Brief report: Association between socio-demographic factors, screen media usage and physical activity by type of day in Spanish adolescents.

This study examined the relationship between socio-demographic factors, screen media time usage, and light, moderate and vigorous activities on weekdays and weekends. Cross-sectional data was collected from 323 Spanish adolescents (mean age 13.59 years) who completed an interview administered recall questionnaire. Structural equation models indicated that male and younger adolescents spent more time on vigorous activities at the weekend, while females and older adolescents showed a greater involvement in light activities both on weekdays and weekends. State school students reported engaging in light and vigorous activities for longer periods than private school students on weekends. TV viewing was negatively linked to vigorous activities during weekdays and to light and moderate activities on weekends. The amount of mobile phone usage, however, was positively linked to light activities during weekdays, but negatively on weekends. The negative relationship between adolescents' use of screen media (TV and mobile phone) and physical activity and its possible displacement, depending on the type of day, added useful comparable knowledge for policies promoting an active lifestyle. Further research is required to provide evidence of the causality in the observed relationships.