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All sorts of moderate exercise can deliver health benefits for patients with type 2 diabetes. To improve glucose tolerance, however, the best approach may be a combination of both aerobic and resistance training.
In a recent randomized controlled study, researchers found that patients who did both types of exercise lowered their mean glycated hemoglobin (A1C) levels by about twice as much as patients whose exercise regimens included only aerobic activity or only weightlifting over 6 months.1
"All of the exercise regimens in this study had a positive impact on blood glucose tolerance," says lead investigator Ronald Sigal, MD, associate professor of medicine, kinesiology, cardiac science, and community health sciences at University of Calgary in Alberta, Canada. "But based on the findings, there is good reason to believe that aerobic and resistance training are complementary."
The study included 251 previously sedentary adult patients (ages
39–70) who had type 2 diabetes for 
6 months and baseline A1C levels
of 6.6–9.9%. To be included, patients had to demonstrate their
motivation to exercise, and they could not be taking insulin or have unstable
heart disease.
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The participants were divided randomly into four groups. One group performed 45 minutes of aerobic training on treadmills or bicycle ergometers, another did 45 minutes of resistance training using weight machines, a third did both 45 minutes of aerobic and 45 minutes of resistance training, and a control group was asked to maintain their activity levels. Each exercise regimen—which gradually increased in duration and intensity—was done three times weekly for 22 weeks. Researchers sought to minimize the influence of diet and medication by requesting that patients stick to a single recommended diet and that their physicians avoid altering their medications.
By the end of the 6-month study, the exercisers' mean A1C levels compared with controls were as follows:
Interestingly, changes in blood pressure and lipid profiles did not differ significantly among the groups after 6 months.
EXPLAINING THE BENEFITS
The researchers' efforts to control intervening effects make the results especially compelling, says Benjamin Levine, MD, professor of medicine at University of Texas Southwestern Medical Center in Dallas and director of the Institute for Exercise and Environmental Medicine at Presbyterian Hospital of Dallas.
"One of this study's greatest strengths is that the researchers took care in equalizing group sizes and patient characteristics and in avoiding the common confounding factors of diet and body weight," explains Levine.
But the fact that patients enrolled in the combination routine exercised longer (90 minutes vs. 45 minutes per session) gives him pause. "Those patients did more work, and more work gets a bigger glucose response," he says. "I'm not fully convinced that greater duration didn't play a role here." Nonetheless, says Levine, "there's still a good theoretical basis for combining these two types of training in patients with type 2 diabetes."
Levine explains that strength training with weights increases muscle size, which in turn increases glucose uptake. Comparatively, aerobic training appears to modulate insulin sensitivity, also improving the muscle cells' sensitivity to insulin, he says.2
An added benefit to combining aerobic and weight-training components may be better patient adherence to regular exercise, notes Sigal. In a 3-month follow-up to the current study, patients who did resistance training as part of their exercise programs were almost twice as likely to have continued exercising regularly after the study as those doing only aerobic activities.
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"Anecdotally, the participants told us that the aerobic activity was more monotonous, so variety may be something that keeps people going," says Sigal. "In addition, they were apt to see the benefits of increased strength more quickly than people who did only aerobic exercise, so that may be motivating as well."
The bottom line, adds Levine, is that exercise of any sort offers a plethora of health benefits for patients with type 2 diabetes, including improved endothelial function and vagal control of the heart, increased bone density, lower blood pressure, weight loss, and improved lipid profile.
"There is absolutely no doubt that, for overweight patients with diabetes, exercise is one of the most important interventions that will influence the course of their disease," he says.
KEEPING IT SAFE
Several patients reported "adverse" events during this study (38% of exercisers vs. 13% of controls). Among the exercisers, most of whom were obese and had been previously inactive, these were largely musculoskeletal aches and pains, in some cases requiring a modification to their exercise plan.
No one needed assistance for hypoglycemic episodes, but some patients required a reduction in their medication during the study. Outright injuries were rare and about equal among the groups.
"Part of the reason people hurt and stop is they go too hard too fast," says Levine. He suggests patients start slowly with small segments of exercise and then gradually increase intensity and duration. Professional guidance is also helpful, he says, and a hospital-based fitness center can be a good place to start.
"Another easy way to start is by just walking 2 or 3 days a week, even in two 10-minute bursts of activity," Levine suggests.
It's also important to note, says Sigal, that the American Diabetes
Association now endorses both aerobic and resistance exercise for most
patients with type 2 diabetes—including patients who are older or who
have long-standing
diabetes.3
Footnotes
For the most up-to-date American Diabetes Association guidelines on exercise, see "Section F: Physical Activity" in the Standards of Medical Care in Diabetes—2007 at http://care.diabetesjournals.org/cgi/content/full/30/suppl_1/S4#SEC8.
References
2. Kraus WE, Levine BD: Exercise training for diabetes: The
"strength" of the evidence. Ann Intern Med 147: 423–424, 2007.
3. American Diabetes Association: Position statement: Standards of medical care in diabetes—2007. Diabetes Care 30 (Suppl. 1):S1 –S41, 2007.
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