Iranian Journal of Ergonomics

Students with musculoskeletal disorders have a high incidence of many factors that can be considered. According to studies, the science of ergonomics and its relation to musculoskeletal disorders is undeniable. These studies reported a clear association between self-reported discomfort and musculoskeletal injury and their association with environmental factors [3, 21]. On the other hand, with the change of the educational system in Iran, the students of the sixth grade have recently moved from the guidance to the elementary level and it is possible that the ergonomics of the elementary schools may not be in line with the needs and anthropometric dimensions of these individuals and this may result in the emergence of co-existing musculoskeletal disorders which has not been investigated to date to the best of our knowledge. The aim of this study was to investigate the relationship between the ergonomics of desk and chair and trunk posture with musculoskeletal disorders in elementary school boys in Karaj.

 

In this cross-sectional study, 346 elementary sixth grade male students of Karaj, Iran, were selected. Height and weight of subjects were measured using digital scales and gauges. A flexible ruler with high internal validity and reliability was used to evaluate kyphosis and lordosis [22, 23]. In order to measure with flexible ruler the location of C7, T2, T12, S2 vertebrae was determined by touch and observation. After marking the vertebrae, a flexible ruler was placed on the spinal cord to take the shape of the spine, then the specified points on the body were marked on a flexible ruler, the ruler was transferred to paper; the curves were drawn on the paper in the same way and the points marked on the curves were also marked. The distance between two points was measured as the length of curvature [L] and the maximum value of curvature depth as [H]. Then, putting the numbers obtained in the formula θ=4Arctang2H.L, the kyphosis and lordosis were measured. Anthropometric measurements and ergonomic dimensions of class equipment were measured using a 50 cm metal ruler. Elbow flexion height was measured at 90 degrees elbow flexion position for height of elbow. In this case, the forearm and seat should be in a parallel status. The popliteal height of the vertical distance from the lower leg to the posterior surface of the knee or popliteal space was measured so that the thigh and calf were positioned at straight and right angles at 90 degrees knee flexion. To measure shoulder height, the vertical distance of the shoulder from the Acromion to the seat surface was considered. Pupil-popliteal length was measured from the posterior surface of the hip to posterior surface of the knee in popliteal space with the knee in 90 degrees flexion. Table height vertical to ground to front edge, bench height vertical to ground highest point and bench depth horizontal distance from seat back to seat at front seat to front bench was measured [25,26]. A 9-item Nordic Questionnaire with acceptable reliability and validity was used to assess musculoskeletal disorders [27]. Spearman correlation test at the significant level of 0.05 was used to analyze the data.

Demographic characteristics of the students are presented in Table 1.
 

Table 1. Demographic characteristics of students, 346 male students of elementary sixth grade of Karaj [n = 346]

The results showed that only 18% of the students had desk height appropriate to the anthropometric characteristics and 80% of the students had desk height greater than the maximum. Bench depth is proportional to 12% of students, while for 82%, it is smaller than the permissible limit and 4% were using benches with depth greater than the maximum permissible. Bench height is in the normal range for 50% of students, 17.1% of students are using benches with height less than the minimum standard and 32% of the desks have heightwith greater than the maximum for students. The results also showed that there was no significant relationship between lordosis and thoracic kyphosis with table and bench dimensions [Table 2].

Table 2. Relationship between table dimensions and class bench with kyphosis anomalies

Table 3 provides information about pain in body areas, the frequency and percentage of pain among students.
 

Table 3. Information about pain areas

Table 4 presents the number of areas with musculoskeletal pain, frequency and percentage of pain among students in nine areas of the body.
 

Table 4. Information on the number of pain areas in the student body

It can be seen in Table 5 that there is only a significant negative relationship between the bench depth component and the Nordic score. The smaller the bench depth, the greater the number of areas with pain in the students.
 

Table 5. Information on Musculoskeletal Pain and Ergonomic Dimensions of Table and Bench

Conclusion

It seems that the ergonomic situation of the Karaj elementary school desks and benches at the sixth grade is not acceptable and therefore it is suggested that standardization be put on the agenda to prevent its possible consequences. On the other hand, it seems that prolonged exposure to inaccurate situations, which may be due to inappropriate ergonomics on the school benches, may have multiple consequences for the students long-term.

We would like to thank the sincere cooperation of the Alborz Education Department. The personal costs of the researchers have been used to implement the project.

 

The authors declared no conflict of interest regarding the publication of this article.