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High Contact Pressure Beneath Backpack Straps of Children Contributes to Pain

High Contact Pressure Beneath Backpack Straps of Children Contributes to Pain Worldwide, 92% to 94% of schoolchildren carry backpacks1,2 and frequently complain of shoulder and back pain.1,3 On average, children load their backpacks between 10% to 22% body weight (BW).4,5 An understanding of how loads are distributed under backpack straps may help identify the source of shoulder and back pain in children. The purpose of this study was to quantify the contact pressures and perceived pain under backpack straps while children carried varying loads. Methods The study was approved by San Diego Children’s Hospital and Health Center (San Diego, Calif) and University of California, San Diego, institutional review boards. Both the legal guardian and the child subject signed the consent form. Subjects’ age, height, and weight were mean ± SD 13.2 ± 0.8 years, 136.5 ± 49 cm, and 62 ± 21 kg, respectively. All subjects reported carrying a backpack during normal daily activity. Five male and 5 female, healthy, normal subjects wore T-shirts and shorts or pants and carried a standard Jansport (San Leandro, Calif) backpack that was loaded at 0%, 10%, 20%, and 30% BW during a standard condition (Figure 1). A single investigator placed the backpack in the same location relative to the anterior aspect of the clavicle. The loading protocol was performed with the subject standing. Figure 1. View LargeDownload Standard condition. The top of the backpack is at shoulder level and the bottom above the buttock. The mean ± SD load placed in the backpack was 6.2 ± 2.0 kg, 12.4 ± 4.1 kg, and 18.6 ± 6.3 kg at 10%, 20%, and 30% BW loads, respectively. Subjects rated their perceived pain using a visual analog scale (0 = no pain to 10 = worst pain imaginable).6 To determine the pressures under the shoulder straps of a backpack, sensors (sensor number 9801; Tekscan, South Boston, Mass) with 96 load cells were positioned beneath each shoulder strap.7 The pressures were allowed to stabilize for 5 seconds, then contact pressures were recorded and averaged over a 25-second period. The region generating the highest pressure was averaged over the recording period. The pressure data are presented as mean ± SE. Data were analyzed using repeated-measures analysis of variance and F tests to correlate the pressure and pain data. A Bonferroni adjustment was used to control for multiple comparisons, and significance was set at P<.05. Results Contact pressure beneath the shoulder straps was significantly increased at 10%, 20%, and 30% BW (P = .03) (Figure 2). The pressures were significantly higher on the right shoulder than the left shoulder at 10%, 20%, and 30% BW (P = .02). Contact pressures were essentially zero with an empty backpack. Perceived pain correlated significantly with increasing contact pressure over the range from 10% to 30% BW (P = .03) (Figure 3). Perceived pain was zero with an empty backpack. Figure 2. View LargeDownload Shoulder contact pressure. Shoulder pressures increased significantly over the 10%, 20%, and 30% body weight conditions (pressure main effect, P = .03). Asterisk indicates P = .002; dagger, P<.001. At each body weight, the contact pressures on the right shoulder were significantly higher than the left shoulder (shoulder main effect, P = .02). Figure 3. View LargeDownload Perceived pain when wearing a backpack. The median perceived pain (0 = no pain to 10 = worst pain imaginable) correlated significantly with increasing contact pressure over the range from 10% to 30% body weight. Asterisk indicates P = .03. Comment Our results indicate that contact pressures beneath the shoulder straps significantly increase at 10%, 20%, and 30% BW load when subjects carry backpacks in a standard condition. In addition, pain significantly correlated with increasing contact pressure. Although the correlation does not indicate a causal relationship between high pressures and back pain, the data suggest a relationship. Furthermore, the pressures at the 10%, 20%, and 30% BW loads on the right or left shoulder are higher than the pressure thresholds (30 mm Hg) to occlude local skin and muscle blood flow.8 Children commonly carry backpack loads of 22% BW4,5; 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 long-term 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. Correspondence: Dr Hargens, 350 Dickinson St, Suite 121, San Diego, CA 92103-8894 (ahargens@ucsd.edu). Back to top Article Information Author Contributions: Dr Hargens had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Funding/Support: This study was supported by the David Sutherland Endowment Fund, San Diego. References 1. Pascoe DDPascoe DEWang YTShim DKim CK Influence of carrying book bags on gait cycle and posture of youths. Ergonomics 1997;40631- 641PubMedGoogle ScholarCrossref 2. Grimmer KAWilliams MTGill TK The associations between adolescent head-on-neck posture, backpack weight, and anthropometric features. Spine 1999;242262- 2267PubMedGoogle ScholarCrossref 3. Burton AKClarke RDMcClune TDTillotson KM The natural history of low back pain in adolescents. Spine 1996;212323- 2328PubMedGoogle ScholarCrossref 4. Watson KDPapageorgiou ACJones GT et al. Low back pain in schoolchildren: occurrence and characteristics. Pain 2002;9787- 92PubMedGoogle ScholarCrossref 5. Negrini SCarabalona RSibilla P Backpack as a daily load for schoolchildren. Lancet 1999;3541974PubMedGoogle ScholarCrossref 6. Bijur PESilver WGallagher EJ Reliability of the visual analog scale for measurement of acute pain. Acad Emerg Med 2001;81153- 1157PubMedGoogle ScholarCrossref 7. Becker RWirz DWolf CGopfert BNebelung WFriederich N Measurement of meniscofemoral contact pressure after repair of bucket-handle tears with biodegradable implants. Arch Orthop Trauma Surg 2005;125254- 260PubMedGoogle ScholarCrossref 8. Kosiak M Etiology and pathology of ischemic ulcers. Arch Phys Med Rehabil 1959;4062- 69PubMedGoogle Scholar 9. Balague FSkovron MNordin MDutoit GWaldburger M Low back pain in schoolchildren: a study of familial and psychological factors. Spine 1995;201265- 1270PubMedGoogle Scholar 10. Vacheron JJPoumarat GChandezon RVanneuville G Changes of contour of the spine caused by load carrying. Surg Radiol Anat 1999;21109- 113PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Pediatrics & Adolescent Medicine American Medical Association

High Contact Pressure Beneath Backpack Straps of Children Contributes to Pain

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References (10)

Publisher
American Medical Association
Copyright
Copyright © 2005 American Medical Association. All Rights Reserved.
ISSN
1072-4710
eISSN
1538-3628
DOI
10.1001/archpedi.159.12.1186
Publisher site
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Abstract

Worldwide, 92% to 94% of schoolchildren carry backpacks1,2 and frequently complain of shoulder and back pain.1,3 On average, children load their backpacks between 10% to 22% body weight (BW).4,5 An understanding of how loads are distributed under backpack straps may help identify the source of shoulder and back pain in children. The purpose of this study was to quantify the contact pressures and perceived pain under backpack straps while children carried varying loads. Methods The study was approved by San Diego Children’s Hospital and Health Center (San Diego, Calif) and University of California, San Diego, institutional review boards. Both the legal guardian and the child subject signed the consent form. Subjects’ age, height, and weight were mean ± SD 13.2 ± 0.8 years, 136.5 ± 49 cm, and 62 ± 21 kg, respectively. All subjects reported carrying a backpack during normal daily activity. Five male and 5 female, healthy, normal subjects wore T-shirts and shorts or pants and carried a standard Jansport (San Leandro, Calif) backpack that was loaded at 0%, 10%, 20%, and 30% BW during a standard condition (Figure 1). A single investigator placed the backpack in the same location relative to the anterior aspect of the clavicle. The loading protocol was performed with the subject standing. Figure 1. View LargeDownload Standard condition. The top of the backpack is at shoulder level and the bottom above the buttock. The mean ± SD load placed in the backpack was 6.2 ± 2.0 kg, 12.4 ± 4.1 kg, and 18.6 ± 6.3 kg at 10%, 20%, and 30% BW loads, respectively. Subjects rated their perceived pain using a visual analog scale (0 = no pain to 10 = worst pain imaginable).6 To determine the pressures under the shoulder straps of a backpack, sensors (sensor number 9801; Tekscan, South Boston, Mass) with 96 load cells were positioned beneath each shoulder strap.7 The pressures were allowed to stabilize for 5 seconds, then contact pressures were recorded and averaged over a 25-second period. The region generating the highest pressure was averaged over the recording period. The pressure data are presented as mean ± SE. Data were analyzed using repeated-measures analysis of variance and F tests to correlate the pressure and pain data. A Bonferroni adjustment was used to control for multiple comparisons, and significance was set at P<.05. Results Contact pressure beneath the shoulder straps was significantly increased at 10%, 20%, and 30% BW (P = .03) (Figure 2). The pressures were significantly higher on the right shoulder than the left shoulder at 10%, 20%, and 30% BW (P = .02). Contact pressures were essentially zero with an empty backpack. Perceived pain correlated significantly with increasing contact pressure over the range from 10% to 30% BW (P = .03) (Figure 3). Perceived pain was zero with an empty backpack. Figure 2. View LargeDownload Shoulder contact pressure. Shoulder pressures increased significantly over the 10%, 20%, and 30% body weight conditions (pressure main effect, P = .03). Asterisk indicates P = .002; dagger, P<.001. At each body weight, the contact pressures on the right shoulder were significantly higher than the left shoulder (shoulder main effect, P = .02). Figure 3. View LargeDownload Perceived pain when wearing a backpack. The median perceived pain (0 = no pain to 10 = worst pain imaginable) correlated significantly with increasing contact pressure over the range from 10% to 30% body weight. Asterisk indicates P = .03. Comment Our results indicate that contact pressures beneath the shoulder straps significantly increase at 10%, 20%, and 30% BW load when subjects carry backpacks in a standard condition. In addition, pain significantly correlated with increasing contact pressure. Although the correlation does not indicate a causal relationship between high pressures and back pain, the data suggest a relationship. Furthermore, the pressures at the 10%, 20%, and 30% BW loads on the right or left shoulder are higher than the pressure thresholds (30 mm Hg) to occlude local skin and muscle blood flow.8 Children commonly carry backpack loads of 22% BW4,5; 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 long-term 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. Correspondence: Dr Hargens, 350 Dickinson St, Suite 121, San Diego, CA 92103-8894 (ahargens@ucsd.edu). Back to top Article Information Author Contributions: Dr Hargens had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Funding/Support: This study was supported by the David Sutherland Endowment Fund, San Diego. References 1. Pascoe DDPascoe DEWang YTShim DKim CK Influence of carrying book bags on gait cycle and posture of youths. Ergonomics 1997;40631- 641PubMedGoogle ScholarCrossref 2. Grimmer KAWilliams MTGill TK The associations between adolescent head-on-neck posture, backpack weight, and anthropometric features. Spine 1999;242262- 2267PubMedGoogle ScholarCrossref 3. Burton AKClarke RDMcClune TDTillotson KM The natural history of low back pain in adolescents. Spine 1996;212323- 2328PubMedGoogle ScholarCrossref 4. Watson KDPapageorgiou ACJones GT et al. Low back pain in schoolchildren: occurrence and characteristics. Pain 2002;9787- 92PubMedGoogle ScholarCrossref 5. Negrini SCarabalona RSibilla P Backpack as a daily load for schoolchildren. Lancet 1999;3541974PubMedGoogle ScholarCrossref 6. Bijur PESilver WGallagher EJ Reliability of the visual analog scale for measurement of acute pain. Acad Emerg Med 2001;81153- 1157PubMedGoogle ScholarCrossref 7. Becker RWirz DWolf CGopfert BNebelung WFriederich N Measurement of meniscofemoral contact pressure after repair of bucket-handle tears with biodegradable implants. Arch Orthop Trauma Surg 2005;125254- 260PubMedGoogle ScholarCrossref 8. Kosiak M Etiology and pathology of ischemic ulcers. Arch Phys Med Rehabil 1959;4062- 69PubMedGoogle Scholar 9. Balague FSkovron MNordin MDutoit GWaldburger M Low back pain in schoolchildren: a study of familial and psychological factors. Spine 1995;201265- 1270PubMedGoogle Scholar 10. Vacheron JJPoumarat GChandezon RVanneuville G Changes of contour of the spine caused by load carrying. Surg Radiol Anat 1999;21109- 113PubMedGoogle ScholarCrossref

Journal

Archives of Pediatrics & Adolescent Medicine – American Medical Association

Published: Dec 1, 2005

Keywords: child,pain

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