The Best Exercise for Diabetics

Summarized by Robert W. Griffith, MD
October 11, 2007

Summary

Both aerobic and resistance exercise have been shown to be beneficial in type 2 diabetes, but their combined use has not been studied before. Now a study has demonstrated the benefits of such a combination on HbA1c levels.

Introduction

Apart from its effects on overweight and cardiovascular issues, physical activity is beneficial in type 2 diabetes, resulting in reduction in HbA1c values by about 0.6%.¹ Both aerobic training and resistance training are of value in diabetes. To date, no study has been undertaken that evaluates the possible benefits of combining both types of exercise, compared with either type alone. This has now been done by Canadian researchers, and the result published in the Annals of Internal Medicine.

What was done

Eight community-based exercise facilities were used. A total of 251 subjects were recruited by various methods. They had to have been diagnosed with type 2 diabetes at least 6 months previously, have an HbA1c between 6.6% and 9.9%, could not be taking insulin, and be relatively inactive during the previous 6 months (i.e. not doing more than 20 minutes' exercise twice a week, or any resistance training). Blood pressure had to be within limits - less than 160 mm hg systolic and 95 mm Hg diastolic.

The participants underwent a 4-week run-in phase to assess their likely adherence to an exercise regime. They performed 15 to 20 minutes aerobic exercise and one or two sets of 8 resistance exercises, under supervision. Only those who attended 10 or more of the scheduled 12 sessions were eligible for the study.

The subjects were then randomly assigned to one of 4 groups: aerobic training, resistance training, combined aerobic-and-resistance groups, or a control group who didn't exercise. The first 3 groups attended an exercise facility 3 days a week, with gradually progressive duration and intensity of work-outs. Aerobic exercise was on treadmills or exercise bicycles - 15 to 20 minutes per session at 60% of maximum heart rate, increasing up to 45 minutes per session at 75% of maximum heart rate. Resistance training consisted of 7 different exercises on weight machines at each session, progressing to 2-3 sets of each exercise at the maximum weight that could be lifted 7-9 times. The combined exercise group did the full aerobic and resistance training program at each session.

The study lasted 22 weeks. Individual exercise training was provided, and a dietician interviewed the participants at intervals. Medications were kept as constant as possible, consistent with good medical care.

The outcomes measured were the HbA1c levels, lipid levels, and blood pressure, measured at 3 and 6 months after enrolment.

What was found

The four groups were similar in age, sex, ethnicity, duration of diabetes, and medication use. The average age was 54, with 62% men, and BMIs averaging 35. Attendance at the exercise sessions averaged 80% for aerobic training, 85% for resistance training, and 86% for the combined exercise.

Reductions in HbA1c levels can be seen in the following table:

	baseline	3 months	6 months
Aerobic exercise	7.41%	7.00%	6.98%
Resistance exercise	7.48%	7.35%	7.18%
Combined exercise	7.46%	6.99%	6.56%
Controls - no exercise	7.44%	7.33%	7.51%

It can be seen that aerobic exercise, resistance exercise, and combined exercise produced significant reductions in HbA1c over the 6-month period, while there was no significant change in the controls. And combined exercise (aerobic plus resistance training) was significantly more successful than either exercise types alone, with an average of 0.9% lowering in HbA1c.

Changes in blood pressure and lipids did not differ among the four groups. As many as 71 of the 188 participants who had exercise regimes reported adverse effects of exercise. These were chiefly musculoskeletal complaints that were adequately treated by modification of the training program. Eleven subjects reported mild hypoglycemia (low blood sugar levels), which were managed by reducing anti-diabetic medication or dietary changes.

Comment

This study provides evidence for what one would have expected from separate evaluations of the benefits of aerobic and resistance training in type 2 diabetics; combining both types of training produces even better results in respect to HbA1c levels. Although the study can be criticized for design (no 'blinding', unequal periods of exercise sessions for the combined vs. the other exercise groups), its findings appear unassailable. As an editorialist in the same issue of the journal puts it: "Failing to prescribe exercise to patients with diabetes is simply unacceptable practice." Now it's up to patients to realize the benefits of a combined exercise program, and to implement one!

Source

• Effects of aerobic training, resistance training, or both on glycemic control in type 2 diabetes. RJ. Sigal, GP. Kenny, NG. Boule,  et al. , Ann Intern Med , 2007, vol. 147, pp. 357--369

Footnotes
1. HbA1c is shorthand for a type of hemoglobin, the oxygen-carrying element in red blood cells. (Hb stands for hemoglobin, and A1c is the designation of the subtype.) It's important because glucose binds to HbA1c and is only released very slowly, so that the HbA1c represents the average blood glucose level over the previous 4 weeks. This makes its measurement far more valuable than just a single blood sugar measurement, which can vary a lot depending on when your last meal was and what it contained.

Related Links
The Variability of Blood Glucose in Diabetics
Obesity Surgery and High Blood Pressure
Surgery for Obesity Helps Treat Diabetes

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