The primary objective of the study is to compare the efficacy of an intervention with high-intensity interval, low volume training (HIIT-LV) or continuous aerobic exercise (CAE) on insulin resistance, insulin sensitivity and percentage of pancreatic β-cell function in adults with metabolic syndrome (MS).

The secondary objective is to compare the efficacy of an intervention with HIIT-LV or CAE on glycosylated hemoglobin, mass and muscle fibre type composition of right thigh and plasma levels of musclin and apelin in adults with MS.

The investigators hypothesized that HIIT-LV is more effective in decreasing insulin resistance and glycosylated hemoglobin and plasma concentrations of musclin and increasing plasma concentrations of apelin, and both mass and muscle fibre type I percentage in thigh, than CAE.

This study is a randomized, controlled, masked (single blind, outcomes assessor) clinical trial, with allocation by the minimization method, with two parallel groups and intention of superiority. It was designed to test the hypothesis that a 12-week program of HIIT-LV, yields larger beneficial effects on insulin resistance, skeletal muscle composition and endocrine function than CAE.

Although aerobic exercise increases cardio-respiratory capacity, modifies risk factors and decreases mortality risk, there is currently controversy and gaps in knowledge over the efficacy of more intense and low-volume physical activities on muscle metabolism in patients with metabolic disorders.

The primary outcome will be the insulin resistance, insulin sensitivity and percentage of pancreatic β-cell function. The secondary outcomes will be the glycosylated hemoglobin, mass and muscle fibre type composition of thigh and plasma levels of musclin and apelin. Assessments will be made before and after the 12-week program. Calculations based on previously results (difference mean 10% and SD 15%) suggest that a total number of 60 patients randomized 1:1 (30 in each group) to the two intervention groups is sufficient to detect larger beneficial effects with HIIT-LV with a p-value of 0.05 (two-sided test) and statistical power of 0.80 (primary endpoint is insulin sensitivity).

Inclusion Criteria:

• Metabolic syndrome defined according to the International Diabetes Federation-criteria.
• Insulin resistance defined according to the HOMA greater than 2.25
• Sedentary lifestyle (less than 60 min of physical activity per week)

Exclusion Criteria:

• Vegetarian diet
• Vitamin D3 supplementation
• Oral contraceptives
• Musculoskeletal diseases or injuries
• Physical, sensory or cognitive impairment
• History of cardiovascular disease (coronary, cerebrovascular, peripheral arterial disease, uncontrolled cardiac arrhythmias).
• Pulmonary diseases
• Acute or chronic inflammatory conditions
• Cancer
• Human immunodeficiency virus infection
• Diabetes mellitus
• Hyperthyroidism
• Pregnancy