| Part 1 General Introduction of Research BackgroundIn this part, an overview on associations of health behaviors with psychological and physical health and factors affecting health behaviors during adolescence were addressed. The current study background in adolescent health behaviors was presented and a summarization about health behavior models and theories were demonstrated in this part.Part 2 Feasibility and Applicability Examination on HAPAObjective To test HAPA model's validity and feasibility among Chinese adolescents in the domain of physical activity; To test variables predicting intention; To test planning's effect between intention and behavior; To test whether social cognitive variables' stage difference exists or not.Participants and MethodsStratified sampling method was conducted.706 participants from middle and high school provided valid data. Constructs in HAPA (risk perception, perceived pros and cons, self-efficacy, action planning) were measured. One-way ANOVA and mediation analysis were conducted to test whether social cognitive variables' stage difference and plannings' mediating effect exists or not.Results and Discussion(1) Results of Variables Predicting IntentionSelf-efficacy (β=.43, p<.001), risk perception (β=-.10, p<.01) and perceived cons (β=-.08, p<.05) were significant predictor on intention and self-efficacy was the strongest predictor among all the variables. Perceived pros (β=.01, p>.05) was not a significant predictor on intention for adolescent PA behavior, indicating that even adolescents perceived the benefits (pros) of regular activity, they yielded to the perceived barriers (cons) and with weak intention for PA participation.(2) Results of Planning Mediating Analysis for Intention, and BehaviorMediating analysis demonstrated that planning was a partial mediator between intention and behavior, intention's indirect effect on behavior was partially mediated by planning, consistent with the assumption of HAPA.(3) Results of Stage CheckingHierarchical Regression analysis results revealed that self-efficacy, risk perception, perceived pros and cons and planning showed different predicting effect on physical activity, supporting the stage presumption in HAPA. Self-efficacy was a universal strong predictor for all the three stages. In preintention stage, self-efficacy (β=.48, p<.001), risk perception (β=-.21, p<.05), perceived pros (β=.21, p<.05) were significant predictor of behavior except perceived cons (β=-.01, p>.05) and planning (β=.06, p>.05), explaining 40%variance of PA change (R2= 0.40).In intention stage, self-efficacy (β=.37, p<.001) and planning (β=.16, p<.01) were significant predictor of behavior except risk perception (β=-.05, p>.05), perceived pros (β=.02, p>.05) and cons (β=-.07, p>.05), explaining 27%variance of PA change (R2= 0.27).In action stage, self-efficacy (β=.17, p<.05), risk perception (β==-.20, p<.001) and planning (β=.28, p<.001) were significant predictor on behavior except perceived pros (β=-.01, p>.05) and cons (β=.01, p>.05), explaining 20%variance of physical activity change (R2= 0.20).(4) Results of Social Cognitive Variables'Stage DifferenceSelf-efficacy (F(2,696)= 44.54, p<.01), risk perception (F(2,681)= 17.30, p<.01), perceived cons (F(2,684)= 20.64, p<.01), action planning (F(2,680)= 97.82, p<.01) and physical activity (F(2,694)= 86.52, p<.01) all showed significant stage difference among preintenders, intenders and actors. Actors had the highest level of self-efficacy, perceived the highest level of pros and the lowest levels of risk perception, had more planning and participated in the most amount of physical activity, no stage difference was found between actors and intenders in perceived pros. Compared to actors, preintenders and intenders perceived higher level of cons. No stage difference was found between preintenders and intenders as to risk perception (t(430)=.52, p=.60) and perceived cons (t(432)= 2.42, p=.06).Part 3 Longitudinal Intervention Study Based on HAPAObjective To test the effectiveness of stage-matched or mis-matched intervention on physical activity change. We hypothesize that risk resource communication intervention would be matched to preintenders and preintenders would benefit most from resource communication intention; Action planning intervention would be matched to intenders and intenders would benefit most from planning intervention; Actors would not benefit from neither risk resource communication nor action planning making intervention for neither of them was matched to actors.Participants and MethodsStratified sampling method was used.693 adolescents completed baseline questionnaire and were randomly designed into resource communication group, strategic planning group and control group. Students in the treatment groups received a one-hour lesson and were given printed materials.534 adolescents completed the follow-up study. PA stage, PA intention and PA frequency were measured at the two time point. A quasi-experimental 3x3x2 between-factors design with repeated measures was chosen.3 stages of change (preintenders, intenders, actors) and three intervention groups (resource communication, planning, control). PA frequency and PA intention were measured at baseline and follow-up and served as the dependent variable.Repeated Measures Analyses of Variance was conducted with stages (preintender, intender, actor) and treatment (risk resource communication, planning, control group) were chosen as between-subjects factors and PA frequency and PA intention were run separately as the dependent variable measured at two points in time four weeks apart (pre-post measures). Missing data were imputed using the Expectation Maximization (EM) algorithm in SPSS.Results and Discussion(1) Repeated Measures ANOVA on PA intention before and after Intervention among Different Groups and StagesFor all the participants:Between group analysis results showed the existence of time effect (F(2,525)= 35.07, p<.001,η2=.12), indicating the significant change of PA intention before and after intervention, no treatment effect (F(2,525)=.83, p=.44) or treatment x stage interaction effect (F(4,525)= 1.03, p=.39) was found, for the whole sample participants consisting of different stages with preintenders, intenders and actors, no intervention was targeted to match the whole group, the results was consistent with the hypothesis; Within group analysis results showed the existence of time effect (F(l,525)=10.41, p<.001,η2=.02), time x intervention interaction effect (F(2,525)= 7.02, p<.10,η2=.03), time x stage interaction effect (F(2,525)= 5.41, p<.005,η2=.02), indicating the existence of significant change of PA intention before and after intervention differed among different intervention groups and stages.Risk Resource Communication Group:Between group analysis results showed a stage effect (F(2,86)= 6.51, p<.01,η2=.13), revealing the significant difference of PA intention between different stages. Within group analysis results showed a time effect (F(1,86)= 19.25, p<.001,η2 =.18), preintenders, intenders and actors all increased their PA participation intention whereas preintenders and intenders benefited most and had the steepest increase. The increase of PA intention for preintenders was consistent with the hypothesis that stage-matched interventions had superiority over mis-matched ones whereas the increase for intenders and actors was unexpected.Planning Group:Between group analysis results showed a stage effect (F(2,220)= 17.45, p<.001,η2=.14), revealing that preintenders had the lowest levels of PA intention whereas actors had the highest level. Within group analysis showed a time x stage interaction effect (F(2,220) = 3.52, p=.03,η2=.03), revealing that planning intervention had different influence on different stages. Preintenders and intenders both benefited from planning intervention, the increase in intenders was consistent with the hypothesis whereas the increase in preintenders was unexpected.Control Group:Only a between group stage main effect (F(2,219) = 21.57, p<.001,η2=.17) was found, no time main effect or time x stage or time x intervention interaction effect was found, revealing that actors remained the highest levels of PA intention than preintenders and intenders, there was no PA intention change in all the 3 stages in control group during the two time point study.(2) Repeated Measures ANOVA on PA frequency before and after Intervention among Different Groups and StagesFor all the participants:Between group stage effect (F(2,525)= 36.50, p<.001,η2=.12), no treatment effect (F(2,525)=.14, p=.87) or stage x treatment interaction effect (F(4,525)= 3.39, p=.85), for the whole sample participants consisting of different stages with preintenders, intenders and actors, no intervention was targeted to match the whole group, the results were consistent with the hypothesis; Within group analysis results showed the existence of time effect (F(1,525)= 13.76, p<.001,η2=.03), time x treatment interaction effect (F(2,525)= 2.36, p<.10,η2=.01), time x stage interaction effect (F(2,525)= 11.24, p<.001,η2=.04), time x stage x treatment interaction effect (F(4,525)= 2.52, p<.05,η2=.02), demonstrating the existence of significant change of PA participation frequency before and after intervention, the change differed across different intervention groups and stages.Resource Communication Group:Between group analysis results showed the existence of stage effect (F(2,86)= 6.05, p<.01,η2=.12); Within group analysis showed a time effect (F(1,86)= 7.14, p<.01,η2 =.08), time x stage interaction effect (F(2,86)= 5.21, p<.01,η2=.11), revealing that the change of PA frequency differed among different stages and different groups before and after the intervention. Preintenders had the steepest increase, consistent with the hypothesis that stage-matched interventions had superiority over mis-matched ones.Planning Group:Between group analysis results showed the existence of stage effect (F(2,220)= 17.61, p<.001,η2=.14). Within group analysis results showed the existence of time effect (F(l,220)= 9.08, p<.01,η2=.04), time x stage interaction effect (F(2,220)= 10.14, p<.001,η2=.08), revealing the significant increase of PA frequency among different stages. Preintenders and intenders showed the steepest PA participation increment. The steep increment in intenders was consistent with the hypothesis that stage-matched interventions had superiority over mis-matched ones whereas the increase in preintenders was unexpected.Control Group:Between group analysis showed the existence of stage effect (F(2,219)= 30.80, p<.001,η2=.22), no time effect (F(1,219) .98, p>.10,η2<.01) or time x stage interaction effect (F(2,219)= 2.50, p>.05,η2=.02), revealing that actors remained the highest levels of PA participation than preintenders and intenders, there was no PA behavior change in all the 3 stages in control group during the two time point.Preintenders showed unexpected increment both in PA intention and behavior change after strategic planning intervention, inconsistent with the study hypothesis. The unexpected intervention effect might be that before intervention, preintenders perceived highest levels of cons and the lowest levels of exercise efficacy and the least amount of planning and stayed in the no intention no action stage. After planning intervention, preintenders increased their planning making strategies and exercise self-efficacy, resulting in the enhancement in PA participation intention and the change in behavior.Part 4 Moderated-Mediation Model in Health Behavior FormationObjective To examine whether the moderated mediation mechanism exist or not in the translating process from intention to behavior change: whether the type of exercise motivation (intrinsically-motivated or extrinsically-motivated) and exercise skill's moderating effect exist or not among intention, planning and behavior change process.Participants and Methods 693 adolescents from middle and high shcool completed the baseline study and 534 of them completed the follow up study. PA intention, exercise motivation (BREQ), exercise skill and physical activity (IPAQ) were measured at baseline. Planning and PA were measured at follow-up four weeks later.Results and DiscussionIn the relation between intention, exercise motivation, exercise skill, action planning and behavior:(1) Mediation Model:Action planning was a partial mediator between PA intention and behavior, the translation from intention to behavior partially came from the effect of action planning;(2) Moderating Mediation Model:Exercise motivation as a ModeratorIn the mediating model, exercise motivation was a moderator between intention, action planning, and behavior, one who had higher levels of intrinsic motivation was apt to form more action planning and thus tended to have more levels of behavior change.(3) Moderated Mediation Model:Exercise Skills as a ModeratorIn the mediating model, exercise skill was a moderator for the translation from action planning making to behavior change, one who grasped more types of exercise skills was apt to execute their action planning and thus tended to have more levels of behavior change. Part 5 General Conclusion(1) Cross-sectional study revealed the existence of stages and social cognitive variables'stage difference in HAPA. The feasibility of HAPA model was validated in the study of physical activity behavior among adolescents.(2) Longitudinal study results partly support the hypothesis that stage-matched intervention had superiority over mis-matched ones: intervention matched to a specific stage had more efficacy than mis-matched to any other stages.(3) Exercise skill and exercise motivation are important moderator for the transition between intention, action planning and behavior change.
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