Physical Activity, Body Composition, and Fitness Variables inAdolescents After Periods of Mandatory, Promoted orNonmandatory, Nonpromoted Use of Step Tracker Mobile Apps:Randomized Controlled Trial

Background: It is not known whether an intervention made mandatory as a physical education (PE) class assignment and aimedat promoting physical activity (PA) in adolescents can create a healthy walking habit, which would allow further improvementsto be achieved after the mandatory and promoted intervention has been completed.Objective: The aims of this study were to (1) investigate whether, after a period of using a step tracker mobile app mademandatory and promoted as a PE class assignment, adolescents continue to use it when its use is no longer mandatory andpromoted; (2) determine whether there are changes in the PA level, body composition, and fitness of adolescents when the useof the app is mandatory and promoted and when it is neither mandatory nor promoted; and (3) analyze whether the covariatesmaturity status, gender, and specific app used can have an influence.Methods: A total of 357 students in compulsory secondary education (age: mean 13.92, SD 1.91 y) participated in the study.A randomized controlled trial was conducted consisting of 2 consecutive 10-week interventions. Participants'PA level, bodycomposition, and fitness were measured at baseline (T1), after 10 weeks of mandatory and promoted app use (T2), and after 10weeks of nonmandatory and nonpromoted app use (T3). Each participant in the experimental group (EG) used 1 of 4 selectedstep tracker mobile apps after school hours.Results: The results showed that when the use of the apps was neither mandatory nor promoted as a PE class assignment, onlya few adolescents (18/216, 8.3%) continued the walking practice. After the mandatory and promoted intervention period (T1 vsT2), a decrease in the sum of 3 skinfolds (mean difference [MD] 1.679; P=.02) as well as improvements in the PA level (MD-0.170; P<.001), maximal oxygen uptake (MD -1.006; P<.001), countermovement jump test (MD -1.337; P=.04), curl-up test(MD -3.791; P<.001), and push-up test (MD -1.920; P<.001) in the EG were recorded. However, the changes between T1 andT2 were significantly greater in the EG than in the control group only in the PA level and curl-up test. Thus, when comparingthe measurements taken between T1 and T3, no significant changes in body composition (P=.07) or fitness (P=.84) were observedbetween the EG and the control group. The covariates maturity status, gender, and specific app used showed a significant effectin most of the analyses performe Conclusions: A period of mandatory and promoted use of step tracker mobile apps benefited the variables of body compositionand fitness in adolescents but did not create a healthy walking habit in this population; therefore, when the use of these appsceased to be mandatory and promoted, the effects obtained disappeared