Effect of Breaking up Prolonged Sitting on Metabolic Flexibility

Although public-health recommendations to engage in moderate-to-vigorous physical activity
(at least 30min, 5 days / week) have been widely promulgated by the government, most people
are physically inactive. Sedentary behaviors, like time spent sitting, are associated with
serious implications on metabolic health, indicating that even in individuals who regularly
exercise a reduction in time spent sitting can confer health benefits. Encouraging recent
evidence shows that walking breaks throughout the day are an effective strategy to offset the
deleterious effects of prolonged uninterrupted sitting. Further data however are needed to
better understand the effect of these microbursts of activity along the day. The
investigators propose in this project to determine the effect of 3 days of frequent
interruption of prolonged sitting on metabolic health in healthy overweight sedentary adults
(n=24), as compared to 3 days including a single long bout of isocaloric exercise or a
control condition where subjects do not exercise but are subjected to prolonged sitting.
Plasma glucose, insulin, triglycerides and free fatty acids concentrations and the use of
substrate (glucose, fat or protein) to provide energy to the body in response to meals
consumption will be measured on day 3 of each of these three conditions. The investigators
will furthermore assess the ability of the participants to perform the interventions on
physical activity at the end of each day over the three days of intervention (2 days in
free-living conditions and one day in a controlled environment). The investigators believe
that this proposed project will provide an initial evidence base for the health benefits of
breaking up prolonged sitting with short bursts of moderate-intensity activity, like walking.
This innovative strategy may be more effective at combating the adverse effects of sedentary
behaviors than more traditional approaches like structured exercise.

Inclusion Criteria:

- overweight but weight stable (less than +/- 3kg over previous 6 months) male and
female adults (n=24) will be recruited.

- age between 19-45 years old,

- a BMI of 27-33 kg/m2,

- inactive (≤ 1.5hr/wk of moderate-to-vigorous activity),

- sedentary (office employees who are spending more than 6hrs/day in sitting position)
and

- English-speaking.

Exclusion Criteria:

- any history of renal, cardiovascular or hepatic diseases,

- type 1 or 2 diabetes,

- cancer,

- pregnancy,

- smoking,

- consumption of drugs or alcohol (>40g/d),

- any medications known to interfere with lipid or energy metabolism,

- known physical activity contraindications, or major illness/physical problems (acute
or chronic) that may limit their ability to perform the walking activities and

- menopause (defined as no menses in the prior 6 months). The use of birth pill control
will be accepted. Women are asked to avoid pregnancy until completion of Condition C.