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Background: Excess adiposity and low lean mass are independent risk factors and contribute to common complications of obesity, including type 2 diabetes (T2D). Physical activity is the cornerstone for obesity and T2D management and can effectively improve body composition and cardiorespiratory fitness (CRF), however, it is poorly adhered to. Alternate efficacious exercise interventions for improving adiposity, lean mass and cardiometabolic disease risk factors in obesity and T2D should be explored. Studies and Methods: The study in Chapter 2 assessed the effect of low-volume high-intensity interval training (HIIT) in comparison to moderate-intensity continuous training (MICT) and non-exercise control (PLA) on fat, lean mass and CRF via systematic review and meta-analysis. The study in Chapter 3 examined the association between adiposity, lean mass, and diabetes severity in overweight/obese individuals with normal glucose tolerance (NGT), pre-diabetes and T2D. A regression analysis was used to determine whether adiposity was an independent predictor of insulin resistance; and a comparison of cardiometabolic disease risk factors between individuals with NGT, pre-diabetes and T2D was undertaken. The study in Chapter 4 assessed the efficacy of MICT or low-volume HIIT versus PLA for improving adiposity, lean mass and CRF in adults with obesity and T2D. Findings: In Study 1, low-volume HIIT significantly improved CRF but was ineffective for improving fat and lean mass when compared to MICT or PLA. Study 2 showed that adiposity and lean mass were significantly associated with insulin resistance, and visceral adipose tissue (VAT) independently predicted insulin resistance beyond traditional cardiometabolic disease risk factors in adults with overweight/obesity and NGT, pre-diabetes and T2D. Individuals with T2D had significantly higher adiposity, lean body mass, and insulin resistance in comparison to NGT and pre-diabetes groups. The final study demonstrated that 12-weeks of MICT or low-volume HIIT significantly improved CRF versus PLA; however, there was no evidence of a benefit on body composition or insulin sensitivity. Conclusions: VAT is a significant predictor of insulin resistance, independently of traditional cardiometabolic risk factors. Individuals with high VAT had greater insulin resistance and were more likely to have T2D. Low-volume aerobic exercise is ineffective for improving abdominal adiposity, lean mass and insulin sensitivity, but is a time-efficient form of exercise for increasing CRF in healthy adults and adults with obesity and T2D. |
