Effects of a five-day evening smartphone restriction on sleep, cognitive, and physical performance in university students: A single-arm repeated measures study stratified by nomophobia.

Evening smartphone use disrupts circadian rhythms and recovery through exposure to blue light and cognitive hyperarousal. Nomophobia: fear of smartphone separation: may limit the effectiveness of digital restriction interventions. To determine the effects of a five-day evening smartphone restriction on objectively measured sleep, cognitive, and physical performance, and to assess whether outcomes differ by nomophobia level. Twenty-eight physically active university students (20.4 ± 1.8 years) were stratified into high (n = 14) and low (n = 14) nomophobia groups using the validated Nomophobia Questionnaire. Participants avoided using smartphones and other blue-light-emitting devices after 6:00 pm for 5 consecutive days. Sleep was monitored using wrist-worn actigraphy (ActiGraph wGT3X-BT); cognitive performance was assessed via Simple and lower-limb reaction time tests; and physical performance via squat jump, Countermovement Jump, and Modified Agility t Test (Optojump) tests. Stress and anxiety were measured at baseline and on Days 1, 3, and 5. Mixed-effects analysis of variance assessed group × time interactions. All participants completed the intervention with 100% compliance. Individuals with low nomophobia showed large to very large improvements in total sleep time (+45 minutes, d = 0.80, P < .001), sleep efficiency (+12%, d = 2.99, P < .001), and wake after sleep onset (-18 minutes, d = 4.60, P < .001). Morning reaction time (d = 0.40, P < .001) and lower-limb reaction speed (d = 1.07, P < .001) improved significantly. Physical performance increased across all tests: squat jump (d = 1.30), Countermovement Jump (d = 1.25), and agility (d = 1.40), with changes exceeding typical short-term training gains. Stress (d = 2.16, P < .001) and anxiety (d = 2.63, P < .001) declined progressively over time. High nomophobia participants exhibited no meaningful improvements and experienced acute stress/anxiety elevations on Day 1. A short-term, technology-based behavioral intervention: complete evening smartphone restriction can significantly enhance sleep quality, cognitive readiness, and physical performance in young adults with low digital dependency. Nomophobia significantly moderates these benefits, highlighting the need for psychological screening and tailored telehealth approaches when designing digital wellness and sleep optimization programs.