Combining aerobic exercise with weight training is the most effective fitness regimen to reduce HbA_1c in type 2 diabetes, a study has found.

The Diabetes Aerobic and Resistance Exercise (DARE) study was a six-month randomised, controlled trial that investigated the effect of aerobic and resistance exercise on HbA_1c, blood pressure, lipid levels and body composition.

It enrolled 251 patients aged 39-70 years who had been diagnosed with type 2 diabetes for at least six months.

Patients had starting HbA_1c levels of 6.6-9.9%, were not prescribed insulin and were not accustomed to regular exercise. Other exclusion criteria included renal failure, uncontrolled hypertension and recent changes in body weight or drug therapy.

Participants were randomised to four groups: an aerobic exercise group (60 patients), a weight training group (64 patients), a combined exercise group (64 patients) and a control group (63 patients).

Patients attended a four-week run-in phase of 10-12 exercise sessions. The exercise groups then received training three times a week with a graded increase in intensity. Running machines and exercise bicycles were used for aerobic exercise. Resistance exercises were performed using weight machines. The combined group received both interventions and therefore spent twice as long exercising as the other groups.

At six months, all interventions saw a significant reduction in HbA_1c compared with the control group, which showed a very slight increase. The mean reduction in HbA_1c was 0.97% in the combined exercise group, compared with 0.51% and 0.38% for the aerobic and resistance exercise groups respectively.

The results showed no difference in lipid levels or blood pressure between the four groups. Patients in the aerobic exercise group had a mean weight loss of 2.2kg (95% CI 3.9-0.6) compared with those in the control group, and a concomitant reduction in waist measurement of 2.1cm (95% CI 4.1-0.2). There were no significant changes in the other intervention groups.

It is disappointing that the study did not find that exercise lowered blood pressure or lipid levels. The lack of weight loss in the combined exercise group may be because of an increase in muscle mass offsetting the loss of fat tissue. It may be that exercise regimens have to be sustained as a long-term lifestyle modification to accrue the full benefit to risk factors.

The study might be criticised for not controlling for time spent exercising in the combination group compared with the single exercise groups; is it the regimen or the time exercising that causes the fall in HbA_1c?

I have always encouraged my patients to exercise aerobically, and now can tailor my advice to motivated patients more accurately.

Sigal RJ, Kenny GP, Boule NG et al. Effects of Aerobic Training, Resistance Training, or Both on Glycemic Control in Type 2 Diabetes. Ann Intern Med 2007;147:357-69