”两优运动“－有氧运动与力量运动相结合或许能够更加有效降低A1Cs

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A Doubly Good Exercise Prescription

Jennifer Reid Holman

All sorts of moderate exercise can deliver health benefits forpatients with type 2 diabetes. To improve glucose tolerance,however, the best approach may be a combination of both aerobicand resistance training.

In a recent randomized controlled study, researchers found thatpatients who did both types of exercise lowered their mean glycatedhemoglobin (A1C) levels by about twice as much as patients whoseexercise regimens included only aerobic activity or only weightliftingover 6 months.¹

"All of the exercise regimens in this study had a positive impacton 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 tobelieve that aerobic and resistance training are complementary."

The study included 251 previously sedentary adult patients (ages 39–70)who had type 2 diabetes for6 months and baseline A1C levels of6.6–9.9%. To be included, patients had to demonstratetheir motivation to exercise, and they could not be taking insulinor have unstable heart disease.

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The participants were divided randomly into four groups. Onegroup performed 45 minutes of aerobic training on treadmillsor bicycle ergometers, another did 45 minutes of resistancetraining using weight machines, a third did both 45 minutesof aerobic and 45 minutes of resistance training, and a controlgroup was asked to maintain their activity levels. Each exercise regimen—whichgradually increased in duration and intensity—was donethree times weekly for 22 weeks. Researchers sought to minimizethe influence of diet and medication by requesting that patientsstick to a single recommended diet and that their physiciansavoid altering their medications.

By the end of the 6-month study, the exercisers' mean A1C levelscompared with controls were as follows:

• 0.5 percentage points lower in patients who did only aerobics;
  
• 0.38 percentage points lower in patients who did only resistancetraining; and
  
• A full percentage point lower in patients doingthe combination routine.
  

Interestingly, changes in blood pressure and lipid profilesdid not differ significantly among the groups after 6 months.

EXPLAINING THE BENEFITS

The researchers' efforts to control intervening effects makethe results especially compelling, says Benjamin Levine, MD,professor of medicine at University of Texas Southwestern MedicalCenter in Dallas and director of the Institute for Exerciseand Environmental Medicine at Presbyterian Hospital of Dallas.

"One of this study's greatest strengths is that the researcherstook care in equalizing group sizes and patient characteristicsand in avoiding the common confounding factors of diet and bodyweight," explains Levine.

But the fact that patients enrolled in the combination routineexercised longer (90 minutes vs. 45 minutes per session) giveshim pause. "Those patients did more work, and more work getsa bigger glucose response," he says. "I'm not fully convincedthat greater duration didn't play a role here." Nonetheless,says Levine, "there's still a good theoretical basis for combiningthese two types of training in patients with type 2 diabetes."

Levine explains that strength training with weights increasesmuscle size, which in turn increases glucose uptake. Comparatively,aerobic training appears to modulate insulin sensitivity, alsoimproving the muscle cells' sensitivity to insulin, he says.²

An added benefit to combining aerobic and weight-training componentsmay be better patient adherence to regular exercise, notes Sigal.In a 3-month follow-up to the current study, patients who didresistance training as part of their exercise programs werealmost twice as likely to have continued exercising regularlyafter the study as those doing only aerobic activities.

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"Anecdotally, the participants told us that the aerobic activitywas more monotonous, so variety may be something that keepspeople going," says Sigal. "In addition, they were apt to seethe benefits of increased strength more quickly than peoplewho did only aerobic exercise, so that may be motivating aswell."

The bottom line, adds Levine, is that exercise of any sort offersa plethora of health benefits for patients with type 2 diabetes,including improved endothelial function and vagal control ofthe heart, increased bone density, lower blood pressure, weightloss, and improved lipid profile.

"There is absolutely no doubt that, for overweight patientswith diabetes, exercise is one of the most important interventionsthat 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, mostof whom were obese and had been previously inactive, these werelargely musculoskeletal aches and pains, in some cases requiringa modification to their exercise plan.

No one needed assistance for hypoglycemic episodes, but somepatients required a reduction in their medication during thestudy. Outright injuries were rare and about equal among thegroups.

"Part of the reason people hurt and stop is they go too hardtoo fast," says Levine. He suggests patients start slowly withsmall segments of exercise and then gradually increase intensityand 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 aweek, even in two 10-minute bursts of activity," Levine suggests.

It's also important to note, says Sigal, that the American Diabetes Associationnow endorses both aerobic and resistance exercise for most patientswith type 2 diabetes—including patients who are olderor who have long-standing diabetes.³

Footnotes

FYI

For the most up-to-date American Diabetes Association guidelineson exercise, see "Section F: Physical Activity" in the Standardsof Medical Care in Diabetes—2007 athttp://care.diabetesjournals.org/cgi/content/full/30/suppl_1/S4#SEC8.

References

1.Sigal RJ, Kenny GP, Boule NG, et al.: Effects of aerobic training, resistance training, or both on glycemic control in type 2 diabetes: A randomized trial.Ann Intern Med147: 357–369, 2007.[Abstract/Free Full Text]

2.Kraus WE, Levine BD: Exercise training for diabetes: The "strength" of the evidence.Ann Intern Med147: 423–424, 2007.[Free Full Text]

3.American Diabetes Association: Position statement: Standards of medical care in diabetes—2007.Diabetes Care30 (Suppl. 1):S1 –S41, 2007.

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