Aim: To compare the study results concerning the correct level of 13- and 15-year-old adolescents` physical activity and impact of selected physical activity determinants (self-efficacy, BMI, gender, domicile) obtained from two nationwide studies out in Poland, using a similar questionnaire in 2006 and 2008.

Material and methods: The material comes from two studies. The first, the 2006 HBSC survey included 2287 15-year-old students (1092 boys and 1195 girls); the second, the 2008 third phase of a prospective, three-phase survey, included 605 13-year-olds (300 boys and 305 girls) born in Poland in January 1995. Questions on physical activity were analysed (MVPA), along with the following determinants: self-efficacy, domicile, gender, body weight and height. Cross-tabulation with chi2 analysis and multilevel modelling were applied.

Results: Physical activity deficiency was found in both examined populations. In study I – 84.8%, in study II – 80.3%. Self-efficacy (p<0.001), gender (p<0.001) and BMI (p<0.04) had an impact on the 15-year-olds` physical activity. In 13-year-olds, only self-efficacy was close to significant relation with physical activity. The results of multilevel logistic regression in study I identified protective factors: male gender [OR=0.41; CI (OR): 0.32-0.53] and strong self-efficacy  [OR=0.66; CI (OR): 0.51-0.85]; while being underweight was identified as a risk factor [OR=2.77; CI (OR): 1.11-6.95]. In study II only strong self-efficacy was found as a protective factor [OR=0.51; CI (OR): 0.30-0.89] against lack of physical activity.

Conclusions: Most of the examined adolescents from study I as well as study II suffered from physical activity deficiency. The share of biological determinants (gender, BMI) in maintaining correct level of physical activity increased with age. A link between physical activity and self-efficacy was demonstrated in the 15-year-olds, while this tendency was identified in the 13-year-olds. The results point to a need for implementing programmes supporting self-efficacy in children under the age of 13 and to carry out assessment of self satisfaction concerning own bodyweight. In preparing these programmes sex differences should be taken into consideration.