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Explaining the effect of a 1-year intervention promoting physical activity in middle schools: a mediation analysis

  • L Haerens (a1), E Cerin (a2), L Maes (a3), G Cardon (a1), B Deforche (a1) and I De Bourdeaudhuij (a1)...



The aim of the present study was to examine the mediation effects of changes in psychosocial determinants of physical activity (attitude, social support, self-efficacy, perceived benefits and barriers) on changes in physical activity.


One-year intervention study with baseline and 1-year post measures of physical activity habits and psychosocial correlates.


Fifteen middle schools.


Boys and girls (n = 2840) aged 11–15 years completed the validated questionnaires during class hours.


The product-of-coefficients test was used to asses the mediating effects. Self-efficacy for physical activity at school was found to be the only significant mediator of physical activity change. Specifically, self-efficacy for physical activity at school partly mediated the effect of the intervention on total and school-related physical activity change in the intervention group with parental support (P < 0.05). None of the other potential mediators, attitudes, social support, perceived benefits and perceived barriers, seemed to have had a positive effect. Even a suppressor effect was found for attitudes. Given that the effects of self-efficacy and attitudes were of opposite direction, the total mediated/suppressed effects of the intervention were not statistically significant.


Positive changes in total and school-related physical activity in adolescents could be partly explained by increases in self-efficacy for physical activity at school through a physical activity intervention in middle schools with parental support. However, the suppressor effect of attitudes decreased this effect. As this is one of the first true mediation analyses in this age group, further research is needed to replicate the importance of these mediators.


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1 Bouchard, C, Shepard, R, Stephens, T. Physical Activity, Fitness And Health: Interventional Proceedings and Consensus Statement. Champaign, IL: Human Kinetics, 1994.
2 Caspersen, CJ, Merrit, RK, Stephens, T. International physical activity patterns: a methodological perspective. In: Dishman, R, ed. Advances in Exercise Adherence. Champaign, IL: Human Kinetics, 1994; 73.
3 Steptoe, A, Wardle, J, Fuller, R, Holte, A, Justo, J, Sanderman, R, et al. Leisure-time physical exercise: prevalence, attitudinal correlates, and behavioral correlates among young Europeans from 21 countries. Preventive Medicine 1997; 26 (6): 845854.
4 Sallis, JF. Age-related decline in physical activity: a synthesis of human and animal studies. Medicine and Science in Sports and Exercise 2000; 32 (9): 15981600.
5 Ajzen, IM, Madden, TJ. Prediction of goal-directed behavior: attitudes, intentions and perceived behavioral control. Journal of Experimental Social Psychology 1986; 22 (5): 453474.
6 Bandura, A. Social Foundations of Thought and Action: A Social Cognitive Theory. Englewood Cliffs, NJ: Prentice-Hall, 1986.
7 Sallis, JF, Prochaska, JJ, Taylor, WC. A review of correlates of physical activity of children and adolescents. Medicine and Science in Sports and Exercise 2000; 32 (5): 963975.
8 De Bourdeaudhuij, I. Behavioural factors associated with physical activity in youth. In: Biddle, S, Sallis, J, Cavill, N, eds. Young and Active. Young People and Health-Enhancing Physical Activity – Evidence and Implications. London: Health Education Authority, 1998; 98–1118.
9 De Bourdeaudhuij, I, Sallis, J. Relative contribution of psychosocial variables to the explanation of physical activity in three population-based adult samples. Preventive Medicine 2002; 34 (2): 279288.
10 Timperio, A, Salmon, J, Ball, K. Evidence-based strategies to promote physical activity among children, adolescents and young adults: review and update. Journal of Science and Medicine in Sports 2004; 7 (1): S20S29.
11 Stone, EJ, McKenzie, TL, Welk, GJ, Booth, ML. Effects of physical activity interventions in youth – review and synthesis. American Journal of Preventive Medicine 1998; 15 (4): 298–3315.
12 Sallis, JF, Mckenzie, TL. Physical education’s role in public health. Research Quarterly for Exercise and Sport 1991; 62 (2): 124137.
13 Sallis, JF, Conway, TL, Prochaska, JJ, McKenzie, TL, Marshall, SJ, Brown, M. The association of school environments with youth physical activity. American Journal of Public Health 2001; 91 (4): 618620.
14 Story, M. School-based approaches for preventing and treating obesity. International Journal of Obesity and Related Metabolic Disorders 1999; 23 (Suppl. 2): S4351.
15 Gortmaker, SL, Peterson, K, Wiecha, J, Sobol, AM, Dixit, S, Fox, MK, et al. Reducing obesity via a school-based interdisciplinary intervention among youth – Planet Health. Archives of Pediatrics & Adolescent Medicine 1999; 153 (4): 409418.
16 Sallis, JF, McKenzie, TL, Conway, TL, Elder, JP, Prochaska, JJ, Brown, M, et al. Environmental interventions for eating and physical activity – a randomized controlled trial in middle schools. American Journal of Preventive Medicine 2003; 24 (3): 209217.
17 Simon, C, Wagner, A, DiVita, C, Rauscher, E, Klein-Platat, C, Arveiler, D, et al. Intervention centred on adolescents’ physical activity and sedentary behaviour (ICAPS): concept and 6-month results. International Journal of Obesity and Related Metabolic Disorders 2004; 28 (Suppl. 3): S96103.
18 Haerens L, De Bourdeaudhuij I, Maes L, Cardon G, Deforche B. School based randomized controlled trial of a physical activity intervention in 11 to 15 year olds. Journal of Adolescent Health 2007; 40(3): 258–65.
19 Green, L, Kreuter, M. Health Promotion Planning: An Educational and Ecological Approach. Mountain View, CA: Mayfield, 1999.
20 McKenzie, TL, Smeltzer, JL. Planning, Implementing and Evaluating Health Promotion Programs: A Primer. Boston, MA: Allyn and Bacon, 2001.
21 Baranowski, T, Anderson, C, Carmack, C. Mediating variable framework in physical activity interventions – how are we doing? How might we do better? American Journal of Preventive Medicine 1998; 15 (4): 266297.
22 Lewis, BA, Marcus, BH, Pate, RR, Dunn, AL. Psychosocial mediators of physical activity behavior among adults and children. American Journal of Preventive Medicine 2002; 23 (2 Suppl.): 2635.
23 Haerens, L, Deforche, B, Maes, L, Stevens, V, Cardon, G, De Bourdeaudhuij, I. Body mass effects of a physical activity and health food intervention in middle schools. Obesity Research 2006; 14 (5): 847854.
24 Ainsworth, BE, Haskell, WL, Whitt, MC, Irwin, ML, Swartz, AM, Strath, SJ, et al. Compendium of Physical Activities: an update of activity codes and MET intensities. Medicine and Science in Sports and Exercise 2000; 32 (9 Suppl.): S498–516.
25 Philippaerts, RM, Matton, L, Wijndaele, K, Balduck, AL, De Bourdeaudhuij, I, Lefevre, J. Validity of a physical activity computer questionnaire in 12- to 18-year-old boys and girls. International Journal of Sports Medicine 2006; 27 (2): 131136.
26 De Bourdeaudhuij, I, Philippaerts, R, Crombez, G, Matton, L, Wijndaele, K, Balduck, AL, et al. Stages of change for physical activity in a community sample of adolescents. Health Education Research 2005; 20 (3): 357366.
27 Haerens, L, De Bourdeaudhuij, I, Maes, L, Vereecken, C, Brug, J, Deforche, B. The effects of a middle-school healthy eating intervention on adolescents’ fat and fruit intake and soft drinks consumption. Public Health Nutrition 2007; 10 (5): 443449.
28 Vandelanotte, C, De Bourdeaudhuij, I. Acceptability and feasibility of a computer-tailored physical activity intervention using stages of change: project FAITH. Health Education Research 2003; 18 (3): 304317.
29 Vandelanotte, C, De Bourdeaudhuij, I, Sallis, JF, Spittaels, H, Brug, J. Efficacy of sequential or simultaneous interactive computer-tailored interventions for increasing physical activity and decreasing fat intake. Annals of Behavioral Medicine 2005; 29 (2): 138146.
30 Sallis, JF, Hovell, MF, Hofstetter, CR, Barrington, E. Explanation of vigorous physical-activity during 2 years using social-learning variables. Social Science & Medicine 1992; 34 (1): 2532.
31 Krull, JL, MacKinnon, DP. Multilevel modeling of individual and group level mediated effects. Multivariate Behavioral Research 2001; 36 (2): 249277.
32 MacKinnon, DP. Contrasts in multiple mediator models. In: Rose JS, Chassin L, Presson CC, Sherman SJ, eds. Multivariate Applications in Substance Use Research New Methods for New Questions. Mahwah, NJ: Erlbaum, 2000; 141160.
33 MacKinnon, DP, Fairchild, AJ, Fritz, MS. Mediation analysis. Annual Review of Psychology 2007; 58 (1): 593614.
34 Bollen, KA. Total direct and indirect effects in structural equation models. In: Clogg, CC, eds. Sociological Methodology. Washington, DC: American Sociological Association, 1997; 3769.
35 Cohen J. Statistical Power Analysis for the Behavioural Sciences, 2nd ed. Hillsdale, NJ: Erlbaum, 1988.
36 Sallis, JF, Owen, N. Ecological Models of Health Behavior. San Francisco, CA: Jossey-Bass, 2002.
37 Duncan, TE, Mcauley, E. Social support and efficacy cognitions in exercise adherence – a latent growth curve analysis. Journal of Behavioral Medicine 1993; 16 (2): 199–2218.
38 Connor, M, Norman, P. Predicting Health Behavior: Research and Practice with Social Cognition Models. Buckingham: Open University Press, 1996.
39 Spittaels, H, De Bourdeaudhuij, I, Brug, J, Vandelanotte, C. Effectiveness of an online computer-tailored physical activity intervention in a real-life setting. Health Education Research 2007; 22 (3): 385396.
40 Miller, YD, Trost, SG, Brown, WJ. Mediators of physical activity behavior change among women with young children. American Journal of Preventive Medicine 2002; 23 (2): 98103.
41 Edmundson, E, Parcel, GS, Feldman, HA, Elder, J, Perry, CL, Johnson, C, et al. The effects of the child and adolescent trial for cardiovascular health upon psychosocial determinants of diet and physical activity behavior. Preventive Medicine 1996; 25 (4): 442454.
42 Haerens L, Cerin E, Deforche B, Maes L, De Bourdeaudhuij I. Explaining the effects of a 1-year intervention promoting a low fat diet in adolescent girls: a mediation analysis. International Journal of Behavioral Nutrition and Physical Activity 2007; 2nd revision.
43 Baranowski, T, Jago, R. Understanding the mechanisms of change in children’s physical activity programs. Exercise and Sport Sciences Reviews 2005; 33 (4): 163168.
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Public Health Nutrition
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