Background: Type 1 diabetes mellitus (T1DM), which represents 5-10% of total cases of diabetes mellitus, is characterized by the destruction of β cells and consequent loss of insulin secretion due a autoimmune process. In diabetic patients, micro (nephropathy, neuropathy and retinopathy) and macrovascular (coronary arterial disease, peripheral artery disease, stroke) complications are major causes of morbidity and mortality. It is recommended that diabetics perform at least 150 minutes (min) per week of moderate aerobic exercise divided into at least three days per week, in addition to performing strength training (ST) on two or more days of the week. Considering that most people with T1DM do not reach recommended levels of physical activity due the fear of hypoglycemia and "lack of time", shorter sessions of exercise that provide several benefits should be encouraged. Conversely, reviews studies have demonstrated that sessions composed by ST exercises or high-intensity interval exercise (HIIE) reduce the risk of hypoglycemia during or after the physical effort, when compared with continuous aerobic exercise in T1DM patients, probably via increased hepatic glucose production and transitory inhibition of peripheral glucose uptake. The high-intensity interval training (HIIT) is known by improving glycemic control and muscular adaptations on lipid metabolism in type 2 diabetes mellitus patients, although no studies have used this model of training in T1DM individuals.

Methods: Twenty-seven sedentary T1DM patients (18-40 yo) will be recruited to this randomized clinical trial. Volunteers will sign an informed written consent before enrollment in the study, which was approved by the Ethics Committee of Federal University of Rio Grande do Sul. Initially, all individuals will participate of a control period lasting four weeks, in which they will be asked to maintain their habitual level of physical activity and the usual eating pattern. After, participants will be randomized in three groups: HIIT, ST or ST+HIIT, each lasting ten weeks, with training sessions performed three times/week in cycle ergometers and/or weight machines. HIIT protocol will be consisted of 10 x 1 min cycling bouts performed \~90% maximal heart rate interspersed with 1 min active recovery. ST will consist of three sets performed at the subjects' 10 repetitions maximum load in seven exercises. Participants in the ST+HIIT will perform both training protocols in the same session.

Before control period and before and after interventions, submaximal strength tests, cardiorespiratory fitness test, 3-day diet record and blood draws will be assessed/performed. Body composition will be evaluated before and after the training period. At the 4th week of interventions, the submaximal strength tests and cardiorespiratory fitness test will be assessed for adjusting loads.

According the normality of data, paired Student's t test or Wilcoxon signed rank test will be utilized to determine differences before and after control period. The homogeneity of variances will be confirmed by Mauchly's test, and a Greenhouse-Geisser correction will be applied to the degrees of freedom if the sphericity assumption is violated. Blood outcomes, maximal oxygen uptake and strength values will be analyzed using a two-way ANOVA (3 conditions vs 2 times) with repeated-measures and subsequent Bonferroni post hoc analysis when required. Statistical Package for Social Sciences (SPSS 19.0 Inc, Chicago, USA) will be utilized and statistical significance set at P \< 0.05.