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Being ActiveA CommentaryFrom the ESPER Department, Old Dominion University, Norfolk, Virginia. Correspondence to Sheri R. Colberg, PhD, ESPER Department, Old Dominion University, Norfolk, VA 23529 (scolberg{at}odu.edu). Physical activity has long been 1 of the 3 cornerstones in diabetes management, but it is by far the most underused. Nowadays, there is no question about whether exercise has beneficial effects on health for most people. In fact, its health benefits are almost unlimited, including improvements in overall glycemia, insulin action, cardiovascular fitness, metabolic function, inflammation control, disease prevention, mental health, and more. The evidence is so strong in favor of regular physical activity that health care providers would be remiss not to recommend it to almost all of the individuals in their care. So why do some health care providers opt not to emphasize its importance? If they do make it an integral part of their recommendations, is it sufficient to just tell patients to "be active"? If patients need more guidance, what duration, intensity, and type of exercise should be recommended? The being active systematic review goes a long way toward answering the above questions. A plethora of clinical exercise trials have now been published, although their outcomes are often apparently in conflict. For example, some find improvements in glycemic control for individuals with type 2 diabetes who participate in regular aerobic activity, while others fail to find any change in this measure of diabetes control. Others show beneficial changes in blood lipids, while some do not. These seemingly contradictory results can often be explained by one of the major obstacles that the review's authors had to overcome: exercise interventions vary widely in their duration (of both individual exercise sessions and length of participation), exercise intensity, and mode of physical activity. Within the realm of exercise duration, it is clear that regular exercise participants (most often followed in prospective studies) fare better. What remains unclear, however, is how many weeks, months, or years of regular physical activity are required to optimize health benefits, control diabetes, prevent complications and diabetes onset, and reverse prediabetic conditions. Clinical trials often follow participants' improvements over a 6- to 16-week period, but it is probable that greater improvements result from a year or longer, and few studies are conducted for that length of time because of logistical, time, and money constraints. As for the actual duration of each exercise session, the recommendations also vary. The US surgeon general recommends that everyone participate in at least 30 minutes of moderate exercise most days of the week, but current knowledge about the dose-response relationship between physical activity and health remains incomplete. Even small amounts of physical activity (as short as 10 minutes per day, on average) have recently been shown to improve cardiorespiratory fitness levels in overweight, postmenopausal women, although fitness is increased more by longer participation.1 In the absence of more definitive answers, such results should still be used to encourage sedentary adults to do some activity even if they find it too difficult to fit in the recommended duration. Exercise intensity presents another conundrum. While intense exercise appears to bestow greater health benefits, does that mean that less intense exercise is not worthwhile? Diabetic individuals in particular may experience comorbidities that limit their ability to engage in more intense activities, such as cardiovascular disease, a higher incidence of silent ischemia, and autonomic neuropathy. Despite inconsistencies in studies to date, it is likely prudent to recommend to our patients to exercise as intensely as possible without making the exercise so hard that they lose the motivation to continue, cause themselves to develop an athletic injury, or put their health acutely at risk. An alternate approach may simply be to recommend pick-up-the-pace training that involves faster intervals that may enhance cardiorespiratory fitness gains and further improve insulin action.2 Finally, as for exercise modes, this systematic review points out that we have yet to reach a definitive conclusion about whether aerobic, resistance, or a combination of both types of training is best. Moderate walking and other forms of aerobic exercise have traditionally been recommended for diabetic individuals, but recent research is challenging that viewpoint.3 With regard to enhanced insulin action, it now appears that resistance training may be as important, if not more so, than aerobic exercise participation. In fact, resistance work may result in greater and more lasting improvements in glucose tolerance without changes in body weight, as evidenced by a recent study.4 Others have found that adding resistance training to ongoing aerobic exercise participation causes further gains in these metabolic improvements.3 Thus, we can conclude that our patients would benefit from either mode of exercise or, more likely, both. This review, while comprehensive, fails to definitively uncover the best clinical practices with regard to physical activity participation. Of course, this failing is not the fault of the authors but rather the result of gaps in our full understanding of the barriers to exercise adherence, the impact of individual variability and existent health complications, and ethnic and cultural differences, to name just a few. While research in this area is ongoing, we still need a better understanding of why, on the whole, so few American adults (with and without diabetes) regularly exercise and how to turn this tide in favor of more wide-spread and sustained exercise participation. If we continue to advise our diabetic patients to lose weight, then we also need to be able to assist them in keeping it off, the most effective means being regular participation in physical activities throughout their lifetime. To further enhance our understanding, we need more rigorous outcomes evaluation of strategies and tools to improve physical activity in populations with diabetes, including ethnic minorities and other groups being ravaged by the current diabetes epidemic. Clinical interventions would also be improved by use of other measures than body mass index or body weight change as outcome measures, particularly because exercisers may be gaining muscle mass while losing body fat, and neither beneficial change would necessarily be evident using just these measures. In conclusion, although much still remains to be elucidated about physical activity, in the absence of more definitive answers, the current knowledge base still strongly supports the assertion that becoming and remaining physically active is critical to living long and well with diabetes.
The Diabetes Educator, Vol. 33, No. 6,
989-990 (2007)
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