We conducted this study to examine the changes in postural angles with various backpack weight in preadolescent children.

We recruited healthy male children between 12–13 years from six schools of Mangalore city. Based on previous literature(2), power analysis with significance of 0.05, power of 0.80, a standard deviation of four degrees, and expected change in any postural angle (reference kept as cranio-vertebral angle) of five degrees were identified to calculate sample size for this study. A minimum sample of 199 is required to detect significant change between baseline and experimental conditions. 410 eligible male participants consented. A smaller portion of female participants also consented for the study but were not included for data analysis due to difficulty in achieving proportional gender representation in sample size. Age cohorts of 12 years and 13 years were made from male participants who volunteered for the study. Stratified random sampling was used to recruit 100 participants for each age cohort and pooled as total test population (n = 209).

The Ethical review committee of Srinivas College of Physiotherapy, Physiotherapy Research Center approved the study procedures. Design, method and measurement procedures were evaluated and approved by the Research and Development Wing of Rajiv Gandhi University of Health Sciences, Bangalore. The study procedure was explained to the recruited participants and informed consent was obtained from the parents or guardian. Permission was also obtained from the school principal and class teacher. Children with congenital and structural abnormalities, musculo-skeletal problems, neurological problems, and acute or post-acute illness were excluded. Nine subjects were excluded due to ill health, larger measurement variability and subject’s absence on the day of measurement. Sample recruitment, selection and measurements were carried out between December, 2007 to February, 2008.

The subjects were instructed to remove their shoes and to stand on the force plate (Bertec Corporation, USA) and the weight was recorded before taking measurements. The subjects were then instructed to stand on the stadiometer and the height in centimeters was noted. From the weight recorded, 5%, 10%, 15%, 20% and 25% of their bodyweight was calculated, which was implemented as their respective backpack loads. The subject was asked to stand erect near a wall with the right lateral side towards the wall to measure the arm length.

Functional reach test: To measure the functional reach of the participants, a point was marked on the wall at the level of the subject’s right acromian process. A leveled yardstick was then fixed to the wall at that point with the help of the marking. Subjects were then asked to stand in a relaxed stance with the shoulders perpendicular to the yardstick. They were asked to extend the elbow with the shoulder at 90 degrees of flexion, make a fist and hold the position for 3 seconds, and that position was then noted. The subjects were then asked to reach, as they could without stepping the outlined foot templates, and to hold for 3 seconds and that position was also noted. Functional reach was recorded as the difference between the two positions.

Postural angles measurements: With the subjects in standing position, adhesive photo reflective markers were placed on the right-sided lateral landmarks, which included the lateral canthus of the eye, the tragus, the greater trochanter and the lateral malleolus. A small photo reflective marker was also placed on the C7 spinous process and ensured that the landmark was detected on the photographs(7).

The subjects were instructed to stand comfortably in a normal standing position and to look straight ahead at a predetermined point on the foot template. To allow for visualization of the greater trochanter marker, the subjects were instructed to move the elbows forward but still touching the body and with minimal shoulder movement. The position was then checked prior to taking the photograph. The photograph was taken within 5 seconds after attaining the position. Sony 8 mega pixels digital camera was attached to an adjustable tripod stand, which was placed at a distance of 3 m from the subject’s right side and was positioned perpendicular to the ground(6-8). Photographs of the subject were taken from the right lateral view(1,6,8-12), without the backpack and serially with backpack weighing 5%, 10%, 15%, 20% and 25% of bodyweight over both shoulders . The Image tool UTHCSA version 3.0 (University of Texas Health Service Center, San Antonio, TX) digitizing software was used for analysis of photographs and to calculate the angles(7). The measured postural angles and their description is detailed in the Table I.

Table I



Postural Angles Measured in the Study 

SPSS 12 version was used to perform repeated measures ANOVA analysis and post hoc test (Bonferroni analysis) for statistical significance. The alpha level was set at P<0.05. SD was calculated to find the variability of the actual data in each postural angle. For Bonferroni analysis, the P value is corrected by a factor of 15. Keeping six groups for comparison, the value was set at P <0.003. Further, Standard error measurement (SEM) of each postural angle was calculated to determine the precision of an estimated mean of a test population.

Eligible participants and their anthropometric characteristics are reported in Table II. Mean functional reach with smaller SD values (30.13 ± 5.11cm), indicates homogeneous postural stability in all the participating preadolescents.

Table II



Subject Characteristics (n = 200)

Analysis of variance (ANOVA) for postural angle for 0% backpack load weight to 25% back pack load weight in preadolescent children popu-lation revealed significant change in all measured postural angles pertaining to backpack weight increments (Table III). The narrow range of SD values indicates the lesser variation among measurements taken from the sample.

TABLE III 



Postural Angles for 0-25% Backpack Load in Preadolescent Children (n= 200) 

A lesser CV angle and higher HON and HNOT angle with increasing backpack loads found in our study is supported by many previous studies (2,3,7,9,13). The smaller CV angle, higher HON angle and HNOT angles indicate the forward head position (FHP) in response to posterior backpack load. Persistent forward head posture was found to be the major cause for many musculoskeletal disorders around neck and shoulder region in adults(13). Lesser CV or FHP has been associated with greater neck disability(13), tension type headaches(14), syndromes of the neck(15), temporomandibular disorders(16), increased incidence of cervical and interscapular pain and headache(17) etc. The striking finding in our study was that decrease in trunk angle and an increase in lower limb angle in response to 5% of backpack load. This sagittal trunk shift may aggravate the dorsal and low back pain(18). These significant alterations in postural angles may cause or precipitate pain related musculoskeletal dysfunction(18-21), significant changes in respiratory parameters(19) and metabolic cost measures(20).

Grimmer, et al.(2) reported similar changes in sagittal position of body segments to adjust the body’s center of gravity to accommodate a posterior load. They, however, could not find evidence to support the ‘rule-of-thumb’ that loads should be limited to 10% of body weight(2). Further, Haselgrove and Straker(21) reported carrying backpack less than 30 minutes actively to school may decrease the odds of back and neck pain.

Absence of female participants was the limitation of this study and this aspect warrants further exploration in terms of higher reports of neck or back pain in female students carrying backpacks(21). Awareness should be created among health care professionals, teachers, parents to restrict backpack load less than 5% of bodyweight by using school locker shelves, compact discs, USB flash drives and need to regularly monitor the musculoskeletal problems associated with carrying heavy backpack load in preadolescent children. So musculoskeletal dysfunction and its relation to preadolescent postural responses to backpack load need to be further explored through longitudinal and prospective studies, respectively to determine whether carrying backpack increases the incidence of regional pain and to correlate these clinical implications on school children.