An inactive lifestyle and low physical fitness are associated with functional somatic symptoms in adolescents. The TRAILS study

Objective: An inactive lifestyle has been associated with functional somatic symptoms (FSS), but findings are contradictory. Moreover, mediating factors in this relationship are unclear. We examined whether low physical activity was related to FSS in adolescents, and whether this association was mediated by low physical fitness.

Methods: This study was part of the Dutch longitudinal cohort study TRAILS, in which 1816 adolescents (mean age 16.3 years, SD 0.7) participated during the third (T3) and 1881 (mean age 19.1 years, SD 0.6) during the fourth (T4) assessment waves. Adolescents' exercise and sedentary behavior levels and the number of FSS were assessed by questionnaires at T3 and T4. Physical fitness (VO2Max) was determined for 687 adolescents by a shuttle run test at T3. The association between physical activity and FSS was examined with bootstrapped linear regression analyses, adjusted for smoking and gender. In addition, bootstrapped mediation analyses were performed.

Results: A lack of exercise (b=0.05, bootstrap 95%--CI: 0.01 to 0.09) and high sedentary behavior (b=0.10, bootstrap 95%--CI: 0.06 to 0.14) at T3 were positively associated with FSS at T3. Since no longitudinal effects were found, shared associations were tested instead of mediation. The associations between a lack of exercise and FSS, and sedentary behavior and FSS were shared with physical fitness (b=0.01, bootstrap 95%--CI: 0.010.02. and b=0.03, bootstrap 95%--CI: 0.010.05).

Conclusion: An inactive lifestyle is associated with increased FSS in adolescents. Only part of this association is shared with low physical fitness.