Background: Type 1 diabetes is characterized by complete or near-complete absence of insulin secretion, generally due to autoimmune disease. Cardiovascular disease (CVD) risk in type 1 diabetes is just as great as in type 2 diabetic individuals of the same age, even though type 1 diabetic individuals usually have fewer additional CVD risk factors. This is likely due to earlier age of onset of diabetes and therefore much longer exposure to hyperglycemia. The incidence of type 1 diabetes is increasing throughout the world. The reasons for this are thought to be environmental although the exact nature of the environmental precipitants is not well understood. In contrast to type 2 diabetes, in which it is clear that aerobic exercise improves glycemic control, studies in type 1 diabetes have generally not found a significant beneficial effect for aerobic exercise on glycemic control, even though there is often reduction in insulin requirements and improved insulin sensitivity. This paradoxical finding may be because individuals with type 1 diabetes are at much higher risk of hypoglycaemia than type 2 and tend to increase their carbohydrate intake in an effort to avoid exercise-induced drops in glucose.

The acute effects of resistance exercise on glycemia in type 1 diabetes have not been established; it is possible that resistance exercise results in a smoother or more predictable decline in blood glucose than aerobic training does, which might reduce fear of hypoglycemia and consequent overcompensation. Resistance exercise training increases insulin receptor protein expression, which is not true of aerobic exercise training .

Study Design: This will be a randomized, controlled trial with a 2 by 2 factorial design (resistance training versus no resistance training; aerobic training versus no aerobic training) in previously inactive subjects with type 1 diabetes. After screening, qualifying subjects will enter a 5-week stabilization/run in period prior to randomization. During this period their diet and insulin therapy will be assessed and optimized, and in weeks 2-5 they will also undergo three supervised sessions of low-intensity exercise per week. Those demonstrating adequate compliance during the run-in period will then be randomized in equal numbers to Aerobic Training (A) progressing to 45 min 3X/wk at 75% of maximum heart rate, Resistance Training (R) 3X/week progressing to 3 sets, 8 repetitions of 8 exercises at the maximum load that can be lifted 8 times (8RM), both Aerobic Training and Resistance Training (AR) or waiting-list control (C). The exercise intervention will take place at YMCAs in metropolitan Ottawa. Subjects cannot be blinded as to group assignment after randomization, but the main study outcomes will be measured by blinded individuals (lab technologists) using objective methods. Subjects randomized to waiting list control will begin a program of their choice (A, R or AR) after all 6-month outcome measures are collected.

Significance: This study addresses questions of clinical and scientific importance. It will help clarify the benefits and risks of aerobic and resistance exercise training in people with type 1 diabetes. Depending on the strength of any differences found, the study will either stand alone or provide pilot data that will set the stage for a larger definitive study. Even if results are substantially different from our expectations, this study will provide valuable new information on the effects of different exercise modalities on metabolic control, body composition, cardiovascular risk factors, and quality of life in this high-risk population.