Influence of cardiorespiratory fitness and exercise training on obesity and metabolic risk

The objective of this thesis was to investigate the role of cardiorespiratory fitness (CRF) and exercise training on obesity and health risk. The first study examined whether CRF attenuates metabolic risk independent of abdominal fat in a large sample of 297 men. The relative risks of having the metabolic syndrome were 1.8 (95% Cl: 1.0--3.1) and 1.6 (95% Cl: 0.9--2.7) times higher in low and moderate CRF compared with high CRF after adjusting for age, visceral and subcutaneous fat (P for trend = 0.06).; In the second and the third study, we examined the influence of 3 month aerobic exercise without weight loss on caffeine-mediated insulin resistance, total and abdominal adiposity and skeletal muscle lipid in previously sedentary middle-aged lean men (n = 8) and obese men with (n = 8) and without type 2 diabetes (T2D) (n = 8). Subjects underwent two hyperinsulinemic-euglycemic clamp procedures, caffeine (5 mg/kg body weight) and placebo (dextrose), in a double-blind, randomized manner before and after a 3 month aerobic exercise. Total and regional body composition was measured by magnetic resonance imaging and computed tomography. At baseline, caffeine ingestion was associated with a significant reduction (P < 0.05) in insulin sensitivity by a similar magnitude in the lean (33%), obese (33%), and T2D (37%) groups by comparison to placebo. After exercise training caffeine ingestion was still associated with a reduction (P < 0.05) in insulin sensitivity by a similar magnitude in the lean (23%), obese (26%) and T2D (36%) groups by comparison to placebo. As expected, all groups had significant improvements (P < 0.01) in CRF. Despite being weight stable, significant reductions (P < 0.05) in total and visceral fat and waist circumference were observed in all groups. Significant increases (P < 0.05) in total muscle mass, high-density muscle area and muscle mean attenuation were also found in all groups.; The observations from these studies suggest that having high levels of CRF is associated with lower metabolic risk independent of abdominal fat. Further, regular exercise is an effective strategy to improve CRF and reduce total and regional adiposity independent of changes in body weight. However, regular exercise did not attenuate caffeine-mediated insulin resistance independent of obesity and T2D.