Introduction
Students’ physical condition in classrooms and study halls can make them suffer from skeletal and muscular disorders. Studies have shown that unfavorable body posture is considered the most important risk factor for musculoskeletal disorders caused by work [1].
The university is the workplace of many students, and chairs have become an important physical element of the classroom and learning environment [7]. Improper design of chairs is one of the causes of poor sitting posture [8], which can lead to poor posture, fatigue, psychological stress, and low performance [7]. Designing a chair based on ergonomic principles can help prevent musculoskeletal disorders [9, 10]. Also, using a properly designed chair reduces fatigue and discomfort in sitting. It allows students to sit comfortably for longer periods, increasing their concentration and learning [11].
 According to the latest available statistics in the academic year 2017-2018, more than 3600000 students were studying in educational centers [13], and the lack of standard tables and chairs can affect their health.
In Iran, few studies have been done in the field of ergonomic chair design for the educational environment [7]. Since most people lean forward or are in different positions while reading or writing, the reading chair’s ergonomic changes can help improve the posture. The main activities of students are listening and paying attention to lessons and conversations, as well as reading and writing. They are placed in different positions to perform these activities [15].
Normal chairs cannot provide different sitting positions. In 2011, a chair called Tipton was designed [13], which, unlike normal chairs, can be placed in two other directions without harming the user’s posture. The user can sit back on this chair and listen to lessons and conversations, or the chair can be directed forward, and the person can do more active things such as writing and reading.
Research done by Barber et al. showed that many people tend to have multiple sitting postures. Therefore, such a chair is necessary to move the support forward to minimize forward rotation of the shoulders and keep the back spine straight [13].
The effectiveness of this design has not been evaluated. The current study aims to evaluate the effectiveness of the ability to change the angle of the chair base on the kinematic behavior of the thoracic and lumbar spine of students by comparing it with a normal library chair using objective and subjective methods. Thus, a chair model was made based on the Tipton chair’s commercial model, referred to as Tipton in the text.

Materials and Methods
This quantitative study used a quasi-experimental analytical design to evaluate the effectiveness of the Tipton chair on the physical condition of the students of the University of Social Welfare and Rehabilitation Sciences (Inter-subjects study). Sampling was done in a non-random manner. The minimum sample size was 25 people, and due to the probability of a 15% dropout, the study was conducted on 30 students (20 women and 10 men). In this study, height, weight, age, and gender were considered contextual variables. 
To collect research data, the following tools were used:
Electrogoniometer device
 The electrogoniometer measures the potential difference between two end blocks and then converts this potential difference into the corresponding joint angle. According to Gray’s anatomy book, a fixed end block was placed on the first lumbar vertebra to measure the angles of the lumbar region. According to the current study, a movable end block was placed on the fifth lumbar vertebra. Also, for measuring the thoracic region, a fixed end block was placed on the first thoracic vertebra, and a movable end block was placed on the twelfth thoracic vertebra [16].
System usability scale (SUS) questionnaire
 This questionnaire was designed in 1996 by John Brooke [17] and is used to evaluate the overall satisfaction of users [18]. In 2014, the validity and reliability of the Persian version of this questionnaire were investigated by Dianat et al. [19]. The validity and reliability of the questionnaire were measured by calculating the Cronbach alpha coefficient as 0.79 and  intraclass correlation coefficient value of 0.96, and these values (more than 0.7) are at the optimal level. The content validity of this questionnaire was confirmed with content validity ratio and content validity index values higher than 0.85 and 0.81, respectively [19].
This questionnaire contains ten 5-choice questions that users answer with a score of 0 to 4 (completely disagree to agree). The total score is between 0 and 100, where a higher score indicates more product usability. The steps of the test are as follows:
In the current study, two upright and detailed postures have been investigated. The person sat on each chair for 5 minutes in the upright posture and then for 5 minutes in the detailed reading posture. At this time, the electrogoniometer continuously recorded the data in the Biometrics Ltd software with a frequency of 20 Hz/s. After 10 minutes sitting on each chair, they were asked to complete the SUS questionnaire.
By measuring the angle of the thoracic and lumbar spine in two sagittal and coronal planes for each person by an electrogoniometer device, the total Mean±SD for each channel in each body position for two chairs was calculated separately for analysis. After calculating the parameters of the range of changes using SPSS software, version 25 and analyzing the statistical test method of repeated measure and the score parameter of the SUS questionnaire through the statistical test of pairwise comparison, the effectiveness of the Tipton chair was evaluated.

Results
All male and female participants in the study were in the 5th to 95th percentile of society regarding height and weight. In the current study, the Mean±SD height of women was 163.7±3.7 cm, and that of men was 179±3.7 cm; the  Mean±SD weight of the women was 65.25±6.4 kg, and that of men was 76.2±4.7 kg. The  Mean±SD body mass index (BMI) of women is 24.3±2.5 kg/m2, and that of men is 23.8±2.1 kg/m2. Also, the  Mean±SD age of participating women was 27.3±6.4 years, and that of the men was 30.3±4.7 years. After calculating the parameters of Mean±SD and range of changes, using SPSS software, version 25 and analyzing with the method of repeated measure statistical test and within the group, the effectiveness of the Tipton chair was evaluated on the dependent variables of the study. A P<0.05 was considered significant in the statistical analysis.
Flexion and extension angles of the back spine
The interaction effect of chair and posture was not significant, with a significance level of 0.058 (Table 1). Also, the chair variable was not significant, with a significance level of 0.072. However, the posture has a significant difference with a significant level of 0.013 on the flexion and extension of the back spine. Also, the results of the comparing the changes in the spine angles in the two chairs showed a decrease in the average range of the changes in the angles in all body positions for both the dorsal and lumbar spine regions in both sagittal and coronal planes in the Tipton chair compared to the normal chair. In the upright body position, the mean range of flexion and back extension changes between the two chairs was not observed, while in the detailed study body position, it decreased by 23%. Also, the results showed that the average range of back flexion and extension changes in both Tipton and normal chairs is higher in the detailed study posture than in the upright posture. 



There is no significant difference between the interaction effect of chair and posture, with a significance level of 0.174 (Table 2). The chair variable with a significance level of 0.003 significantly differs in lumbar flexion extension. This significant difference is in the direction of a 16% decrease in the average range of changes in lumbar flexion-extension angles in the upright posture.



A 43% decrease in the body was a closer study in the Tipton chair than in the normal chair. While with the physical posture variable with a significance level of 0.162, there was no significant difference in lumbar spine flexion extension (Table 3).



Lateral flexion angles of the lumbar spine
Table 4 shows no significant difference between the chair and posture, with a significance level of 0.595. The study’s findings showed that the chair variable with a significance level of 0.009 significantly differs in the average range of changes in lumbar lateral flexion angles, the average range of changes in lumbar lateral flexion angles in both upright postures, and a detailed study in the Tipton chair. Compared to the normal chair, it has decreased by 28%. Also, the physical posture variable with a significance level of 0.009 significantly affects the changes in lumbar lateral flexion, the average of which in both Tipton and normal chairs in the detailed study posture is lower than the upright posture.



Comparing the results of the sus questionnaire between the use of normal and tipton chairs
Paired t-test was used to compare the scores of the SUS questionnaire for the normal and Tipton chairs in the study participants. According to Table 5, the results of the statistical analysis showed that the normal and Tipton chairs have a significant difference from each other with a significance level of less than 0.05, which is in line with the increase of the average points of the SUS questionnaire in the Tipton chair compared to the normal chair.




Discussion
The current study showed that the Tipton chair could reduce the average range of body angle changes in the dorsal and lumbar spine regions. Also, comparing the changes of spine angles in two postures, in the assessment of back flexion and extension angles, showed that in both normal and Tipton chairs, the average range of changes in posture is more closely studied than in upright posture. The average range of changes in flexion and lumbar extension angles in both normal and Tipton chairs in the detailed study posture is lower than in the upright posture.
The results of evaluating the changes in lateral flexion angles of the back show a decrease in the average range of changes in the body posture of the detailed study compared to upright on a normal chair and an increase of this value in the Tipton chair. Meanwhile, the average range of lumbar lateral flexion angle changes in the normal and Tipton chairs in the detailed study posture was lower than the upright posture. Also, there was a significant relationship in examining the effect of chair type and posture on the lateral flexion range of the back spine. Still, no significant difference was observed between the postures.
The study’s results on the effect of posture type showed that the range of changes in flexion and extension of the lumbar spine, unlike the back spine, in the two postures of upright and detailed studies do not have significant differences with each other. The results of the average range of flexion and extension changes of the lumbar spine in the present study showed that the chair type variable causes a significant difference. Also, the range of lumbar lateral flexion changes showed a significant difference in both chair and body position variables in the participants, which is consistent with the results of Kim et al.’s study [20]. They evaluated lumbar flexion angle and hip tilt on three types of flat surface seating, a forward-leaning wedge (10° incline) and a backward-leaning wedge. They concluded that there was a significant difference in the degree of lumbar flexion among different sitting levels. The degree of lumbar flexion when people sat on the forward-inclined wedge was significantly reduced compared to the level surface and the backward-inclined wedge. A backward-leaning wedge increases the flexion of the lumbar spine. The study’s findings showed that sitting on a forward-leaning wedge can be beneficial in minimizing lumbar bending [20].
Intolo et al. designed two ergonomic pelvic and lumbar-pelvic cushions to adjust the seat by increasing the slope of the seat floor. This study showed that the participants who reported mild pain without a pillow reported no pain while using a lumbar-pelvic pad to increase the slope of the chair floor after 10 minutes [21].
In the current study, the level of satisfaction of the participants regarding the use of two chairs was evaluated through the SUS questionnaire, and the results showed that the satisfaction level of the participants in using the Tipton chair is 20% higher compared to the normal chair. These results are consistent with Intolo et al.’s study regarding reducing pain in participants sitting on a cushioned (slanted) chair. Also, the results of the SUS questionnaire showed an increase in satisfaction of 25% in women and 7% in men. This difference can be originated from the difference in the anthropometric dimensions of women and men. In the current study, the  Mean±SD height of women was 163±3.7 cm, and that of men was 179±3.7 cm.

Conclusion
Comparing the changes of the spine angles in the two chairs shows a decrease in the average range of the angle changes in all body positions for both the dorsal and lumbar spine regions in both sagittal and coronal planes in the Tipton chair compared to the normal chair. In the upright posture, the mean range of flexion and back extension changes was not different between the two chairs. Examining the scores of the SUS questionnaire also showed that both normal chairs and Tipton have a significant difference, which indicates a 19% increase in participants’ satisfaction with the Tipton chair compared to the normal chair. Also, the results of this study indicate that women are more satisfied with the Tipton chair than men, and the observed difference in their level of satisfaction can be originated from the difference in the anthropometric dimensions of women and men. 
One of the limitations of the current research was the time limit and the prolongation of the study due to the impossibility of accessing students for evaluation due to the restrictions related to COVID-19 and the non-cooperation of several samples due to the conditions of COVID-19. Also, the impossibility of conducting experiments outside the university due to the need to supervise supervisors on the work steps was another limitation of this research. Considering the increase in users’ satisfaction with the Tipton chair compared to the normal chair, it is suggested to investigate the level of students’ concentration in using the Tipton chair. It is also recommended to investigate the effectiveness of using the Tipton chair in other age groups, such as children and students. It is suggested to use a larger number of samples in future research to generalize the results to society more confidently.

Ethical Considerations

Compliance with ethical guidelines
All ethical principals are considered in this article. the particopants were informed about the purpose of the research and it's implementation stages. they were also assumed about the confidentiality of their information. They were free to leave the study whenever they wished. and if desired, the resrach results would be available to them.

Funding
This paper was extracted from the MSc thesis of Masoumeh Zakeri in Department of Ergonomics, University of Social Welfare and Rehabilitation Sciences.

Authors' contributions
Conceptualization, supervision, financing, investigation, data analysis, visualization, editing and finalization the manuscript: Amirsalar Jafarpisheh, Reza Osquei Zadeh and Masoumeh Zakeri; Drafting the manuscript and resources: Masoumeh Zakeri; Methodology: Amirsalar Jafarpisheh, Reza Osquei Zadeh, Masoumeh Zakeri and Mohsen Vahedi. 

Conflict of interest
The authors declared no conflict if interest.

 

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