| Since China's reform and opening up,there was a rapid development of its economy,which cannot be separated from the efforts from various industries.The construction industry,an important contributor to economy,has grown over in recent years in China,and it tightly links to many other industries(e.g.manufacturing,finance,healthcare and energy).There was an increasing in the number of construction enterprises,number of employed persons and the gross output value of construction in recent years.Despite the importance of the construction industry,it has been identified as one of the most hazardous industries with the high incidence of accidents and the construction work has been identified as one of the top dangerous jobs.One possible reason could be the nature of the construction project that is labor-intensive,complex,temporary and dynamic.Preventing the accidents and reducing the casualties has been a core problem in the construction industry,it has attracted many experts,scholars and practitioners in this filed.In construction industry,there are various types of occupational fatal and nonfatal injuries(e.g.fall from a higher level,collapse,struck by objects,crane-related accidents and mechanical injuries in China),in which falls or fall-related injuries are a leading cause.The most direct contributor to fall events is body's losing balance.There are many factors that lead to losing balance for construction workers,such as working environment factors,management factors and health conditions etc.However,the instability of working postures and its interaction with other factors,like lifting load,standing surface condition are also important factors,which are easily ignored.Plenty studies have investigated the postural stability.However,previous studies focused more on the effects of some fall-risk related factors,like age,health condition,lifting load,or used above parameters to distinguish different sample groups,like young and old people,novice and expert workers etc.Lacking focused studies on the instability of working postures,less consideration to the subjective balance perceptions and its correlation with objective measures,ignorance of the interaction effects between different factors are the limitations of current studies.Moreover,optics-based passive motion capture system and force plates were widely used for acquiring center of pressure(COP)and based of support(BOS)data,which are quite expensive as well as difficult to setup.All above limitations make it difficult to apply the research findings into the practice.In addition,few studies were found that developed a postural assessment model and then developed a complete,low-cost and portable postural stability assessment system for construction workers.Recently,the Nintendo Wii Balance Board(WBB;Nintendo,Kyoto,Japan)is increasingly used in the assessment of postural control and interventions for balance rehabilitation,and has been investigated as potential balance test substitutes.Its low cost and portability make it an attractive alternative to current methods of measuring balance in research settings.Many previous studies demonstrated feasibility and accuracy of assessing COP trajectory using the Wii Balance Board.Besides,due to the rapid development of inertial sensing technology and human motion reconstruction techniques,IMU sensors are also increasingly being used in the assessment of human body balance or postural stability study.Based on above analysis,this research aims to develop a postural stability assessment model for construction workers,and a novel,low-cost working postural stability assessment system,in which low-cost and portable Nintendo Wii Balance Board is used as a COP data acquisition hardware.Firstly,this research investigated the fatal occupational injuries(FOI)in the construction industry in China,and compared tshe profile of FOI in construction industry in three countries: China,the United States(U.S.)and South Korea.Based on the statistical data officially published by the government of these three countries,the status,main accident types,causes and prevention of fatal occupational injuries in the construction industry,especially the fall-related injuries,were studied.This study found that the percentage of construction industry FOI over all industries was higher than that of workforce;China recorded the highest average number of FOI and the lowest mortality rate in construction industry;there was an increasing in the number of workforce in all three countries;the total number of FOI in the U.S.construction industry significantly increased,while it significantly decreased in China and in South Korea;the construction industry has been consistently suffering a lot from high fatal occupational injuries,in which “Fall from a higher level” was the top one common accident type and “Struck by” took the second place.Secondly,the accuracy of the base of support(BOS)measuring methods was investigated,since the interaction between center of pressure(COP)and BOS is an important variable for human body balance study.The standard method of measuring BOS is using optics-based motion capture system,which is expensive and difficult to setup.Recently,the rapid development of the inertial sensing technology and human motion reconstruction techniques made it possible to measure BOS using IMU-based motion captures system,however,its accuracy need to be validated.The IMU-based BOS measured by using Xsens MVN BIOMECH inertial sensor based human motion capture system,and footprint-based BOS measured manually were selected in the experimental study for accuracy testing.Results showed that there was a higher accuracy of footprintbased BOS than Xsens-based BOS.The relative errors of footprint-based BOS in the area of BOS,distance between toes(T-T)and distance between heel centers(H-H)were 0.009% ~ 6.089%,0.025%~2.435% and 0.375%~5.728%,respectively,and the position error range of vertexes was 4.686 mm ~ 13.120 mm.High errors were found of Xsens-based BOS,the errors on BOS area ranged from-12.6% to +64.6% depending on the type of experimental tasks.There was a significant effects of motions/postures on the accuracy of Xsens-based BOS and the knees' flexion motion impacted the accuracy significantly.When there was no knees' flexion,BOS area and two side lengths(T-T and H-H)were smaller than the real(-10.3 for BOS area,-4.6% for T-T and-13.9% for H-H in average).When there was knees' flexion,BOS area and two side lengths were always larger than the real(+30.4% for BOS area,+35.8% for T-T and +32.7% for H-H in average).The findings suggested that using footprints to measure static BOS was accurate and could be considered as a good reference in our study.And caution should be taken when using Xsens MVN BIOMECH to estimate BOS and foot position related measurements,especially for postures/motions with knees' flexion.Thirdly,the experimental study on postural stability assessment in construction workers was conducted.A 6(posture)*2(load)*2(standing surface)full factorial design was used.The working postures,lifting load,and standing surface slope were considered in the experiment,and their interaction effects were analyzed.Various types of data were recorded when 30 participants performed each of 6 working postures under 4 experimental conditions,including the subjective rating(0-10,the difficulty level to keep body in balance)on postural stability acquired by using the questionnaire,kinematics data recorded by using Xsens MVN BIOMECH human motion capture system,the footprintbased BOS and the COP data obtained by using the developed Nintendo Wii Balance Board based data acquisition system.Results showed:(1)The reliability of subjective rating on postural instability was high.There was a relatively low absolute difference(<0.65)between before-and-after subjective ratings on postural instability.The reliability,as assessed by ICC,was excellent under F+10(ICC(3,1)=0.919)and S+10(ICC(3,1)=0.940)conditions,good under F+0 condition(ICC(3,1)=0.890),and moderate under S+0 condition(ICC(3,1)=0.673).(2)Subjective rating on postural instability was statistically significantly different over different postures in all conditions(Flat+0KG: F(1.545,44.814)= 16.562,p=0.000;Flat+10KG: F(3.362,97.508)= 51.254,p=0.000;Slope+0KG: F(3.338,96.788)= 30.700,p=0.000;Sloe+10KG: F(3.775,109.470)= 53.942,p=0.000);there was a statistically significant mean difference in the subjective rating on postural instability between 0 KG and 10 KG lifting load conditions(t(359)=25.115,p<0.0005 d = 1.32),and between flat and slope standing surface conditions(t(359)=5.063,p<0.0005 d = 0.27).(3)There was a significant three-way interaction between working postures,lifting load and standing surface slope(F(3.476,100.803)= 6.517,p=0.000 <.0005.There was a statistically significant simple two-way interaction between standing surface and load for full squatting posture(P2)(F(1,29)= 20.730,p=0.000 < 0.05),but not for the other postures.There were statistically significant simple two-way interactions between posture and load for both flat(F(2.616,75.860)= 47.518,p=0.000 < 0.05)and slope(F(5,145)= 24.295,p=0.000 < 0.05)standing surfaces.There was a statistically significant simple two-way interaction between standing surface and working postures for without load(0KG,F(1.671,48.472)= 18.526,p=0.000 < 0.05),but not for with load condition.Thus,not only multiple factors,but also their interaction effects should be considered when assessing postural instability.(4)The correlation between subjective ratings and objective measures was studied.The objective measures included: A.the measures with only COP considered,B.the measures with both COP and BOS considered and C.the IMU based acceleration of different body segments.Results indicated that there was a strong correlation between most of the objective measures and the subjective rating,measured by Pearson correlation coefficient,in which the mean velocity and total length of COP in anteroposterior direction were the strongest(r=0.718)and the time to contact BOS took the second place(r=0.710).(5)Full squatting posture(P2)was very different in postural instability from the other postures that it's more stable with lifting a load than without a load on the flat standing surface,and it's more stable on the sloped standing surface than on the flat standing surface when without lifting a load.To sum up,the participants were able to rate their perceptions on the postural instability;three studied factors had significant effects on the postural instability and there were significant interactions between every two factors;there was a relatively high correlation between subjective ratings and most of the objective measures.Fourthly,postural instability assessment model was developed based on the experimental data,by using multiple linear regression(Principle components regression and Step-wise regression).In the model,four choices were provided when selecting the predictors with: A.only COP considered,B.both COP and BOS considered,C.COP,BOS and functional stability region(FSR)considered,D.COP,BOS and the acceleration of body segments considered.And then,above predictors were selected based on the domain knowledge,correlations with the subjective ratings and mathematical methods(e.g.step-wise regression).To overcome the multicollinearity problem which happens when the independent variables are close to being collinear,principle components regression and step-wise regression were used.Several assessment models were built by using above two kinds of regression methods and four choices of predictors/variables.However,only three models with COP,COP-BOS,COP-BOS-Acceleration considered by using step-wise linear regression were finally selected considering the real practice and purpose of this study.Afterwards,the validation of the developed model was conducted by comparing the assessment results with the real subjective rating scores(residual analysis)and the assessment results from commercial software 3DSSPP.In the residual analysis,70% of all the participants' data was randomly selected to be used as regressor data for building assessment model,and 30% was used for testing the performance.This processing was repeated 5 times.In the comparison with 3DSSPP,five participants were randomly selected for testing,their related experiment data was used for postural instability assessment by using 3DSSPP.The subjective rating scores were used as the ground truth of the postural instability levels.The residual analysis results showed that the mean absolute value of residuals was within 1.4 with a standard deviation around 1.0,and the mean value of residuals was within 0.5 with a standard deviation around 1.5.However,a relatively large maximum absolute value of the residuals was found,which was around 5.0 and should be cautious when using the selected models.The comparison with 3DSSPP showed the performance of selected models was better.And,there was a big difference between the results from 3DSSPP and the golden reference,that all postures in all conditions were evaluated as the same instability level in 3DSSPP.On the contrary,the three developed assessment models provided a more reasonable assessment scores when comparing the results with the real subjective ratings.In conclusion,several postural stability assessment models were developed and compared,the validation study showed a good performance of the three selected assessment models.Lastly,the postural stability assessment system was developed based on above assessment models.This system included data acquisition system,data analysis and postural stability assessment system.(1)Data acquisition system: Nintendo Wii Balance Board(WBB)and PC are the main components of the hardware.The software was developed on Microsoft C # Windows Presentation Foundation(WPF)platform,which could realize the functions of Bluetooth pairing and connection between WBB and PC,calibration of WBB,raw signal data acquisition of WBB,calculation and acquisition of COP,and data visualization.(2)Data analysis and postural stability assessment system,developed on the MATLAB App Designer platform,was designed for analyzing COP,BOS and acceleration data,and for postural stability assessment based on developed assessment models.The main functions included data visualization and pre-processing of the raw COP,BOS and IMU sensors data,data loading and saving,measures calculation and postural stability assessment etc.In details,the data analysis system included four modules: A.Basic information input module,to realize the function of loading and saving some basic information,such as subjects' information,experimental tasks information and BOS information.B.Data pre-processing and visualization module,it's designed mainly for pre-processing the COP,BOS and acceleration data,including data cutting,filter setting,data loading and saving.C.Measures calculation module,to calculate all the objective measures those related to COP,BOS or accelerations.D.Postural stability assessment module,this module enables users to conduct the postural stability assessment based on developed models and generate an assessment report.Above developed postural stability assessment system is accurate,economical and easily generalized.In conclusion,the construction industry in China develops rapidly and contributes a lot to the economy.However,due to the nature of the construction project that is laborintensive,complex,temporary and dynamic,the construction industry has been identified as one of the most hazardous industries with the high incidence of accidents.Among various types of occupational fatal and nonfatal injuries in construction industry,falls or fall-related injuries are a leading cause.And,the most direct contributor to fall events is body's losing balance.There are many factors that lead to losing balance for construction workers,in which the instability caused by working postures is an important factor that easily to be ignored.Expensiveness of measuring instrument,lacking focused studies on the instability of working postures,less consideration to the subjective balance perceptions and its correlation with objective measures,ignorance of the interaction effects between different factors are the limitations of current studies.In this research,the fall risk of construction workers was studied from the view of postural stability assessment and a complete,novel,low-cost postural stability assessment system was developed.The main research finding can be summarized in brief as following.(1)International comparisons in the fatal occupational injuries among China,the U.S.and South Korea indicated that the construction industry has been suffering from consistently higher fatal occupational injuries and in particular occupational fatal falls from heights.(2)The study on the accuracy of Xsens-based BOS and foot-pints based BOS showed considerable errors in Xsens-based BOS,and significant effects of postures/motions on the accuracy of Xsens-based BOS.The findings suggested that using footprints to measure static BOS was accurate and could be considered as a good reference.(3)Experimental study on postural instability assessment in construction workers showed the participants were able to give a reliable subjective rating on postural instability;there were significant effects of working postures,lifting load and standing surface slope on the postural instability;there were significant interactions between every two factors;there was a relatively high correlation between subjective ratings and objective measures.(4)With multiple factors considered,several working postural stability assessment models were developed for construction workers based on the experimental data.Validation study showed a good overall performance based on the residual analysis and a better performance than the commercial software 3DSSPP.(5)A complete,novel and low-cost postural stability assessment system was developed.This system included data acquisition system,data analysis and postural stability assessment system with various functions.The developed system is economical,easily generalized and can be a promising commercialized postural stability assessment system for industry,clinical and home usage.The above findings can be used to evaluate the fall risk for construction workers,and also can be helpful to further establish a design guideline for safer working postures and working posture-flows to improve human body balance and prevent falls for different construction trades. |
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