Effect of Ergonomic Intervention on Cognitive Function of Office Workers

Abstract

Background:

Different domains of cognitive function are important in some jobs, such as office work. Ergonomic risk factors may affect cognitive function.

Aim:

This study was designed to assess the effect of an ergonomic training intervention on the cognitive function of office workers.

Materials and Methods:

This was a before-after study performed in 2020 in Yazd, Iran on female office workers. Cognitive function (working memory, attention, and response time) was assessed by Wechsler working memory and Stroop tests before and after the intervention. Ergonomic intervention consisted of an ergonomic modification of the workstation and a training program about ergonomic principles of office work. Data were analyzed by SPSS (ver. 24) using paired t-test and the multiple regression linear model.

Results:

Mean age and work experience of the participants were 35.38 ± 1.60 and 8.54 ± 1.24 yr., respectively. Forward visual memory, response time, and interference time were significantly changed after the intervention, but the change in other aspects of cognitive function (i.e., memory span, backward visual memory, and interference score) was not statistically significant. Marital status, age, and working hours significantly affected working memory, test duration and response time, and number of errors, respectively.

Conclusion:

This study showed that ergonomic intervention (modification of workstation and training) may significantly affect some aspects of cognitive function in office workers.

INTRODUCTION

During the last 50 years, new technologies, especially computer use, has changed workstations and has led to an increased number of sedentary jobs.[1] It has been estimated that most of the office workers in Australia spend about 75% of their workday in a sedentary position. Prolonged sitting (more than 4 h a day) is associated with some adverse health effects, such as metabolic, cardiovascular, and musculoskeletal disorders.[1] Workplace interventions such as ergonomic modifications and posture change during a static position in the workplace may decrease some adverse effects of prolonged sitting.[2,3] Recently, besides metabolic and musculoskeletal disorders, the effect of static or sedentary posture or nonergonomic situations on cognitive function has raised concern as well.[4]

Office work, in order to be performed perfectly, needs many aspects of cognitive function. A cognitive function consists of such domains as perception, attention, memory, and decision-making,[5,6] which is probably affected by many factors, such as work tasks, time of work, shift work, some environmental factors, and even body posture during work.[7,8] The effect of body posture on cognitive function is important, especially in the tasks which require a high level of attention and concentration.[9] Inappropriate body posture can lead to increased human errors and delay in information processing.[8]

Most office works are routinely performed in a sitting and mostly static position. Many office workstations lack the standards of an ergonomic workstation, which may affect physical and cognitive aspects of health. The effects of ergonomic modifications and workplace exercises on physical health have been widely assessed, but their effects on cognitive function are controversial. Workstation redesign especially using ergonomic and appropriate chairs may have an important role in the workers’ performance and comfort.[10] Ergonomic intervention in the workplace in order to design a better workstation, and workplace exercises may improve cognitive function and performance.[2,11] Some studies have shown a better cognitive function in nonsitting work positions.[7,12,13] Employees have reported less tiredness and higher concentration in nonsitting positions,[4] but Magnon et al.[14] (2018), in a systematic review, did not find a significant effect of reducing sedentary behavior on cognitive function. Schwartz et al. (2018)[15] and Russel et al.[1] did not find a significant effect of intermittent sitting and standing positions on cognitive function, but in another study on telephone operators, standing position increased productivity.[16] Schwarz et al.[15] (2018) found that body posture did not affect response time, concentration, and work pace, but Mohammadi et al.[11] (2018) found that cognitive function is affected by work posture. Baker et al.[17] in two different studies found that two hours of sitting computer work increased problem-solving errors, but the attention did not change, and two hours of standing computer work increased discomfort and deteriorated reaction time and mental state, while creative problem-solving improved.[18]

So, due to inconsistent results in the previous studies, this study was designed to assess the effect of an ergonomic intervention program, including ergonomic modification of the workstation and training about ergonomic workstation standards and workplace exercises, on the cognitive function of office workers.

MATERIALS AND METHODS

This was a before-after study performed in 2021 in Yazd, Iran. Participants were female office workers of the Public Health school in Shahid Sadoughi University of Medical Sciences who were randomly selected from all office workers. The number of male office workers was small, so only females were selected. In order to decrease the effect of environmental factors, the participants were selected from one school, and their participation in the study was voluntary. Inclusion criteria were the following: work experience of at least 1 year as an office worker, age between 25 and 45 years, and at least 2 h of computer work in their work shift. Those with sleep disorders and consumption of psychiatric drugs did not enter the study.

Demographic information (age, work experience, and average working hours a day) was collected through a questionnaire. Then, a researcher-made questionnaire was used to assess the ergonomic features of the workplace by an expert occupational hygienist, and ergonomic risk factors were recorded in each workstation to be used in designing the training content.

Cognitive function assessment

Cognitive function was assessed for each participant in her workstation in similar situations at 11 o’clock AM. Wechsler working memory and Stroop tests were used in this regard. Working memory was assessed using Wechsler working memory test. Other studies have used this test for measuring working memory.[16] In this test, a set of digits (from three to nine digits) are presented on the monitor, and the participant should repeat the digits in forward and backward directions. In the end, forward and backward visual memory and memory span will be measured. After two errors, the test is terminated.

Attention and response time were measured by the Stroop test. In this test, four words (green, blue, red, and yellow) are presented on the monitor for 2 s with 0.008-s time interval. Forty-eight words are congruent with the color (e.g., word “green” with green color), and 48 words are incongruent with the color (e.g., word “green” with blue color). The participants should respond to the color of the word not its meaning, and press the specific button on the keyboard. Attention is determined by calculating the interference score by subtracting the number of incongruent correct answers from congruent correct answers. Response time is determined by calculating interference time which is calculated by subtracting response time to incongruent words from congruent words.

Intervention

After initial evaluations of the workstation and performing cognitive tests, an ergonomic intervention was performed. The intervention consisted of two parts: 1. one session of training ergonomic principles of office work with an emphasis on ergonomic risk factors of the participant’s workstation which were extracted in the previous stage, including the standard arrangement of the workstation, adjusting the chair, appropriate posture during work, microbreaks, and stretching exercises in the workplace. Trainings were performed by an expert occupational hygienist separately for each participant by face-to-face education. The training session lasted about half an hour for each participant; 2. ergonomic modification of the workstation including adjusting the chair height and standard positioning of mouse, keyboard, and monitor. No change was made to workplace equipment. One month after the intervention, cognitive tests were performed again at the same situations. During this period, the workstations were checked every other day to answer the questions of the participants and seek any environmental or other confounding factors.

Statistical analysis

Data were analyzed by SPSS (ver. 24) using paired t-test and multiple regression linear model. Uni-variate analysis showed that some demographic factors affected the responses, so the effects of age, marital status, and working hours on the results of the tests were assessed in a regression model. In this model, the initial result of each test was used as a confounder in the model.

Ethical issues

This study was the result of a master’s thesis in occupational health and was approved by the ethics committee of Shahid Sadoughi university of medical sciences (code: IR.SSU.SPH.REC.1399.083). Informed consent was obtained from each participant.

RESULTS

Totally, 37 female office workers entered the study. Table 1 shows the demographic data of the participants.

Table 1.

Demographic data of the participants

Variable	Mean±SD
Age (yr.)	35.38±1.60
BMI (Kg/m2)	24.84±3.84
Work experience (Yr.)	8.54±1.24
Working hour (hr.)/day	7.59±0.19
Education
Bs.	12 (3.24%)
Msc.	24 (64.9%)
PhD	1 (2.7%)

Forward visual memory and response time were significantly changed after the intervention. Table 2 compares various cognitive variables before and after an intervention.

Table 2.

Comparison of cognitive variables before and after intervention

Cognitive variable	Mean±SD		P
	Before intervention	After intervention
Working memory
Memory span	6.49±0.26	7.08±0.23	0.07
Forward visual memory	7.46±2.86	8.91±2.67	0.01
Backward visual memory	8.92±2.95	9.18±2.84	0.60
Attention and response time
Test duration (s)	95.67±11.95	90.89±13.34	0.004
Response time (s)	2005.02±238.62	1901.89±269.53	0.002
Number of errors	0.55±1.52	0.44±0.84	0.77
Interference score	2.00±1.38	0.41±0.34	0.11
Interference time	70.05±11.10	48.64±7.65	0.01

Some demographic variables significantly affected various parameters of cognitive function [Table 3]. Marital status significantly affected working memory, but age and work experience did not significantly affect this cognitive parameter. Age, but not marital status and working hours, significantly affected test duration and response time after the intervention. Number of errors was significantly affected by working hours.

Table 3.

Effect of age, marital status and working hours, on various cognitive parameters

Cognitive variable	Regression coefficient (P)
	Age	Marital status	Working hours	Baseline
Working memory
Memory span	0.028 (0.247)	1.204 (0.036)*	0.174 (0.316)	0.38 (0.005)*
Forward visual memory	0.069 (0.143)	2.753 (0.008)*	0.157 (0.625)	0.371 (0.012)*
Backward visual memory	0.017 (0.611)	0.626 (0.428)	1.036 (<0.001)*	0.523 (<0.001)*
Attention and response time
Test duration (s)	0.396 (0.016)*	−3.242 (0.372)	0.954 (0.425)	0.674 (<0.001)*
Response time (s)	7.891 (0.023)*	−63.766 (0.422)	23.131 (0.351)	0.665 (<0.001)*
Number of errors	−0.014 (0.117)	0.036 (0.872)	0.177 (0.010)	0.417 (<0.001)*
Interference score	0.000 (0.987)	−0.269 (0.463)	−0.163 (0.152)	0.614 (<0.001)*
Interference time	0.065 (0.930)	24.033 (0.174)	10.598 (0.053)	0.356 (<0.001)*

*Significant effect

DISCUSSION

In this study, the effect of an ergonomic intervention (i.e., ergonomic modification and training) on cognitive function was assessed in office workers. Wechsler working memory and Stroop tests were used to assess cognitive function before and after ergonomic intervention in female office workers. The results showed that forward visual memory, response time, and interference time were significantly changed after the intervention, and some demographic and occupational variables, especially age, significantly affected the participants’ response after the intervention.

To assess short-term and active working memory, memory span was measured using the Wechsler working memory test. This test can assess forward visual memory, backward visual memory, and memory span based on the golden digit (7 ± 2), and its score is usually between 5 and 9 in adults. A greater score of working memory shows a better memory function. Some previous studies have assessed the effect of different variables on working memory. Barella et al.[19] found that posture modification positively affects working memory. Chang et al.[20] in a systematic review found a positive effect of exercise on short-term memory.

In this study, consistent with Russel et al. study,[1] the scores of all aspects of working memory (i.e., memory span, and forward and backward visual memory) were increased after the intervention, but the difference was significant only for forward visual memory which was consistent with the study of Bantoft et al.[21], although the level of significance for memory span was near significance and increasing sample size may lead to a significant difference. Working memory is a part of a cognitive system that stores information and also holds some information while performing mental tasks.[21] Working memory affects attention and concentration as well.[22,23] So, its deficit may lead to errors in the workplace.

In the current study, attention and response time were assessed by the Stroop test. This test has been designed to measure attention and cognitive flexibility by visual processing. The interference score shows attention, and the response score shows response or reaction time. Usually, response time to congruent words is shorter than incongruent ones. When interference time is shorter, the time of stimulus control is shorter and the participant can differentiate between the color and the meaning in a shorter duration of time. The interference score is an index of human brain capability in the management of new tasks. A lower interference score shows better performance, fewer errors, and higher attention. In the current study, the interference score was decreased after the intervention, although this decrease was not statistically significant.

Test duration was significantly decreased after the intervention, which shows a higher speed of the participants in response and reaction. This result was consistent with the results of Mohammadi et al.[11] and inconsistent with the studies conducted by Shwartz et al.[15,24], although it should be considered that in all of these studies the intervention was different from the current study. Response time significantly reduced after the intervention, but the change in the number of errors was not statistically significant. Zhang et al.[25] in a study on students found that dynamic workstation cannot affect the results of the Stroop test, although again the intervention was different from our study and the results cannot be compared.

The interference score in the current study was decreased after the intervention, which shows a lower probability of error and a better performance in the workplace; although the decrease was not statistically significant, the difference was large and a larger sample size may lead to a significant difference. Mohammadi et al.[11] found that the interference score and selective attention in the standard sitting position were better than in other positions. Russell et al.[1] found that after their intervention, attention was improved. Unfortunately, we could not find a study with a similar intervention to the current study.

In this study, interference time after the intervention was significantly decreased, which shows a higher speed and lower response time, which was inconsistent with the results of Schwartz et al.[15] Most studies on the effects of ergonomic modification in the workplace have been conducted on musculoskeletal complaints and disorders.[26,27]

Some factors may affect cognitive function in the workplace. Working hours, shift work, work posture, and some environmental exposures are among the factors which have been assessed in different studies.[15,24,28,29] Ergonomic interventions to improve work posture, workplace arrangement, microbreaks, and stretching exercises have been shown to improve discomfort, fatigue, and musculoskeletal complaints in different jobs,[3,26,30] but the effect of interventions on workers’ cognitive function is controversial by now. Most studies in this regard have assessed the effect of changing work posture on cognitive function. Schwartz et al.[15,24] in two different studies found that sit-stand work posture as an ergonomic modification cannot affect cognitive function in short and medium-term durations. They showed that intermittent work posture did not affect response time, concentration, and work speed,[15] which was inconsistent with the results of the current study, although our modification was an ergonomic modification of the workplace and training, they compared two different work postures. Russel et al.[1] could not find a significant effect of intermittent sitting and standing postures on cognitive function in office workers. Mohammadi et al.[11] conversely found that work posture can significantly affect cognitive function. Bantoft et al.[21] assessed the effect of standing and walking during work on cognitive function and did not find a significant effect. Magnon et al.[14] in a systematic review found that interventions to reduce sedentary behavior are not associated with changes in cognitive function. Sohrabi and Babamiri[31] found a significant effect of an ergonomic training intervention on musculoskeletal complaints of office workers, but this effect was not observed on productivity and some variables of quality of work life.

In the current study, marital status significantly affected the difference after the intervention, so the impact of the intervention was higher in single individuals than married ones, which is probably due to family or social preoccupations in married individuals. Age and work history did not affect working memory, but it was affected by daily working hours. Response time was significantly increased by age. Increased daily working hours significantly increased the number of errors after the intervention.

Limitations

This study had some limitations. The participants were only females, so the results cannot be generalized to males. The assessment was done one month after the intervention, so the long-term effects of the intervention could not be assessed. The small sample size may have affected the significance of some differences. We could not change any nonergonomic equipment due to monetary constraints, and our modification consisted only of standard arrangement and adjustment of different equipment in the workstation.

CONCLUSION

This study showed that ergonomic intervention including training and ergonomic modification of the workstation may significantly affect some aspects of cognitive function (i.e., forward visual memory, response time, and interference time) in office workers in short-term duration. Larger studies with higher sample size, other ergonomic interventions, and also the longer duration of the assessment are recommended.

Author contributions

All authors have contributed in this study in the following roles: ZM (proposal preparation, data collection, preparing article draft), GH (initial concept, data interpretation, final preparation of manuscript), SB (data analysis, data interpretation, preparation of initial draft), and AHM (initial concept, data interpretation, preparation of initial draft, final preparation of manuscript).

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.