Interaction of body mass index and age in muscular activities among backpack carrying male schoolchildren.

Background: The complex and limited understanding of the interactions among multiple factors associated with back pain occurrence among schoolchildren might explain the current inconclusive and contradictory findings on the issue. The global increase in the prevalence of childhood overweight and obesity, which reportedly affects children's physical abilities, calls for concern among school/children ergonomists and other stakeholders.

Objective: The study investigated the interaction of body mass index (BMI) and age on the muscular activities, backpack height and perceived level of pain arising from carrying different weight of backpacks.

Methods: Surface electromyography analysis of erector spinae and trapezius muscular activities was conducted on 47 primary schoolchildren aged between 8 and 11 years. Repeated measure ANOVA were carried out on the data.

Results: There was significant difference in all the measures of muscular activities, backpack height and pain rating at different levels of backpack weight. However, the children were only significantly fatigable in the erector spinae muscles of the lower back and not in the trapezius of the upper back. The interactive effect of BMI was more pronounced than the children's age.

Conclusions: The study shows that it is not appropriate for all schoolchildren to have the same backpack weight limit and obese schoolchildren should carry a lower bag-to-body ratio of backpack weight. The younger children also need an appropriate bag surface-to-trunk ratio size of backpack as they were more affected by the position of the backpack.