ßÉßɱ¬ÁÏ

Topic

Scroll or stroll? Screen time’s Displacement of Physical Activity in Canadian Adolescents

Department of Psychology

Date & location

• Thursday, August 14, 2025

• 9:00 A.M.

• Virtual Defence

Reviewers

Supervisory Committee

• Dr. Megan Ames, Department of Psychology, ßÉßɱ¬ÁÏ (Supervisor)

• Dr. Stuart MacDonald, Department of Psychology, UVic (Member)

• Dr. Sam Liu, School of Exercise Science, Physical and Health Education, UVic (Outside Member) 

External Examiner

• Dr. Nevin Harper, School of Exercise Science, Physical and Health Education, UVic 

Chair of Oral Examination

• Dr. John Lutz, Department of History, UVic 

Abstract

Few Canadian adolescents adhere to the recommended 2 hours of daily screen time, increasing their risk for poor health outcomes. However, the literature remains conflicted about how screen time affects mental health. I investigated two hypotheses that examine this issue. Namely, the Displacement Hypothesis proposes that screen time has a negative effect on mental health by displacing movement behaviours, such as physical activity and sleep. Alternatively, the Goldilocks Hypothesis suggests this association is non-linear, and that only high levels of screen time negatively impact mental health while low-to-moderate levels are not harmful. Using intensive longitudinal data (self-report surveys and FitBit measurements), I tested these hypotheses by examining: 1. the linear association between screen time and physical activity or sleep, 2. if the displacement of physical activity or sleep explains the association between screen time and mental health, and 3. if there is evidence for a non-linear association between screen time and mental health. The final sample included 89 adolescents (mean age = 14.96; 63% Girls, 31% boys, 6% transgender/non-binary). Results partially supported the Displacement Hypothesis, showing that daily fluctuations in screen time negatively predicted daily physical activity, but not sleep. Results did not support the Goldilocks Hypothesis, as there was no evidence to support a non-linear association between screen time and mental health. These results call into question the practical validity of screen time guidelines and highlight the need to promote physical activity and mindful digital media use on days when adolescents engage in more screen time than usual.