Background: Within the Self-Determination Theory (SDT) framework, the first major study aim was to investigate the SDT tenets in an obese adolescent population by examining the factor structure of the Behavioural Regulation in Exercise Questionnaire-2 (BREQ-2) and by investigating associations between physical activity (PA) and motivation in obese adolescents. The second aim was to study differences in motivation according to adolescents' educational level, since lower educated obese adolescent are a sub-risk group for lower PA levels among the obese adolescents. The third aim was to investigate whether attending a residential obesity treatment program could lead to an increase in autonomous motivation towards PA and to see if the treatment effect on motivation was different in low versus high educated youth.
Methods: For the first study aim, the sample comprised 177 obese adolescents at the start of a 10-month multidisciplinary residential obesity treatment program (BMI = 35.9 ± 6.0 kg/m², 15.1 ± 1.5 years, 62% girls). A subsample of 65 adolescents (stratified by educational level) were divided into low (n = 34) versus high educated (n = 31) as part of the second and third study aim. Motivation was assessed using the BREQ-2 and PA using the Flemish Physical Activity Questionnaire.
Results: Exploratory factor analysis showed sufficient validations with the original factor for 17 out of 19 BREQ-2 items. Significant positive correlations were found between PA and the composite score of relative autonomy (r = 0.31, p < 0.001), introjected (r = 0.23, p < 0.01), identified (r = 0.31, p < 0.001) and intrinsic regulation (r = 0.38, p < 0.001). Higher educated adolescents scored higher on the composite score of relative autonomy, introjected, identified and intrinsic regulation at the start of treatment (F = 3.68, p < 0.001). The composite score of relative autonomy, external, identified and intrinsic regulation significantly increased during treatment for all adolescents (F = 6.65, p < 0.001). Introjected regulation significantly increased for lower educated adolescents (F = 25.57, p < 0.001).
Conclusions: The BREQ-2 can be used in an obese adolescent population. Higher levels of autonomous motivation towards PA were related to higher PA levels. Adolescents had increases in both autonomous and controlled forms of motivation during treatment. Special attention for lower educated adolescents during treatment is needed, as they have a lower autonomous motivation at the start of treatment and an increase in introjected regulation during treatment.