Actividad física y uso sedentario de medios tecnológicos de pantalla en adolescentes

The benefits associated with an active lifestyle demands a special attention when we speak about children and youth because of their impact in both short- and long-term effects. Therefore, physical activity becomes a key issue for the social and health policies of the different public administrations. If we take into consideration the concern that physical activity arouses among Spanish adolescents, we add the increasing use of screen media devices teenagers are experiencing and which could decrease or determine their daily physical activity. This PhD dissertation is an epidemiologic-based research on a sample of 2983 students of Secondary School Education and Sixth Form (12- to 18- years old). Self-report questionnaires were administered in order to measure the patterns of physical activity and sedentary screen media usage (television, computer and videogames). In this sense, differences biased by the sociodemographical variables sex, grade and socioeconomical status and the type of the day of the week were purposes of this study. Another aim was to find evidence about whether the behaviours could be explained by the displacement hypothesis mechanism. The results show that Spanish adolescents, in general terms, spend an average of 54 minutes per day doing moderate-to-vigorous physical activity, accomplishing the current physical activity guidelines only the 37% of the sample (60 minutes of moderate-to-vigorous physical activity daily). Analyses of variance indicated that boys are more active than girls, physical activity diminishes as youth get older and youth with higher socioeconomic status are more active than those with lower socioeconomic status. Regarding the use of screen time devices, adolescents spend an average of 3 hours per day viewing TV, using computer and videogames. Of the total sample, only the 27.2% of adolescents accomplish with the current sedentary guidelines (<2 hours/day). While there are not differences by sex in TV viewing or computer use, boys engage more in videogames than girls. Regarding the grade, the adolescents who spend greater amounts of time using the screen media devices are those who study Years 10 and 11 (aged between 14 and 15 years old). Furthermore, the results revealed that adolescents with lower socioeconomic status watch more TV and use less the computer than those with higher socioeconomic status. The results by type of the day show that youth spend more time engaged in television, computer and videogames (from 141 to 224 minutes) and less time in moderate-to-vigorous physical activity (from 45 to 36 minutes) during weekends. On the other hand, positive and negative associations were observed between both behaviours (physical activity and sedentary screen media usage). However, the magnitudes of these associations are not strong enough to state that these behaviours can be explained by the replacement hypothesis mechanism. Therefore, the results of this study show inconsistency in front of this theory. In view of our results, further studies are needed to investigate these issues in depth. Similarly, there is a clear need for public awareness about the lack of strategies and promotion policies that address the needs identified in this study in order to deal with the low levels of physical activity and the increasing use of technological screen media that adolescents are experiencing nowadays.