Aerobic and Resistance Training Improve Glycemic Control in Type 2 Diabetes

September 18, 2007 — Aerobic and resistance training each improve glycemic control for patients with type 2 diabetes mellitus, but the improvement is greatest when both forms of exercise are combined, according to the results of a randomized controlled trial published in the September 18 issue of the Annals of Internal Medicine. An accompanying editorial suggests that exercise should be approached as a prescription.
"We know that aerobic exercise improves glycemic control, [but] we didn't really know too much about what kind of exercise is the most beneficial and how much of it," lead author Ronald J. Sigal, MD, MPH, from the University of Calgary in Canada, said in a news release. "In particular there wasn't much known about resistance exercises when we started planning this study. At the time, some thought that resistance exercise is not useful or even dangerous for some people with diabetes."
In this 26-week study at 8 community-based centers, 251 adults with type 2 diabetes mellitus were randomized to performing 45 minutes of aerobic training 3 times per week, 45 minutes of resistance training 3 times per week, 45 minutes each of both 3 times per week, or no exercise. Age range was 39 to 70 years. Participants were not exercising regularly at baseline, had received a negative stress test result or cardiology clearance, and demonstrated adherence to exercise during a 4-week run-in period.
The primary endpoint was the change from baseline in hemoglobin A1c (HbA1c) level at 6 months, and secondary endpoints were changes in body composition, plasma lipid values, and blood pressure.
Compared with the control group, decrease in HbA1c level was –0.51 percentage point in the aerobic training group (95% confidence interval [CI], –0.87 to –0.14) and –0.38 percentage point in the resistance training group (95% CI, –0.72 to –0.22). In the combined exercise group, HbA1c level decreased by –0.46 percentage point vs aerobic training alone and by –0.59 percentage point vs resistance training alone.
This decrease in the combined exercise group is striking, considering that an absolute decrease of 1.0% in HbA1c level has been associated with about a 15% to 20% decrease in risk for myocardial infarction or stroke and about a 25% to 40% decrease in risk for diabetes-related eye disease or renal disease.
Changes in blood pressure and lipids were not significantly different between groups, but adverse events were more common in the exercise groups.
"For people who had fairly good blood sugar control at the beginning of our study, those who did both aerobic and resistance exercise had further improvements in glucose control," Dr. Sigal said.
"The bottom line is that doing both aerobic and resistance exercise is the way to maximize the effects of exercise on blood glucose control in type 2 diabetes."
Study limitations include lack of generalizability to patients who are less adherent to exercise programs, lack of blinding, and total duration of exercise being greater in the combined group than in the aerobic training and resistance training groups.
The Canadian Institutes of Health and the Canadian Diabetes Association supported this study. The authors have disclosed no relevant financial relationships.
In an accompanying editorial, William E. Kraus, MD, and Benjamin D. Levine, MD, from the University of Texas Southwestern Medical Center at Dallas, urge clinicians to respond to these findings by incorporating exercise assessment and counseling into every clinic visit.
"Imagine an inexpensive pill that could decrease the hemoglobin A1c value by 1 percentage point, reduce cardiovascular death by 25%, and substantially improve functional capacity (strength, endurance, and bone density)," Drs. Kraus and Levine write. "Diabetes experts would be quick to incorporate this pill into practice guidelines and performance measures for diabetes."
Ann Intern Med. 2007;147:357-369, 423-425.