Previous research has shown that time spent viewing TV or in self-reported sedentary behaviors is related to suboptimal cognitive functioning in older adults. However, not all sedentary behaviors show negative relationship with cognitive functions and most studies focused on leisure time sedentary behaviors. Consequently, these studies were unable to assess the relationship between daily volume of sedentary time and cognitive functions. Physiological adaptations to sedentary lifestyle include adverse cardio-metabolic profiles and low-grade inflammation. These physiological responses contribute to suboptimal brain and cognitive functions. Chronic stress has been negatively related to cognitive functions in youth and adults. Socio-economic status is one of the correlates of sedentary behaviors and higher levels of chronic stress have been observed among individuals with low socio-economic status. Thus, individual differences in chronic stress may help explain the associations between sedentary time, physical inactivity and suboptimal cognitive functioning. Furthermore, it is important to ascertain which biological pathways may be specific to excessive engagement in sedentary time. Adolescence and young adulthood are the most opportune periods to study these relationships due to low prevalence of chronic disease and comorbid conditions compared to middle-aged and older adults, high levels of sedentary time (adolescents are the most sedentary group after older adults, and European adolescents spend on average 7.5 hours per day sedentary) and protracted development of higher order cognitive functions yielding them amenable to behavioral interventions during these developmental periods.