School backpacks: It's more than just a weight problem

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Work 34 (2009) 481–494 DOI 10.3233/WOR-2009-0949 IOS Press

School backpacks: It’s more than just a weight problem Nancy R. Talbotta,∗ , Amit Bhattacharyab , Kermit G. Davisb , Rakesh Shukla b and Linda Levin b a

Department of Rehabilitation Sciences, College of Allied Health Sciences, University of Cincinnati College, Cincinnati, OH, USA b Department of Environmental Health, College of Medicine, University of Cincinnati, Cincinnati, OH, USA

Received 17 August 2009 Accepted 31 August 2009

Abstract. The objectives of this study were to 1) describe the characteristics of the backpacks used by students 10–18 years of age, 2) describe self reported pain related to backpack use and 3) evaluate the relationship between self reported pain and perceived backpack weight, duration of backpack use and posture when wearing a backpack. A cross-sectional survey of 871 students assessed the features of the backpack carried; the self perceived backpack weight, duration and posture; and any backpack related pain. Results indicate that 99% of students surveyed carry backpacks, 83% carry their backpacks over both shoulders and the presence of adjustable shoulder straps were the most common feature of the backpacks. Half of the students perceive their backpack as heavy and 46% indicate they carry the backpack 10–20 minutes to and from school. Pain attributed to backpack use was reported by 33.5% of the students. Perceived backpack weight, duration of backpack carriage, posture, gender and school district were significantly associated with reported symptoms. Although other socioeconomic and demographic characteristics may contribute to backpack related pain, this study suggests that students perceive a relationship between backpack use, the duration of use, posture and pain supporting the suggestion that simple weight-based controls of backpacks may not be sufficient to eliminate pain perceived as due to backpack use. Keywords: Pain, students, posture, back, shoulder, biomechanical load

1. Introduction As society has become more mobile, the physical demands on children have changed. Students now carry books and supplies to, from and often during school in a bag referred to as a backpack, knapsack, rucksack, book satchel, book bag or book pack. It has been estimated that over 40 million students across the United States carry their school materials in backpacks [37] and serious concerns about the harmful effects of backpacks are growing [35]. Recommendations of a limit of backpack weight have been made [1,8,54] and guidelines for safe back pack use are outlined by mul∗ Address for correspondence: Nancy Talbott, University of Cincinnati, PO Box 670394, Cincinnati, OH 45267-0394, USA. Tel.: +1 513 558 7475; Fax: +1 513 558 7474; E-mail: [email protected].

tiple professional associations including the American Academy of Orthopedic Surgeons, the American Physical Therapy Association and the American Occupational Therapy Association. Currently, however, limits are loosely based on a small amount of scientific literature concerning the effects of backpacks on posture, muscle activity, gait and exertion [2,7,13]. Traditionally, the limits put forth in the guidelines have corresponded to percent of body weight. For example, a limit of 10% of the body weight has been proposed [1, 7,54] independent of the age of the student and without accounting for age, maturation and growth differences. Two characteristics of backpack use that are consistently discussed as potentially influencing the effects backpacks have on the body include backpack weight and the duration of backpack carriage. School backpacks weighing up to 30 kg (66 lbs) have been report-

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N.R. Talbott et al. / School backpacks: It’s more than just a weight problem

ed in the literature [30] with amounts carried ranging from an average of 10.2% of the body weight [20] to amounts that exceed 20% or even 25% of the body weight [35,52]. Although quantification of the amount of time a backpack is used is less studied than backpack weight, Grimmer and Williams [21] did report that longer durations of carrying loaded backpacks appeared to be strongly associated with low back pain for boys and girls. Young and associates also suggested that the time a heavy backpack was carried was associated with back pain [58] and Chiang, et al. suggest that time may be a critical factor in students reporting backpack related back pain [11]. Studies of the relationships between both factors, i.e. different backpack weights and different lengths of carrying the backpack, and backpack related pain are needed to further clarify any relationships. Currently, the association between backpack use and musculoskeletal symptoms is also not clear. Pascoe [37] reported muscle soreness as the most commonly reported physical symptom (67.2%) followed by back pain (50.8%), numbness (24.5%) and shoulder pain (14.7%). However, the association between pain and backpack weight may not be direct. The lifetime prevalence of low back pain in adolescents has been found to range between 10% and 60% [5,25,29,31,40]. Multiple factors have been found to be correlated with the low back pain including a high body mass index, (> 25 kg/m2 ), feelings of depression and anxiety, a history of low back pain in siblings or in parents, daily smoking, decreased lumbar extension, decreased flexibility of the hamstrings, decreased endurance and strength of the abdominal and back muscles [15,25,32,39,50]. Other studies have shown no association between back pain in adolescents and clinical examinations, strength, postural deviations, flexibility, BMI, parental pain or smoking [6,27,42]. At the same time, age, gender and physical activity have also been identified as potential contributors to low back pain. The complicated nature of low back pain may contribute to the mixed findings of an association between backpack use and complaints of pain and other symptoms. Viry et al. [53] indicated that backpack use was significantly related to low back pain. Shier-Neiss et al. also reported that children with back pain were more likely to carry a heavier backpack and to use their backpack more during the school day [44]. Others, however, have questioned this relationship [17,28,55]. Wiersema et al. [56] reported that an estimated 12,688 acute injuries were associated with backpack use between 1999 and 2000 but indicate that the majority are due

to tripping over the backpack (28%) or getting hit by a backpack (13%) and result in injuries to the head and face (22%), hand (14%) or wrist/elbow (14%). Wearing a backpack accounted for only 13% of the injuries and the back was the area of complaint in only 11% of the cases. These numbers, however, are based on data from the US Consumer Product Safety Commission and do not reflect total injuries, only those treated in hospital emergency departments. These acute episodes are also less reflective of symptoms that occur more gradually. The evidence, however, that backpain in adolescents is associated with an increased risk of low back pain in adulthood [10,24] and the lack of agreement about the short or long term affects of backpack use supports a continued need to clarify the relationships between pain and backpack use. Identifying the types of backpacks commonly used including the features of those backpacks will assist in understanding how backpacks are worn while characteristics such as weight and the amount of time a backpack is carried can illuminate mechanical elements and how these relate to symptoms. Therefore, this study is designed to investigate these multiple factors as perceived by students with the aims of identifying trends in a large population. More specifically, the objective of this study is to 1) describe the backpacks currently used by students in selected school districts, 2) describe the self reported pain students relate to backpack use and 3) determine the association between self reported pain in children in grades 4–12 in selected school districts and perceived backpack weight, time carried and posture.

2. Methods 2.1. Study design A cross-sectional questionnaire survey was administered to students within three school districts, hereafter referred to as school district A (SDA), school district B (SDB) and school district C (SDC). Students in SDA completed the survey in the autumn, within a month of the start of the school year while students in SDB and SDC completed the survey in the spring, at the end of the school year. The timing of the distribution of the survey was dictated by the participating school district but did permit a comparison of reported symptoms at the beginning and the end of the school year. A survey was chosen for the design due to the desire to have a large number of participants in the study who


represented a range of ages. While laboratory measures would provide more objective measures, survey questionnaires are widely used to investigate low back problems in adolescents [47], to document backpack use [20] and to assess the discomfort and activities of children [12]. Self reported scales of postural deformities in patients with idiopathic scoliosis have also been utilized with strong correlation reported between responses and curve magnitude [43]. 2.2. Participants Three school districts in the metropolitan area of Cincinnati, Ohio, USA took part in this study. All of the schools were outside the city’s urban school district and were similar for racial diversity, student expenditure and student performance. All the children in grades 4 through 12 (9–18 years of age) in SDA and SDB and in grades 4–8 in SDC were invited to complete the questionnaire. High school students in SDC did not participate due to lack of permission from the individual high schools in the district. 2.3. Questionnaire The questionnaire utilized in this study was modified from the survey utilized by Grimmer and Williams [20]. Their original tool collected information about the backpack features, time spent carrying the backpack, activity after school, medical conditions and symptoms. For this study, additional questions was modified to reflect information needed to assess backpack features more in detail, patterns of backpack carriage, self perceived weight of the backpack, self perceived time the backpack was worn each day, and self perceived pain and posture. Lists of backpack characteristics (straps, belts, wheels) and methods of carriage (one shoulder, two shoulders) were incorporated into the questionnaire to record the backpack features and method of carriage. Self-perceived weight was indicated by students as being light, medium or heavy. A list of times of backpack carriage both to school and from school (0–5 minutes, 6–10 minutes, 11–15 minutes, 16–24 minutes, > minutes) was used to record carriage times. Posture was assessed by questions dealing with perception of position (stooped, leaning forward, leaning sideways, no change) and the perception of time spent standing upright (all of the time, most of the time, some of the time, very little, always bent over). Two questions were used to record the perception of pain. One was general in which students circled yes or no to the question

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“Do you have any pain at the present time that you believe is due to wearing your backpack/bag? ”. The second provided a list of specific types of symptoms (muscle soreness, lower back pain, neck pain, tingling in arms/legs, upper back pain, leg pain, arm pain, other) for the student to check. The specific questions related to each of these areas and can be found in Table 1. The questionnaire was piloted with a small group of children (n = 3) as well as a group of parents and teachers (n = 4). Repetitive questions were removed and verbiage modified for a younger age group reading level (Flesch Kincaid Grade level of 7.5). The final questionnaire was approved by the University of Cincinnati’s Institutional Review Board as well as the principals and superintendents of each school district.

2.4. Distribution and collection of questionnaires As required by the school districts, three methods of distribution and collection of the questionnaire were utilized. Method one involved the homeroom teacher (the teacher responsible for the first meeting of the day) passing out the survey and asking students to return the survey to the homeroom teacher. This method was utilized in grades 4–8 in SDB and SDC. Method two involved the homeroom teacher passing out the survey and asking students to return the survey to the investigators in a study provided self addressed stamped envelope. This method was utilized in grades 4–12 in SDA. Method three involved mailing the survey to the home address of students and asking students to return the survey to the investigators in a study provided self addressed stamped envelope. This method was utilized in grades 9–12 in SDB. Return rates for each method were similar.

2.5. Data and statistical analyses Data was entered into an Excel spreadsheet and SAS used for descriptive analysis. Frequencies of all factors were completed with significant univariate trends being identified with chi-square tests. Multivariate statistical models for each of the responses to questions about pain were developed to determine the association of with self-perceived backpack weight, duration of backpack carriage, age, gender, school, and posture. Odds ratios were also calculated for these models.

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Table 1 Backpack Questionnaire. Data for the study was obtained from a backpack questionnaire. The questions in the table reflect the information gathered to describe the subjects who filled out the questionnaire (Questions 1, 2 and 3); to determine the characteristics of backpacks used by subjects (Questions 4 and 5); and to record the perceived backpack weight (Question 6), time carried to and from school (Questions 7 and 8), method of carriage (Questions 9 and 10), posture (Questions 11 and 12) and pain and pain related symptoms (Questions 13–16) Demographics BACKPACK CHARACTERISTICS

BACKPACK WEIGHT BACKPACK CARRY TIME

METHOD OF BACKPACK CARRIAGE

POSTURE

PAIN AND RELATED SYMPTOMS

1. Student’s age 2. Student’s grade 3. Student’s sex 4. What type of bag is used most often to carry books and classroom supplies to and from school? Backpack Gym Back/Duffle Bag Other type bag No bag used, books carried in arms 5. How often are the following features of a backpack/bag used (Circle one answer for each feature)? Waist Belt Don’t have it Never Sometimes Always Chest Strap Don’t have it Never Sometimes Always Wheels Don’t have it Never Sometimes Always Adjustable shoulder Straps Don’t have it Never Sometimes Always Padded Shoulder Straps Don’t have it Never Sometimes Always 6. Please rate the weight of the bag on a normal school day (Circle one) Light Medium Heavy 7. How long is the student’s backpack/bag normally carried on the way to school (Check one)? Do not include time sitting on the bus. Less than 5 minutes 6–10 minutes 11–15 minutes 15–24 minutes 25 minutes or more 8. How long is the student’s backpack/bag normally carried on the way home from school (Check one)? Do not include time sitting on the bus. Less than 5 minutes 6–10 minutes 11–15 minutes 15–24 minutes 25 minutes or more 9. Please check the description of the way in which the backpack/bag is normally carried to and from school: Over both shoulders In front using both hands Over the right shoulder Over the left shoulder In the right hand In the left hand Rolled Other (please describe) 10. Please list any reason that the backpack is carried in the manner chosen in the above question: 11. When walking with your backpack/bag, would you say you stand up straight (Check one): All of the time Most of the time Some of the time Very little Always bent over when wearing backpack/bag 12. When walking with your backpack/bag, do you assume any of the following postures (Check any that apply)? Stooping Leaning forward Leaning sideways None of the above 13. Do you have any pain at the present time that you believe is due to wearing your backpack/bag? No Yes 14. If yes, list the areas that where the pain is located 15. As a result of your backpack/bag, have you noticed any of the following (check all that apply)? Muscle soreness Upper Back Pain Lower Back pain Leg Pain Neck pain Arm Pain Tingling in arms/legs Other 16. If you checked any of the above, have you seen a health professional (doctor, nurse, trainer, therapist) regarding the condition? No Yes


3. Results 3.1. Response rate 871 surveys were received. Of those responding, 104 (11.9%) were in grade four, 87 (10%) were in grade five, 130(14.9%) were in grade six, 118 (13.5%) were in grade seven, 94(10.7%) were in grade eight, 160 (18.4%) were in grade nine, 75(8.6%) were in grade ten, 78 (9%) were in grade eleven and 26 (3%) were in grade twelve. Forty one percent were males and 59% were females. The sample size (n = 871) represented 18% of all students in the three school districts. The majority of students in all school districts were Caucasian (90% in SDA, 92% in SDB, 97% in SDC) with the remainder African American (3% in SDA, 2% in SDB, 1% in SDC) or other minorities (7% in SDA, 6% in SDB, 2% in SDC). The average expenditure per pupil was $7,221 in SBA, $10,250 in SDB, and $7,358 in SDC. In all of the school districts, the student graduation rate from high school was above 90%. Of those responding 99.9% (870/871), reported using a backpack. The 870 surveys were included in data analysis. 3.2. Backpack characteristics and method of carriage Backpacks were found to have many common features with students using them similarly across the grades. Adjustable shoulder straps were the most common characteristic with 807 students reporting having this feature and 90% of those with these straps used this feature. Padded shoulder straps were also common as they were found in 88% of the backpacks and used 87% of the time. Hand straps were found in 69% of the backpacks but used by only 47% of the students. Backpack with wheels were reported present by only 17% of the students with only 2.9% indicating they actually pulled the backpack and used the rolling feature. The waist belt was common to 46% of the respondents and chest straps to 29% of the backpacks but less than 25% of the students used these features. The majority of the students (82%) typically carried their backpack over both shoulders. More males than females (p = 0.0106) carried the backpack over one shoulder. A greater percentage of students in fourth, eleventh and twelfth grades also reported carrying their backpacks over one shoulder when compared to students in grades 5 through 10 (p = 0.0004). When asked why students carried their backpack in a given

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manner, safety and comfort (32.9%), education or best way (26.6%) and heavy weight (12.3%) were most frequently given as the reason. Among students who reported carrying the backpack over two shoulders, comfort (36.3%), education or best way (28.5%) and heavy weight (13.3%) were still found to be the reason for the chosen method of carriage. However, in students who reported carrying the backpack reasons included not enough time to put on both straps (12.53%), habit (11.0%), distribution of weight (15.3%) and ease of carrying (22.4%). 3.3. Backpack weight and posture Backpacks were perceived as being heavy, medium and light by 49%, 46% and 5% of the students, respectively. A greater percentage of students in the 4 th , 11th and 12th grades perceived their backpacks as being light while a greater percentage of 9 th grade students perceived that their backpacks were heavy. Of the 870 students, 12% reported carrying their backpack less than 10 minutes, 25% carried it 10 to 19 minutes and 61% carried it over 20 minutes to and from school on a given day. The percent of students who carried their backpack for over 20 minutes was greatest for 6th , 7th , 8th and 9th grade students and least for 10–12 th graders but these differences were not significant. In response to the survey question “How often do you stand up straight while wearing a backpack?” 26% reported they stand up straight very little or were always in a bent position, 26% reported they sometimes stand up straight and 48% of the respondents reported they standup straight always or most of the time. In describing their perception of their posture, a stooped or forward leaning posture while carrying the backpack was identified by 68.2% of the respondents, 2.9% indicated they leaned to the side only, 3.5% indicated they stooped/leaned forward as well as leaned to the side (combination of forward and lateral flexion), and 25.3% reported they always stood up straight. 3.4. Pain Of those surveyed, 33.5% of the students reported that they were currently experiencing pain that they attributed to backpack use with 54% of the respondents reporting at least one symptom that they attributed to the backpack. Low back pain (LBP) was most frequently reported (33.2%) followed by muscle soreness (24.4%), neck pain (23.5%), upper back pain (UBP)

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N.R. Talbott et al. / School backpacks: It’s more than just a weight problem Table 2 Backpack Characteristics. The percent of students who report they have or do not have a hand strap, a waistbelt, a chest strap, wheels, adjustable shoulder straps and/or padded shoulder straps are listed. Adjustable shoulder straps and padded shoulder straps are found on the majority of backpacks. Over 80% of the backpacks reportedly did not have wheels while 14.15% of those students reportedly had wheels indicate that they do not use the wheels

Always Don’t Have It Never Sometimes

Hand Strap 4.19 22.61 28.23 44.98

Waistbelt 0.71 52.14 38.21 8.93

Chest Strap 2.15 69.14 26.20 2.51

Wheels 0.95 83.12 14.15 1.78

Adjustable Shoulder Straps 76.26 3.24 2.52 17.99

Padded Shoulder Straps 82.15 8.87 1.06 7.92

Table 3 Perceived Weight of Backpack, Duration of Backpack Carriage and Method of Backpack Carriage by Gender and Grade. The perception of backpack weight, minutes of backpack carriage and method of backpack carriage are divided by gender and grade. Chi square tests indicate perceptions of backpack weight are significantly different by gender and grade. Females report heavier backpack and longer times of carriage. Younger students (4th grade) report lighter backpacks. Duration of backpack carriage, while less in younger and older students, is not significant. Method of backpack carriage varies significantly by grade and gender. More males report carrying their backpack over one shoulder. More younger students (students in grade 4) report rolling their backpack Perceived Weight of Backpack

% of Total Population Gender % of Females % of Males Grade % of 4th % of 5th –6th % of 7th –8th % of 9th –10th % of 11th –12th

Heavy 49.31

Medium 45.75

Light 4.94

52.6 44.6 p = 0.04

43.6 48.8

3.7 6.7

8.6 47.0 50.0 63.0 45.1 p < 0.001

65.7 48.4 47.2 33.2 46.1

25.7 4.7 2.9 3.8 8.8

Minutes of BP Carriage < 10 12.15

Method of BP Carriage Both = Both Shoulders One = One Shoulder Both One Rolled Other 82.07 13.22 1.38 3.33

20–29 24.42

> 30 37.43

11.6 23.1 12.8 27.6 p = 0.001

21.0 29.0

44.4 30.6

85.1 10.4 77.7 17.3 p = 0.01

1.4 1.4

3.1 3.6

31.4 27.8 23.7 25.8 37.4 p = 0.08

18.1 19.9 21.3 21.0 14.1

5.7 8.8 7.1 7.2 2.0

75.2 15.3 80.7 13.8 86.7 12.3 85.5 11.9 74.5 14.7 p = 0.0004

5.7 1.8 0.5 0 1.0

3.8 3.7 0.5 2.6 9.8

(10.5%), arm pain (5.8%), tingling (4%), and leg pain (3.6%). When asked if the subject sought treatment from a doctor, therapist or other medical personnel for the pain associated with the backpack wear, only 3.3% of the individuals reported that they had received such treatment. 3.5. Univariate associations for pain There were significant differences (p < 0.002) in the reporting of pain, LBP, and muscle soreness in the different school districts (up to 20% difference). Perceived pain was impacted (p < 0.03) by grade level (see Table 5) with the highest rates occurring in grades 8th to 11th . Age had similar trends as grade. In general, females reported more discomfort (p < 0.0001) than males (Table 5). Females had 15% more general pain, 16% more LBP, 14% more neck pain, 13% more muscle soreness, 9% more UBP, and 3% more arm pain than males.

10–19 25.00

44.8 43.5 47.9 45.5 46.5

There was a significant association (p < 0.0001) between pain and perceived weight, pain and time carrying the backpack, and pain and posture while carrying the backpack (Table 4). Pain was more likely to be reported if weight was perceived as heavy although pain was also reported by 14.7% of individuals who perceived their backpack as light. Low back pain was the most common specific symptom reported by individuals who perceived the backpack weight as “heavy” (45%) followed by muscle soreness (34%) and neck pain (29%). There was also a positive association between the time the backpack was carried and reports of pain. As the reported time carrying the backpack to school or the time carrying the backpack from school increased, individuals reported significantly more pain, LBP, UBP, muscle soreness, and neck pain (p < 0.0001). When the ratings for time carrying the backpack to and from were added to represent a “total” time categorical variable, a steady increasing trend was found for longer times carrying the backpack (see Table 4). The combination of carrying the back-

Table 4

1.96 4.87 14.41 16.36 19.66 p < 0.0001

19.15 p = 0.0002 12.99 p = 0.0002 17.05 p = 0.03 6.15

Perception of time spent standing straight while wearing the backpack All of the time 113 15.69 11.56 9.8 Most of the time 308 19.48 23.05 14.61 Some of the time 222 40.99 38.29 30.63 Very Little 110 53.64 49.09 39.09 Always Bent over 117 56.41 57.26 40.17 p < 0.0001 p < 0.0001 p < 0.0001

Perception of posture while wearing the backpack Stooped position 141 52.48 54.61 p < 0.0001 p < 0.0001 Leaning forward 585 42.05 41.71 p < 0.0001 p < 0.0001 Leans to the side 88 43.18 44.32 p = 0.05 p = 0.02 No change 130 9.23 7.69 29.58 p < 0.0001 31.79 p < 0.0001 36.36 p = 0.01 5.38

7.5 8.38 14.71 16.07 75 p < 0.0001

25 31.47 42.35 48.21 100 p < 0.0001

18.75 21.83 34.12 32.14 100 p < 0.0001

Perceived Duration of Backpack Carriage < 10 minutes 246 24.58 10–19 minutes 394 31.22 20–29 minutes 170 44.12 30–39 minutes 56 51.79 > 40 minutes 4 100 p < 0.0001

36.17 p = 0.0001 29.74 p < 0.0001 34.09 p = 0.01 7.69

9.8 12.66 27.93 42.73 40.17 p < 0.0001

18.33 20.81 35.29 28.57 75 p < 0.0001

7.09 p = 0.01 4.79 p = 0.01 9.09 p = 0.003 0

0 1.3 6.31 5.45 5.98 p = 0.003

2.92 3.55 3.53 3.57 25 p = 0.22

7.8 p = 0.25 5.98 p = 0.66 10.23 p = 0.06 8.46

1.96 3.9 7.66 6.36 10.26 p = 0.03

5 5.33 7.65 1.79 50 p = 0.001

5.67 p = 0.20 4.79 p = 0.03 5.68 p = 0.33 1.54

0.98 2.92 4.5 2.73 8.55 p = 0.03

2.92 2.79 5.88 5.36 25 p = 0.06

7.09 p = 0.01 4.27 p = 0.03 4.55 p = 0.501 1.54

1.96 1.62 4.05 7.27 4.27 p = 0.06

3.75 2.28 4.12 3.57 25 p = 0.10

Relationship of Perception of Backpack Weight, Time of Backpack Carriage and Posture to Perception of Pain and Related Symptoms. The percent of students reporting pain, soreness, tingling or medical treatment are listed by perception of backpack weight, time of backpack carriage and posture. Chi-square tests were completed to analyze associations between the perceived symptoms and perceived backpack weight, carry time and posture. Results indicate that as the perception of weight, time and forward bending increase, the percent of students reporting pain or pain related symptoms also increases. When analyzing the perception of posture, individual chi square tests were performed to compare each response of posture (stooped, leaning forward and side leaning) to no change n Pain Low Back Pain Muscle Soreness Upper Back Pain Neck Pain Leg Pain Arm Pain Tingling Medical Treatment Perceived Backpack Weight Heavy 429 45.92 45.22 33.8 14.45 29.14 4.66 6.99 5.59 4.2 Medium 399 22.06 21.55 15.54 5.76 18.55 2.51 4.51 2.01 2.51 Light 42 14.71 14.71 8.82 2.94 11.76 0 5.88 0 2.94 p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p = 0.001 p = 0.14 p = 0.41 p = 0.02 p = 0.54

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Table 5 Relationship of Perceived Pain and Discomfort with Grade, Gender and School district. The percent of students reporting pain, soreness, tingling or medical treatment are listed by grade, gender and school district. Chi-square tests were completed to analyze associations between the perceived symptoms and grade, gender and school district. Results indicate that grade (a reflection of age), gender and school district are significantly associated with reported pain, low back pain, muscle soreness, upper back pain and arm pain. Chi-square tests involving school district are reported for comparisons between all districts. As SDC only included students in grades 4–8, results tests were repeated to compare only SDA and SDB n

Pain

Low Back Pain

Muscle Soreness

Upper Back Neck Pain Pain

Leg Pain

Arm Pain

Tingling

Medical Treatment

Grade 4 5 6 7 8 9 10 11 12

104 87 130 118 94 160 75 77 25

19.23 13.46 32.18 22.99 26.92 29.23 30.51 33.9 39.36 38.3 41.25 42.53 34.67 42.67 45.45 44.16 40 32 p = 0.004 p < 0.0001 p

3.85 4.6 3.08 3.39 1.06 4.38 2.67 6.49 0 p = 0.79

0.96 3.45 8.46 7.63 6.38 5 2.67 12 0 p = 0.03

0.96 4.6 4.62 2.54 4.26 5.63 4 3.9 0 p = 0.76

1.92 1.15 3.85 1.69 2.13 4.38 4 9.09 0 p = 0.17

Gender Female Male

511 359

39.92 39.92 29.55 14.09 29.16 4.11 24.51 23.68 16.99 5.01 15.32 2.79 p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p = 0.30

7.05 3.9 p = 0.05

4.31 3.06 p = 0.35

4.31 1.95 p = 0.06

11.54 6.73 21.84 3.45 20 10.77 22.03 9.32 25.53 6.38 35 17.5 32 10.67 27.27 16.88 20 0 = 0.004 p = 0.006

12.5 19.54 28.46 20.34 22.34 30.63 24 24.68 28 p = 0.08

School District SDA 534 27.72 27.9 19.29 16.85 21.54 5.81 9.36 2.43 5.43 SDB 286 45.8 44.76 34.27 0 29.02 0 0 5.59 0 SDC 49 24.49 24.49 22.45 0 12.24 0 0 6.12 0 All districts p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p = 0.01 p = 0.0004 p < 0.0001 p < 0.0001 p = 0.009 Only SDA and SDB p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p = 0.02 p < 0.0001 p < 0.0001 p = 0.02 p = 0.009

pack more than 40 minutes to and from school resulted in 100% of the students having pain, LBP, and muscle soreness and 75% of these individuals having neck and upper back pain, however only 4 students reported this length of duration of carriage. Self reported pain, LBP, UBP, neck pain, muscle soreness, leg pain, and medical treatment were also greater in those individuals who also reported a posture of leaning forward, stooping or leading sideways (Table 4). Results show that the number of individuals who reported medical intervention was very low and included only 3.3% of those individuals reporting pain. Reports of standing in a stooped position or with a forward lean, however, were significantly associated with the number of students seeking medical treatment (p < 0.05). 3.6. Multivariate associations with pain outcomes Table 6 shows the results of the multivariate logistic regression models that were developed for pain, LBP, neck pain, muscle soreness, UBP, and arm pain. In all the models, school, gender, grade, weight, posture, and time variables were included. All the following odds ratios (ORs) are controlled for all other factors in

the models and include 95% confidence intervals (CIs). Perceived backpack weight (heavy vs. light) had an OR of 1.64 (CI 1.21–2.25) with pain; an OR of 1.50 (CI 1.10–2.03) with low back pain; and an OR of 1.50 (CI 1.04–2.04) for muscle soreness. Self reported posture (little/never standing up straight vs. most of the time/all of the time standing up straight) also was a significant factor in all models with ORs ranging from 1.35 for muscle soreness to 1.48 for general pain. The presence or absence of a forward lean (stooping/leaning forward vs. no leaning or stooping) was also a significant factor in all models for pain (p < 0.05). Females were found to be more at risk of pain, LBP, muscle soreness, neck pain, and upper back pain than males. The way the backpack was reportedly carried (over both shoulders vs. over one shoulder) was found to be a significant a risk factor for UBP and arm pain (ORs > 1.68) but not for general pain, LBP, neck pain or muscle soreness indicating there was a greater risk for both UBP and arm when wearing a backpack on one shoulder than when wearing on both shoulders. The interactions of all factors, including the interaction between time carried and weight of the backpack, were entered into each of the logistic regression models but after it was


489

Table 6 Multivariate logistic regression for pain outcomes. The outcomes of pain, low back pain, neck pain, muscle soreness, upper back pain, arm pain, leg pain, tingling and medical treatment were modeled using multivariate logistic regression. Variables of school district, gender, grade, perceived backpack weight (BP Weight), perceived carriage time of the backpack (BP Time), perception of the way the backpack is carried (Way Carried), perception of the time spent in the upright posture (Posture) and the perception of the presence or absence of forward leaning when carrying the backpack (Forward Lean) were included in the models. Analysis was completed with and without all interactions. As there were no significant interactions found, results above list the intercept for each variable in the model and the associated p-value for models without the interactions Estimate p-value PAIN Intercept −5.338 School 0.551 < 0.0001 Gender −0.649 0.0002 Grade 0.137 0.0002 BP Weight 0.495 0.001 BP Time 0.402 < 0.0001 Way Carried 0.036 0.79 Posture 0.394 < 0.0001 Forward Lean 0.562 0.01 UPPER BACK PAIN Intercept −1.707 School −3.471 < 0.0001 Gender −0.993 0.001 Grade 0.129 0.03 BP Weight 0.423 0.09 BP Time 0.314 0.03 Way Carried 0.516 0.003 Posture 0.313 0.006 Forward Lean 0.563 0.03

Estimate p-value LOW BACK PAIN Intercept −5.103 School 0.542 < 0.0001 Gender −0.670 0.0001 Grade 0.189 < 0.0001 BP Weight 0.402 0.01 BP Time 0.37 < 0.0001 Way Carried −0.134 0.33 Posture 0.36 < 0.0001 Forward Lean 0.566 0.01 MUSCLE SORENESS Intercept −5.564 School 0.618 < 0.0001 Gender −0.648 0.0006 Grade 0.128 0.001 BP Weight 0.377 0.03 BP Time 0.319 0.001 Way Carried 0.137 0.32 Posture 0.301 0.0001 Forward Lean 0.928 0.0002

determined the interactions were not significant, final models excluded these interactions.

4. Discussion Before the results can be discussed in detail, several considerations regarding the methodology must be elaborated upon including the generalization of results, the response rate, the cross sectional subjective study design and the multidimensional etiology of adolescent pain. In choosing the participants in this study, the school districts involved in this study represented the typical suburban school district in the Cincinnati area and they may not have been totally representative of all school systems. According to the National Center for Education Statistic, the average minority enrollment in the 500 largest school districts in the United States was 24.8% African American and 29.6% other minorities. In addition, the average expenditures per pupil were $6,506 for all districts in the United States. These figures are different from those in the school districts participating in this study. Policies regarding backpack wear may also further differentiate school districts. Students in some school districts are permitted to carry backpacks throughout the day while others must store the backpack between classes and still others pro-

Estimate NECK PAIN Intercept −3.46 School 0.192 Gender −0.688 Grade 0.072 BP Weight −0.059 BP Time 0.290 Way Carried 0.152 Posture 0.422 Forward Lean 0.636 ARM PAIN Intercept −1.857 School −2.853 Gender −0.439 Grade 0.058 BP Weight 0.365 BP Time 0.009 Way Carried 0.568 Posture 0.332 Forward Lean −0.293

p-value

0.18 0.0002 0.07 0.72 0.003 0.26 < 0.0001 0.01 < 0.0001 0.21 0.42 0.22 0.96 0.001 0.02 0.45

hibit the use of backpacks. In each of the schools participating in this study, grade school children (grades 4–8) were not permitted to carry backpacks throughout the day. Students in grades 9–12 had the option of storing the backpack or carrying it from class to class. Considering each of these potential variables, it is evident that the results of this study would be most applicable to similar suburban school systems and least applicable to those with dissimilar ethnic populations, economic resources and backpack policies. The response rate of the study may also impact the interpretation of results. It is likely that the low response rate was due to sampling strategy. All students were given an opportunity to respond but the questionnaires could not be distributed, completed and collected in a single classroom setting. Returns were dependent on students mailing the questionnaires or bringing them back to the school. These requirements may have been considered too difficult or time consuming and limited the return rate. In addition, responses from SDB and SDC reflected end of the year perceptions while the survey of SDA was scheduled early in the school year. Response rate may have been better if follow up letters or contacts were used. However, these follow-ups would have changed the times of assessment possibly altering the difference between perceptions at the beginning of the school year and those at the end. Perhaps

490


Table 7 Odds ratios for pain outcomes. Adjusted odds ratios (OR) as well as the lower limit (LL 95%) and the upper limit (UL 95%) of the 95% confidence interval for the odds ratio are listed for the outcomes of pain, low back pain, neck pain, upper back pain, muscle soreness and arm pain. Comparisons are indicated (comparison values of 1:0) OR School SDB:SDA Gender Male: Female Grade 9–12: 4–8 BP Weight Heavy: Light BP Time > 30 mins: 30 mins: < 30 mins Way Carried One shoulder: two shoulders Posture Always bent over/little time standing straight: always/most of the time up straight Forward Lean Stooped or leaning forward: no change in posture

UL 95%

1.74 0.52 1.15 1.64 1.50 1.04 1.48

LL 95% PAIN 1.34 0.37 1.07 1.21 1.24 0.80 1.28

1.75

1.16

OR

2.25 0.73 1.23 2.25 1.80 1.34 1.72

LL 95% UL 95% LOW BACK PAIN 1.72 1.33 2.24 0.51 0.37 0.72 1.21 1.12 1.30 1.50 1.10 2.03 1.44 1.20 1.74 0.88 0.67 1.15 1.42 1.24 1.66

1.21 0.50 1.07 0.94 1.34 1.64 1.53

2.65

1.76

1.89

1.17

2.62

OR

OR LL 95% UL 95% UPPER BACK PAIN 0.03 0.01 0.13 0.37 0.20 0.68 1.14 1.01 1.28 1.53 0.94 2.47 1.37 1.03 1.81 1.68 1.18 2.37 1.37 1.10 1.71

OR LL 95% UL 95% MUSCLE SORENESS 1.86 1.41 2.45 0.52 0.36 0.76 1.14 1.05 1.23 1.50 1.04 2.04 1.38 1.13 1.67 1.15 0.88 1.50 1.35 1.16 1.58

0.06 0.65 1.16 1.44 1.01 1.76 1.39

1.76

2.53

0.75

0.89

more significant, follow ups for SDB and SDC would have occurred following the completion of the school year or at a time when some students were taking final yearly examinations. Backpack use would have been different during these exams or during vacation from school potentially altering responses within the school district. While the percent participation (18%) was less than desired, the number of respondents was large and represented all grades between 4 th and 12th grade. The cohort represents one of the largest groups of schoolaged children in the United States and permits comparisons of age, gender, school district and backpack wear along with symptoms of pain in multiple body regions. Further, the study found similar values of LBP as those found in the literature. The prevalence of reported pain related to backpack use in the current student (34%) is less than the 46.1% reported by Negrini and Carabalona [34] but similar to the 32.5% reported by Goodgold et al. [18]. The fact that the percent reporting pain is less than or equal to what has been found in other cohorts suggests that the sampling technique was not biased toward a population who have perceived difficulties with backpacks. It must also be acknowledged that the outcomes in this study reflect subjective responses that are crosssectional. Perceptions are not objective and responses

2.49

1.55

4.14

OR

LL 95% UL 95% NECK PAIN 0.92 1.60 0.35 0.73 1.00 1.16 0.69 1.30 1.10 1.62 0.90 1.52 1.31 1.78

1.19

3.01

LL 95% UL 95% ARM PAIN 0.14 0.24 0.32 1.29 0.92 1.22 0.80 2.59 0.72 1.42 1.25 2.49 1.06 1.84

0.35

1.59

themselves may not reflect current health status. At the same time, the use of perceptions of weight and discomfort is prevalent in the literature [18,26,44]. SheirNeiss et al found consistent self-reporting of back pain and backpack use [44]. Jones et al. [29] utilized a questionnaire to asses low back pain history in children aged 11–16 years and concluded that the questionnaire approach was both reliable and valid. Suggestions by others also support the use of a questionnaire approach with children [45,46] as an effective method to assess pain. There is some indication that posture may be better assessed using inclinometers or goniometers [23] although the perception of the presence or absence of trunk deformities has been validity in children with scoliosis [43]. The perception of pain in adolescents, however measured, is a multidimensional phenomenon and many demographic and psychosocial factors associated with pain in children [50,55] were not recorded on the questionnaire used in this study. Previously reported factors that are associated with back pain in children include time spent watching television [3,51],higher body mass index [20,44], family history of back pain [4,14] and psychological profiles [4,16]. Physical factors such as tight hamstrings and tight quadriceps have also been related to the development of low back pain [16]. The


perception of pain found in this study could certainly have been influenced by any or all of these factors and prevents any determination of a causal relationship between the reported pain and backpack wear, weight and posture. At the same time, the perception by students that the pain is related to backpack wear is important. New episodes of back pain are more common in individuals with a history of low back pain [57] and may have implications for the development of pain in adulthood. Whether the pain reported in this study is actually due to backpack wear or not, is not possible to determine, but the perception that pain is present due to the backpack should not be ignored. The fact that this was a cross sectional study prevents the ability to examine increases or decreases of pain over time. While perceptions between the different age groups can be compared, other factors such as environment, physical activity, work responsibilities and family history could account for changes between ages or grades. Causal relationships between all factors cannot be made and caution must be used since there is potential that the link between perceived weight, perceived time carrying the backpack, the perceived pain outcomes and age or grade might be due to factors not measured in this study. In spite of these potential limitations, the current study does relate backpack use to subjective pain and discomfort. In this study, both perceived backpack weight and the perceived duration of the backpack carriage were significantly associated with reports of backpack related pain or pain related symptoms. The lack of a significant effect of the interaction of perceived backpack weight and perceived duration of backpack carriage indicates each can be considered independent influences as post-hoc power values were above 0.90. The study results indicate that the greater the report of the time the backpack is carried or the greater the perceived weight of the backpack, the greater the number of individuals reporting pain or pain related symptoms – LBP, UBP, and muscle soreness. The consistent effects of reported backpack weight and carry time on pain indicates that the impact of backpacks could result from carrying backpacks that are perceived as either heavy or light. In other words, even carrying a light backpack for a long period of time may result in pain development. This finding may explain the similarities and differences found in other studies investigating weight and back pain. An increase in backpack weight and weight greater than 20% of the body weight have been found to be associated with back pain [22, 53]. In contrast, studies by Van Gent et al. [52] and

491

by Negrini and Carabalona [34] found no significant association with backpack weight and back pain. Time carried, however, was found to be associated with back pain [11,34]. The results from these studies and the current study suggest that the factor of time and not just weight is an important consideration in determining the affects of backpacks. The present study also found a significant association of pain outcomes with grade (a reflection of age), school district, and gender. Female students in grades 8–11 had a greater risk of reporting backpack related symptoms than younger students or students who were male. These findings are similar to those reported by Young et al. [58] and Grimmer and Williams [20]. One explanation of this could be that older grades are required to carry more books to and from school. Another explanation might be that maturation may play a role as peak growth rates occur at around 13 years for girls and 15 years for boys [48]. Students in grades 7–10 would be progressing through this growth period and have a greater disposition towards pain due to backpack use. Similarly, the rates for development would be different in males and females. The finding of greater reports of pain in females as compared to males is consistent with other literature [20,38,49]. While Negrini and Carabalona [34] found no statistical differences between genders, van Gent et al. [52] and Skaggs and associates (2006) reported significantly greater neck, shoulder and back complaints in girls than in boys. In the current study, the differences in pain levels between females and males were independent of grade (i.e. differences existed in all grades). The variable stages of development at one grade could explain the difference in responses between males and females when adjusted for age. In addition to gender and age, school district was a significant risk factor in this study. It is possible that the timing of the questionnaires may be the potential explanation for this. Students in two of the school districts (SDB and SDC) completed the questionnaires at the end of the school year (Spring) after having carried backpacks for nine months while the remaining school district (SDA) responded during the first month of their school year (Autumn). Those students who completed questionnaires in the autumn had significantly lower percentages of perceived pain, LBP, muscle soreness, and neck pain but had greater percentages of UBP, arm pain, leg pain, and medical treatment. These results suggest that students returning to school and carrying backpacks may go through an adjustment period in which they are susceptible to pain in the arms, upper

492


back, and legs. The adjustment period may also result in more acute trauma that results in medical treatment. On the other hand, long-term exposure (e.g. cumulative exposure over the school year) may be associated with more general pain and muscle soreness as well as LBP and neck pain. Finally, reported posture while carrying a backpack was also a significant factor in many of the logistic regression models for pain outcomes. A study by Murphy et al. [33] found significant associations between a flexed sitting posture and neck and upper back pain in schoolchildren while several laboratory studies have documented changes in posture when standing and walking while wearing a backpack. Grimmer and associates [21] found changes in the craniovertebral angle, an angle formed at the intersection of a horizontal line and a line drawn from the tragus of the ear and the spinous process of C7 and an effect of backpack weight on the horizontal movement of markers on the ear, neck, shoulder, hip, thigh, knee and ankle [19]. As weight was applied, anatomical points moved more anterior in an apparent dose-response relationship. This trunk flexion with a resulting neck extension was noted at all weights implying that postural deviations occur below the 10% bodyweight load. Anatomically, the changes in posture could result in strain on musculoskeletal structures, placing complex loads (shear and compression) on the ligaments, vertebral components or the muscles. Similar reports of trunk and neck postural changes have also documented a forward movement [9, Chow, 2007 #719]} although some have found no changes or a posterior movement [2] As studies have shown that there is an association between back pain in children and sitting [36,41,51], additional trunk flexion when standing while wearing a backpack may decrease the opportunity for a more upright posture. Changes in posture may also relate to the maintenance of balance and be a consideration for the acute injuries reported in hospitals [56]. In summary, the current study documented the characteristics of backpacks used by children in grades 4–12 and investigated the relationship of self reported backpack use with self-reported pain in children in grades 4–12. Perceived pain and pain related symptoms were found to be significantly associated with both perceived backpack weight and the duration of time the backpack is reportedly carried. This information suggests that both heavy and light backpacks may have detrimental effects for the wearer. While suggested backpack guidelines have addressed backpack weight, the time carried should also be considered. In addition, this

study found that the perceptions of backpack related pain were not just related to backpack weight and time carried but also to perceived posture, gender, grade and school district. These factors, along with other physical and psychosocial factors shown to be associated with adolescent pain [50], should be considered in future studies of the effects of backpacks.

Acknowledgements We would like to thank the students who participated as well as the parents, teachers, school administrators, and PTA officers of the three school districts for their assistance in the study. We would like to also thank Polly Freeman, Cyndy Cox, and Chunhui Hu for their assistance in data collection and analyses. Finally, we would like to acknowledge the Department of Environmental Health for funding this research.

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Copyright of Work is the property of IOS Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.

Copyright of Work is the property of IOS Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.