Effects of Microbouts of Activity on Metabolic Health

Population studies suggest that time spent in sedentary behaviors is associated with all-cause mortality including obesity, diabetes, and cardiovascular diseases, independent of time spent in exercise. Frequent interruptions to sedentary time are however beneficially associated with metabolic health outcomes, even in individuals who exercise regularly. The goal is to use integrative approach to understand the biological mechanisms that underlie these associations in a longitudinal intervention study in overweight sedentary adults. The investigators believe that the proposed study will provide an initial evidence base for the health benefits of breaking up prolonged sitting with short bursts of activity. This innovative strategy may be more effective at combating the adverse effects of sedentary behaviors than more traditional approaches.

To compare the effects of 6-weeks of microbursts of moderate-intensity activity to a calorically equivalent single bout of 45 minutes of moderate-intensity exercise training, both performed 5 days per week for a total of 45 minutes, in free-living sedentary overweight adults on:

Aim 1: plasma inflammatory and cardiometabolic health biomarkers in association with total energy expenditure and time spent in sedentary behaviors.

H1: Microbursts of activity will result in higher daily energy expenditure and lower time spent sedentary, as respectively measured with doubly labeled water and accelerometry, than traditional exercise training. This will be associated with healthier inflammatory Interleukin 1 alpha (IL1a), Interleukin 6 (IL6), Interleukin 10 (IL10), Tumour Necrosis Factor alpha (TNFa) and cardiometabolic (triglycerides, cholesterol, C-Reactive Protein (CRP), High-density lipoprotein (HDL), and Low-density lipoprotein (LDL) profiles compared to those obtained with traditional exercise training program.

Aim 2: 24-hr total fat and carbohydrate oxidation, exogenous carbohydrate oxidation, dietary fat trafficking between oxidation and incorporation into muscle lipid fractions, and mitochondrial function.

H2: Both one single continuous bout and microbouts of activity will increase 24-hr total (whole-room calorimetry) and dietary (D31-palmitate) fat oxidation due to greater mitochondrial lipid oxidation (high resolution respirometry) and lower incorporation of dietary fatty acid into muscle lipid fractions (D31-palmitate), as compared to baseline sedentary control condition. Microbouts of activity will further result in greater increases in 24-hr total (whole-room calorimetry) and exogenous (U-13C6 glucose) carbohydrate oxidation and in mitochondrial carbohydrate-linked oxidation, than traditional isocaloric exercise training.

Aim 3: Whole-body insulin sensitivity and daily glucose mean and variability. H3: Both one single continuous bout and microbouts of activity will improve whole-body insulin sensitivity Intravenous Glucose Tolerance Test (IVGTT) compared to the baseline sedentary condition, but the improvement will likely be higher with the microbouts of activity. However, only the microbouts of activity will improve postprandial glycemia and the daily oscillations in glucose level as measured by CGM.

Exploratory aim: Self-perceived appetite and hunger.

Eligibility Criteria:
Inclusion Criteria:

* Overweight but weight stable (+/- 3kg over previous 6 months) sedentary male and female adults (n=30) will be recruited.
* Ages between 18-45 years old
* BMI of 25-35 kg/m2
* Sedentary ( self report \< 150min/wk of moderate-to-vigorous activity or less than 6,500 steps per day as measured for 5 days in free-living conditions with a pedometer).
* The use of birth pill control will be accepted

Exclusion criteria:

* Any history of renal (present or past kidney failure, kidney transplant, dialysis or kidney cysts),
* Uncontrolled hypertension
* Cardiovascular (present or past atherosclerosis, heart attack, ischemic stroke, heart failure)
* Hepatic diseases (past or present hepatitis B or C, fibrosis, cirrhosis, NAFLD/NASH)
* Type 1 or 2 diabetes
* Cancer
* Smoking
* Consumption of drugs (marijuana included)
* Consumption of alcohol (\>40g/d)
* HIV positivity
* Psychiatric disorders
* Any medications known to interfere with lipid or energy metabolism
* Known physical activity contraindications
* Major illness/physical problems (acute or chronic) that may limit their ability to perform the walking activities