Restitution and the Impact of Various Ways of Carrying a Schoolbag on Body Posture Features in Transversal Plane at 7-Year-Old Students of Both Sexes

Abstract

Introduction: The aim of the research program was to demonstrate which of the analyzed methods of carrying a 4-kilogram backpack disturbs the statics of body posture in the transverse plane the least.

Material and Method: Body posture tests were carried out in a group of 65 students aged 7, using the projection moiré method in 4 positions: 1st - habitual posture, 2nd - after 10 minutes of loading, 3rd - one minute after removing the load, 4th - after two minutes after removing the load.

Results: The correlations between the differences in the value of the transversal plane features in the habitual posture and the value after a 10-minute load with a 4-kilogram backpack and with the value after a 2-minute restitution were analyzed.

Conclusions: (1) Among boys, carrying a 4-kilogram backpack on the back-chest disturbs the static body posture in the transversal plane the least; the most on the right shoulder. Among girls, the least on the back-chest, the most on the chest. (2) Among boys, after a 2-minute restitution, the disturbances in body posture statics in the transversal plane are the smallest after carrying a 4-kilogram backpack on the back, and the greatest after the right hand drag mode. Among girls, the smallest disturbances occur when carrying obliquely on the right shoulder and the left hip, and the greatest disturbances occur with the right hand drag mode.

Keywords: Children’s Health, Moire Topography, Physical Fitness, Postural Asymmetry Factor

Introduction

Posturogenesis proceeds in stages, including acceleration of body height and weight, balance and coordination, to ultimately achieve a certain individual stability - habitual posture. Decreased physical activity, increased body weight, school bags overloading, backpack straps asymmetry, the way of putting on and taking off backpacks and the increased use of electronic devices are reflected in body posture disturbances. There is quite a lot of literature on the impact of a school backpack on a student’s body posture. There is little work on the effects of different ways of carrying a backpack on body posture, even though in developed countries the backpack is usually carried on the back. The doctors and physiotherapist’s statements end with general recommendations that the student should not carry a heavy school bag, and that the weight that should be evenly distributed on the student’s back should not exceed 10-15% of the student’s body weight. Carrying school supplies can take various forms. The manually carried load should ensure versatility and disturb the ongoing posturogenesis as little as possible [1]. According to Knapik, et al. [1] and Voll and Klimt [2], the load carried on the back is an appropriate way to precisely and symmetrically load the spine while maintaining stability. However, as studies by Mrozkowiak [3-14], Mrozkowiak and Słodkowska [14] and Troussier [15] have shown, musculoskeletal problems related to the use of a backpack are becoming an increasing problem among school-age children. Hypothetically, this is influenced by the combination of several elements like: way of carrying location of the backpack on the back, size, shape and distribution of the load, carrying time, physical characteristics and physical fitness [1,16]. The dynamic research known so far includes attempts to determine the impact of factors related to backpack carrying on the health and safety of adults and occasionally children. The maximum loads recommended in early studies ranged between 25% and 40% of body weight [16]. The author also suggested that the load requirements of adult women should be lower than those of adult men due to physiological and biomechanical differences. Research by Brzęk, et al. [17] conducted in a group of 7-9-year-old students in the number of 155 showed a linear tendency to carry an increasing weight of a backpack. In the authors’ opinion, this was one of many reasons for the increased percentage of children with progression of trunk rotation and thoracic kyphosis angle. The difference in the length of the straps had a significant impact on increasing the rotation of the upper thoracic spine, the thoracolumbar junction, and also on reducing lumbar lordosis in the group of girls. If we assume that carrying backpacks is a dynamic activity, it is a mistake to collect data from measurements of children in static positions. Some dynamic studies collected data from participants walking with backpacks for short periods of time, but included only adults [18] or did not include the location of the backpack on the back [19-21]. Some studies examined school-age children while walking with variously distributed loads, but focused on a specific research goal, e.g. pressure on the shoulders [22].

The author’s interest in the issue results from the persistently high percentage of static postural disorders in students of the oldest kindergarten group and I-III grades of a primary school, the constantly proclaimed opinion on the negative impact of the method of carrying school supplies on the statics of body posture, and the lack of clear recommendations on optimal and negative contraindications. The aim of the research program was to demonstrate which of the analyzed ways of carrying a 4-kilogram school backpack had the least negative impact on the selected features of body posture in the sagittal plane.

Research Material

Children from randomly selected kindergartens in the West Pomeranian and Greater Poland Voivodeships participated in the research. Defects and body posture disorders were not an exclusion criterion from participation in the research programme. The division of respondents into those from rural and urban environments was abandoned since this feature will never constitute a homogeneous group and the cultural and economic boundaries of both environments are blurring. Qualification for the programme was made according to the scheme: if the respondent was 6 years, 6 months and 1 day old and under 7 years of age, he or she was classified as a 7-year-old. This allowed to use previously developed normative ranges appropriate for this age and gender category, diagnosing the quality of the body posture found on the day of the examination. A total of 65 students participated in the programme, of which 53.84% (35 people) were girls and 46.15% boys (30 people).

Subject of Research

The photogrammetric method used, using the projection moiré phenomenon, determines the value of several dozen features describing body posture. Four angles of the pelvis and trunk in the transversal plane, as well as body weight and height were selected for statistical analysis. It was guided by the need for the most reliable and spatially complete look at the child’s body posture, which allowed for full identification of the measured characteristics (Table 1, Figure 1,2).

Table 1: List of registered torso and morphological features.

Source*: Own research.

Figure 1: An example of a record sheet of measurements of the posture features of the spine-pelvis syndrome.

Source*: Own research

Figure 2: The angle of rotation of the pelvis in the transversal plane (KSM).

Research Method

The research was conducted in accordance with the principles of the Declaration of Helsinki. For their implementation, consent was obtained from: the student and his legal guardian, the kindergarten teacher and management, the bioethics committee (KEBN 2/2018, UKW Bydgoszcz). Prior to the measurements, the children were trained to avoid stress related to the research procedure and the implementers (Picture 1). During the research, the kindergarten teacher’s assistant of the studied group was always present, which was to ensure the children’s emotional stability. The measurements were carried out in accordance with the developed procedure, always using the same tools, in the same conditions and by the same people. They were also encouraged to keep the anthropometric points marked on the skin with a marker, which was to effectively eliminate deviations in their repeated marking. The research was carried out by a physiotherapist with 20 years of experience in body posture diagnostics using the projection moiré method.

Picture 1: Instruction of the examined children.

The method used, which uses the projection moiré phenomenon, determines the value of several dozen features describing body posture (Picture 2). It allows determining the impact of different methods of carrying a container with school supplies on body posture and the restitution of the value of features after removing the load [23,24]. Differentially loaded posture was provided with a custom-designed diagnostic frame was provided to ballast the body posture (utility model no. W.125734). The presence of an assistant during the examination was dictated by the need to minimize the time passing from the removal of the load to the moment of the second registration of the values of postural features. Every effort has been made to ensure that the loaded frame is individually adapted to the child’s body type. The assumed 10-minute load time was the average time to walk from home, given in the questionnaire completed by parents [25]. The load was determined by averaging the weight of school supplies carried by first-grade children from a randomly selected primary school, which was 4kg. Selected body posture features were measured in 4 positions. First position - habitual posture (Picture 3). Second position - posture after 10 minutes of load (in the last 5 seconds) (Picture 4-12). Third position – posture one minute after removing the load (Picture 3). Fourth position - posture two minutes after removing the load (Picture 3). The load was intended to imitate the way of carrying school supplies with the right or left hand drag mode (Picture 4,5) on the right or left shoulder (Picture 6,7) obliquely on the right or left shoulder and at the heteronymous hip (Picture 8,9) on the back, (Picture 10) on the chest, (Picture 11), on the back-chest (Picture 12). The subject could move freely. This is consistent with Mrozkowiak’s previous research results, which show that after this time the values of body posture features may return to their initial values [26]. When diagnosing the habitual attitude on the first day of the research program, it could be assumed that it was appropriate and relatively constant for each student. However, to maintain the reliability of the research, it was assumed that any inconsistency with the feature values from the first edition of the measurements may affect the final research result. Therefore, before imposing the load prescribed by the procedure, the features of the habitual posture were always determined as a reference for dynamic changes in the diagnosed features. The children’s height and weight, as well as the weight of the carried school supplies, were measured using a medical balance before the first day of the study.

Picture 2: Diagnostic station for body posture using the projection moiré method.

Picture 3: Position 1st: Demonstration of habitual posture.

Picture 4: Position 2nd: Right hand drag mode load demonstration.

Picture 5: Position 2nd: Left hand drag mode load demonstration.

Picture 6: Position 2nd: Right shoulder loading demonstration.

Picture 7: Position 2nd: Right shoulder loading demonstration.

Picture 8: Position 2nd: Demonstration of oblique loading on the right shoulder and left hip.

Picture 9: Position 2nd: Demonstration of oblique loading on the left shoulder and right hip.

Picture 10: Position 2nd: Demonstration of the load on the back.

Picture 11: Position 2nd: Chest load demonstration.

Picture 12: Position 2nd: Demonstration of the load on the back-chest.

The measurement station for selected body posture features consists of a computer and a card, a program, a monitor and a printer, a projection and reception device with a camera for measuring selected parameters of the pelvis-spine complex. The subject’s position and the camera were spatially oriented in accordance with the contours on the camera and in relation to the line of the child’s toes (Figure 2). It was possible to obtain a three-dimensional image by displaying lines with precisely defined parameters on the child’s back, which fall on the body and are distorted depending on the configuration of its surface. Owe to the use of a lens, the subject’s image was received by a special optical system with a camera and then transmitted to the computer monitor. The distortions in the line image recorded in the computer’s memory were processed by a numerical algorithm into a contour map of the examined surface. The obtained image of the back surface enabled a multi-aspect interpretation of body posture [27].

To minimize the risk of errors in measuring selected posture features, the following testing procedure was developed [23]:

The subject’s habitual posture against the background of a white, slightly illuminated sheet: free, unforced posture, with feet slightly apart, knees and hip joints straight, arms hanging along the body and eyes looking straight ahead, with the back to the camera at 2.5 meters from it, toes at a line perpendicular to the camera axis.

Marking the points on the skin of the examined person’s back: the top of the spinous process of the last cervical vertebra (C7), the spinous process being the top of thoracic kyphosis (KP), the spinous process being the top of lumbar lordosis (LL), the place of transition from thoracic kyphosis to lumbar lordosis (PL), the lower angles shoulder blades (Łl and Łp), posterior superior iliac spines (Ml and Mp), vertebra S1. A white necklace was placed around the subject’s neck to clearly mark points B1 and B3. Long hair was tied to reveal the points. C7.

After entering the necessary data about the subject (name and surname, year of birth, weight and body height, comments: about the condition of the knees and heels, chest, past injuries, surgical procedures, diseases of the musculoskeletal system, gait, etc.), a digital image of the back in each of the tested positions was registered in the computer memory from the middle phase of free exhalation.

Processing of the recorded images takes place without the participant’s participation. After saving the mathematical characteristics of the photos in the computer’s memory, the values of the features that spatially describe the body posture are printed (Figure 1).

Research Questions and Hypotheses

The result of its own experience is the research question: which of the analyzed methods of carrying school supplies disturbs the body posture in the transversal plane the least and which the most during a two-minute restitution and a 10-minute transport? The results of our own research allow us to conclude that the smallest disturbances occur in the dimensions of body posture in the transversal plane when carrying two containers on the back-chest or on the back, the largest disturbances occur when carrying the container with the right or left hand drag mode. The smallest differences in the value of the examined features after 2-minute restitution will occur after carrying on the back-chest, and the largest differences will occur after with the right or left hand drag mode.

Statistical Methods

In order to achieve the aim of the research, which was to determine the method of carrying that had the least and the most negative impact on body posture in the frontal plane, a meta-analysis was performed in which the unit of analysis were the values of features describing body posture, and not the individual subjects. Two appropriately calculated variables were analyzed.

• The amount of change during loading – the differences between the 1st and 2nd measurement expressed as a percentage of absolute values. For example, an average of 11.32 means that the value of posture characteristics between the 1st and 2nd measurement changed on average by 11.32%. Therefore, the higher the average percentage, the greater the change in the effect of a given way of carrying (immediately after its use), which can be interpreted as less desirable method of carrying.

• The value of the change after restitution - the differences between the 1st and 4th measurement expressed as a percentage in absolute values. For example, the average of 11.32 means that the value of posture characteristics between the 1st and 4th measurement changed on average by 11.32%. Therefore, the higher the average percentage, the greater the change in the effect of a given way of carrying after restitution (2 minutes after removing the load), which can be interpreted as a less desirable way of carrying.

Applying the above assumptions, it should be assumed that the values of the variable in changes after restitution should always be smaller (optimally equal to 0) than the changes immediately after carrying in a given way. To compare the analyzed carrying methods in terms of the value of changes during carrying and after restitution, the Kruskal-Walli’s test was used, preceded by the Kolmogorov- Smirnov normality test.

The Kolmogorov-Smirnov test was used to determine whether the distributions of the analyzed variables measured at the ratio level were consistent with or deviated from the normal distribution, which is crucial for choosing appropriate tests in the main part of the statistical analysis. The following symbols are used in the tables: K-S - the statistics of the Kolmogorov-Smirnov test, N - the number of included cases, “p” - the significance of the Kolmogorov- Smirnov test. Two levels of statistical significance were adopted: p<0.01, marked with *, and p<0.05, marked with *. In each of these cases, the distribution of the analyzed variable differs significantly from the normal distribution. The Kruskal-Wallis’s test was used to determine whether more than two groups differed from each other in a statistically significant way, in terms of variables measured at the ordinal level or in terms of variables measured at the ratio level, but whose distribution statistically significantly deviated from the normal distribution. The following symbols are used in the tables: M - arithmetic mean, Me - median, SD - standard deviation, H - Kruskal- Wallis’s test statistics, p - significance of the Kruskal-Wallis’s test. Two levels of statistical significance were adopted: p<0.01, marked with **, and p<0.05, marked with *. In each of these three cases, the difference between at least two groups can be described as statistically significant. In the case of this test, it is also necessary to determine which groups are statistically significantly different from each other - if the test shows a significant difference at least at the p<0.05 level. For this purpose, a multiple comparison test was performed, and its results were presented with the abbreviation R.I. (Significant Differences), which groups are statistically significantly different from each other and what is the direction of this difference (< or >). Comparisons were made in the frontal plane separately among girls and boys.

Results Obtained

In total, the research conducted in a group of 65 students of both sexes allowed for the registration of 5395 values of features describing habitual posture and in dynamic positions, body weight and height. The average body weight among girls was 24.46kg, body height 123.87, and among boys 24.56kg and 123cm, respectively. All children had a slim body type, according to the Rohrer weight-height index [28]. Information was also obtained through a survey conducted among 65 parents of children enrolled in the research project [25].

Statistical analysis showed in the case of carrying (differences between the 1st and 2nd measurement) by the boys that the smallest changes in body postures were caused via carrying the two containers on the back-chest, and the largest changes in the right shoulder. The Kruskal-Wallis’s test did not show any statistically significant differences between transport methods (Table 2, Figure 3).

Note*: G-KL – Spine-chest carrying; G – Transpine carrying, P.bark-L.biodro –Obliquely carrying on the right shoulder – Left hip, Ciąg PR – Right hand drag mode, L.bark-P.biodro – Obliquely carrying on the left shoulder – right hip, L.bark – Left shoulder or left hand carrying, P.bark – Right shoulder or left hand carrying, Ciąg LR – Left hand drag mode, KL – Chest carrying.

Figure 3: Comparison of differences between the 1st and 2nd measurement of the values of body postures in the transversal plane in the analyzed methods of transport in 7-year-old students of both sexes n=65.

Table 2: Comparison of individual carrying methods in terms of the value of differences between the 1st and 2nd measurement among boys in the transversal plane n=30.

Source*: Own research.

Table 3: Comparison of individual carrying methods in terms of the value of differences between the 1st and 4th measurement among boys in the transversal plane n=30.

Source*: Own research.

The smallest changes in body postures in the restitution phase (differences between the 1st and 4th measurement) are caused by carrying on the back, and the largest changes when with the right hand drag mode. The Kruskal-Wallis’s test did not show any statistically significant differences between carrying methods (Table 3, Figure 3).

Considering the results of the girls’ statistical analysis, it was observed that the smallest changes in body posture during carrying (differences between the 1st and 2nd measurement) of the backpack are caused by carrying the weight of school supplies on the back/ chest, and the largest changes occur on the chest. The Kruskal-Wallis’s test did not show any significant differences between carrying methods (Table 4, Figure 4). The smallest differences in changes in the value of body posture features in the restitution phase (differences between the 1st and 4th measurement) are caused by the oblique carrying on the right shoulder and at the left hip, and the largest differences in the right hand drag mode. The Kruskal-Wallis’s test did not show any statistically significant differences between carrying methods (Table 5, Figure 4).

Note*: G – Spine carrying, G-KL – Spine-chest carrying, P.bark-L.biodro – Obliquely carrying on the right shoulder – Left hip, L.bark-P.biodro – Obliquely carrying on the left shoulder – right hip, KL – Chest carrying, P.bark – Right shoulder or hand carrying, L.bark – Left shoulder or hand carrying, Ciąg PR – Right hand drag mode, Ciąg LR – Left hand drag mode.

Figure 4: Comparison of the differences between the 1st and 4th measurements of body posture characteristics in the transversal plane after the analyzed methods of transport in 7-year-old students of both sexes n=65.

Table 4: Comparison of individual carrying methods in terms of the value of differences between the 1st and 2nd measurement among girls in the transversal plane n=35.

Source*: Own research.

Table 5: Comparison of individual carrying methods in terms of value differences between the 1st and 4th measurement among girls in the transversal plane n=35.

Source*: Own research.

Discussion

School bags with school supplies carried by children as part of their daily physical work become a health problem. It is believed that the large weight of a school bag or incorrect wearing of a backpack causes excessive load on the spine, which may cause long-term problems in the muscular and skeletal system and cause anxiety for parents and children [15, 29,30]. In Malaysia, school-age children carrying bags filled with books weighing approximately 10kg. (approx. 50% of the weight of the carrier), are a problem that the Ministry of Education has addressed. The proposed changes did not fully solve the problem. Bags on wheels, pulled with the left or right hand, recommended by the British health service, were experimentally introduced. Due to various inconveniences like difficult manipulation of the wheelchair on the stairs, troublesome storage in the classroom and crossing a crowded corridor and bus, the proposal was withdrawn [31]. Later measurements by Ismail, et al. [32] show that the average weight of schoolbags for 14-15-year-old students was 4.89kg, and for 11-12-year-olds - 4.63kg. Whittfield, et al. [33] reported that in New Zealand the average school bag weight was 6.6kg for all age groups. Carrying systems are widely used in recreational and professional environments. Various types of bags for carrying school supplies are routinely used throughout most years of education. The growth of spinal structures takes longer than that of other tissues of the skeletal system. External stress, such as carrying a backpack, can affect growth, development and maintaining good posture. Therefore, students may be influenced by both internal and external factors, which may increase their susceptibility to injury. The association between carrying a school bag and musculoskeletal pain in the neck, back and shoulders has been well documented. The incidence of back pain reaches up to 30-51% of minors and requires medical intervention in 4-31% of individuals [34,35]. Ruscoe [36] examined the influence of the weight, methods and time of carrying a school bag on the body posture of students aged 10-17. Comparing the values of selected body posture features in an annual cycle, he did not show any spine asymmetry, shoulder protrusion or scoliosis. Other studies show that both the weight of the backpack and the carrying time had an impact on body posture. There was progression of head flexion in the sagittal plane when transporting the backpack, especially with a large mass. Wearing a backpack weighing 15% of body weight turned out to be too difficult to maintain an individual habitual posture [29]. Research by Bettany-Saltikov, et al. [37] showed that carrying the weight of school supplies on the back (both shoulders) did not cause significant changes in the values of body posture in the frontal plane, but significantly reduced the angle of thoracic kyphosis in the sagittal plane. Carrying on the right shoulder significantly increased the asymmetry of the line of the spinous processes of the spine in the frontal plane and reduced the angle of thoracic kyphosis in the sagittal plane. The authors believe that carrying a load of 17% of body weight causes significant changes in the alignment of the spine. Voll and Klimt [2] claim that back pain may be a sign of a more disturbing problem, especially in children under 10 years of age. However, most of these types of episodes in children are not serious and disappear without treatment. Other authors have shown that a heavy school bag slunging over the shoulder may lead to severe muscular dystonia, distortion of the natural curvature of the spine and protrusion of the shoulders [38]. Goh’et, et al. [39] examined the way children carried a school bag and observed that all students wearing a heavier backpack adopted a compensatory posture (flexion of the trunk in the sagittal plane). Karzan, et al. [40] observed that the incorrect way of carrying a backpack, combined with time and distance, additionally created favorable conditions for the occurrence of neck and shoulder pain. Studies by Khalil [41], Abrahams [42] and Mackie [43] have shown that carrying school supplies with the left or right hand drag mode is a direct cause of musculoskeletal disorders. Qallaf’s research [44] showed that carrying a school bag asymmetrically (on one shoulder or in one hand) leads to asymmetry in muscle activity and creates favorable conditions for asymmetric positioning of the torso and shoulders. Research by Brzęk, et al. [17] showed that the weight of school bags after one school year influenced the progression of body posture defects, especially features related to rotation. The authors also observed that the asymmetry of backpack straps was noticeably stronger in the group of girls. The difference between them may affect some posturometric parameters. Hsu, et al. indicated that children carrying backpacks on one shoulder must balance the weight of the bag by tilting their heads to the opposite side [45]. Moreover, this strategy creates high torque around the spine, which can cause scoliosis. Troussier, et al. [15] noted a significant correlation between back pain and carrying a school bag in one hand or on one shoulder. Viry et al. [46], Whittfield et al., [33] reported a significant relationship between disorders of the skeletal and muscular system (SAMSD) and the weight of school bags. Troussier, et al. [16] showed SAMSD in 25.4% of girls and 15.2% of boys, the studied children. This was confirmed by the reports of Ismail, et al. [32], who found SAMSD in 36.6% of the examined children, with girls reporting symptoms more often than boys. In adolescents aged 14-15, complaints occurred in 37.8% of cases in the neck area, 31.9% in the shoulder area, and 19.3% in the thigh area. During the week, 22.7% of children aged 14-15 years reported pain, and those aged 11-12 years, 8.2%. Research carried out in Indonesia by Yanto, et al. [47] showed that 30% of children aged 11-12 years reported pain in the upper part of the thigh, and the most frequently reported musculoskeletal pain was in the shoulder area (16.4%), neck (14.5%) and legs (12.7%). Mikkelsson, et al. [48] showed that compared to 30.5% of school children included in the study, headache occurred at least once a week in 54% of children who also reported musculoskeletal pain. Jones, et al. [49] believe that pain in the musculoskeletal system may be related to somatic symptoms occurring in childhood.

Conclusions

a) Among boys, carrying a 4-kilogram backpack on a back-chest disturbs the static body posture in the transversal plane the least, the most on the right shoulder. Among girls, the least on the back-chest, the most on the chest.

b) Among boys, after 2-minute restitution, postural static disturbances occurred in the transversal plane are the smallest after transporting a 4-kilogram backpack on the back, the largest after right hand drag mode. The smallest disorders among girls occur in carrying obliquely on the right shoulder and left hip, the greatest with the right hand drag mode.

Acknowledgement

None.

Conflict of interest

None.

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