Arch Pediatr Adolesc Med volume 159, issue 12, P1186 2005 DOI: 10.1001/archpedi.159.12.1187

Why Blame Milk?

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Joan M. Lappe
Abstract:

BW 4,5 ; pressures at 20% BW were 70 mm Hg (left shoulder) and 110 mm Hg (right shoulder).Limitations of our study include a relatively small sample size of 10 children and a short duration of data collection (30 seconds). The sample size may increase the likelihood of a type II error; power analysis indicates a power of 0.95 and a type II error of 5%. However, most comparisons were significant. Because this is the first study to document pressures beneath the loaded backpack in children, 30 seconds was selected as an initial period to measure contact pressures. This time was relatively brief because the load was too great for some subjects to endure for more than 30 seconds. Contact pressures during the 30-second period were stable within each recording period. The longterm effect of prolonged high contact pressure and asymmetric load are unknown. Because children typically carry backpacks for 30 to 60 minutes per day, 9 longer recording durations may be worthwhile in future studies.The higher contact pressures over the right shoulder compared with those over the left shoulder are probably due to posture. The present study did not study posture per se. However, other studies have noted that posture changed when shoulders were asymmetrically loaded. 10 Long-term differential loading of the right and left shoulders may alter spinal curvature and produce back pain.In summary, avoiding the use of heavy backpacks may prevent backpack pain and related injuries in children. Based on our findings of high-contact pressures and asymmetric shoulder loading, the reported average backpack load of 22% is too high. We recommend that backpack loads be minimized to promote comfort and safety.

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