The overall objectives are to: 1. Assess mechanisms underlying HIIT-induced improvements in insulin resistance at the whole-body, tissue, and cellular levels. 2. Systematically compare different HIIT regimens to help identify effective "doses" of HIIT that may be optimal for improving metabolic health in obese adults. 3. Assess the ability/willingness of obese subjects to adhere to a long-term HIIT program. Findings from these studies will greatly expand knowledge about the effects of HIIT on metabolic health, and will provide valuable information for development of programs aimed at maximizing key metabolic benefits of exercise.
If subjects are eligible for the study, they will be randomized into one of two different exercise training groups. Before training (and twice after 3 months of training) subjects will participate in a "clinical study" in which they will be required to stay overnight in the hospital. During the clinical study, the research team will perform a series of metabolic tests. Before and after the 3 months of training, the research team will assess subjects "free-living" 24h blood sugar control using a Continuous Glucose Monitor (CGM). The research team will measure several other relevant clinical markers (e.g., whole body and regional body fat assessments \[Dual Energy X-ray Absorptiometry (DEXA) and Magnetic Resonance Imager (MRI)\], hepatic lipid accumulation \[MRI analysis\], blood lipid profile, resting metabolic rate, glycated hemoglobin \[hemoglobin A1c\]). After the first 3 months of training, adherence to the subjects assigned training program will be tracked for the next 9 months (1 year of training in total). One year after initiating a training program, subjects will be asked to return to the clinic for a quick follow-up visit where the research team will complete some standard clinical assessments (e.g., body weight, body composition, blood pressure, and a blood sample).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
NONE
Enrollment
120
(HIIT) 10 x 1 min. at \~90%HRmax - with low intensity warm-up, recovery, and cool down - total of 25 min/session .
Moderate-intensity continuous training (MICT) = steady-state exercise at 60-70%HRmax for 45min. Representing a commonly prescribed exercise program.
Suzette Howton
Ann Arbor, Michigan, United States
Insulin Sensitivity
A hyperinsulinemic-euglycemic clamp was used to assess peripheral insulin sensitivity. Briefly, a primed, continuous infusion of insulin (40 mU/m\^2/min) was administered; blood glucose was assessed every 5 minutes and 20% dextrose (D20 enriched with \[6-6 d2\]glucose) was infused at a variable rate to accommodate changes in blood glucose in order to maintain blood glucose at the participants' overnight fasted levels. About 2 hours after beginning the insulin infusion, when blood glucose concentration stabilized without further changes in the rate of D20 infusion for ≥ \~20 minutes, arterialized blood samples were collected every 5 minutes during the final 20 minutes of the clamp for the determination of steady state tracer-labeled glucose enrichment in plasma to calculate the rate of glucose disposal.
Time frame: Change from Baseline after 3 months of exercise training
VO2peak
Change in aerobic capacity between baseline and after 3 months of training
Time frame: Change from Baseline after 3 months of exercise training
Resting Metabolic Rate
energy expenditure while at rest
Time frame: Change from Baseline after 3 months of exercise training
Hepatic Fat %
Change in abundance of fat in the liver - reported as % area (measured by MRI)
Time frame: Change from Baseline after 3 months of exercise training
Visceral Fat Area (cm^2)
Change in fat accumulation in the visceral region - measured by MRI
Time frame: Change from Baseline after 3 months of exercise training
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