Does bone structure and metabolism contribute to improved insulin sensitivity following exercise in overweight and obese men?

Euglycaemic, hyperinsulinaemic clamp: acute effects of exercise Participants will attend our laboratory twice for the experimental trials after an overnight fast. The two trials (exercise or rest) will be conducted 2-4 weeks apart. Session 1: In order to determine the basal (rest) insulin sensitivity as well as resting levels of other biochemical markers, insulin clamp will be performed at rest. In this session two muscle biopsies will be taken, one before and one after 2 hours of insulin clamp. Session 2: In order to examine the effects of exercise on markers of bone formation and resorption as well as insulin sensitivity, mitochondria respiration and glucose control participants will perform high intensity interval exercise (as described below). In this session 3 muscle biopsies will be taken: at baseline, at the start of the insulin clamp (1 h post-exercise) and after the insulin clamp. Insulin clamp will commence after 1 h of recovery. Blood samples: Blood samples will be taken through an intravenous catheter. Muscle biopsy: Muscle biopsy (2 in session 1 and 3 in session 2) will be taken from the vastus lateralis. After a local anaesthetic (1% Xylocaine) being injected into the skin and fascia above the vastus lateralis, a small incision will be made and a muscle sample (~150 mg) will be excised. Session 2: acute high intensity interval exercise: The high intensity exercise protocol will consist of 5 x 4 minute intervals at 90-95% peak heart rate (peak HR), separated by 2 minutes of active recovery consisting of gentle cycling at 50% of peak HR. Peak heart rate will be defined as the highest heart rate measured during the incremental test. Other assessments will be performed once at baseline (within 2-4 weeks prior session 1). Anthropometric measurements (10 min): Height will be measured with the participants standing barefoot on a stadiometer (minus/plus 0.5cm). Weight will be measured with participants wearing just light clothes whilst standing on a calibrated scale. Waist circumference will be measured with a steel tape and taken midway between the iliac crest and the lower border of the ribs. Three measurements will be taken and the mean of the two closest measures will be recorded. Dual-energy x-ray absorptiometry, DXA (15 min). Dual-energy X-ray absorptiometry (DXA) (GE Lunar Pxodigy, Software version 9.1, Madison, USA) will be used to assess total body fat and lean body mass (LBM). In addition, the DXA and GE Lunar Pxodigy software will be used to assess fat mass in the abdominal region as well as bone mineral density to exclude osteoporosis. The participants will be asked to lie-down on their back on the DXA table in light closing (no metal) or a gown for approximately 10-15 minutes while the machine scans their body. High-resolution 3D-pQCT (15 min) 3D-pQCT will be assessed in the distal tibia and radius. High-resolution peripheral quantitative computed tomography-(HR-pQCT) (XtremeCT; Scanco Medical AG, Bassersdorf, Switzerland) will be used in this study, which provides the ability to quantitatively assess volumetric bone mineral density (vBMD), as well as geometric and micro-structural features of human cortical and trabecular bone in a compartmental fashion in the distal radius and tibia. The participants will be asked to seat on a chair with their hand or lower leg inserted into the machine. The scan of each site is 3 minutes and in that time the participant will be asked not to move. Both the arm and lower leg will be supported during the scan. The effective dose is approximately 0.004 microSv for each site. The CVs for the HR-pQCT method for bone mineral density parameters are very low (<1%), with moderate CVs for the morphometric measures (4%-6%). Fasting blood samples. A blood sample will be collected from the antecubital vein using a venepuncture technique after an overnight fast of at least 10 hours. Blood will be centrifuged and analysed for total cholesterol, triglyceride, high-density lipoprotein (HDL), low density lipoprotein (LDL), glucose, insulin, c-peptide, high sensitive C-reactive protein (CRP), hepatic enzymes and HbA1c. In addition blood will be analysed for markers of bone formation and bone resorption. Peak aerobic capacity test Aerobic power (VO2peak) will be assessed during a symptom-limited graded exercise test on a cycle-ergometer. The test will start after a 5-minute period at rest. The protocol consists of an initial intensity of 20W, then an increase to 10-20W per minute. The test will be terminated when a participant’s rating of perceived exertion will reach “very hard” [Borg scale = 17], or before that if the patient wishes to stop or clinical signs or symptoms of metabolic or cardiorespiratory abnormalities appeared. Expired respiratory gases will be collected through a breath-by-breath (BxB) pneumotach system connected to gas analysers. The BxB data will be integrated for each 15 sec interval, and the mean values for VO2, VCO2 and ventilation (VE) will be used for that interval. The gas analyser was calibrated immediately before each test using gases that had been calibrated at alpha standard. Heart rate will measure at rest and during the incremental test by 12-lead electrocardiography (Mortara, X-Scribe II, Milwaukee, WI, USA).