Original article Adolescents'personal beliefsabout suff icient physical activity aremore closely related to sleep and psychological functioning than self-reported physical activity:A prospectivestudy

Christin Lang ,Serge Brand ,Flora Colledge,Seastian Ludyga,Uwe P¨uhse,

Markus Gerber b,*

a School of Psychology,Flinders University,Adelaide,SA 5001,Australia

b Department of Sport,Exerciseand Health,University of Basel,Basel 4052,Switzerland

c Psychiatric Clinics(UPK),Center for Affective,Stressand Sleep Disorders(ZASS),Universityof Basel,Basel 4012,Switzerland

Abstract Background:Preliminary evidenceamong adultssuggeststhat thewaysin which individualsthink about their physical activity(PA)behavior is more closely associated with their well-being than self-reported PA.This study therefore aimed to examine whether and how self-reported PA and personal beliefs about suff icient PA are associated with sleep and psychological functioning in a sample of Swiss adolescents,using both cross-sectional and prospectivedata.Methods:An overall sample of 864 vocational students(368 girls,17.98±1.36 years,mean±SD)was followed prospectively over a 10-month period.At each measurement occasion,participants f illed in a series of self-report questionnaires to assess their PA levels,their personal beliefs about whether or not they engage in suff icient PA,sleep(insomnia symptoms,sleep quality,sleep-onset latency,and number of awakenings),and psychological functioning(depressive symptoms,quality of life,perceived stress,and mental toughness).Results:Adolescents who believe that they are suff iciently physically active to maintain good health reported more restoring sleep.No differences in sleep were found between adolescents who meet PA recommendations vs.those who do not.Additionally,adolescents who believe that they were suff iciently physically active also reported better psychological functioning.This close relationship between adolescents'beliefsabout their PA involvement and their sleep and psychological functioning wascorroborated in the prospective analyses.Conclusion:Cognitive factors should be studied more intensively when elucidating the relationship among PA,sleep,and psychological functioning in young people,particularly when aiming to develop new exercise interventions targeting psychological outcomes.2095-2546/©2019 Published by Elsevier B.V.on behalf of Shanghai University of Sport.This is an open access article under the CCBY-NC-ND license.(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords:Adolescents;Beliefs;Mental health;Physical activity;Psychological well-being;Public health recommendations;Sleep

1.Introduction

Previous research has shown that among adolescents,higher physical activity(PA)levels are positively associated with restoring sleep.1,2Positive relationships are also observed between higher PA levelsand favorablepsychological functioning,including decreased symptoms of depression,3,4higher quality of life,5,6lower stress levels,7,8and more positive attitudes toward oneself and life in general.9,10However,although thehealth-enhancing potential of PA among adolescentsiswell documented,many adolescents reduce their PA levels during thisperiod of life,11-13particularly femaleadolescents.1

A key issue in developing effective interventions to enhance PA levels among this age group is a deeper understanding of cognitive processesand behavior for the following reasons.First,previous investigations have shown that adolescents are generally aware that suff icient PA is important to maintain good health.14,15In fact,a study among college students showed that improving health was the strongest motivator toward exercise engagement.16Although thisisa desirable outcome,it may partially explain the low interest in engaging in more PA because this population generally reports a good health perception.17,18Second,Corder et al.19have shown that a large proportion of adolescents(53%of girls,34%of boys)inaccurately rate themselves as physically active,although accelerometer data showed that they are not as active as they report.Third,Gerber et al.20havesuggested that thesleep-promoting effects of PA might be less based on behavioral patterns but rather depend on individuals'appraisals about being suff iciently physically active and f it.More specif ically,their study of 862 university students revealed that individuals who evaluated their PA level asinsuff icient experienced moresleep disturbances,ruminated more about unresolved problems,and tended to worry more about diff iculties initiating and maintaining sleep.This pattern of results could not be conf irmed for reported time spent in PA,and whether they had met the health-related PA recommendations.20The generalizability of these f indings is limited,however,because Gerber et al.20assessed a relatively homogeneoussampleof young adults(all university students),focused on one specif ic outcome(sleep),and the study design was cross-sectional.Therefore,our study intends to expand this previous research by examining how self-reported PA and personal beliefs about suff icient PA are associated with a wider range of health outcomes(sleep and psychological functioning),in a younger and broader population(vocational students from varied professional f ields),and by including prospective data.Gaining a deeper understanding of the consequences of these personal beliefs may help improve current approaches aimed at developing effective health interventions targeting adolescents PA levels,sleep,and psychological functioning.

Given this background,the general purpose of the present study was to examine whether and how self-reported PA and personal beliefs about suff icient PA are associated with sleep and psychological functioning in a sample of Swiss adolescents,using both cross-sectional and prospective data.Based on previous literature,21we expected participantswho met the PA recommendationsoutlined by the Centersfor Disease Control and Prevention(CDC;http://www.cdc.gov/physicalactiv ity/basics/)to show better sleep quality and psychological functioning than peers who reported PA levels below these recommendations.Additionally,weexpected that positivepersonal beliefs about suff icient PA would be associated with restoring sleep and favorable psychological functioning in both cross-sectional and prospectivedata.20

2.Methods

2.1.Participantsand procedures

The population is based on a(nonrepresentative)convenience sample of 2 vocational schools located in the Germanspeaking part of Switzerland.Students from both schools volunteered to take part in a prospective study(n=434 students from school A,n=430 students from school B).Students with varying professional specialties were included(e.g.,polytechnicians,retail assistants,industrial clerks,structural draftsmen,hairdressers).

The questionnaires were completed in a quiet classroom in a group setting.A researcher was present to answer questions from the students.All participants were assured conf identiality and provided written informed consent.All procedures were in line with the Declaration of Helsinki,and the local ethical committee(Ethics Committee of Northwestern and Central Switzerland;EKNZ)approved the study.At baseline and after 10 months,participants completed 2 identical batteries of psychological questionnairesin paper-and-pencil format.The f irst measurement took place approximately 2 weeks after the beginning of the school year(September),whereas the second measurement was performed about 1 month before the end of the school year(May).The dropout rate from baseline(n=1242)to follow-up was 30%(n=378),leading to an overall sample of 864 participants,including 368 girlsand 496 boys(age:17.98±1.36 years,body mass index(BMI)=22.13±2.97 kg/m2).To be included,all participants had to have valid baseline data for both self-reported PA and personal beliefsabout suff icient PA.

2.2.Measures

2.2.1.PAlevelsand personal beliefsabout suff icient PA

Items from the International Physical Activity Questionnaire-Short Form(IPAQ-SF)22were used to assess selfreported moderate-to-vigorous PA(MVPA).Previousresearch with adolescents showed that the predictive value of this instrument for cardiorespiratory f itnessissimilar to accelerometers.23Participants reported the number of days(from 0 to 7)for(a)vigorous PA(exercise or participation in high-intensity activitiesand sportssuch asaerobicsor fast bicycling)and(b)moderate PA(e.g.,bicycling at a regular pace,low-intensity sports).Participants also indicated the average duration(in minutes)for the days they engaged in these activities.Multiplication of frequency and duration scores resulted in an estimate of weekly hours invested in vigorous PA and moderate PA.The CDCguidelineswereused to dividethewholesample into adolescents meeting PA recommendations and adolescents failing to meet these recommendations.Adolescents had to report either(a)at least 150 min of moderate-intensity PA per week,(b)75 min of vigorous-intensity aerobic activity per week,or(c)an equivalent mix of moderate-and vigorousintensity aerobic activity(of at least 150min per week)to meet PA recommendations(see http://www.cdc.gov/physica lactivity/everyone/guidelines/adults.html).This classif ication was used to successfully discriminate between adolescents with low vs.high burnout symptomsin previousresearch.24

Personal beliefs about suff icient PA were assessed with a single item from the Swiss Health-Enhancing Physical Activity(HEPA)Survey 1999,25which asked participants whether they thought that their current PA level was suff icient for the maintenanceof good health(0=no,1=yes).

2.2.2.Sleep

Sleep complaints were assessed with the Insomnia Severity Index,26which is a brief insomnia screening measure that is often used in treatment research as an outcome measure.Answersaregiven on 5-point rating scalefrom 0(not at all)to 4(very much).Because of time constraints,only 4 of the 7 items were considered.These items refer to the criteria for insomnia described in the Diagnostic and Statistical Manual of Mental Disorders IV27by measuring diff iculty in falling asleep,diff iculties maintaining sleep,early morning awakening,and low satisfaction with sleep(e.g.,“How often did you feel impaired during the last 2 weeks due to problems with falling asleep?”).Higher sum scoresref lectmoresleep complaints.

Additional information about sleep quality was collected with a7-item German adaptation of the Pittsburgh Sleep Quality Index.28All items of this index referred to 2 typical weekdays and were anchored on an 8-point Likert scale referring to emotional states just after waking up in the morning(perceived quality of sleep,restoration,and mood),during daytime(sleepinessand concentration),and beforegoing to bed(sleepiness and mood).Possible answers ranged from 1(e.g.,very bad sleep quality)to 8(e.g.,very good sleep quality).Thesum score was calculated across the 7 items to obtain an overall sleep quality score,with higher scores ref lecting better overall sleep quality.In addition,sleep onset latency(in minutes)and thenumber of awakeningsduring nighttimewereassessed.

2.2.3.Psychological functioning

Depressive symptoms were measured with a 15-item short version of the Center for Epidemiologic Studies Depression Scale(CES-D),29which assesses cognitive,emotional,motivational,behavioral,and somatic aspects associated with depression(e.g.,During the past week,“I felt sad”,“I felt lonely”,or“I felt depressed”).Evidence of the validity and adequate internal consistency of this instrument has been reported previously.30Answersweregiven on a 4-point Likert scale from 0(＜1 day/week)to 3(5-7 days/week).Items were summed to obtain an overall score,with higher scores ref lecting more depressive symptoms.The critical cutoff for the German version of the CES-D is 17,with 94%of the individuals abovethisthreshold being diagnosed with depression.30

The Adolescent Stress Questionnaire31was used to assess adolescents'stress.Becauseof time constraints,a30-item version was used,which proved to have acceptable psychometric properties.32,33Responseswere given on a 5-point Likert scale ranging from 1(not at all stressful or irrelevant)to 5(very stressful)in reference to the past 3 months and for a broad range of stressors(e.g.,arguments at home,teachers expecting too much from them,pressureto f itin with peers,concernsabout their future).Itemsweresummed to obtain an overall score,with higher scoresref lecting higher perceived stresslevels.

Quality of life was measured with 3 items from the Satisfaction with Life Scale.34A sample item is:“In most waysmy life is close to my ideal.”Possible answers ranged from 1(strongly disagree)to 7(strongly agree).Previousstudieswith various populations demonstrated the validity and adequate reliability of the Satisfaction with Life Scale.34A sum score wasbuilt,with higher scoresref lecting higher quality of life.

Mental toughness was assessed with the 18-item short form of the Mental Toughness Questionnaire(MTQ).35Mental toughness measures a person's tendency to cope with the demands of environmental stressors(e.g.,“Even when under considerablepressure Iusually remain calm,”“Igenerally feel in control”).35Mental toughness is considered as an indicator of mental health because previous studies revealed that individuals with high scores reported lower stress levels,less frequent depressive symptoms,and higher quality of life.32,36The short and long forms of the MTQ were highly correlated in previous studies,35and the validity and reliability of the MTQ instruments has been documented.32Responses were given on a 5-point Likert scale from 1(strongly disagree)to 5(strongly agree).A sum score was calculated,with higher scores ref lecting higher mental toughness.

2.2.4.Confounders

School(0=School A,1=School B),age(in years),sex(0=female,1=male),family f inancial situation compared to peers(continuous variable from 1=much worse to 5=much better),and BMI were considered as confounders.BMI was calculated based on participants'self-reported body weight(in kilograms)and body height(in meters),with the following formula:body weight/body height2(kg/m2).

2.3.Data analysis

Dropout analyses were performed using univariate analyses of variance(ANOVAs)based on baseline data,comparing students who dropped out and peers who took part in the baseline and follow-up data assessment(no covariates were considered in theseanalyses).Descriptivestatisticswerecalculated for all study variables.In a f irst step,2 separate two-way multivariate analyses of covariance(MANCOVAs)were performed(for sleep and psychological functioning)to test whether adolescentswho meet PA recommendationsor who believe that they are suff iciently physically active report more favorable sleep and psychological functioning.In a second step,a series of two-way univariate analyses of covariance(ANCOVAs)were carried out to examine group differences separately for each outcome.In all modelsthat included covariates(MANCOVAs and ANCOVAs),thefollowing variableswereincluded asrandom effects:school,age,sex,family f inancial situation,and BMI.Finally,to examine whether positive beliefs about suff icient PA and meeting PA recommendations(assessed at baseline)predict sleep and psychological functioning 10 months later,hierarchical regression analyses were performed.Variables were introduced in the following order:baseline levels of sleep or psychological functioning(Step 1),confounders(Step 2),self-reported PA(Step 3),and personal beliefs about suff icient PA(Step 4).Acrossall analyses,thelevel of probability wasset at p＜0.05.All statisticswerecalculated with SPSS Version 24.0 for Apple Mac.(IBM Corp.,Armonk,NY,USA).

3.Results

3.1.Dropout analyses

At baseline,dropouts were older,F(1,1240)=19.58,p＜0.01, η2=0.02, reported higher insomnia scores,F(1,1240)=7.00,p＜0.01,η2=0.01,and perceived more stress,F(1,1240)=5.21,p＜0.05,η2=0.00.By contrast,no differences were observed with regard to school,sex,family f inancial situation,BMI,sleep quality,sleep-onset latency,number of awakenings,depression,quality of life,and mental toughness(all p＞0.05).

Table1Descriptivestatisticsand psychometric propertiesof all outcomevariablesat baseline.

3.2.Descriptive statistics

Descriptive statistics for all outcome variables at baseline are shown in Table 1.In total,14%(n=121)of the students exceeded the critical value of＞17 on the CES-D,35%(n=300)did not meet PA recommendations,and 33%(n=289)felt that they were insuff iciently physically active.Among adolescents above the PA recommendations(n=564),75%(n=425)correctly believed that they were suff iciently physically active,whereas25%(n=139)did not.By contrast,among students who were below the PA recommendations(n=300),only 50%(n=150)accurately rated their PA level asbeing too low(Table2).

3.3.Sleep and psychological functioning:associationswith adolescents'PAlevelsand personal beliefsabout suff icient PA

3.3.1.Cross-sectional analyses

With regard to sleep,the MANCOVA yielded a signif icant multivariatemain effect for personal beliefsabout suff icient PA, Wilks-Lambda:F(4,823)=5.08,p＜0.01,η2=0.02.Theresults of the univariate ANCOVAs(see the next paragraph for more detail)indicate that students who believe that they are suff iciently physically active reported better sleep.No signif icant main effect was found for self-reported PA,Wilks-Lambda:F(4,823)=2.03,p=0.09,η2=0.01.Similarly,the interaction term between self-reported PA and personal beliefs about suff icient PA was nonsignif icant,Wilks-Lambda:F(4,823)=0.81,p=0.52,η2=0.00.With regard to psychological functioning,a multivariatemain effect occurred for personal beliefsabout suff icient PA,Wilks-Lambda:F(4,852)=10.59,p＜0.01,η2=0.05,but not for PA,Wilks-Lambda:F(4,852)=0.86,p=0.49,η2=0.00.Similarly,no signif icant interaction effect was found,Wilks-Lambda:F(4,852)=1.15,p=0.33,η2=0.01.Theunivariate ANCOVAs(see the next paragraph for more detail)indicated that adolescents who believe that they are suff iciently physically activereport better psychological functioning.

Table 2 provides the descriptive statistics separately for adolescentswho wereabove vs.below the PA recommendations.

Table2 Means and SD of dependent variables at baseline,and ANCOVAs comparing adolescents below vs.above PA recommendations,and adolescents who believe vs.do not believethat they aresuff iciently physically active,aswell asinteractionsbetween these2 factors.

Table 3Hierarchical multiple regression analyses predicting sleep and psychological functioning at follow-up with baseline scores of sleep and psychological functioning, social and demographic background, self-reportedPA, and personal beliefs about sufficient PA as predictor variables.

The inferential statistics of the univariate ANCOVAs are also presented in Table2.After controlling for school,sex,age,family f inancial situation,and BMI,the univariate two-way ANCOVAs showed a main effect for personal beliefs about suff icient PA acrossalmost all outcomes.In contrast,for self-reported PA,a signif icant main effect occurred only for 2 variables(number of awakenings and mental toughness).Thus,adolescents who believe that they are suff iciently physically active scored higher on all indicators of sleep and psychological functioning,even when simultaneously considering self-reported PA and after controlling for confounders.Finally,independent of their personal beliefs,adolescents who met the PA recommendations reported a lower number of awakenings and achieved higher mental toughness scores.No signif icant two-way interaction effects occurred for any of theoutcomevariables.

3.3.2.Prospectiveanalyses

Table 3 provides the results of the hierarchical regression analyses.Levels of explained variance in the total model(R2)ranged from 12.2%(number of awakenings)to 33.3%(insomnia).After controlling for baseline levels of sleep or psychological functioning(Step 1)and confounders(Step 2),meeting PA recommendations was associated with fewer depressive symptoms and higher mental toughness at follow-up(Step 3).When personal beliefs were introduced in the fourth step,this variable explained additional variance in insomnia,sleep quality,depressive symptoms,quality of life,and mental toughness.Positive personal beliefs about suff icient PA at baseline were associated with more restoring sleep and psychological functioning after 10 months of follow-up.None of the interaction terms between PA and personal beliefs about suff icient PA weresignif icant(datanot shown).

4.Discussion

The key f indings of the present study are that adolescents who believe that they are suff iciently physically active to maintain good health report more restoring sleep and better psychological functioning.The differences in sleep and psychological functioning between adolescents who believe that they engagein suff icient PA vs.peerswho do not wascorroborated in the prospective analyses,highlighting that personal beliefs about suff icient PA were a stronger predictor of sleep and psychological functioning than self-reported PA.These f indings support the notion that cognitive factors should be studied more intensively when elucidating the relationship among PA,sleep,and psychological functioning in young people,particularly when aiming to develop new exercise interventions targeting psychological outcomes.In other words,although the benef icial effects of MVPA for health have been well documented over the past few decades,37,38simply increasing the levels of PA may not obtain the full return on investment with respect to improving sleep and psychological functioning.

Our data only partly support previous research,39,40showing that physically active adolescents report more restoring sleep.Although we did not f ind a multivariate main effect for self-reported PA,a univariate main effect indicated that physically active adolescents report fewer awakenings after sleep onset.Moreover,a univariate main effect occurred for mental toughness,showing that physically active adolescents are more mentally tough.This pattern of results accords well with previous research9and is important because mental toughness proved to be associated with stress resilience9and psychological well-being in young people.41Nevertheless,the differences between adolescents above vs.below the PA recommendations were of relatively small magnitude,as highlighted previously by Biddle and Asare42in their review on therelationship between PA and mental health in children and adolescents.

Our data strongly support the notion that positive personal beliefsabout suff icient PA are associated with more restoring sleep and favorable psychological functioning.Accordingly,we corroborated adult research showing that a perceived lack of PA is more strongly related to mental health outcomes than self-reported PA.20Importantly,our study expands adult research in the sense that we were also able to provide prospective evidence showing that adolescents'positive beliefs about their PA involvement predicted fewer sleep complaints,better sleep quality,fewer depressive symptoms,greater quality of life,and more mental toughness after 10 months of follow-up.Against evidence reported in previous research,3,43self-reported PA at baseline wasweakly,but statistically signif icantly,associated with decreased depressive symptoms at follow-up.The diverging results found in our study and previous research might be due to the fact that in the present sample,we assessed older adolescents in vocational education and training,whereas prior investigations mostly examined younger students attending academic schools.That self-reported PA was not associated across time with quality of life and sleep is at odds with previous research.2,6,40Nevertheless,these divergences might be attributable to the fact that in our study,personal beliefs about adolescents'PA levels were considered for the f irst timein combination with self-reported PA.

As mentioned previously,individual appraisals about being suff iciently physically active may be closely related to mental health outcomes,as mental health parameters are also inf luenced by cognitive-emotional factors.44For instance,cognitive models of insomnia claim that cognitive processes such as attention,perception,memory,reasoning,beliefs,attributions,and expectations play a fundamental role in the onset and maintenance of sleep complaints.45Moreover,researchers have emphasized that depressive episodes might result in a progressive change of dysfunctional information processing,46which might lead to particularly negative belief structures.47Furthermore,that adolescents with positive beliefs about their PA involvement reported higher degrees of mental toughness is not surprising,because mental toughnessis per se def ined asa cognitive-emotional mind-set characterized by the feeling of being inf luential in daily life experiences,by staying committed when problems occur,and by the belief that coping with change offers the opportunity for personal growth.35Thus,it can be assumed that adolescents with positive beliefs about their level of PA also score more highly on psychological constructs such as selfeff icacy,48optimism,49and self-control,50which might contribute to increased psychological functioning and sleep.In a similar vein,a recent study showed that adult exercisers who believed that regular exercising was healthy more strongly benef ited from exercise on both the subjective and neurophysiological level,compared with participants who had less positive beliefs about the health-enhancing potential of regular exercise.51Oberste et al.52have also shown that exerciseinduced facilitation of cognitive function is not based on physiological factors only,so that the expectation of such an effect might be necessary to elicit benef its to cognitive and mental health.This can be understood as an indication that the belief of engaging in a healthy behavior promotes psychological well-being.However,it cannot be ruled out that psychological functioning has an impact on personal beliefs about PA.In this respect,adolescents with high psychological functioning and high sleep quality have no reason to doubt that their actual behavior complies with a behavior that allowsthe maintenance of good health.

Finally,our f indings accord well with a previous study among British adolescents,showing that many youngsters tend to over-or underestimate their PA levels.Although Corder et al.19reported that between 34%and 53%inaccurately rated themselves as being suff iciently physically active,this percentage amounted to 50%in the present sample.However,our study also showed that,among students who in fact met recommended levels of PA,about one third inaccurately rated themselves as being insuff iciently active.We assume that many adolescents are not aware of current PA recommendations.25Moreover,assessing PA via selfreports is a challenge among the adolescent population,53although the validity of the IPAQ hasbeen established previously.23Therefore,it was no surprise that self-reported and subjective beliefs about suff icient PA were not“a perfect match”in the present population.To summarize,our crosssectional f indings suggest that cognitive-emotional processes and appraisalsaremoreclosely related to psychological functioning and sleep in adolescentsthan their self-reported levels of PA.

The strengths of this study were(a)its relatively large sample size;(b)the use of standardized and validated measures to assess PA,sleep,and psychological functioning;(c)the reference to internationally accepted standards to categorize adolescents into groups that were above vs.below PA recommendations;(d)the inclusion of an item to assess personal beliefs about suff icient PA that has proved useful in previous research with young adults;(e)the application of multivariate teststo avoidα-error inf lation;and(f)the inclusion of prospective data to corroborate cross-sectional relationships.

Despitethesestrengths,we acknowledgethat the resultsof the present study should be interpreted in light of certain limitations.First,the assessment of PA was based on students'self-reports.Although previous studies showed that many people f ind it diff icult to accurately estimate their PA levels,54researchers have shown that the IPAQ-SFisreasonably well correlated with physical f itness.23However,any selfreported PA is prone to memory bias.55Therefore,adolescents with better memory capacity might be able to recall PA more correctly;at the same time,better memory is associated with improved psychological functioning.56It cannot be ruled out that this link partially inf luenced the association found between psychological functioning and meeting the PA guidelines.Second,the CDC offers separate PA recommendations for children(6-17 years old)and adults(18-64 years old)(see http://www.cdc.gov/physical/activity/basics).Although some of the adolescents were younger than 18 years in the present sample,we decided to use the adult standards.This seemed justif ied because Swiss vocational students typically have working hours similar to those of adult employees.Third,a specif ic focus was placed on vocational students.Because a majority of Swiss adolescents(≥70%)attend vocational schools,57this is a relevant target population.However,caution is needed when generalizing the f indings to high school students,younger children,or older student populations.Moreover,although our sample included students with heterogeneous professional focus,we acknowledge that our population was based on convenience sampling and may therefore not be representative of the entire population of vocational students in Switzerland(e.g.,students from other schools in the German-or French-speaking part of Switzerland)or in other German-speaking countries with similar VET systems.Fourth,although we found that positive baseline personal beliefs about suff icient PA predicted favorable sleep and psychological functioning at follow-up,the prospective analysesdid not account for possible changes in PA over time.58Moreover,we did not systematically collect information about reasons for dropout.Accordingly,wecan only speculatewhy dropoutswereolder,reported higher stresslevels,and had higher insomniascores,which limits the generalizability of the f indings.However,similar main effects for personal beliefs about suff icient PA were found for all outcome variables if dropouts were included in the cross-sectional analyses(results provided as supplementary material online).Finally,our regression model was based on the premise that PA would predict sleep and psychological functioning.However,it is just as plausible that sleep and psychological functioning affect adolescents'PA behavior and personal beliefs about suff icient PA.59First,previous research with younger and older populations has shown that the relationship between depressive symptoms and PA is most likely reciprocal.58,60,61Second,scholars have emphasized previously that among depressed people,dysfunctional cognitive-emotional processes such as feelings of hopelessness,pessimism,and a tendency to postpone tasks might negatively affect the motivation and selfcontrol capacity needed to initiate and maintain regular PA.44Accordingly,previous studies showed that patients with major depressive disorders reported lower exercise intentions,lower exercise-related self-eff icacy,morenegativeoutcomeexpectations,and increased perceptionsof situational barriers.62

The present study explored new territory by examining the links between PA,personal beliefs about suff icient PA,sleep, and psychological functioning.Although the study provides novel insights,from a practical perspective,the data raise just as many questions as they provide answers:for instance,is it desirable that adolescents have positive personal beliefs about suff icient PA without being suff iciently physically active?Our answer is clearly“no”,because many studies have shown that regular PA is positively associated with relevant health outcomes such as cardiovascular risk markers,63lower risks of overweight/obesity,64and an increased capacity to deal with stress.65,66Research also shows that single PA episodes have positive effects on executive function,67which in turn is an important indicator of academic achievement.68Another question is whether sleep and psychological functioning will be impaired among adolescents who inaccurately overestimate their PA levels if they shift toward more realistic personal beliefs about suff icient PA.Although it is not currently possible to answer this question,we f irmly believe that adolescents should betaught in detail how much PA is needed to maintain good health,because poorly def ined goals may impede goaloriented behavior.69,70This is particularly important for adolescents who have negative beliefs about their own PA levels,although they fulf ill the recommendations outlined by the CDC.We also believe that moresystematic effortsare needed to teach students how they can monitor their PA levels(e.g.,via pedometers and accelerometers)or visualize their physical f itness to become more aware of possible improvements.71As outlined by Kanfer and Saslow,72such an approach might be helpful in shifting self-evaluation from an unfavorable to a more favorable one.In line with this notion,interventions have shown that it is possible to increase adolescents'PA levels by using pedometers in combination with goal-setting strategies.73-75

5.Conclusion

This is the f irst study showing that adolescents'beliefs about their own PA behavior predict variancein sleep and psychological functioning beyond self-reported PA.Therefore,cognitive factors should be explored more extensively in the study of the relationship between PA and mental health.Finally,more research is needed to examine how adolescents can learn to more realistically rate their PA behavior,and how changesin these self-evaluationsmay affect their well-being.

Acknowledgment

Thisstudy wassupported by agrant from the Swiss Federal Off icefor Sports(BASPO).

Authors'contributions

CL made substantial contributionsto conception and design of the study,was responsible for the acquisition of data,was responsible for the analysis and interpretation of data,drafted the manuscript SB made substantial contributions to conception and design of the study,was responsible for the analysis and interpretation of data,critically reviewed and revised the initial draft;FC was responsible for the analysis and interpretation of data,critically reviewed and revised the initial draft;SL was responsible for the analysis and interpretation of data,critically reviewed and revised the initial draft;UPand MG made substantial contributions to conception and design of the study,critically reviewed and revised the initial draft.All authors have read and approved the f inal version of the manuscript,and agree with theorder of presentation of the authors.

Competinginterests

Theauthorsdeclarethat they haveno competing interests.

Supplementarymaterials

Supplementary material associated with this article can be found,in theonlineversion,at doi:10.1016/j.jshs.2018.03.002.

References

1.Lang C,Brand S,Feldmeth AK,Holsboer-Trachsler E,P¨uhse U,Gerber M.Increased self-reported and objectively assessed physical activity predict sleep quality among adolescents.Physiol Behav 2013;120:46-53.

2.Kalak N,Gerber M,Kirov R,Mikoteit T,Yordanova J,P¨uhse U,et al.Daily morning running for 3 weeks improved sleep and psychological functioning in healthy adolescents compared with controls.J Adolesc Health 2012;51:615-22.

3.Rothon C,Edwards P,Bhui K,Viner RM,Taylor S,Stansfeld SA.Physical activity and depressive symptoms in adolescents:a prospective study.BMCMed 2010;8:32.doi:10.1186/1741-7015-8-32.

4.Johnson CC,Murray DM,Elder JP,Jobe JB,Dunn AL,Kubik M,et al.Depressive symptoms and physical activity in adolescent girls.Med Sci Sports Exerc 2008;40:818-26.

5.Anokye NK,Trueman P,Green C,Pavey TG,Taylor RS.Physical activity and health related quality of life.BMC Public Health 2012;12:624.doi:10.1186/1471-2458-1112-1624.

6.Gopinath B,Hardy LL,Baur LA,Burlutsky G,Mitchell P.Physical activity and sedentary behaviors and health-related quality of life in adolescents.Pediatrics2012;130:167-74.

7.Mojord IE,Moksnes UK,Eriksen L,Espnes GA.Stress and happiness among adolescents with varying frequency of physical activity.Perc Mot Skills2011;113:631-46.

8.Park S.Associationsof physical activity with sleep satisfaction,perceived stress,and problematic Internet use in Korean adolescents.BMC Public Health 2014;14:1143.doi:10.1186/1471-2458-1114-1143.

9.Gerber M,Kalak N,Lemola S,Clough PJ,P¨uhsea U,Elliot C,et al.Adolescents'exercise and physical activity are associated with mental toughness.Ment Health Phys Act 2012;5:35-42.

10.Brand S,Kalak N,Gerber M,Clough PJ,Lemola S,Bahmani DS,et al.During early to mid adolescence,moderateto vigorousphysical activity is associated with restoring sleep,psychological functioning,mental toughnessand malegender.JSport Sci2017;35:426-34.

11.Caspersen CJ,Pereira MA,Curran KM.Changes in physical activity patterns in the United States,by sex and cross-sectional age.Med Sci Sports Exerc 2000;32:1601-9.

12.Meyer U,Roth R,Zahner L,Gerber M,Puder JJ,Hebestreit H,et al.Contribution of physical education to overall physical activity.Scand J Med Sci Sports2013;23:600-6.

13.van Mechelen W,Twisk JW,Post GB,Snel J,Kemper HC.Physical activity of young people:the Amsterdam Longitudinal Growth and Health Study.Med Sci Sports Exerc 2000;32:1610-6.

14.Watson B.Youth beliefs about health and physical activity.J Appl Dev Psychol 1992;13:257-69.

15.Barker-Ruchti N,Barker D,Sattler S,Gerber M,P¨uhse U.Sport—“it's just healthy”:locating healthism within discourses of social integration.J Ethnic Migration Stud 2013;39:759-72.

16.Kilpatrick M,Hebert E,Bartholomew J.College students'motivation for physical activity:differentiating men's and women's motives for sport participation and exercise.JAm Coll Health 2005;54:87-94.

17.Scheidt P,Overpeck MD,Wyatt W,Aszmann A.Adolescents'general health and wellbeing.In:Currie C,Hurrelmann K,Settertobulte W,Schmidt R,Todd J,editors.Health and health behaviour among young people.Geneva:World Health Organization;2000.p.34-8.

18.Sygusch R.Youth sport-youth health.An overview of the current state of research (Jugendsport-Jugendgesundheit).Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz2005;48:863-72.[in German].

19.Corder K,van Slujis EM,Goodyer I,Ridgway CL,Steele RM,Bamber D,et al.Physical activity awareness of British adolescent.Arch Pediat Adolesc Med 2001;165:603-9.

20.Gerber M,Brand S,Holsboer-Trachsler E,P¨uhse U.Fitness and exercise as correlates of sleep complaints.Is it all in our minds?Med Sci Sports Exerc 2010;43:893-901.

21.Foti KE,Eaton DK,Lowry R,McKnight-Ely LR.Suff icient sleep,physical activity,and sedentary behaviors.Am J Prev Med 2011;41:596-602.

22.Craig CL,Marshall AL,Sj¨ostr¨om M,Bauman AE,Booth ML,Ainsworth BE,et al.International Physical Activity Questionnaire:12-country reliability and validity.Med Sci Sports Exerc 2003;35:1381-95.

23.Ottevaere C,Huybrechts I,De Bourdeaudhuij I,Sj¨ostr¨am M,Ruiz JR,Ortega FB,et al.Comparison of the IPAQ-A and Actigraph in relation to VO2maxamong European adolescents:the HELENA study.J Sci Med Sport 2011;14:317-24.

24.Elliot C,Lang C,Brand S,Holsboer-Trachsler E,P¨uhse U,Gerber M.The relationship between meeting vigorousphysical activity recommendations and burnout symptoms among adolescents:an exploratory study with vocational students.JSport Exerc Psychol 2015;37:180-92.

25.Martin BW,M¨ader U,Calmonte R.Attitudes,knowledge and behavior of the Swiss population with regard to physical activity.Findings from the Physical Activity Survey 1999(Einstellung,Wissen und Verhalten der Schweizer Bev¨olkerung bez¨uglich k¨orperlicher Aktivit¨at:Resultate aus dem Bewegungssurvey 1999).Schweiz Zs Sportmed Sporttraumatol 1999;47:165-9.[in German].

26.Gerber M,Lang C,Lemola S,Colledge F,Kalak N,Trachsler EH,et al.Validation of the German version of the Insomnia Severity Index in adolescents,young adults and adult workers:results from three cross-sectional studies.BMC Psychiatry 2016;16:174.doi:10.1186/s12888-12016-10876-12888.

27.American Psychiatric Association.DSM-IV.Diagnostic and Statistical Manual of Mental Disorders.4th ed.Washington,DC:American Psychiatric Association;2000.

28.Buysse DJ,Reynolds CF,Monk TH,Berman SR,Kupfer DJ.The Pittsburgh Sleep Quality Index:new instrument for psychiatric practice and research.Psychiatry Rev 1989;28:193-213.

29.Radloff LS.The CES-D Scale:a self-report depression scale for research in the general population.Appl Psychol Measurement 1977;1:385-401.

30.Hautzinger M,Bailer M.CES-D,Centersfor Disease Control Depression Scale(ADS,Allgemeine Depressionsskala).G¨ottingen:Beltz;1992.[in German].

31.Byrne DG,Davenport SC,Mazanov J.Prof iles of adolescent stress:the development of the Adolescent Stress Questionnaire(ASQ).J Adolesc 2007;30:393-416.

32.Gerber M,Kalak N,Lemola S,Clough PJ,Perry JL,P¨uhse U,et al.Are adolescents with high mental toughness levels more resilient against stress?Stress Health 2013;29:164-71.

33.Lang C,Feldmeth AK,Brand S,Holsboer-Trachsler E,Pu¨hse U,Gerber M.Stressmanagement in physical education class:improved coping skills can mediate stress perceptions in adolescents.J Teach Phys Educ 2016;35:149-58.

34.Pavot W,Diener E.The Satisfaction with Life Scale and the emerging construct of lifesatisfaction.JPos Psychol 2008;3:137-52.

35.Clough P,Earle K,Sewell D.Mental toughness:the concept and its measurement.In:Cockerill I,editor.Solutions in sport psychology.London:Thomson Learning;2002.p.32-46.

36.Gerber M,Brand S,Feldmeth AK,Lang C,Elliot C,Trachsler EH,etal.Adolescentswith high mental toughnessadapt better toperceived stress:alongitudinal study with Swissvocational students.Pers Ind Diff 2013;54:808-14.

37.Bouchard C.Physical activity and health:introduction to the doseresponsesymposium.Med Sci Sport Exerc 2001;33(Suppl.6):S347-50.

38.Katzmarzyk PT.Physical activity,sedentary behavior,and health:paradigm paralysisor paradigm shift?Diabetes2010;59:2717-25.

39.Brand S,Beck J,Gerber M,Hatzinger M,Holsboer-Trachsler E.Evidence of favorable sleep-EEG patterns in adolescent male vigorous football playerscompared to controls.World JBiol Psychiatr 2010;11:465-75.

40.Lang C,Kalak N,Brand S,Holsboer-Trachsler E,P¨uhse U,Gerber M.The relationship between physical activity and sleep from mid adolescence to early adulthood.A systematic review of methodological approaches and meta-analysis.Sleep Med Rev 2016;58:32-45.

41.Brand S,Kalak N,Gerber M,Sj¨ostr¨om M,Ruiz JR,Ortega FB,etal.During early and mid-adolescence,greater mental toughness is related to increased sleep quality and quality of life.JHealth Psychol 2016;21:905-15.

42.Biddle SJ,Asare M.Physical activity and mental health in children and adolescents:areview of reviews.Br JSports Med 2011;45:886-95.

43.Toseeb U,Brage S,Corder K,Dunn VJ,Jones PB,Owens M,et al.Exercise and depressive symptoms in adolescents:a longitudinal cohort study.JAMAPediatrics2014;168:1093-100.

44.Gerber M,Holsboer-Trachsler E,P¨uhse U,Brand S.Exercise is medicine for patientswith major depressivedisorders.But only if the“pill”istaken!

Neuropsychiatr Dis Treat 2016;12:1977-81.

45.Harvey AG.A cognitive model of insomnia.Behav Res Therapy 2002;40:869-94.

46.Segal ZV,Williams JM,Teasdale JD,Gemar M.A cognitivescienceperspective on kindling and episodesensitization in recurrent affective disorder.Psychol Med 1996;26:371-80.

47.Monroe KL,Harkness SM.Life stress,the“kindling”hypothesis,and the recurrence of depression:considerations from a life stress perspective.Psychol Rev 2005;112:417-45.

48.Bandura A.Self-eff icacy:the exercise of control.New York,NY:Freeman;1997.

49.Scheier MF,Carver CS.Dispositional optimism and physical well-being:the inf luence of generalized outcome expectancies on health.J Personal 1987;55:169-210.

50.Tangney JP,Baumeister RF,Boone AL.High self-control predicts good adjustment,lesspathology,better grades,and interpersonal success.JPersonal 2004;72:271-322.

51.Mothes H,Leukel C,Jo HG,Seelig H,Schmidt S,Fuchs R.Expectations affect psychological and neurophysiological benef its even after a single bout of exercise.JBehav Med 2017;40:293-306.

52.Oberste M,Bloch W,H¨ubner S,Zimmer P.Do reported effects of acute aerobic exercise on subsequent higher cognitive performances remain if tested against an instructed self-myofascial releasetraining control group?A randomized controlled trial.PLoSOne2016;11:e0167818.doi:10.1371/journal.pone.0167818.

53.Corder K,Ekelund U,Steele RM,Wareham NJ,Brage S.Assessment of physical activity in youth.JAppl Physiol 2008;105:977-87.

54.Lee PH,Macfarlane DJ,Lam TH,Stewart SM.Validity of the International Physical Activity Questionnaire Short Form(IPAQ-SF):a systematic review.Int J Behav Nutr Phys Act 2011;8:115.doi:10.1186/1479-5868-1188-1115.

55.Prince SA,Adamo KB,Hamel ME,Hardt J,Connor Gorber S,Tremblay M.A comparison of direct versusself-report measuresfor assessing physical activity in adults:a systematic review.Int J Behav Nutr Phys Act 2008;5:56.doi:10.1186/1479-5868-5-56.

56.Llewellyn DJ,Lang IA,Langa KM,Huppert FA.Cognitive function and psychological well-being:f indings from a population-based cohort.Age Ageing 2008;37:685-9.

57.Organization for Economic Co-operation and Development(OECD).Education at a glance 2016:OECD indicators.Paris:OECD Publishing;2016.

58.Lindwall M,Gerber M,Jonsdottir I,B¨orjesson M,Ahlborg GJ.The relationships of change in physical activity with change in depression,anxiety,and burnout:a longitudinal study of Swedish healthcare workers.Health Psychol 2014;33:1309-18.

59.Motl RW,Birnbaum AS,Kubik MY,Dishman RK.Naturally occurring changes in physical activity are inversely related to depressive symptoms during early adolescence.Psychosom Med 2004;66:336-42.

60.Lindwall M,Larsman P,Hagger MS.The reciprocal relationship between physical activity and depression in older European adults:a prospective cross-lagged panel design using SHARE data.Health Psychol 2011;30:453-62.

61.Jerstad SJ,Boutelle KN,Ness KK,Stice E.Prospective reciprocal relations between physical activity and depression in female adolescents.J Consult Clin Psychol 2011;78:268-72.

62.Kr¨amer L,Helmes AW,Bengel J.Understanding activity limitations in depression:integrating the concepts of motivation and volition from health psychology into clinical psychology.Eur Psychologist 2014;19:278-88.

63.Ekelund U,Luan J,Sherar LB,Esliger DW,Griew P,Cooper A,et al.Moderate to vigorous physical activity and sedentary time and cardiometabolic risk factors in children and adolescents.JAMA 2012;307:704-12.

64.Ortega FB,Ruiz JR,Sj¨ostr¨om M.Physical activity,overweight and central adiposity in Swedish children and adolescents:the European Youth Heart Study.Int J Behav Nutr Phys Act 2010;4:61.doi:10.1186/1479-5868-1184-1161.

65.Gerber M,Ludyga S,M¨ucke M,Colledge F,Brand S,P¨uhse U.Low vigorousphysical activity isassociated with increased adrenocortical reactivity to psychosocial stress in students with high stress perceptions.Psychoneuroendocrinol 2017;80:104-13.

66.Martikainen S,Pesonen AK,Lahti J,Heinonen K,Feldt K,Pyh¨al¨a R,et al.Higher levelsof physical activity areassociated with lower hypothalamicpituitary-adrenocortical axisreactivity to psychosocial stress.JClin Endocrinol Metabol 2013;98:619-27.

67.Ludyga S,Gerber M,Brand S,Holsboer-Trachsler E,P¨uhse U.Acute effectsof moderateaerobic exerciseon specif ic aspectsof executivefunction in different age and f itness groups:a meta-analysis.Psychophysiol 2016;53:1611-26.

68.Best JR,Miller PH,Naglieri JA.Relationsbetween executivefunction and academic achievement fromages5 to 17 in alarge,representativenational sample.Learn Ind Diff 2011;21:327-36.

69.Locke E,Latham G.Building apractically useful theory of goal setting and task motivation:a35-year odyssey.Am Psychologist 2002;57:705-17.

70.Sniehotta F.Towards a theory of intentional behaviour change:plans,planning and self-regulation.Br JHealth Psychol 2009;14:261-73.

71.Gerber M,Holsboer-Trachsler E,P¨uhse U,Brand S.Author'sreply to the Letter to the Editor“Exerciseis medicine for depression:even if the‘pill'issmall”of Hallgren,Stubbsand Vancampfort.Neuropsychiatr Dis Treat 2016;12:2717-20.

72.Kanfer FH,Saslow G.Behavioral analysis:an alternative to diagnostic classif ication.Arch Gen Psychiatr 1965;12:529-38.

73.Shimon JM,Petlichkoff LM.Impact of pedometer use and self-regulation strategies on junior high school physical education students daily step counts.JPhys Act Health 2009;6:178-84.

74.Lubans DR,Morgan PJ,Tudor-Locke C.A systematic review of studies using pedometers to promote physical activity among youth.Prev Med 2009;48:307-15.

75.Schof ield L,Mummery WK,Schof ield G.Effects of controlled pedometer-intervention trial for low activeadolescent girls.Med Sci Sports Exerc 2005;37:1414-20.