People with type 2 diabetes should undergo strength training two or three times a week, get at least 150 minutes of aerobic exercise per week, and go no more than 2 consecutive days without a workout, according to new guidelines on exercise in diabetes – the first in 10 years – from the American College of Sports Medicine and the American Diabetes Association.
“It is now well established that participation in regular [physical activity] improves blood glucose control and can prevent or delay [type 2 diabetes], along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life,” the groups wrote in the introduction to the new guidelines (Med. Sci. Sports Exerc. 2010;42:2282-303).
The guidelines were produced using results from nearly 300 studies, the vast majority of them published within the past decade. While the ACSM and ADA's 2000 guidelines had also emphasized aerobic exercise, the strength recommendations are new, said Sheri Colberg-Ochs, Ph.D., of Old Dominion University in Norfolk, Va., a member of the ACSM and a coauthor of the guidelines.
“You can see some really dramatic improvements in glucose control with resistance training,” Dr. Colberg-Ochs said in an interview. And the combined exercise may be better still: A recent study of sedentary men and women with type 2 diabetes (n = 262), which was published too late to be considered in crafting the guidelines, showed that a combination of aerobic and resistance training improved hemoglobin A1c levels better than did either aerobic or resistance training alone, Dr. Colbert-Ochs noted (JAMA 2010;304:2298-9.)
Many of the exercise benefits described in the guidelines are independent of weight loss, and indeed the guidelines' authors noted that the exercise requirements alone were probably insufficient to produce significant weight change. But they also emphasized that even highly overweight and sedentary people need to be encouraged to exercise, as the benefits of exercise for type 2 diabetes far outweigh known risks.
Though people with high cardiovascular risk factors would benefit from a physician evaluation before starting to exercise, the authors said, most people do not need to consult a doctor before beginning a modest program of brisk walking, for example, Dr. Colberg-Ochs said. “To tell people to go to their doctor gives them the wrong impression – that exercise is dangerous – and sets up an unnecessary barrier. So we relaxed the recommendation” in the new guidelines, she said.
That said, Dr. Colbert-Ochs added, people must be eased into an exercise program. “You would not just get someone off the couch and say go get 150 minutes – that would be ridiculous. One of the things I personally prescribe is small lifestyle changes. Just getting people moving around and taking more steps starts to build some basic endurance.”
Dr. Colberg-Ochs said that the guideline had recommended 150 minutes of aerobic activity plus two or three weight workouts per week because “most of the existing studies were limited in that they only looked at certain amounts of time. The only thing we could say for sure is there wasn't enough evidence telling people they could do less.”
For resistance training, the authors wrote, each session “should minimally include 5-10 exercises involving the major muscle groups (in the upper body, lower body, and core) and involve completion of 10-15 repetitions to near fatigue per set early in training progressing over time to heavier weights (or resistance) that can be lifted only 8-10 times.”
Aerobic training means working at between 40% and 60% of maximal aerobic capacity, which in many people is achieved by brisk walking, the authors wrote. The guidelines also promoted increasing unstructured daily movement, including the use of a pedometer, but viewed flexibility training as an add-on and not a substitute for aerobic training and weights. Tai chi and yoga were excluded from the recommendations for thus-far insufficient evidence of benefit in preventing or controlling type 2 diabetes.
The guidelines also reported that for people with type 2 diabetes:
▸ Aerobic training may slightly reduce systolic blood pressure, but reductions in diastolic BP are less common.
▸ Supervised training resulted in greater compliance and blood glucose control than did unsupervised training.
▸ Blood lipid responses to training are mixed, but may result in a small reduction in LDL cholesterol with no change in HDL cholesterol or triglycerides. Combined weight loss and exercise may be more effective than exercise alone.
▸ Increased exercise can reduce symptoms of depression and improve health-related quality of life.
▸ Exercise is possible when blood glucose levels exceed 300 mg/dL without ketosis, provided the patient is feeling well and is adequately hydrated.