title: Asymmetric loads and pain associated with backpack carrying by children.
abstract: BACKGROUND
  Shoulder and back pain in school children is associated with wearing heavy backpacks. Such pain may be attributed to the magnitude of the backpack load and the manner by which children distribute the load over their shoulders and back. The purpose of this study is to quantify the pressures under backpack straps of children while they carried a typical range of loads during varying conditions.
  
  
  METHODS
  Ten healthy children (aged, 12-14 years) wore a backpack loaded at 10%, 20%, and 30% body weight (BW). Backpacks were carried under 2 conditions, low on back or high on back. Pressure sensors (0.1 mm thick) measured pressures beneath the shoulder straps.
  
  
  RESULTS
  When walking with the backpack straps over both shoulders, contact pressures were significantly greater in the low-back condition than in the high-back condition (P = 0.004). In addition, when children carried the backpack in the low-back condition, mean pressures (+/-SE) over the right shoulder were as follows: 98 +/- 31, 153 +/- 48, and 170 +/- 54 mm Hg at 10%, 20%, and 30% BW, respectively, which were significantly higher (P < 0.001) than those over the left shoulder (46 +/- 14, 92 +/- 29, and 90 +/- 29 mm Hg, respectively). Perceived pain with the backpack over 1 shoulder was significantly greater (P = 0.002) than that for donning with both shoulders in the low-back condition.
  
  
  CONCLUSIONS
  Pressures at 10%, 20%, and 30% BW loads on the right or left shoulder, during low-back or high-back conditions, are higher than the pressure thresholds (approximately 30 mm Hg) to occlude skin blood flow. Furthermore, asymmetric and high pressures exerted for extended periods of time may help explain the shoulder and back pain attributed to backpacks.
authors.affiliation: Department of Orthopaedic Surgery, University of California-San Diego, 350 Dickinson Street, San Diego, CA 92103, USA.
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Macias
authors.forename: Gita
authors.initials: G
authors.lastname: Murthy
authors.forename: Henry
authors.initials: H
authors.lastname: Chambers
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001416:Back Pain / Q000145:classification / Q000209:etiology* / Q000503:physiopathology; D002648:Child; D004867:Equipment Design; D005260:Female; D006801:Humans; D017770:Lifting / Q000009:adverse effects*; D008297:Male; D010147:Pain Measurement; D011312:Pressure; D020069:Shoulder Pain / Q000145:classification / Q000209:etiology* / Q000503:physiopathology; D013334:Students / Q000706:statistics & numerical data*; D016474:Weight-Bearing