Background: Finding behavioral changes in youth during the COVID-19 pandemic may provide a better image of the negative impact of quarantine on their mental and physical health. The purpose of the present research was to examine the smartphone usage status, sleep pattern, health-related quality of life, and physical activity among adolescents from before to during the COVID-19 confinement.

Methods: The present study used a descriptive-comparative design. The participants were 384 male and female students aged 16 to 18 years (mean age of 16.84±1.06 years) in grades 11 and 12 from the high-schools of Golestan province, Iran, in 2020. Screen time, sleep pattern, health-related quality of life, and physical activity were measured using standard questionnaires. Paired-Sample t test was employed to compare the means of the constructs of the study from “before” to “during” the COVID-19 pandemic. Independent t test was used to measure gender differences.

Results: Results shed light on the increments in smartphone use and decrements in sleep quality, health-related quality of life, and physical activity among adolescents from “before” to “during” the COVID-19 pandemic (all p <0.001). Girls had significantly higher use of smartphones in both “before” (P=0.003) and “during” (p <0.001) the pandemic compared with boys. However, no other gender differences were found among male and female adolescents (all P>0.05).

Conclusion: The findings of this study revealed the effects of policies related to COVID-19 pandemic on health-related behaviors among adolescents and emphasized the importance of adopting appropriate coping strategies to promote healthy lifestyle during confinement.