Author: Melanie Heath
Heath, Melanie, 2023 How sleep mediates the relationship between physical activity and mood in adolescents, Flinders University, College of Education, Psychology and Social Work
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Sleep problems and mood difficulties can substantially impact adolescents’ lives. Yet, the multiple interrelationships between physical activity, sleep, and mood make physical activity interventions a viable option to prevent and treat these difficulties. This thesis aimed to explore if sleep mediates the ‘physical activity - mood’ connection; through sleep onset latency (SOL), total sleep time (TST), and sleep timing (chronotype and circadian rhythm timing). The mediations were explored using different designs and measurements throughout the thesis.
The uniqueness of adolescent sleep, and the links between physical activity, sleep, and mood are introduced in Chapter 1. The proposed TST mediation emulated the typical beneficial effect of physical activity on sleep and mood; more physical activity → longer TST → better mood. As evening physical activity is often considered detrimental to sleep, this was reflected in the proposed models; more evening physical activity → worse sleep (longer SOL, later sleep timing) → worse mood.
Initial support for the models was found in Chapter 2 in a large (N = 1,367) cross-sectional sample of adolescents. The data fit the mediation models; more physical activity → better sleep (longer TST, shorter SOL, earlier chronotype) → better mood. The models were significant for the total sample and for girls, but not boys, highlighting potential sex differences. Unexpectedly, evening physical activity (after 6 p.m.) was not linked with worse sleep or mood.
Temporal relationships were assessed in Chapter 3 with a sample of 19 adolescent girls. Assessments took place over 1 week using objective actigraphy to measure sleep and physical activity, and daily ecological momentary assessments of mood. Chronotype acted as a mediator; more evening physical activity → earlier chronotype → better mood. TST mediations varied from day-to-day. On Wednesday, Friday, and Sunday; more physical activity → shorter TST → mood change. Mood improved on Friday and Sunday, but worsened on Wednesday. Again, evening physical activity (within 3 hours of bedtime) was not detrimental to sleep.
In a laboratory setting, Chapter 4 assessed the impact of a 5-day physical activity intervention in adolescent boys with a late chronotype. Eighteen boys were randomly allocated to 45 minutes light-intensity treadmill-walking, or 45 minutes sitting. Objective measures assessed sleep (dim light melatonin onset via saliva assay) and physical activity (heart rate monitoring). In this experimental study, the mediation models were not supported. Although morning activity advanced the circadian rhythm (walking group 28-minute circadian advance; sitting group 19-minute delay), mood was not significantly related to sleep or physical activity.
This thesis found evidence that sleep mediates the relationship between physical activity and mood through sleep timing, TST, and SOL. Notable sex differences were found. The mediations were significant in girls, but not in boys. Physical activity’s beneficial effect on sleep and mood indicates that it may prove helpful in the prevention and treatment of sleep and mood difficulties in adolescent girls. The finding that evening physical activity was not detrimental to sleep and mood will be instructive for clinicians providing physical activity recommendations to adolescents.
Keywords: adolescent, sleep, physical activity, mood, mediation, chronotype, depression, sex differences, repetitive negative thinking
Subject: Psychology thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Education, Psychology and Social Work
Supervisor: Dr Ryan Balzan