with heart disease, arthritis, or asthma, elderly individuals over 85 years old, teenagers, pre-teens, or postmenopausal women, to name a few diverse groups.

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Last Modified Date: June 27, 2013

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