No kidding: low back pain and type of container influence adolescents’ perception of load heaviness

Purpose The relationship between low back pain (LBP) and the lifting/carrying of loads is still a matter of great discussion. In teenagers, the weight of the school bag has been considered to play a pathogenic role in LBP but the relationship between the actual weight of the school bag and LBP symptoms does not seem to be a straightforward one. Numerous factors have been identified that influence the perception of weight. This study aimed to evaluate the influence of low back pain and the type of container on the perception of load heaviness by healthy teenagers. Methods A convenience sample of 80 healthy teenage males (mean ± SD age 13.9 ± 2.1 years) was recruited from the members of two local sports clubs. The volunteers were evaluated during one of their training sessions. Information about a history of consequential LBP was gathered by questionnaire. Subjects were invited to estimate the weight of three bags (a typical school bag, a sports bag with the logo of a well-known brand, and a neutral bag) containing two different loads (total weights approximately 3 and 5 kg). Results Consequential LBP (i.e., LBP requiring medical attention and/or interfering with usual sports activities) was reported by 26.2 % of them. The majority of the LBP episodes occurred ≥3 months before the tests. Overall, teenagers significantly ( p ≤ 0.05) underestimated the weight of the sports bag compared with the school bag and the neutral bag. Compared with those with no LBP, subjects with a history of LBP overestimated the weight of the heavier load. Conclusions Our results suggest that several subjective variables significantly influence the perception of load heaviness. Until we have a better understanding of the mechanical role of the backpack weight versus the perception of its weight in the aetiology of LBP, any recommendations about the schoolbag weight limit should be viewed with caution.