High evening smartphone use drives sleep debt and lower morning affect in athletes

In athletic populations, adequate sleep is critical for performance, recovery, and emotional well-being. However, behavioural habits such as late-night smartphone use may disrupt sleep and circadian alignment, leading to sleep debt and impaired morning functioning. This study examined associations between pre-sleep smartphone use, sleep debt (defined as the difference between average sleep duration on work/schooldays and free days), and morning affect in athletes. A sample of 174 Portuguese athletes (aged 15-65) completed questionnaires assessing sleep patterns, pre-sleep smartphone use, and morning affect. Participants were grouped as high (daily) vs. low/moderate (≤6 days/week) smartphone users. Greater sleep debt significantly predicted lower morning affect (ρ = -0.215, p = 0.004), especially among high smartphone users (ρ = -0.30, p = 0.001). While smartphone use did not significantly predict sleep debt, high use was marginally associated with lower morning affect. Mediation analysis showed sleep debt did not account for the association between smartphone group and next-day morning affect, suggesting a more direct association with bedtime screen exposure. Findings indicate that frequent pre-sleep smartphone use is associated with poorer mood upon waking, reflecting immediate sleep disruptions rather than accumulated sleep loss. Given prevalent evening screen use in athletes, promoting healthier pre-sleep routines may support emotional recovery and performance readiness.