Background: Juvenile-onset type 1 (insulin-dependent) diabetes is associated with a 15 year reduction in life expectancy, primarily due to cardiovascular disease (CVD). Poor blood glucose (glycemic) control, reflected in elevated hemoglobin A1c (HbA1c) is a major risk factor for diabetes complications; each 1% absolute reduction in HbA1c leads to a 15-20% reduction in risk of a major cardiovascular event, and a 25-37% reduction in risk of microvascular disease. Exercise is appealing as a potential non-pharmacological intervention to improve glycemic control. However, while aerobic exercise (e.g. walking, running) improves insulin sensitivity, most published studies found that aerobic exercise did not improve glycemic control in type 1 diabetes. This paradoxical finding is likely due to the tendency of type 1 diabetic individuals to decrease their insulin doses and/or increase carbohydrate intake more than necessary in order to avoid exercise-induced hypoglycemia. In comparison to aerobic exercise, the smaller acute rise in glucose uptake associated with resistance exercise may offer the metabolic benefits of exercise while minimizing risk of exercise-induced hypoglycemia. Only two small published studies (n=8 and 10; men only) evaluated resistance exercise (weight lifting or exercises with weight machines) in type 1 diabetes, but their results were promising. In a crossover trial, glycemic control was significantly better during resistance training than during non-exercise control (HbA1c 5.8% versus 6.9%; absolute difference 1.1%). In a before-after study, combined aerobic and resistance exercise reduced absolute HbA1c by 0.96%. People with type 1 diabetes who already do regular aerobic exercise would likely be open to starting an additional form of exercise if it were proven to improve glycemic control. We therefore wish to evaluate the incremental effect of resistance training on HbA1c in already-aerobically-active type 1 diabetic individuals in a randomized, controlled trial.
Primary research question: In type 1 diabetic individuals who already engage in regular aerobic exercise, does adding a 6-month resistance training program result in improved glycemic control as reflected in reduced HbA1c compared to aerobic training alone?
Secondary research questions: In type 1 diabetic individuals who already do regular aerobic exercise, does adding a 6-month resistance training program have favourable effects on body composition, non-traditional and traditional CVD risk factors, and quality of life vs. aerobic exercise alone?
Exploratory research questions: What is the incremental effect of resistance training on insulin requirements and frequency of hypoglycemia? Do changes in glycemic control, body composition, or quality of life during the resistance training intervention predict exercise participation during the subsequent 6 months? How cost-effective is it to add the resistance training program?
Methods: Type 1 diabetic subjects aged \≥16 yr who perform aerobic exercise \≥3 times per week but not resistance exercise, will be recruited at three centres (Ottawa, Toronto and Calgary). They will first enter a 5-week run-in period, including 3X/week supervised low-intensity resistance exercise training in weeks 2-5. During run-in, in addition to verifying adherence to the exercise program, intense efforts will be made to optimize diabetes care including frequent interaction with the study diabetes nurse/educator and dietitian, intensification and adjustment of insulin therapy. Subjects attending \≥80% of the exercise sessions and demonstrating good compliance with diabetes care during run-in will then be randomized to either resistance training or waiting list control for weeks 6-26; in either case they will continue aerobic exercise at their usual volume and intensity with support from an Exercise Specialist, use pedometers and report exercise in activity logs. Resistance exercise training in the intervention group will progress to 3 sets of 8 reps of 8 exercises at 8RM (maximum weight that can be lifted 8 times while maintaining proper form). Background diabetes care will be provided throughout, in a protocolized manner for both exercise and control subjects, with all insulin adjustments done by study research staff.
Significance: Reduced risk of long-term complications of type 1diabetes is tightly linked to better glycemic control, which is often difficult to achieve. This study will provide valuable information regarding the extent to which resistance exercise can improve glycemic control and other important risk factors for complications in people with type 1 diabetes who are already aerobically active.
