Ideal posture is the position in which the body is held in an upright, vertical position against the force of gravity while sitting, standing and lying down (1). Many studies have been done to determine the ideal posture in sitting, standing, lying down and even in walking (1). These studies have suggested that good posture means training the body to stand, walk, sit and lie in a position where the least strain force is placed on the muscles and ligamentous structures either during movement or weight bearing activities (1). The ideal and proper posture has importance because of its benefits in keeping bones and joints in the good alignment for the proper use of muscular structures; reducing the stress force placed on the ligaments (fibrous tissue that connects bones to other bones), preventing the spine from being held in an abnormal position, and avoiding muscular pain and backache (1).
The backpack is considered a form of manual load carriage which provides versatility and this form of load carriage is extensively used by mountain hikers, soldiers, as well as school students (2). It is a proper method to load the spine while stability is kept. However, these forms of load carriage bring many musclo-ligamentous problems to the surface and these problems are common among school students (3). Children carry as much as 30% to 40% of their body weight by using backpacks (3). This fact emphasizes the negative effect of improper positioned and heavyweight backpacks on the different body structures especially
Shoulder posture, spine alignment, lung function and even walking endurance (2, 4).
In this study, the effect of improperly positioned and heavy backpacks on the posture of primary , intermediate and secondary school students who are between 10-18 yrs. old is investigated.
Many studies have been done to prove the effect of position, heaviness and models of backpacks on students. These studies separately tested the effect on different body structures and the abnormalities that can happen to each structure which can affect students over a long term period of time.
A study was done by WUNPEN CHANSIRINUKOR et al, in 2001, to assess the effect of backpacks on cervical and shoulder posture of high school students. Six females and seven males voluntarily participated in this study. The maximal load of backpacks was 15% of each student’s body weight. Prior to data collection the weight (kg) and height (cm) of each student was measured. Three angles were formed to objectively measure the loading effect on each participating student. The first angle, (craniohorizontal), is the angle resulting from the intersection of a horizontal line through the tragus of the ear and a line joining the tragus of the ear and external canthus of the eyes. The second angle (craniovertebral), is the angle formed between the horizontal line through the spinous process of C7 and a line to the tragus of the ear. The third angle (sagittal shoulder posture) is the angle formed by the intersection of a horizontal line through C7 and a line between the mid-point of the greater tuberosity of the humerus and the posterior aspect of the acromion process. After that, every student was tested under different loading conditions using different weights of backpacks with the maximum load to be 15% of body weight. The students were photographed and the study concluded that the craniovertebral angle was significantly decreased (which means increased forward head position) while carrying a backpack weighing 15% of body weight which indicated that the weight of the backpack has a dramatic effect on the cervical and shoulder posture. It was suggested the weight of the backpack be less than 15% for high school students (2).
Another study was done by ALICE YE-MEEN JONES et al, 2001, to assess the effect of shoulder loading by backpacks on forced expiratory lung volumes of primary school children and compare the results with that of an assumed kyphotic posture. For this study, forty three primary school students (18 males, 25 females) from different schools in China, aged between 9-11 years old, were tested using a spirometer while they were adopting each one of the following five conditions in a random order:
Standing with assumed kyphosis.
Standing with a backpack weighing 10% of the body weight.
Standing with a backpack weighing 20% of body weight.
Standing with a backpack weighing 30% of the body weight.
After that, the forced expiratory volume in the first second (FEV1- the volume of air that can be forced out taking a deep breath), the forced vital capacity (FVC – vital capacity measured when the student is exhaling with maximal speed and effort), and peak expiratory flow rate (PEF – the greatest rate of airflow that can be obtained during forced exhalation) were measured under each condition. The study concluded that both FEV1 and FVC decreased significantly in the condition of assumed kyphosis and when the load in the backpack increased to be 20 and 30 % of body weight. Lung volumes were restricted when a school bag load was heavier than 10% of the child body weight (5).
Another similar study was done by PAUL D.ROBINSON et al, in 2003, to assess the effect of load carriage on movement kinematics and respiratory parameters in children while walking. To perform this study, fifteen male students were randomly selected from a primary school with a mean age of 10.31years. Prior to the study, each studentaa‚¬a„?s weight (Kg) and height (cm) were measured and a two-strap school bag was used because it is the most-used backpack in Chinese schools. These bags were filled with books to weigh 10%, 15% and 20% of each student’s body mass. Interference effects were eliminated by dividing the students into four days of trials where they underwent four walking trials on the treadmill with constant speed (1.1 meters per second and time of 20 minutes) in each of the following conditions:
Walking with a backpack without a load ( 0% of body mass)
Walking with a backpack with 10% of body weight.
Walking with a backpack with 15% of body weight.
Walking with a backpack with 20% of body weight.
During the four trials of each student, respiratory masks were used to measure tidal volume ( Tv) and the breathing frequency (Fr) while a 3-CDD video camera ( 50HZ) was positioned laterally to each student with the lens axis perpendicular to the movements plane ,and the camera was positioned at the level of the hip. After the trials were performed, the measurements were taken and they concluded that there is a linear relationship between the backpack weight and the increase in trunk inclination and breath frequency accompanied with a decrease in the trunk range of motion. The significant increase in trunk inclination and decrease in range of motion was with a load of 20% of body mass while the significant increase in ventilation while walking was with loads of 15% and 20% of body mass which suggested that 10% of body weight is the proper load for 10 year old school children (4).
Another study was done by YOULIN HONG et al in 2003, to assess the response of the gait and the trunk to backpack load during level walking in children. Eleven primary school students aged between 9-10 years were randomly chosen for this study with the informed consent of their parents. Prior to the study, each studentaa‚¬a„?s weight and height were measured. A twoaa‚¬”dimension video camera was placed 12 m to the sagittal plane of each student to record the locomotion. Each student then wore a two-strap backpack that weighed 0%, 10%, 15% and 20% of his body mass while he walked with normal cadence (number of steps per minute) around the perimeter of the basketball court. This study concluded that there is no significant effect of the backpack loading on the gait pattern but with the backpack weight of 20% of body weight, there was a significant change in the trunk inclination which made the researchers suggest that the musclo-skeletal changes in the trunk can be reduced by using a backpack that weighs less than 15% of the student body mass (6). A study was done in 2005 by DANIEL H.K. et al at the University of Hong Kong to study the effect of backpack on the gait pattern of normal adolescent girls. To complete the experiment, 22 normal school students with age of 10-15 yrs. were recruited; 25 mm diameter retro-reflective markers were attached to the student’s skin at eight landmarks in the pelvis and lower limbs to analyze their gait pattern. Each participant was walking under each of the following conditions:-
Walking without a backpack.
Walking with a backpack loaded with 7.5% of the body weight.
Walking with a backpack loaded with 10% of the body weight.
Walking with a backpack loaded with 12.5% of the body weight.
Walking with a backpack loaded with 15% of the body weight.
The backpacks used were commonly used double strapped backpacks in Chinese schools. The gait was analyzed and the results were: decrease in the step length ,cadence and walking speed accompanied proportionally with increasing load and significant increase in the double limb support time and stride time. The conclusion was the increasing in the backpack loads to 15% of the body weight resulted in significant alteration in the gait pattern of adolescent girls with the joint kinematics of proximal joints (pelvic and hip ) more affected than distal joints (knee and ankle) (7).
Not all studies were concerned with spine abnormalities that can result from backpack carrying. A study was done by R.E.E. MOTMAS et al in 2006 at the University of Belgium to study the effect of different models of bags on trunk muscle activity. Nineteen college students (9 males and 10 females) participated in the study voluntarily with age of 20-25 yrs. E.M.G electrodes were attached to the bilateral erector spinae muscles and rectus abdominals. Each student was tested under the following bag models with a load of 15% of their body weight:
Standing erect with extended knees for 30 seconds with shoulder bag.
Standing erect 30 seconds with traditional backpack.
Standing erect 30 seconds with front bag.
Standing erect 30 seconds with double bag model.
All bags were filled with books to reach 15% of each studentaa‚¬a„?s body weight. The activity of the erector spinae and rectus abdominis muscles was recorded using superficial attached E.M.G electrodes.
The traditional backpack reduced the E.M.G muscle activity of erector spinae while muscle activity of rectus abdominis increased significantly to counterbalance the backward trunk leaning. In the condition of wearing a front bag, the activity of the erector spinae muscle was increased to twice as much as normal. It was concluded that shoulder bags should be avoided because they caused an increase in the contra lateral muscle activity and reduced ipsilateral muscle activity. No significant difference was recorded between wearing a double bag with unloading situation (8).
A study was done by YUSSUF S.S.M. ALKHABBAZ et al, 2008, to measure the effect of the backpack heaviness on the trunk and lower extremity muscle activity and on the posture of the trunk. In this study, nineteen male university students with a mean age of 21 years (plus or minus 3) participated in the experiment voluntarily. The criteria of exclusion were: L.B.P. that extended more than six months, recent injury, postural deformities and recent spine surgery. Two students were excluded due to L.B.P. that extended more than six months. Prior to experimenting, the body weight and height of each student were measured. Each student performed each of the following four experimental conditions:
Standing with backpack of 10% of the body weight.
Standing with backpack of 15% of body weight.
Standing with backpack of 20% of the body weight.
The same backpack was used for all students and it was filled with sand to be equivalent to the previous weights. After each trial each student was allowed to take a 1 minute rest. Muscle activity of trunk muscles (erector spinae and rectus abdominis) and lower limb muscles ( vastus medialis and biceps femoris) were recorded in every trial using E.M.G. electrodes attached to muscles superficially while trunk inclination,side flexion and rotation were analyzed using VICON analysis system. The conclusion was the rectus abdominis activity increased significantly and in a proportional relationship with an increase in the backpack loading while no significant change occurred to the erector spinae, biceps femoris and vastus medialis muscles activity. In the trunk the same backward inclination was adapted. A backpack of 20% of the body weight caused the most significant muscular and postural change so the study recommended that it should be avoided (9).
Finally, a study was done by SHARIFA ALWAIH S.R.AHMED in 2009 at the College of Science and Technology in the University of Malaysia. In this study, two healthy boys aged 6-8 years participated voluntarily. Prior to the experiment, the body weight and height of each student were measured. Each student was prepared to walk under each of following four conditions:-
Walking without a backpack ( 0% of body weight)
Walking with a backpack (10% of body weight)
Walking with a backpack ( 15% of body weight)
Walking with a backpack (20% of body weight)
The backpacks used in this experiment were commonly used double- strapped backpacks. In each condition the child was asked to walk in an 8m track at his preferred speed and then he was allowed to take a five minute rest. Specialized cameras were used to record the participant’s movement in every condition. It was concluded that carrying a backpack with a load of 15-20% of the body weight during level walking caused a significant increase in the trunk inclination angle for children of six years old but there was no significant difference in trunk inclination with a backpack weighing 0-10% of the body weight (10)
Conclusion and Recommendation
The previous studies were done by multiple universities and researchers in different countries of the world and the conclusion of each mentioned study was similar to the results of other studies in proving the effect of heaviness, models and position of backpacks on the different body structures of primary, intermediate and high school students. In summary, the backpacks are commonly used forms of manual load carriage that help many people including mountain hikers, soldiers and school students to carry their equipment and books in a simple way that equalizes the distribution of the carried load on the body different joints. This type of load carriage if overloaded or carried in an improper way, may cause many abnormalities in different body structures including the neck, spine, back ,lower limbs and even the lungs and consequently, can lead to neck pain, back pain, thoracic kyphosis , joint degeneration, and decrease in the lung capacity walking endurance. These abnormalities can turn into deformities in the long term and then it may be difficult to correct them. The mentioned previous studies suggest the weight of backpacks not exceed 20% of body weight to avoid the abnormalities that can result while 15-20% of body weight load has a moderate effect on the body. The studies had a common recommendation to the students and their parents to make the backpack weight not exceed 10% of the student body weight which equals approximately 4.80 kg for primary school students and 5.80 kg for intermediate and secondary school students to be safe for students.