Judging from improvement in hemoglobin A1c, the combination of aerobic and strength training is needed to improve diabetic blood sugar levels. Both types of exercise—when considered alone—did not improve diabetes control, according to the latest research in the Journal of the American Medical Association.
One type of resistance training
One of the things that impressed me about Dr. Richard Bernstein’s book, Diabetes Solution, was his strong advocacy of weight training, also known as resistance training and strength training. Weight lifting is a typical example.
Prior studies had shown exercise-induced improvements (reductions) in hemoglobin A1c, a great test for overall diabetes control, in the range of o.66% to 1.0% (absolute change, not relative). That’s comparable to what we see with many drugs. Much easier to pop a pill though, huh?
One earlier study showed hemoglobin A1c lowered by 0.4% with resistance training, 0.5% with aerobic training, and 1.0% with combined resistance/aerobic. But folks doing both aerobic and resistance were exercising 270 minutes a week—39 minutes a day—which was significantly more than the people just doing one type of exercise. [This was the DARE study: Diabetes Aerobic and Resistance Exercise.]
Investigators at the Pennington Biomedical Research Center in Louisiana wondered which type of exercise would be more effective, comparing the same minutes per week of activity.
They randomized 262 sedentary type 2 diabetics to one of four groups: control, aerobic exercise, resistance training 3 days a week, or combined aerobic and resistance training (resistance twice weekly). All three groups exercised for about 140 minutes a week—just 20 minutes a day, on average—for nine months. Exercise intensity was 50 to 80% of maximum oxygen consumption (determined by a baseline treadmill stress test). Nearly all participants were on diabetic drugs; 18% were on insulin. I think the aerobic group exercised on treadmills.
Participant characteristics: Women were 64% of the total. Average age 56. Forty-seven percent were non-white (114 black, 10 Hispanic/other). Average body mass index was 35. Average hemoglobin A1c was 7.7%. Not too many people dropped out of the study before it was over.
No serious adverse event occurred during exercise. The authors didn’t mention the occurence of hypoglycemia.
The combination training group dropped their hemoglobin A1c average by 0.34% (p = 0.03). The pure resistance and aerobic exercisers didn’t show any improvement over the control group.
The combination group lost 1.6 kg body weight on average compared to the control group. Pure resistance and aerobic exercisers’ weights didn’t differ from the control group. [Remember, this was not a weight-loss study.]
The authors write:
The failure of the aerobic group to lose a substantial amount of weight (or fat) has been reported in numerous aerobic exercise trials, which may be due to aerobic training resulting in [higher] energy intake, expenditure compensation, or both.
If you’re trying to lose excess fat weight, resistance training appears to win over aerobic exercise.
Doing either aerobic execise or resistance exercise for an average of 20 minutes a day will not improve hemoglobin A1c levels in most type 2 diabetics. We can assume blood sugars aren’t lower either. It takes a combination of both types of exercise to lower hemoglobin A1c.
A hundred and forty minutes of exercise weekly—just 20 minutes a day—is not too much to ask for, if improved health and weight management are the goals. More would be better.
Over nine months, the control group ended up needing more diabetic drugs. The combination training group decreased its drug use.
Dr. Bernstein may still by right to stress resistance training over aerobic. I bet he’d say these folks weren’t exercising enough. The study at hand suggests that it’s important to do both types of exercise, especially if you’re not going to put much time into it.
The details of the resistance training program are probably important. You can read the study yourself and decide if participants were on a good regimen. I’ve little expertise in that area.
Diabetics taking insulin, sulfonylureas, and meglitinides are at risk for hypoglycemia during exercise. The study authors made little mention of this, so it may be safe to assume it wasn’t a problem. Certified diabetes educators saw participants monthly, which may have nipped the problem in the bud.
Steve Parker, M.D.
Reference: Church, T., Blair, S., Cocreham, S., Johannsen, N., Johnson, W., Kramer, K., Mikus, C., Myers, V., Nauta, M., Rodarte, R., Sparks, L., Thompson, A., & Earnest, C. (2010). Effects of Aerobic and Resistance Training on Hemoglobin A1c Levels in Patients With Type 2 Diabetes: A Randomized Controlled Trial JAMA: The Journal of the American Medical Association, 304 (20), 2253-2262 DOI: 10.1001/jama.2010.1710