Grant: Master's Award: Canada Graduate Scholarships

BACKGROUND: The association between insulin resistance and obesity is well established. The continual increase in both conditions indicates that existing strategies for prevention and treatment are inadequate and new approaches are required to combat this major health concern. Currently, exercise is one of the primary treatments for reducing abdominal obesity. However, the optimal dose of exercise to improve insulin sensitivity and abdominal obesity is unclear. There has been increasing public interest on the effects of high intensity interval training and its impact on health outcomes. Extremely high intensity exercise, that rely primarily on anaerobic metabolic process such as the Tabata protocol (4 minutes exercise total per session) (1), has been shown to elicit training adaptations in young healthy people similar to those of traditional endurance training despite less total training time (2). However, the effects of this type of exercise training on insulin sensitivity in a high-risk abdominally obese population have not been fully elucidated. In addition, the weight and adiposity reduction capabilities of these types of training protocols are unknown. This study will employ criterion methods for measuring insulin sensitivity and routine imaging methods to determine the impacts of high intensity exercise on abdominal adiposity and insulin sensitivity. OBJECTIVE: To determine if high intensity interval training improves insulin sensitivity and abdominal obesity to a different extent than a longer duration, traditional aerobic exercise treatment. HYPOTHESIS: Based on previously published findings (3), it is predicted that high intensity training will elicit equivalent improvements in insulin sensitivity and abdominal obesity compared to a traditional aerobic exercise program, despite the shorter total exercise time. EXPERIMENTAL APPROCHES: Participants will be recruited from Kingston, Ontario and the surrounding area. Inclusion criteria includes: (1) abdominal obesity (males >102 cm; females> 88 cm), (2) sedentary behaviour, (3) ages 30-60 years. Exclusion criteria include: (1) smoking, (2) cardiovascular comorbidities, and (3) the use of lipid lowering medication. Body mass and height will be measured using a calibrated scale and wall-mounted standiometer, respectively. Waist circumference will be measured at the superior border of the iliac crest. A graded maximal exercise test will be used to determine cardiorespiratory fitness (VO2peak) prior to study initiation as well as after. Participants will be randomized into one of 3 groups; control (no exercise), moderate continuous aerobic exercise, or high-intensity intervals (Tabata protocol)(1) for 4 weeks. The criterion method hyperinsulinemic-euglycemic clamp will be used to determine insulin sensitivity before and after the intervention. MRI will be used to asses changes in adiposity before and after the exercise intervention. In addition, fasting blood samples will be used to establish participant inflammation status. SIGNIFICANCE: This study will provide a basis for understanding the effects of exercise intensity on insulin sensitivity in abdominally obese individuals at risk for chronic disease. Ultimately, this will help refine of therapeutic guidelines established for the treatment of obesity and insulin management. References: 1. Tabata et al. (1997). Med Sci Sports Exerc;29(3):390-395. 2. Gibala et al. (2006). J Physiol;252(3):901-911. 3. Tjonna et al (2008). Circulation; 118: 346-354.