The weight of pupils’ schoolbags in early school age and its influence on body posture

Postural development progresses through a series of stages that occur while children are of school age [1]. During this period, dynamic and rapid changes in growth are observed [2, 3]. The first of these periods, discussed in this report, coincides with the start of a primary education of the child. The second period includes puberty, when the child is between 13 and 15 years old [1, 4]. The transition to more sedentary lifestyle in a world of sedentary behaviors [5, 6] (for example, several hours of sitting during learning at school and at home, watching TV, and using PC [7, 8]) and the reduction in physical activity [9, 10] in favor of extra activities performed mostly in sitting positions, such as learning foreign languages or playing musical instruments [11] might lead to obesity [12–15]. All of these changes are negative factors that lead to the development of postural disorders. Young children adapt to these changes, although not always in an appropriate and favorable way [16].

On the one hand, posturogenesis is affected by the characteristics of growth spurt period, while on the other hand, posturogenesis is also affected by improper static body positions, e.g. in classrooms which are not spacious enough [16]. Important elements which should also be taken into consideration are school bag weight, quality and fit (i.e., shoulder strap size adjustment, strap asymmetry and the method of putting on and taking off the backpack). Biomechanically, the center of gravity acts on the support quadrangle and ensures stability in standing position [17]. Static and dynamic postural sways are particularly important elements while carrying a school bag. Young children adopt adaptive strategies [18] very quickly, compensating to align particular body segments in relation to one another and these adjustments may lead to postural abnormalities, e.g. within the sagittal plane over a long period of time [19, 20]. 90% of scoliosis are idiopathic – the causes are not known. For young children especially with bad posture or spine deformities, the care on ergonomic behavior is much more important [21, 22]. The worst case scenario occurs when a postural abnormality of idiopathic origin is neglected because these modifiable factors cannot be controlled or changed [23].

Research in this area show that although the average loads vary greatly between studies, the majority of reports indicate that the loads carried by pupils are greater than the recommended limits [24, 25]. Some researchers hypothesize that the use of heavy backpacks may contribute to the high reports of back pain, bad body posture and it is a frequent cause of discomfort for schoolchildren [26]. Moreover, asymmetry in school bag straps (most often adjusted to be too short) causes muscle imbalance. If the school bags of inactive pupils are overloaded, then the risk of serious postural abnormalities greatly increases, as these children are still within the critical period of posturogenesis [1, 4, 27]. Unfortunately, according to the Chief Sanitary Inspectorate, the majority of pupils carry overloaded school bags. On August 25, 2009, the Minister of National Education Regulation approved a maximum load for younger pupils equal to 10–15% of their body mass [Journal of Laws, No. 130, item 1130] [28]. Children in early primary school are not conscious of their health or the potential threat of postural abnormalities because they are not informed. Even if they are informed in this topic, following the principles of ergonomics is extremely difficult and it takes time to modify the pattern encoded in the central nervous system.

Habits which they exhibit are often exemplifications of improper behaviors of their older schoolmates and observations of the world around them, because they imitate to gain acceptance [16]. The problem of overloaded school bags was a very important question which emerged while the hypothesis for this study was being created. This problem has been identified but not yet solved. The research presented in this study is only a portion of a larger scientific project.

The aim of this study was to analyze if the change in school bag weight has been associated with the change of children body posture and to describe how school bag characteristics (straps/weight) may affect the back health.

This was an observational study in which a group of pupils in primary schools in the region of Silesia in Poland has been examined. Examinations have been conducted twice for the same group of children: first, at the beginning of the school year (initial examination), second – after 10 months (final examination). The sample size was calculated using the sample size calculation for proportions. Assumed prevalence of posture disorders of 38–39% as it was reported in the study of Pokrywka et al., 2011 [29] and margin error of 6% with a confidence level of 95% and a population size of 500 to give a sample size of 168 pupils [30] have been used.

The study included a group of 155 pupils between 7 and 9 years old (mean age = 7.6 ± 0.6). The study was based on the prevention study within the framework of a project under resolution No. KNW – 1 – 002/N/1/0 conducted by the Medical University of Silesia, involving the study of children, adolescents, their parents and teachers in the region of Silesia from 2011 to 2016. There were two subgroups according to sex: 68 (43.9%) girls and 87 (56.1%) boys. All of the pupils in both groups had proper body posture. Pupils were selected on the basis of body posture examination; if no irregularities or mild asymmetries (e.g., spatial body position within shoulder blades and shoulders) have been observed, they were included in the study. All of the children included in the study have been assessed by the first author during the initial examination under the same conditions, using classic tools and tests for body posture evaluation (suggested for use by SOSORT) [31]. Children were excluded from the study if they were diagnosed with scoliosis or if they revealed serious posture abnormality in three planes. These children were referred to an orthopedic specialist for further evaluation. Other exclusion criteria were as follows: below the age of seven or above the age of nine, regular training in after – school sport clubs, exemption from physical education classes because of frequent infections or orthopedic injuries and moving to school by car. 155 children were chosen for the final analysis. Remaining children were excluded from the study because of a “growth spurt” which has been detected in excluded children and could have influenced the results of the posture evaluation.

Data collection

In the examined group height and weight of the body have been measured and BMI has been calculated and further interpreted as a BMI percentile [32, 33]. School bag weight has been measured as a total value of two measurements during one school day and then repeated after 10 – month interval using a tared scale before the start of exams. Measurements have been carried out for the same group of children. As the examined pupils received seven lessons every day (i.e., from 8:30 to 14:50), no significant differences in school bag weight have been noted between particular days. The length of straps, appropriateness of the technique used to put on and take off a school bag and the symmetry of both straps have been also assessed. This investigation was a part of large project conducted by the first author connected with exemplifications patterns [23]. Children have been visually evaluated for the correctness of putting on and taking off backpacks. Trunk flexion (bending) or trunk extension and straight knees combined with trunk rotation (backpack positioned relative to the body on the right or the left side of the body) have been considered as erroneous. Raising a backpack through a squat (backpack set close to the body in the middle of the line) has been evaluated as correct. School bag weight (Fig. 1) has been measured on a tared medical scale. Lengths of straps have been measured in centimeters using centimeter tape.

Estimated weight of the school bags based on the recommendation of the Minister of National Education has been separately calculated for each pupil (maximum load for younger pupils equal to 15% of their body mass) and predicted value has been calculated as a percentage of exceeded weight of schoolbags of the pupils permissible for weight of the pupils.

To properly position a school bag on the back of the pupil, the middle of a bag was placed at the middle of the back of the pupil.

Body posture measurement has been performed according to the following methodology. Three measurements of the torso rotation angle were recorded with a Pedi-Scoliometer while the pupil stood in the Adam’s test position: in the peak of cervical kyphosis, in thoracolumbar junction and in the peak of lumbar lordosis. The highest torso rotation angle measurement from each level was recorded. In scoliometer examination, the angle of trunk rotation (ATR) has been adopted as a norm at the level of ≤ 3°. Based on the obtained results, the Hump Sum indicator was calculated to avoid a mistaken overdiagnosis of body posture abnormalities [34]. Next, the plumb line deflection has been evaluated starting from the gluteal cleft. The plumb line has been projected from the external occipital protuberance to the gluteal cleft, and its right or left deflection was expressed in centimeters. Subsequently, angles of kyphosis and lordosis have been measured according to the Dobosiewicz methodology [35] using a digital inclinometer (Saunders TMX – 127). Pelvis and shoulder blade positions have been measured using a ruler and a Pedi – Scoliometer (Fig. 2).

Body posture characteristics were described using following parameters:

1. 1.

   Plumb line (projected from external occipital protuberance) falling down on gluteal sulcus – distance from gluteal cleft ≤ 0,5 cm (Figure No. 2a),

    
2. 2.

   The level of shoulder blades position measured using a ruler and scoliometer ≤ 2^o Figure No. 2b),

    
3. 3.

   Angle of trunk rotation (ATR) measured with scoliometer ≤ 3°for each spine section Figure No. 2c),

    
4. 4.

   Thoracic kyphosis and lumbar lordosis angles in median plane measured using digital inclinometer, included in the range of values 24–36 °described by Dobosiewicz (Figure No. 2d)

    
5. 5.

   Matthias test to evaluate postural muscle endurance during a minimum of 30 s (Figure No. 2e) [36].

    

Following factors were taken into account: school bag weight and school bag straps characteristics. Changes in school bags straps in the final examination – relative to a preliminary examination were recoded into three categories: stabilization, shortening and elongation. Body height, torso rotation angle, angles of kyphosis and lordosis, position of shoulder blades, deflection of the plumb line from the gluteal cleft and Hump Sum indicator were also taken into account. In addition, variables concerning unnecessary things in a school bag (but in opinion of pupils – „indispensable”) were also collected. The analyses of differences between examinations were performed with great attention to details. The results for both examinations (initial and final) have been analyzed independently and then compared (obtained differences between results were assessed and evaluated – dependency assessment).

The purpose of the study was to evaluate body posture changes and describe their relationship with school bag characteristics in pupils aged 7–9 years. This study showed that children wear heavy school bags which mean weight in the initial study was 6.3 ± 0.8 (range between 4.7 and 9.0 kg). A tendency to carry slightly heavier school bags was noted in boys. The increase of torso rotation exceeding norms was observed in 35.2% of girls and in 60.9% of boys. The increase of kyphosis angle over norms indicated by Dobosiewicz was noted in 77.9% of girls and in 62.8% of boys.

Factors which could affect the variability of the results sought to be eliminated. The study included institutions (schools) which head classes with a fixed number of seven teaching hours every day throughout the school year. The division of subjects into particular days did not affect the weight of backpacks. In addition, very strict criteria for inclusion in the study allowed to eliminate factors which may affect the development of body posture. A shortcoming is the lack of reliable observation of children (ergonomic behaviors) on the way to school and back - therefore it was not a subject of the analysis.

Irrespective of the type of small deviations from the proper body posture, important negative changes were observed over the course of the year. Body posture is influenced by many endogenous and exogenous factors [23]. Because of the fact that endogenous factors were not always under our influence, exclusion and inclusion criteria were selected very precisely. One of those exclusion criteria was the evidence of a growth spurt [2, 3] because it is a period during which irregularities in body posture often appear [37, 38]. A growth spurt is caused by a rapid increase in bone length and is followed by certain limitations of muscular elasticity (especially of postural muscles) which enable this rapid growth [39]. The second important exclusion criterion was a long absence from physical education classes, most often because of allergies or frequent infections [40].

Reduced participation in physical activity [9, 12, 13], especially during this time of transition from a dynamic to a static lifestyle, may itself cause an imbalance in the tension of antagonist postural muscles and may lead to serious posture disorders with time [1]. Although there are some simple methods to address this problem [41, 42, 43], they require a great deal of adult control (parents, legal guardians or teachers) during early primary school [23]. In this study, such solutions and their influence on body posture and school bag weight have not been presented because results in this field greatly vary. Exogenous factors [44] may be strongly modified, e.g., by attaining a proper position during sitting, standing, learning or playing, by reducing school bag weight during early primary school, by adjusting school bags and by shortening straps which are too long.

The inversely proportional relationships of strap length to the depth of kyphosis and lumbar lordosis angle are understood from a biomechanical point of view, as they are the result of the distribution of moments and forces caused by the school bag load [45]. For instance, child attempting to balance a school bag placed too high on his/her back will lean forward and overload the spine [45, 46]. This adaptation leads to an imbalance of antagonist muscles, such that the torso muscle activity dominates as a functional effect [47]. When parents buy a school bag for their first grader, they consider its price, weight and the profile of the spine of the child and back of the school bag [23]. Previous work of the author confirmed that school bags were generally chosen appropriately but the pupils improperly adjusted their school bags or swapped school bags for an outdoor – style backpacks during third grade or higher.

School bag itself did not address all of the ergonomic aspects; school bags were most frequently placed too high, what forced children to lean forward and overload their spines [47, 48]. The overloading was then resolved by increased thoracic kyphosis and lumbar lordosis angles [19, 49, 50]. Another problem is that the maximum load approved for younger pupils is equal to 10–15% of their body mass [23, 50, 51]. This factor is not sufficient. Presented research showed that only 23% of examined children had a postural muscle endurance of 30 s. If the Matthias’s test position was held for less than 5 s, then the burden of the overloaded school bag would exacerbate this failure. This burden may lead to posture abnormalities. These results should prompt a broader discussion.

Due to the fact that these studies were observational and lasted a full school year, it was difficult to eliminate all of the confounding factors which may have a direct impact on changes in body posture. One of them is the growth spurt – but this factor has been completely eliminated. Probably, longer observation will allow to draw wide – ranging conclusions about the impact of the backpack (its weight, straps asymmetry, asymmetry straps, proper wearing and simple ergonomic principles) on the body posture especially in the higher grades. Evaluation of the same study group after cyclic training on ergonomics in the context of the author's program "my healthy spine” should be analyzed further.

The unsatisfying results of studies conducted over several years encouraged the author to introduce a prophylactic program “My healthy spine at school” in Poland [16, 23]. During practical classes, children learned about the structure and function of the spinal column, about proper and improper movement patterns when learning and playing, and about the causes of postural disorders and how they may affect their physical abilities as adults [16, 23]. Parents of the children were also instructed on how to create an ergonomic workplace for their children and how to constantly control an ideal body position. Detailed analysis of behavioral training aspects has been performed, and the weight of a school bag of the pupil was a significant factor to consider. The spine protection program is required on account of a sedentary lifestyle and the increasing rate of postural defects/deformations which occur during the development from youth to adolescence [16, 23]. Data from 6 years of practice have been collected for further research and analysis – maybe these data will provide an ideal strategy to diminish or even eliminate the effects of modifiable exogenous factors of body posture irregularities.

School bags of the pupils were heavier than the recommendation in 79% of boys and in 64% of girls. Weight differences of the school bags after one school year have influenced changes in body posture abnormalities, especially in rotation parameters. Backpack straps asymmetry is noticeably stronger in the group of girls and the difference between braces may have an impact on posturometric parameters. Lack of proper backpack lifting skills tends to create programs and training systems in this regard.