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Adolescent standing postural response to backpack loads: a randomised controlled experimental study
Grimmer K, Dansie B, Milanese S, Pirunsan U, Trott P
BMC Musculoskeletal Disorders 2002 Apr 17;3(10):Epub
clinical trial
3/10 [Eligibility criteria: Yes; Random allocation: No; Concealed allocation: No; Baseline comparability: No; Blind subjects: No; Blind therapists: No; Blind assessors: No; Adequate follow-up: Yes; Intention-to-treat analysis: No; Between-group comparisons: Yes; Point estimates and variability: Yes. Note: Eligibility criteria item does not contribute to total score] *This score has been confirmed*

BACKGROUND: Backpack loads produce changes in standing posture when compared with unloaded posture. Although 'poor' unloaded standing posture has been related to spinal pain, there is little evidence of whether, and how much, exposure to posterior load procedures injurious effects on spinal tissue. The objective of this study was to describe the effect on adolescent sagittal plane standing posture of different loads and positions of a common design of school backpack. The underlying study aim was to test the appropriateness of two adult 'rules-of-thumb' that for postural efficiency, backpacks should be worn high on the spine, and loads should be limited to 10% of body weight. METHOD: A randomised controlled experimental study was conducted on 250 adolescents (12 to 18 years, randomly selected from five South Australian metropolitan high schools. Sagittal view nine experimental conditions: combinations of backpack loads (3,5 or 10% of body weight) and positions (backpack centred at T7, T12 or L3). Sagittal plane photographs were taken of unloaded standing posture (baseline), and standing posture under the experimental conditions. Posture was quantified from the x (horizontal) coordinate of each anatomical point under each experimental condition. Differences in postural response were described, and differences between conditions were determined using Analysis of Variance models. RESULTS: Neither age nor gender was a significant factor when comparing postural response to backpack loads or condition. Backpacks positioned at T7 produced the largest forward (horizontal) displacement at all the anatomical points. The horizontal position of all anatomical points increased linearly with load. CONCLUSION: There is evidence refuting the rule of thumb to carry the backpack high on the back. Typical school backpacks should be positioned with the centre at waist or hip level. There is no evidence for the 10% body weight limit.

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