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ORIGINAL ARTICLE
Year : 2021  |  Volume : 25  |  Issue : 3  |  Page : 138-146
 

The relationship of grip and pinch strength to musculoskeletal disorders in female carpet weavers in Southeastern Iran, 2019


1 Departments of Occupational Health, Faculty of Health, Kerman University of Medical Sciences, Kerman, Iran
2 Department of Occupational Health, Faculty of Health, Kerman University of Medical Sciences, Kerman; Department of Occupational Health, Faculty of Health, Jiroft University of Medical Sciences, Jiroft, Iran
3 Department of Biostatistics and Epidemiology, Faculty of Health, Kerman University of Medical Sciences, Kerman, Iran
4 Department of Environment Health Engineering, Faculty of Health, Jiroft University of Medical Sciences, Jiroft, Iran

Date of Submission17-Jun-2020
Date of Decision06-Jul-2020
Date of Acceptance17-Sep-2020
Date of Web Publication9-Oct-2021

Correspondence Address:
Dr. Mostafa Mohammadian
Kerman University of Medical Sciences, Haft Bagh-e-Alavi Road, Kerman
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijoem.IJOEM_223_20

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  Abstract 


Background: The repetitive and prolonged exertion of grip and pinch strength are current among carpet weaver tasks. The three objectives of this study were (1) to investigate the relationship between symptoms of musculoskeletal disorders and grip and pinch strength of carpet weavers in carpet weaving workshops in Kerman province, (2) to compare the grip and pinch strength of carpet weavers with normal values, and (3) to identify the relationship between hand postures of carpet weavers during work and force exertion. Methods: In this cross-sectional study, grip strength and key, tip and palmar pinch strengths of 101 female carpet weavers aged 20 to 71 years were measured in Kerman province, in 2018. Nordic Musculoskeletal Questionnaire (Extended version) was also used to evaluate musculoskeletal disorders. Results: Bivariate and multivariate linear regression analyses showed that participants who suffered from musculoskeletal disorders had lower grip and pinch strength than others and this decrease was statistically significant in upper back, wrists/hands, and knees. Moreover, there was a significant difference between grip and three types of pinch strength of carpet weavers and normal values. Furthermore, for both hands, the grip strength in the position recommended by American Society of Hand Therapists was significantly greater than that in the normal position carpet weavers usually adopt. Conclusion: Based on the results, the high prevalence of musculoskeletal disorders has led to a significant decrease in the grip and pinch strength of carpet weavers. Therefore, it is necessary to undertake ergonomic interventions in designing the carpet weaving workstation.


Keywords: Grip strength, musculoskeletal disorders, pinch strength


How to cite this article:
Nejad NH, Mohammadian M, Haghdoost AA, Charkhloo E. The relationship of grip and pinch strength to musculoskeletal disorders in female carpet weavers in Southeastern Iran, 2019. Indian J Occup Environ Med 2021;25:138-46

How to cite this URL:
Nejad NH, Mohammadian M, Haghdoost AA, Charkhloo E. The relationship of grip and pinch strength to musculoskeletal disorders in female carpet weavers in Southeastern Iran, 2019. Indian J Occup Environ Med [serial online] 2021 [cited 2021 Nov 28];25:138-46. Available from: https://www.ijoem.com/text.asp?2021/25/3/138/327923





  Introduction Top


Work-related Musculoskeletal Disorders (WMSDs) are one of the main health problems among workers all over the world.[1] Moreover, these disorders have become the most costly health problems in industrialized and industrially developing countries.[2] In this regard, certain epidemiological studies have investigated the relationship between musculoskeletal disorders and risk factors in the workplace including repetitive tasks, body posture during work, force exertion, duration of exposure, workplace, work environment conditions, psychological factors, social factors, and individual characteristics.[3],[4],[5] However, the working conditions in hand-woven carpet industry are such that musculoskeletal injuries such as deformity of spine and fingers are considered as distinctive features of this occupation; factors such as continuous and prolonged exertion of force by fingers as well as awkward posture are possible reasons for such musculoskeletal disorders.[2]

In order to fulfill their tasks, carpet weavers need to implement a combination of grip strength and pinch strength. Grip Strength is defined as the power of the combined contraction of extrinsic and intrinsic muscles of hand that flex hand joints[6],[7]; it reflects the total muscle strength of the upper extremities and is also related to other muscle strengths of the body.[8] Hand grip strength occurs when objects are held by the thumb, fingers or both and the palm. In pinch strength, nevertheless, any one finger or combination of fingers is used to manipulate objects in coordination with thumb movements without having contact with the palm.[9] Investigation of grip strength is of particular significance in evaluating upper extremity injuries as well as in determining job qualification of those suffering from local hand injuries, such as rheumatoid arthritis or muscular dystrophy.[10]

High hand force exertion is an independent risk factor for carpal tunnel syndrome and hand and wrist tendonitis.[11] Ergonomists have demonstrated that the increase in carpal tunnel pressure is a reaction to force exertion especially in pinching activities.[12] Silverstein et al. conducted a research to investigate cumulative trauma disorders (CTDs) in 574 active workers from six different industrial sites in Michigan. The results of this study revealed the existence of significant positive associations between hand wrist CTDs and high force-high repetitive jobs.[13]

The impact of working conditions on work-related musculoskeletal disorders can best be understood if the working status and conditions of people are properly recognized. Moreover, prevention programs can be proposed and proactively and effectively applied only through thorough investigations and researches conducted by ergonomic experts.[14] Therefore, it seems necessary to evaluate repetitive and prolonged grip and pinch strength of workers in carpet weaving industry. This study was conducted to test the following hypotheses among carpet weavers in Kerman province.

  1. There is a relationship between symptoms of musculoskeletal disorders and grip and pinch strength in carpet weavers.
  2. Carpet weavers have lower grip and pinch strength than normal people.
  3. There is a relationship between carpet weavers' hand posture during work and force exertion.



  Methods Top


Research population

The present research is a descriptive-analytical cross-sectional study. The census sampling method was adopted in this study to select participants from among those working in carpet weaving workshops in Kerman province in 2018. Hence, 101 participants (all females) working in workshops in Ravar, Rafsanjan, Kerman, Golbaf, and Kouhbanan entered the study and 29 were removed from the study due to reasons such as being absent during the study (12 cases), not meeting the inclusion criteria (9 cases) or being unwilling to participate (8 cases).

In this study, the possibility of participation of adults (those over 20 years of age) working in carpet weaving workshops in Kerman province was considered as an inclusion criteria for entering the study. The exclusion criteria included having work experience of less than 1 year, having pain due to hand surgery, fracture or any other disease like scoliosis, osteoporosis, and mental illnesses (which affect the strength of the upper extremities), suffering from cardiovascular, neurological or metabolic diseases, having skeletal disorders due to accident or other causes, pregnancy, and being hospitalized short before the study. Prior to conducting the research, all stages of the study were reviewed for ethical considerations and the ethics code was obtained from the Ethics Committee of Vice Chancellor for Research in Kerman University of Medical Sciences. Moreover, the objective of the research and research methodology were fully explained to workers, and they were assured that their personal information would remain confidential.

Measuring grip and pinch strength

In this study, three types of hand pinch strength (tip, key, and palmar) as well as grip strength of carpet weavers were measured according to the method proposed by Mathiowetz et al.[15] and as per the recommendations by the American Society of Hand Therapists (ASHT).[16] For measuring grip strength, ASHT recommended a sitting position with the arms close to the torso without rotation, the elbow flexed at 90 degrees, the forearm in neutral position and the wrist slightly extended (0–15 degrees) with 0–15 degrees of ulnar deviation. The three types of pinch strength (tip, key and palmar) were also measured using the method proposed by Mathiowetz et al.[15]

For the statistical analysis, grip strength values of carpet weavers were compared with normative strength scores of adults in Iran.[10] Moreover, in this study, the values of grip strength of women in the standard position described above were compared with the values of grip strength while working with the normal posture of forearm and arm carpet weavers usually adopt during the work. Among carpet weavers, two postures were common (with elbow joint angles of 80 and 115 degrees) as shown in [Figure 1].
Figure 1: Common postures carpet weavers normally adopt during work: a. angle: 80°, b. angle: 115°

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In this study, anthropometric parameters of height (in centimeters) and weight (in kilograms) were measured. Hence, the influence of Body Mass Index (BMI) on musculoskeletal disorders was also investigated. Body mass index is calculated as a person's weight divided by height in meters squared and is classified in four groups of underweight (BMI under 18.5), normal (BMI 18.5–25), overweight (BMI 25–30), and obese (BMI over 30).

Tools and equipment

Jamar Hydraulic Dynamometer (Sammons Preston Rolyan) was used to measure grip strength. Three types of pinch strength (tip, key and palmar) were measured using Pinch Gauge (Saehan SH5005). Moreover, height and weight were measured by Portable Stadiometer (Seca 213) and digital flat scale (seca 813), respectively. The calibration of measuring instruments, especially strength measuring equipment, was controlled during the study.

Nordic Musculoskeletal Questionnaire (Extended version) (NMQ-E) was used in this study to evaluate musculoskeletal disorders. This questionnaire has been successfully used in a number of studies by ergonomic researchers and its validity and reliability are confirmed.[17]

Procedures

At the beginning of the test, the procedures of carrying out the research were explained to carpet weavers and their oral consent was obtained for participation in the study. Regarding the low level of literacy of carpet weavers, questions about demographic characteristics as well as inclusion and exclusion criteria were asked orally and then recorded in the relevant forms. Thereafter, the Nordic Questionnaire (Extended version) was completed via personal interviews with those carpet weavers who had the criteria to enter the study. Then, the height and weight (in kilograms) of participants were measured and after getting acquainted with dynamometer and Pinch Gauge, the women were seated in the standard position (as recommended by ASHT). In this position, the grip strength was measured for both hands and the mean of three attempts to exert maximum strength on dynamometer handle was recorded as the test result in the analysis. Based on the method proposed by Mathiowetz et al.,[15] three types of pinch strength (tip, key and palmar) were also measured two consecutive times for each hand and the maximum strength was recorded as the test result for each type of pinch strength. Moreover, to prevent muscle fatigue, there were 2-3 minutes of rest between each test.[16] At the end, the women were asked to return to work. While participants were working, they were asked to maintain the normal posture they usually adopt during work, hold the dynamometer in their hand and exert their maximum strength three times. Finally, the mean results for each hand were recorded as grip strength of normal working posture.

Statistical data analysis

In order to analyze the data, the information was first described using measures of central tendency and dispersion index. Then, with regard to parametric data, the relationships between these factors were analyzed by means of appropriate statistical tests with a significant level of 0.05. Accordingly, Pearson correlation test was used to analyze the relationship between quantitative variables. Furthermore, independent t-test was applied to investigate the difference between grip strength or work experience among musculoskeletal disorders in different parts of the body. To compare grip strength with normal values, one sample t-test was performed to determine the significance of the difference. Finally, to analyze the influence of different variables on grip and pinch strength, Stepwise multiple regression analysis was used. In this analysis, we explored different strengths separately because of the possible interactions between these strengths and the other factors such as the demographic and anthropomorphic variables. In addition, in multivariate regression model, we compared the association between the strengths and main factors using standard regression coefficients. All data were analyzed using SPSS25 statistical software.


  Results Top


Mean ages of the female carpet weavers were 46.33 ± 9.26 years [Table 1]. There was a significant difference between grip and all types of pinch strength (tip, key, and palmar) of carpet weavers and those of normal persons [Table 2]. Moreover, for both dominant and non-dominant hands, there was a significant difference between grip strength in the position recommended by ASHT and the one in the normal position carpet weavers usually take (P < 0.0001) [Figure 2].
Table 1: Demographic information of carpet weavers (n=101)

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Table 2: Difference between grip and pinch strength of female carpet weavers and normative information of Iranian population(in kilogram force)

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Figure 2: Difference between grip and pinch strength of carpet weavers and normal values according to age group

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The analysis of the prevalence of musculoskeletal disorders revealed that both during the study and the last 12 months before the study, 90% of carpet weavers (91 participants) suffered from musculoskeletal disorders at least in one region of the body. The highest severity of musculoskeletal disorders was in upper back, knees, and shoulders [Figure 3]. The results showed a significant relationship between grip and pinch strength and musculoskeletal disorders in knees, elbows, wrists, and upper back regions [Table 3]. Moreover, musculoskeletal disorders of knees and upper back regions had a significant relationship with grip and pinch strengths in linear regression analysis [Table 4].
Table 3: Results of the analysis of the relationship between grip and pinch strength(of dominant hand) and musculoskeletal disorders in carpet weavers

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Table 4: Stepwise multiple regression analysis results of grip and pinch strengths in carpet weavers(dominant hand; n=101)

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Figure 3: The prevalence of musculoskeletal disorders among carpet weaver

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Female carpet weavers suffered chronic pain mostly in their upper back (7.13 ± 7.31 years), low back (7.08 ± 7.48 years), shoulders (5.60 ± 5.64 years), neck (5.46 ± 5.80), elbows (4.85 ± 6.13), and wrists/hands (4.76 ± 5.45). The analysis also showed that, on average, women suffered from pain in hips/thighs for 4.83 (2.04) years, in knees, for 4.74 (5.80) years and in ankles/feet for 4.04 (4.87) years. Furthermore, at least 2 and at most 24 carpet weavers could not go to work due to musculoskeletal pains and disorders in the last 12 months [Table 5].
Table 5: Frequency(%) of positive responses of carpet weavers to the questions in Nordic Questionnaire(n=101)

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There was no significant relationship between the demographic variables and grip and pinch strength. Moreover, the analysis of the relationship between demographic variables and musculoskeletal disorders revealed that there was only a significant relationship between work experience of participants and musculoskeletal disorders of shoulder, elbow, wrists, knees, and feet (P < 0.05).


  Discussion Top


This study investigated the relationship between grip and pinch strength and musculoskeletal disorders in carpet weavers. To determine the impact of this job (which requires highly repetitive tasks and prolonged exertion of force) on reducing the ability to exert force, the grip and pinch strength were compared with the normal values of the population. The results indicated that those who suffered from musculoskeletal disorders had lower grip and pinch strength, which was statistically significant in some parts of the body [Table 3]. Furthermore, there was a significant difference between the hand strength of carpet weavers and normal values (P-value < 0.05). The comparison of grip and pinch strength in standard and normal postures also proved a significant difference (P-value < 0.05). In fact, the grip and pinch strength of carpet weavers were significantly lower than normal values of the population and hand posture in standard position (90 degree as recommended by ASHT) led to a higher strength than in the normal position carpet weavers used to adopt (P-value < 0.05).

Independent t-test was performed to determine the difference between grip and pinch strength of participants with symptoms of musculoskeletal disorders in nine regions of the body and that of participants with no symptoms of musculoskeletal disorders. The results of this test revealed that carpet weavers suffering from musculoskeletal pain in elbow and knee joints had a lower grip strength and this difference was statistically significant. Moreover, there was a significant decrease in tip pinch strength and palmar pinch strength of participants with musculoskeletal disorders in upper back and wrists/hands, respectively (P-value < 0.05) [Table 3]. Sande et al. carried out an empirical study to examine the strength of three groups of female industrial workers (all participants were female like in the present study) including those without MSDs, with mild MSDs and with severe MSDs and reported results that were similar to those of the present study.[18] The results showed that as the severity of musculoskeletal disorders among the groups increased, the strength of female workers significantly decreased.

The multivariate linear regression test was performed to determine the impact of each of the quantitative variables (anthropometric and demographic factors) as well as the qualitative variables (musculoskeletal disorders in different regions of the body) and also to identify the influence of the potential confounding variable on grip and pinch strength [Table 4].

The results indicated that from among the quantitative variables, only height had a positive linear effect on all types of pinch and grip strength of carpet weavers. Accordingly, taller participants had a higher grip and pinch strength. The multivariate regression analysis confirmed the effect of musculoskeletal disorders of knee on reducing the grip strength of female carpet weavers. However, the linear effect of the elbow joint on decreasing the grip strength was not statistically significant. The significance of the effect of this region in bivariate analysis was probably due to the impact of the confounding variables (e.g., age, height, or weight).

The results of multivariate regression analysis of the three types of pinch strength as well as those of bivariate analysis revealed a significant decrease in tip and palmar pinch strength. Hence, participants with symptoms of musculoskeletal disorders in their back and knee had a significantly lower tip pinch strength than other carpet weavers. Nevertheless, in bivariate analysis, there was no significant relationship between tip pinch strength and musculoskeletal disorders in the knee joint. In both bivariate and multivariate analyses, palmar pinch strength of carpet weavers with symptoms of musculoskeletal disorders in the wrists/hands was significantly lower than that of other participants [Table 4]. The results of the linear regression analysis in the research conducted by Yang and Cho indicated that working hours per day, years of work experience and age had a strong relationship with musculoskeletal disorders in wrist.[19] In previous studies, the relationship between grip strength and cognitive impairment,[20] heart failure,[21] smoking[22], and other factors have been analyzed; however, few studies have been dedicated to investigate the relationship between hand strength and musculoskeletal disorders (MSDs).

In this study, grip and three types of pinch strength (tip, key, and palmar) of female carpet weavers were significantly lower than normal values. This decrease was more obvious in pinch strength than in grip strength [Table 2]; [Figure 2]. Based on these results, it can be concluded that the nature of the carpet weaving job, which involves repetitive tasks and requires prolonged and high force exertion, is the cause of this decrease. In fact, In UED injuries, the strength plays the role of an intensifier during the repetitive task or grip.[23] The task of carpet weaving involves repetitive motions with a one-second cycle and on average, about 50 knots are tied per minute. The increase in the number of repetitions in working cycle is regarded as a risk factor for cumulative trauma disorder (CTD). This disorder has probably led to myasthenia and has consequently decreased grip and pinch strength of carpet weavers in comparison with the normal values.

Based on the results of this study, the grip strength of participants in the normal postures they usually adopt during carpet weaving (with elbow joint angles of 80 and 115 degrees) was significantly lower than that in the standard posture (90 degrees). The results of the present study were compatible with those of the study by Mathiowetz et al. which reported that the highest values of grip and pinch strength were in standard elbow flexed position (90 degrees).[24] Kong, however, found no significant difference between grip strength at 90° elbow flexion angle and that at 0° and 45°.[25]

The comparison of the strength of participants in the standard posture recommended by ASHT with that in the position carpet weavers normally take determined the maximum strength. This can be used as a criterion to adjust the level of working set for carpet weavers so that they can adopt the proper elbow posture (90 degrees). In fact, in this position, carpet weavers would be able to exert maximum grip strength in fulfilling their tasks particularly the task of using Deilam (a tool used to firmly push the horizontal weft against the fabric) which requires high force exertion.

With accordance to the high prevalence of musculoskeletal disorders in wrist among carpet weavers, improper wrist posture can be regarded as a cause of these disorders. Mogk et al. conducted an experimental study to investigate the response of the forearm musculature to combinations of three wrist postures (flexed, neutral and extended) and three forearm postures (pronated, neutral and supinated) and grip force.[26] The results demonstrated that forearm rotation influenced grip force generation only when the wrist was flexed; in this case, force decreased from supination to pronation. Moreover, the results of the study by Bhargava et al. on grip strength measurements at two wrist extension positions showed that grip strength at 15 degrees wrist extension was significantly greater than that at 35 degrees.[27] Based on the results of the present study, it is recommended that in addition to the height of the seat and other physical factors pointed out in the studies by Choobineh et al.,[2],[28],[29] wrist and elbow angles (which are of higher grip and pinch strength outputs) also be taken into consideration in designing the carpet weaving workstation and tools.

According to the findings, 90% of female carpet weavers suffered from musculoskeletal disorders at least in one region of the body during the last 12 months. The prevalence of these disorders was reported 100% in computer users,[19] 96% in veterinarians,[30] 89% in control room operators[1] and 77.2% in surgeons (86.2% females and 72.4% males).[3] In fact, the prevalence of these disorders in these studies, as in the present study, was proved higher than 75%.

Among female carpet weavers, the highest prevalence of musculoskeletal disorders was in shoulders (60%), knees (55%), wrists/hands (54%), neck (51%), low back (49%), and upper back (41%), respectively [Table 5]; [Figure 3]. The previous studies also reported a high prevalence of musculoskeletal disorders in these regions of the body. Accordingly, microscope users,[31] ready-made garment workers,[17] sonographers,[32] control room operators,[1] surgeons,[3] nurses[33] and truck drivers[34] had a high prevalence of musculoskeletal disorders in the upper extremity.

For musculoskeletal disorders, in addition to the type of task, gender differences may also be considered as an effective factor, nevertheless, the type of task and the duration of activity appear to be more important factors. The results of comparing posture and muscle control patterns between male and female computer users indicated that females had higher symptom scores for the upper trunk and extremities and only wrist region reached the significant level.[19] However, Otto et al. did not observe any significant difference between women and men in muscular and perceptual responses to a fatiguing task with the arm held horizontal at shoulder height.[35] Although the results on this issue are controversial, it is likely that women complain more of musculoskeletal pain than men do.[36]

There was a significant relationship between musculoskeletal symptoms and long working hours among Korean wage workers (18% of participants worked more than 52hours per week).[5] In the present study, most female carpet weavers worked at least 10 hours a day and more than 60 hours a week. The high prevalence of musculoskeletal disorders (more than 90%) amongst carpet weavers can be related to long working hours. In fact, lack of sufficient rest has led to cumulative trauma disorders (CTD). Measuring grip strength, nonetheless, can predict the consequences of factors associated with CTD easily and rapidly.[23]

Cheng et al. believed that long working hours almost always increase musculoskeletal disorders and injuries.[4] Therefore, carpet weavers reported chronic musculoskeletal pain. The pain in upper back, lower back and shoulders lasted on average about 7 years by the time of the study. In addition, there was a significant relationship between work experience of carpet weavers and musculoskeletal disorders of the shoulders, elbows, wrists, knees and feet, which is compatible with the results of the study by Yang and Cho on computer users.[19]

Musculoskeletal disorders are considered multifactorial. Since carpet weavers usually receive low wages and socio-psychological rewards, it is possible that these factors may contribute to the intensification of symptoms of musculoskeletal disorders among them. In this regard, the results of the study by Sekkay et al. showed that there was a strong correlation between “High effort-reward imbalance”, “lifestyle”, socio-psychosocial risk factors and musculoskeletal disorders in Canadian truck drivers.[34] Thus, it is recommended that in future studies, the effect of socio-psychosocial, physical and anthropometric factors on symptoms of MSDs in carpet weavers be further studied. Moreover, it is recommended to investigate the effect of working hours of this occupation on the grip and pinch strengths in future researches. The dispersion of carpet weaving workshops in different cities and villages around Kerman province with large distances from each other was the limitation of this research which prolonged the sampling process.

Based on the results of the present study, the high prevalence of musculoskeletal disorders has led to a significant decrease in the grip and pinch strength of carpet weavers. This decrease was also significant compared with the normal values of grip and pinch strength. Moreover, due to the importance of ergonomic interventions, in designing the carpet weaving workstation, it is necessary to adjust weaving height as well as the height of the seat so that the elbow angle is at 90 degrees (in which there are higher grip and pinch strength outputs).

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.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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