Regular exercise is a cornerstone in the prevention and the management of cardio-metabolic risk factors. Some of the beneficial effect of exercise training occurs through metabolic flexibility' enhancement. Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand, and previous literature has shown that individuals living with obesity have an impaired metabolic flexibility compared to lean individuals. However, there is a lack of empirical evidence on the impact of sprint interval training on metabolic flexibility and whether this translates into clinically meaningful outcomes.

This study will evaluate the impact of 4-week sprint interval training in normal weight individuals as well as individuals living with obesity on acute and chronic metabolic flexibility, irisin secretion and insulin sensitivity.

Inclusion Criteria:

• Adults (Ages 19-60)
• Physically inactive for individuals living with obesity (not meeting Canadian Physical Activity Guidelines)
• Normal Weight (BMI ≥ 18.5 < 25.0 km/m2)
• Obesity (BMI ≥ 30.0 km/m2)

Exclusion Criteria:

• Individuals with Type 2 Diabetes.
• Individuals with impaired glucose tolerance.
• Individuals living with obesity that partake in regular exercise training / meet the Canadian Physical Activity Guidelines.
• Individuals with a condition or injury that may impact the ability to perform exercise or may be worsened by exercise.
• Individuals currently being treated with corticosteroids or atypical antipsychotics, as these agents significantly influence carbohydrate metabolism.
• have experienced >10% weight loss or enrolled in weight loss program within six months of enrolment.
• require use of medication(s) known to affect insulin sensitivity or secretion within the last 30 days.
• Medication(s) known to cause weight gain.
• weight loss medication(s).