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In recent years, a growing significance has been placed on the engagement of adolescents in physical activity (PA), given the decrease in active time and the increase in sedentary activities and screen time []. These behaviors have negatively impacted the health of adolescents by increasing the risk of cardiovascular disease and other associated chronic diseases []. This situation has prompted the implementation of new practices that have been shown to be effective in increasing the level of sports practice in adolescents [,]. In this context, interventions that incorporate electronic devices have gained relevance [], given their extensive use during the COVID-19 pandemic and their integration into the daily lives of adolescents [].
Mobile sports apps have emerged as valuable resources in promoting PA among adolescents [], and it has been observed that interventions with mobile devices have made it possible to increase moderate-intensity PA and daily step count among users []. This has also had a positive impact on the health of the adolescent population because the use of these mobile apps has improved their body composition and fitness levels [,], which are fundamental for their subsequent development [,]. This is because adolescents who are overweight or obese have a high probability of remaining so in adulthood [], with the associated high health risk for cardiovascular and respiratory diseases []. On the contrary, adequate levels of body fat, within the limits considered healthy [], as well as an adequate physical fitness level, especially good cardiorespiratory fitness, are indicators of adequate health and serve as preventive factors against various diseases in adulthood [].
In this regard, mobile apps seem to be effective tools for improving the health status of adolescents and for preventing future health risks. It is crucial to emphasize that the effectiveness of increasing adolescents’ PA level through mobile apps was evident only in studies in which the use of these apps was mandatory. Specifically, the promotion of app use as an assignment in physical education (PE) classes played a significant role in achieving positive outcomes [,]. Furthermore, it is worth noting that no major differences were found in the effects achieved by the intervention when comparing the different mobile apps used, as long as they were all step trackers []; however, the gender of the adolescents was shown to be a determinant factor in the benefits obtained because female adolescents used these apps more often than male adolescents during the mandatory and promoted intervention period, which led to significant differences in the benefits obtained in BMI, corrected calf girth, fat mass, and physical fitness []. Therefore, the mandatory use of apps seemed to be effective in this population, although it should be noted that a previous study showed that the first weeks of the intervention were the most effective in the adolescent population due to the novelty of the intervention, but as the intervention progressed, the effects were reduced []. This is a relevant aspect because there is a considerable loss of adherence after the first weeks of the intervention [], which could negatively influence the overall benefits obtained.
In addition to the loss of adherence, there are also periods in the school calendar when PA decreases, such as holiday breaks. These are characterized by the absence of students from school, which makes it difficult to promote the use of this type of intervention as a PE class assignment. This has a particular significance because prior research has revealed a detraining effect, wherein the gains in body composition and fitness achieved during an aerobic intervention period were subsequently lost, leading to a regression to preintervention levels [].
Therefore, it is essential to verify whether, after a period of mandatory and promoted use of step tracker mobile apps as a PE class assignment, which has shown beneficial effects on body composition and physical fitness in previous research [], it is possible to create a healthy walking habit in adolescents and to have them continue using the apps when they are neither mandatory nor promoted to try to avoid detraining effects. This would allow us to define strategies to compensate for the loss of adherence and decrease in PA level observed during holiday periods, similar to previous research on flexibility in adolescents []. However, no previous research is known to have analyzed whether the effects achieved throughout a period of mandatory and promoted use of step tracker mobile apps are maintained over time when their use is neither mandatory nor promoted as a PE class assignment. Furthermore, previous studies in this area have not analyzed whether the effects of such interventions may depend on the maturity status of adolescents, although numerous studies have shown that the rate of maturation during adolescence varies between individuals []. Thus, this factor may condition the changes in body composition and fitness variables in adolescents [].
ObjectivesTherefore, considering the absence of previous research analyzing whether adolescents aged 12 to 16 years continue their walking practice with step tracker mobile apps when their use is no longer mandatory and promoted as a PE class assignment, as well as the influence that covariates such as maturity status, gender, and specific app used may have on the results, the aims of this study were to (1) investigate whether, after a period of mandatory and promoted use of a step tracker mobile app as a PE class assignment, adolescents continue to use it when its use is no longer mandatory and promoted; (2) determine whether there are changes in PA level, body composition, and fitness of adolescents when the use of the app is mandatory and promoted as a PE class assignment, as well as whether maturity status, gender, and specific app used can have an influence on the results; and (3) analyze whether there are changes in PA level, body composition, and fitness of adolescents when the use of the app is neither mandatory nor promoted as a PE class assignment, as well as whether maturity status, gender, and specific app used can have an influence on the results.
HypothesesOn the basis of the aims of the research and previous research involving technological devices (eg, wearables) or websites, it is hypothesized that adolescents will stop using the mobile app during the period of nonmandatory and nonpromoted use (H1); that there will be significant differences in PA level, body composition, and fitness of adolescents during the mandatory and promoted period, influenced by maturity status and gender but not by specific app used (H2); and that some of the benefits achieved by adolescents during the mandatory and promoted period will be lost after the mandatory and promoted intervention has been completed, with the results being influenced by maturity status and gender but not by specific app used (H3).
The intervention in this study was carried out by replicating the methodology of previous research [], the main difference being that this research analyzed what happens to the study variables when the mandatory intervention ends and becomes a nonmandatory, nonpromoted intervention. Our new research design comprised 3 data collection periods (T1: baseline, T2: after 10 weeks of mandatory and promoted app use, and T3: after 10 weeks of nonmandatory and nonpromoted app use) with a total duration of 26 weeks. T1 took place in the first 2 weeks (weeks 1-2); the mandatory intervention with the step tracker mobile apps promoted as a PE class assignment took place in the following 10 weeks (weeks 2-12); T2 took place in the next 2 weeks (weeks 13-14); the use of the step tracker mobile apps was neither mandatory nor promoted during the following 10 weeks (weeks 14-24); and T3 took place in the last 2 weeks of the study (weeks 24-26). shows the timeline of the study. The intervention began on January 9, 2023, and ended on June 23, 2023.
Figure 1. Timeline of the study. This study was a randomized controlled trial. It followed the CONSORT (Consolidated Standards of Reporting Trials) guidelines [] and was preregistered at ClinicalTrials.gov (NCT06164041). A convenience sampling method was used to recruit adolescents from accessible educational institutions.
The study used a specific research model ().
Table 1. Research model.Variable typeConstructGroups includedVariables includedIndependentPhysical activity levelApp use group and control groupSubjective assessment of the level of physical activityDependentKinanthropometric and body composition variablesApp use group and control groupBody mass; height; BMI; sitting height; sum of 3 skinfolds; corrected arm, thigh, and calf girths; waist girth; hips girth; waist to hip ratio; muscle mass; and fat massDependentPhysical fitness variablesApp use group and control groupVO2maxa, CMJb test, curl-up test, and push-up testCovariatesVariablesApp use group and control groupMaturity status, gender, and specific app usedaVO2max: maximal oxygen uptake.
bCMJ: countermovement jump.
Ethical ConsiderationsThis study was approved by the institutional ethics committee of the Catholic University of Murcia (code CE022102) and adhered to the guidelines set forth by the World Medical Association and the Declaration of Helsinki. Adolescents who expressed willingness to participate in the study were required to sign an informed consent form, with both adolescents and their parents acknowledging their understanding of the study aims and procedures.
ParticipantsWe recruited participants from 2 compulsory secondary schools located in Murcia. These schools were chosen because of their large student population in secondary education within their respective localities. Initially, the research team contacted the schools to provide a detailed explanation of the study’s procedure and objectives. If a particular school declined to participate, the school with the next largest number of students in the locality was approached. Once the school’s approval was obtained, the PE department heads were contacted. Subsequently, a face-to-face meeting was arranged with interested students and their parents to discuss the study further.
The minimum sample size necessary for the study was calculated using RStudio software (version 3.15.0; Posit Software PBC) and followed the methodology used in previous studies [], in which the SD value (0.64) from previous studies that used a similar design with 3 data points to measure changes in PA among adolescents was used []. With an estimated error (d) of 0.067 and a CI of 95%, the required sample size was determined to be 350 adolescents.
illustrates the flowchart for the selection of the sample. The final sample comprised 357 adolescents aged between 12 and 16 years. The participants were assigned to the different groups using a cluster randomized design []. Group assignment was concealed from the researcher who analyzed each participant’s compliance with the inclusion and exclusion criteria. The inclusion criteria for the study were as follows: (1) enrollment in 1 of the selected educational institutions, (2) aged between 12 and 16 years, (3) completion of all questionnaires and physical tests during the 3 measurement periods (T1, T2, and T3), (4) attending the kinanthropometric and body composition assessment sessions, and (5) absence of any pathology or injury that would hinder participation in the tests or measurements conducted. The exclusion criteria were as follows: (1) missing >20% of the mandatory PE sessions throughout the academic year, (2) lack of a mobile phone, (3) failure to meet the minimum mandatory weekly distance requirement in the experimental group (EG) when app use was mandatory and promoted, (4) changing schools or class group during the course of the intervention, (5) starting or ending any form of PA (for reasons unrelated to the study) during the intervention that could alter the PA level being assessed as part of the study, and (6) having presented with any illness during the follow-up period that would have prevented the participant from engaging in their usual PA.
Figure 2. Sample selection flowchart. Randomization and BlindingAfter the recruitment and selection of the adolescents, meetings were held with the teachers to provide them with a clear understanding of the trial’s purpose and the randomization process. Parents or legal guardians of the potential participants at each school were notified through a letter that explained the study’s objectives and procedures. The principal investigator, along with other uninvolved investigators, carried out the randomization process using a computer-generated random number table. The randomization assigned all students within the same class at each school to the same mobile app group. The classes were randomly assigned to participate as intervention or control classes. A total of 16 classes were finally randomized, of which 11 (69%) were included in the EG and 5 (31%) in the control group (CG). The ratio chosen for the randomized clusters was 2:1 (for every 2 classes included in the EG, 1 was included in the CG) because previous research with mobile apps has highlighted the lack of adherence to mobile apps, and we wanted to ensure that we had enough participants in the EG to account for a possible high dropout rate (close to 35%) from hindering the extrapolation of the results []. The control classes were instructed to continue their regular PE classes, while the intervention was offered to them after the final data collection took place. Baseline measurements were taken before the randomization process. All measurers were blinded to the group to which each individual belonged during the second and third measurements, as well as to the individual’s ratings in the previous measurements.
InstrumentsThe instruments used in this study were the same as those used in previous investigations [] because these are valid and reliable in the adolescent population.
Questionnaire MeasurementA sociodemographic questionnaire developed ad hoc was administered to obtain data on the age and gender of the participants, their regular PA, and the occurrence of injury or illness, following the pattern of previous studies [].
PA level was measured using the Physical Activity Questionnaire for Adolescents (PAQ-A) []. This questionnaire had been previously validated in Spanish and showed satisfactory reliability, with an intraclass correlation coefficient of 0.71 for the final score [].
Kinanthropometric and Body Composition MeasurementThe anthropometric measurement included 3 basic parameters (body mass, height, and sitting height), 3 skinfold measurements (triceps, thigh, and calf), and 5 girth measurements (arm relaxed, waist, hips, thigh, and calf) []. Measurements were performed by anthropometrists (level 3 and level 4) accredited by the International Society for the Advancement of Kinanthropometry [].
The anthropometric instruments used were the same as those used in previous research []: a Harpenden skinfold caliper, a Lufkin W606PM anthropometric tape measure, a Tanita BC418-MA segmental scale, and a Seca 213 stadiometer. All instruments were calibrated before the beginning of each of the measurements (T1, T2, and T3).
The following derived variables were calculated from the anthropometric measurements: BMI, muscle mass [], fat mass [], sum of 3 skinfolds (triceps, thigh, and calf), waist to hip ratio (waist girth/hips girth), and corrected girths of the arm (arm relaxed girth – [π × triceps skinfold]), thigh (middle thigh girth – [π × thigh skinfold]), and calf (calf girth – [π × calf skinfold]) []. The body composition formulas have been used in previous research [] and are the ones most often recommended for evaluation in this population [].
The maturity offset was calculated according to the procedure established by Mirwald et al [] and using gender-specific formulas: –9.37 + 0.0001882 × ((height – sitting height) × sitting height) – 0.0022 × (age × (height – sitting height)) + 0.005841 × (age × sitting height) – 0.002658 × (age × weight) + 0.07693 × (weight / height). The result of the maturity offset equation is expressed in years from the age at peak height velocity (PHV) when the result is positive and in years to the age at PHV when the result is negative.
The same anthropometrist performed the T1, T2, and T3 measurements on each participant to reduce interevaluator error. The intra- and interevaluator technical errors of measurement [] were 0.02% and 0.04% for basic measurements, 1.09% and 1.87% for skinfolds, and 0.03% and 0.08% for girths. The correlation coefficients of the anthropometrists with respect to a level 4 expert anthropometrist were 0.96 for basic measurements, 0.91 for skinfolds, and 0.93 for girths.
Physical Fitness MeasurementsCardiorespiratory fitness was evaluated using the 20-meter shuttle run test. The test ends when the adolescent is unable to complete the required distance in the indicated time twice consecutively or when he or she reaches exhaustion. Upon completion of the test, the final speed at which the adolescent concluded the shuttle run was used to calculate their maximal oxygen uptake (VO2max) []. This test has high validity and reliability for the determination of VO2max [].
Lower limb explosive strength was assessed by means of the countermovement jump (CMJ). Adolescents had to perform a 90-degree knee flexion at maximum speed, keeping the back fully straight with hands placed on the hips, followed by a maximal knee extension to jump []. The adolescents were required to execute a maximal jump while maintaining their hands on their hips throughout the test. The jump height was determined by measuring the flight height achieved during the jump [].
For the measurement of abdominal strength and endurance, we used the curl-up test. For the execution to be valid, the adolescents had to keep their feet fully supported on the floor and their arms crossed on the chest, and the trunk flexion had to allow the upper back to be lifted off the floor []. The test ended when the time was up (1 min) or when the participant reached exhaustion.
The push-up test was used to evaluate upper body strength. The repetition was valid if the adolescents managed to fully extend their arms and return to the 90-degree position []. The adolescents had to perform as many push-ups as possible in 1 minute. The test ended when the time was up (1 min) or when the participant reached exhaustion.
ProcedureThe procedure used was also similar to that used in previous research [], but the difference was that in this study, the intention was to discover how adherence to the intervention changed when the intervention was no longer mandatory or promoted as a PE class assignment and how this affected the variables analyzed. Therefore, unlike previous studies [], this study comprised 3 measurement periods (T1, T2, and T3), with 2 interventions carried out consecutively. The first one was mandatory and promoted as a PE class assignment, and the second one was neither promoted nor promoted as a PE class assignment.
The data collection process followed the same protocol as in previous research [,], with the sociodemographic and PAQ-A questionnaires completed first, followed by the anthropometric measurements. Once these were completed, the fitness tests were explained and performed randomly, twice each, with the 20-meter shuttle run test performed last and only once. The physical test protocol adhered to the guidelines set forth by the National Strength and Conditioning Association, with the aim of minimizing interference between tests and allowing sufficient recovery time from the exertion and metabolic demands of the assessments [].
To minimize bias in the measurements, they were carried out under the same conditions for all students. The PE class hour was used for the measurements and the adolescents were always measured at the same time and on the same day of the week at T1-T2-T3. The questionnaires were completed in a reserved space in which the adolescents did not have any distractions that could have conditioned their answers. In addition, while the researchers resolved any possible doubts, in no case did they condition the adolescents’ responses. For the anthropometric measurements, the air-conditioned locker rooms of the sports pavilion were used to minimize variability due to temperature and humidity fluctuations across the 3 measurement periods. To conduct the physical tests, the indoor sports pavilion at each school was used, which was specifically chosen to eliminate the influence of atmospheric variables that could potentially affect the results and introduce bias.
Mobile App InterventionBefore starting the intervention, 465 adolescents participated in pretest measurements (T1; ). The mandatory and promoted intervention lasted 10 weeks, during which the adolescents were required to use 1 of the 4 selected apps: Pokémon Go, Pacer, Strava, or MapMyWalk. These apps were selected based on their implementation of a substantial number of behavior change techniques [] specifically designed to effectively enhance PA level among users. Moreover, they have already been used in previous research with adolescents, with participants demonstrating good adherence []. The assignment to each of the app groups was randomized by class group. Thus, initially, an equal number of adolescents was assigned to use each app (Pokémon Go: 75/300, 25%; MapMyWalk: 75/300, 25%; Pacer: 75/300, 25%; and Strava: 75/300, 25%). Of the 465 adolescents, 165 (35.5%) were assigned to the CG.
Before starting the mandatory and promoted intervention, the adolescents were provided with instructions on the proper use of step tracker mobile apps. The aim of the first phase was for students, after receiving instructions on the correct use of the apps, to use them in a manner guided by the PE teachers so that they could become familiar with their use and interface. For this purpose, after randomization, a meeting was held with each of the class groups that were assigned to the EG. In this meeting, the students installed the app corresponding to their class group, and an explanation on the functioning of each was provided to them. Any doubts were resolved by the researchers and the PE teachers. The researchers in charge of explaining how the apps worked were not involved in the measurements or subsequent analysis because they knew which student belonged to each app group and which student belonged to the CG. Once each app had been described and its use explained, a training plan was drawn up to be followed during the period of mandatory and promoted use. During the initial week, the adolescents were instructed to achieve a minimum of 5000 steps or cover a distance of at least 3.19 km each time they used the app. It was established that approximately 1565 steps equals 1 km []. This minimum distance was defined to ensure that the adolescents exceeded the sedentary threshold []. The initial distance was progressively increased weekly until reaching a distance of 15,520 steps or 8 km each time they used the app. In addition, the researchers followed up with the PE teachers to ensure that the distance was completed by the students every week.
The adolescents were motivated to use the app for a duration of 10 weeks, aiming for a minimum use of 3 times per week. This frequency aligned with the PA recommendations set forth by the World Health Organization []. The duration of 10 weeks was justified based on previous research with adolescents, in which a short or moderate duration (6-12 wk) was more effective for producing changes than a longer duration [], and to be able to adjust it to the duration of the academic year. To encourage the use of the mobile apps during the period of mandatory and promoted use, PE teachers rewarded participation in the study with up to 1 point in the final PE grade for those who completed the study.
After the mandatory and promoted intervention with the mobile apps, posttest 1 measurements were carried out (T2). This was followed by a 10-week period in which the use of the apps was no longer promoted or mandatory as a PE class assignment, after which posttest 2 (T3) measurements were taken. During this period of nonmandatory and nonpromoted use, the adolescents could continue to use the mobile apps voluntarily, just as they would in their daily lives. The adolescents who continued to use the apps were recorded.
In both the mandatory and promoted and the nonmandatory and nonpromoted periods, a researcher who did not participate in the data collection process recorded the distance (in kilometers) and the number of steps taken by each participant after using the mobile apps daily.
A total of 357 adolescents participated in the final measurements (Pokémon Go: n=47, 13.2%; MapMyWalk: n=45, 12.6%; Pacer: n=53, 14.8%; Strava: n=71, 19.9%; and CG: n=141, 39.5%), while 108 adolescents dropped out of the program (Pokémon Go: n=28, 25.9%; MapMyWalk: n=30, 27.8%; Pacer: n=22, 20.4%; Strava: n=4, 3.7%; and CG: n=24, 22.2%; ). Adolescents who, despite the mandatory and promoted use, did not start using the mobile app were considered to have dropped out, as were those who did not complete at least 25% of the total training volume required because previous research has shown that this is the minimum volume needed to produce significant changes in body composition and fitness variables []. Adolescents who completed at least 25% of the training volume required were retained in their respective app groups, those who exceeded 25% of the required training volume but did not complete the entire intervention received up to half a point in the final PE grade, and those who dropped out or did not complete at least 25% of the training volume did not receive any bonus point in the final PE grade.
Data AnalysisThe normality of the data was assessed using the Kolmogorov-Smirnov test, alongside analyses of skewness, kurtosis, and variance. As the variables exhibited a normal distribution, parametric tests were used for their analysis. Three repeated measures ANOVAs were performed. On the first, the group factor was used as the grouping variable; on the second, the time point factor was used; and on the third, the differences in the changes between the CG and EG at the different time points were assessed. In this way, intra- and intergroup differences were determined for each of the study variables. A subsequent Bonferroni analysis made it possible to determine the statistical differences between each of the pairs compared. Three analyses of covariance were also performed to determine the influence of the covariates maturity status, gender, and specific app used on the results obtained for the study variables. Effect size was analyzed using partial eta-squared (ηp²) and was defined as small (≥0.10), moderate (≥0.30), large (≥0.50), very large (≥0.70) or extremely large (≥0.90). These translate into 0.20, 0.60, 1.20, 2.0 and 4.0 for standardized differences in means []. A P value <.05 was used to establish statistical significance. The data analysis was performed using SPSS software (version 25.0; IBM Corp).
Of the 357 adolescents, 186 (52.1%) were male, and 171 (47.9%) were female. Of the 186 male adolescents, 26 (14%) used Pokémon Go, 35 (18.8%) used Strava, 29 (15.6%) used Pacer, 25 (13.4%) used MapMyWalk, and 71 (19.9%) were in the CG. Of the 171 female adolescents, 21 (12.3%) used Pokémon Go, 36 (21.1%) used Strava, 24 (14%) used Pacer, 20 (11.7%) used MapMyWalk, and 70 (40.9%) were in the CG. The mean age of the male adolescents was 13.91 (SD 1.22) years, with a mean maturity offset of 0.20 (SD 1.39) years. Their mean body mass was 55.68 (SD 13.09) kg, and their mean height was 164.59 (SD 10.07) cm. The mean age of the female adolescents was 13.89 (SD 1.21) years, with a mean maturity offset of 1.50 (SD 0.90) years. Their mean body mass was 52.53 (SD 10.92) kg, and their mean height was 158.76 (SD 6.32) cm.
Of the 216 adolescents in the EG during the period of mandatory and promoted use of the app, only 18 (8.3%) continued to use the apps independently during the nonmandatory and nonpromoted period. The average distance walked by these adolescents was 47.69 (SD 23.80; range 5-200) km in the 10 weeks of nonpromoted and nonmandatory use.
Differences in the EG and CG at the Different Study Time Pointsshows the differences in the measurements taken in the EG and CG at the different study time points (T1, T2, and T3). Significant differences in the PA level were observed exclusively within the EG: it was higher at T2 than at T1 (P<.001) but lower at T3 than at T2 (P=.03). No differences were found between T1 and T3 (P=.47) either in the EG or in the CG in any of the comparisons. In terms of the anthropometric and body composition variables, body mass and height significantly increased in both EG and CG between T1 and T2 (P<.001) and T1 and T3 (P=.002-.008), but no differences were found between T2 and T3 (P=.23-.99). In the sum of 3 skinfolds, the EG showed a significant decrease between T1 and T2 (P=.02), but a significant increase was found between T2 and T3 (P=.03). All corrected girth (P<.001-.049) and muscle mass (P<.001-.007) measurements showed significant increases in both groups between the 3 time points, including hips girth (P<.001-.03). By contrast, BMI (P=.01-.99), sitting height (P=.11-.99), fat mass (P=.07-.99), and waist girth (P=.23-.99) did not show differences in any of the groups in any of the comparisons.
Table 2. Differences in the experimental group (EG) and the control group (CG) during the different study time points (intragroup differences).Variable and groupT1, mean (SD)T2, mean (SD)T3, mean (SD)Mean difference (T1–T2)P valueMean difference (T1–T3)P valueMean difference (T2–T3)P valueF test (df)ηp²Subjective level of physical activityaVO2max: maximal oxygen uptake.
bCMJ: countermovement jump.
Regarding physical fitness, VO2max significantly increased in the EG between T1 and T2 (P<.001), but it significantly decreased between T2 and T3 (P=.005). The CG exhibited no discernible differences. The CMJ score significantly increased at T2 compared to T1 (P=.04) and remained elevated at T3 compared to T1 (P=.03). In the CG, the adolescents showed a higher score at T3 than at T1 (P=.003) and T2 (P=.03). The curl-up test showed a significant increase in the EG between T1 and T2 (P<.001), which remained the same at T3 (P<.001), while in the CG, the increase was smaller and was only observed between T3 and T1 (P=.001). Finally, in the push-up test, an increase was observed in the score between T1 and T2 (P<.001), which remained, although it was less pronounced, at T3 (P=.01) only in the EG ().
As shown in , the covariate maturity status was a determinant factor in the differences found in the EG for the variables PA level, body mass, height, sum of 3 skinfolds, corrected girths, hips girth, waist to hip ratio, muscle mass, VO2max, CMJ test, curl-up test, and push-up test between T1 and T2 (P<.001-.04); for the variables PA level, sum of 3 skinfolds, corrected arm girth, hips girth, muscle mass, and VO2max between T2 and T3 (P<.001-.03); and for the variables height, corrected girths, hips girth, waist to hip ratio, muscle mass, CMJ test, curl-up test, and push-up test between T1 and T3 (P<.001-.04). For the CG, significant differences were observed in body mass, height, BMI, corrected girth, hips girth, waist to hip ratio, and muscle mass between T1 and T2 (P<.001-.02); in corrected girths, hips girth, muscle mass, and CMJ test between T2 and T3 (P<.001-.03); and in height, corrected girths, hips girth, waist to hip ratio, muscle mass, CMJ test, and curl-up test between T1 and T3 (P<.001-.01).
The effect of the covariate gender on the study variables is shown in . It was a determinant factor in the differences found in the EG in PA level, body mass, height, sum of 3 skinfolds, corrected girths, hips girth, waist to hip ratio, muscle mass, VO2max, CMJ test, curl-up test, and push-up test between T1 and T2 (P<.001-.04); in PA level, sum of 3 skinfolds, corrected arm girth, and VO2max between T2 and T3 (P<.001-.04); and in height, corrected girths, hips girth, waist to hip ratio, muscle mass, CMJ test, curl-up test, and push-up test between T1 and T3 (P<.001-.01). In the CG, this covariate was a determinant factor in the differences found in body mass, height, BMI, corrected girths, hips girth, waist to hip ratio, and muscle mass between T1 and T2 (P<.001-.047); in BMI, corrected girths, hips girth, and muscle mass between T2 and T3 (P<.001-.002); and in height, corrected girths, hips girth, waist to hip ratio, muscle mass, CMJ test, and curl-up test between T1 and T3 (P<.001-.02).
The covariate specific app used () was not shown to be influential either in the differences found in PA level or in anthropometry variables and body composition, although it was influential in the changes in VO2max (T1-T2: P=.004; T2-T3: P=.007) and the curl-up test (T1-T2: P<.001; T1-T3: P<.001).
Differences Between the EG and CG in the Study Variables at the Same Time Point During the Research Periodshows the differences between the EG and CG in the study variables at the 3 time points (T1, T2, and T3). The differences at the 3 time points were significant in the sum of 3 skinfolds (P=.01-.03), in hips girth (P=.003-.02), and fat mass (P=.02-.03), as well as in the curl-up test at T2 (P=.047). The rest of the variables showed no significant differences between the 2 groups at any of the time points.
Table 3. Differences between the experimental group (EG) and control group (CG) at the study time points (intergroup differences).Variable and time pointEG, mean (SD)CG, mean (SD)Mean difference (EG–CG)P valueF test (df)ηp²Subjective level of physical activity
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