title: Interaction of body mass index and age in muscular activities among backpack carrying male schoolchildren.
abstract: 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.
authors.affiliation: Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia.|Department of Mechanical Engineering, College of Engineering, W.U. Federal Polytechnic, Birnin Kebbi, Kebbi State, Nigeria.
authors.forename: Ademola James
authors.initials: AJ
authors.lastname: Adeyemi
authors.affiliation: Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia.
authors.forename: Jafri Mohd
authors.initials: JM
authors.lastname: Rohani
authors.affiliation: Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia.
authors.forename: Mat Rebi Abdul
authors.initials: MR
authors.lastname: Rani
mesh_terms: D000367:Age Factors; D001416:Back Pain / Q000209:etiology*; D015992:Body Mass Index; D002648:Child; D004576:Electromyography; D006801:Humans; D017770:Lifting / Q000009:adverse effects*; D008297:Male; D018763:Muscle Fatigue; D064170:Paraspinal Muscles / Q000503:physiopathology*; D064171:Superficial Back Muscles / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology
keywords: Back pain; electromyography; school ergonomics