Active Voice: How much exercise is needed to improve insulin resistance?
By Francesca Amati, M.D., Ph.D. Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Dr. Amati is a research group leader in the Department of Physiology at the University of Lausanne, Switzerland. Specialized in internal medicine with a research background in exercise physiology, her main research focuses on insulin resistance and the mechanisms by which physical activity prevents or treats chronic diseases such as diabetes. This commentary presents Dr. Amati’s views associated with the research article she and her colleagues published in the May 2012 issue of ACSM’s Medicine and Science in Sports and Exercise® (MSSE).
Regular exercise is one of the first lines of defense against type 2 diabetes (T2D). Insulin resistance is a key component of T2D and is often present for many decades before the onset of T2DM. While some cross-sectional and prospective intervention studies have demonstrated the beneficial effect of endurance exercise on the improvements of insulin resistance in healthy and pre-diabetic states (such as impaired glucose tolerance), other studies report contradictory results with either no effect of exercise on insulin sensitivity or the observation of an effect only if performed at relatively high intensity.
Beyond the current recommendations to engage in at least 150 minutes of moderate-intensity endurance exercise each week (see ACSM Position Stand, for example), unanswered questions with important clinical and practical questions remain. Some examples are: “Will a sedentary person obtain improvements in insulin sensitivity if exercising less then 150 min/week?”, “Will the gain be proportionally greater if exercising more?”, and “Will someone with a high degree of insulin resistance respond better then someone with a relatively lower insulin resistance?” Our recent study in MSSE was conducted to examine the dose-response effect of exercise on improvements in insulin sensitivity during physical training in previously sedentary adults.
Fifty-five men and women (age range 25-75) enrolled in a 16 weeks supervised moderate-intensity aerobic exercise program. Exercise modes included mostly stationary bicycling and treadmill walking, with some running and rowing. The primary finding of this study is a graded positive dose-response relationship between the exercise performed and the improvements in insulin sensitivity. Exercise dose was defined as kilocalories expended per week, thus taking into account exercise intensity, frequency and duration. Interestingly, our data shows that for the same volume of exercise, a person with lower insulin sensitivity at baseline with improves to a greater degree than a person with relatively higher insulin sensitivity at baseline. A further increase in exercise volume promotes additional improvement in insulin sensitivity.
We found no statistical evidence that the relationship between the amount of exercise and the improvements of insulin sensitivity was different for those subjects exercise above or below a weekly volume of 900 kcal/week; that level represented about 150 min/week at a moderate intensity. Notably, even an exercise dose of 400 kcal/week, corresponding to only 40-50% of that recommended in current guidelines, was associated with a significant improvement in insulin sensitivity. We believe that our observation of a graded exercise dose-response change in insulin sensitivity is relevant for clinical settings and particularly diabetes prevention programs. Taken together, these data support the concept that more insulin resistant individuals at greater risk for developing T2D can attain greater benefit by performing more exercise – however, there is no obvious exercise volume threshold for these benefits. It appears that, in terms of improving insulin sensitivity, more is likely better than a little, and a little is better than nothing.