Jung Yong Kim

Biomechanical Measuring Techniques for Evaluation of Workload

It is necessary to quantitatively evaluate the workload of workers in order to improve the level of safety and efficiency as well as to prevent workers from musculoskeletal disorders. The purpose of this study is to introduce biomechanical methods that are largely used to quantitatively evaluate workload. The biomechanical methods use kinematics and kinetics to analyze the movement and force of biomechanical body. Motion analysis, joint angle measurement, ground reaction force, mathematical model, and electromyography (EMG) were introduced as a tool or device for biomechanical evaluation. In this study, the special feature of each method was emphasized and important tips for field measurement were summarized. The information and technique disclosed in this summary can be used to evaluate and design the workplace better by effectively control the workload of field workers.

The User Characteristics of Different Age Groups to Design Mobile Phone

The purpose of this study is to investigate the user characteristics in different age groups by investigating the level of satisfaction and preference of design and function of mobile phone. 160 subjects participated in the experiment. Subjects with different ages were selected and divided into four groups: young age group (20 to less than 45), 1 st middle age group (45 to less than 55), 2 nd middle age group(55 to less than 65), and elderly group(over 65). A questionnaire was developed based on the previous design guideline, and additional questions were made to test newly developed function and design of the mobile phone. In particular, depth interviews were conducted in order to have a proper response from old subjects who have difficulties in completing written questionnaire. In result, it was found that except for price the major criterion to purchase mobile phone was the design, and the function of phone was the next except for elderly group. In the case of elderly group, the screen size is the first. Statistical results indicated that 37.5% of the young age group, 22.5% of 1 st middle age group, 22.5% of 2 nd middle age group and 10.0% of the elderly group preferred the design to function when they purchase mobile phones. Most elderly people were not satisfied with the supplementary function of the mobile phone. The 1 st middle age group did not know exactly how to use the supplementary service although they were willing to use it. Regarding the emotional preference on the type of phone, the sliding type was preferred most. Current results can be used to anticipate the future trend of mobile phone and design a user-friendly product for the aged population.

The Effects of Wearing Spandex Underwear on Muscle Activity and Heart Rate

Objective: The purpose of this study was to analyze the effects of wearing spandex underwear on the muscle activity and heart rate during flexion and extension of trunk and knee joint. Background: Back pain continues to be the leading overall cause of physical illness and lowering productivity in workplace. Recently, the utility of assistive garment or back belt have been discussed to lessen the back pain as well as to preserve the right posture. Method: Ten males and ten females participated in the experiment. Gender, wearing spandex underwear and postures were used for independent variables, and muscle activity, the level of asymmetry of muscle activity and variation of heart rate were used as dependent variables. Muscle activity and heart rate were measured during flexion and extension of trunk and knee joint. Results: When wearing spandex underwear, the muscle activity was relatively low compared to the condition not wearing the spandex underwear. The symmetry of muscle activity and the variation of heart rate were statistically significant at the 0.05 significance level. In particular, it was found that the symmetry of muscle activity increased while wearing spandex underwear. Conclusion: Spandex underwear has an effect that can reduce asymmetry of right and left muscles which are relevant to leg because spandex underwear equally supports right and left low-back muscles. Application: The spandex underwear used in this study can apply to the rehabilitation as an useful assistive device.

Quantitative Comparison of the E-book and Paper-book by using Eye-tracker

Objective: The aim of the study is to evaluate the difference of legibility between e-book and paper-book by using eye-tracker. Background: Despite of many researches on the e-book and paper-book, there are few researches on the difference between e-book and paper-book. In addition, the researches on the e-book were only dependent on the e-book reader. This study focused on the comparison of e-book and paper-book controlled with the same environments. Method: This study was conducted with 2×3 within-subject design. Independent variables include the types of book (e-book, paper-book) and font sizes (8pt, 10pt, 12pt). Dependent variables are four measures of fixation duration, saccade length, blink rate and subjective discomfort. Analysis of Variance (ANOVA) with repeated measured design was used to investigate the main and interaction effects of independent variables on each of the dependent variables. The multiple comparisons were performed by post hoc analysis and Bonferroni correction was applied. Results Fixation duration at e-book was longer than paper-book (p<0.01). Saccade length at e-book was shorter than paper-book (p<0.05). Blink rate at e-book was higher than paper-book (p<0.1). Subjective discomfort at e-book was higher than paper-book (p<0.1). Legibility at 8pt was better than 10pt, 12pt (p<0.01) in fixation duration, saccade length and subjective discomfort. Conclusion: It was found that the legibility at e-book are worse than paper-book from this study. These results indicated that the legibility of e-book was needed to be validated and improved to replace the paper-book. Application: This study suggests improving something related to fixation duration, saccade length, blink rate and subjective discomfort for betterment of e-book.

Analysis of Human Body Suitability for Mattresses by Using the Level of PsychoPhysiological Relaxation and Development of Regression Model

Objective: The purpose of this study is to find the level of physical relaxation of individual subject by monitoring psychophysiological biofeedback to different types of mattresses. And, the study also aims to find a protocol to make a selection of the best mattress based on the measured information. Background: In Korea, there are an increasing number of people using western style bed. However, they are often fastidious in choosing the right mattress for them. In fact, people use their past experience with their old mattress as well as the spontaneous experience they encounter in a show room to finally decide to buy a bed. Method: Total five mattresses were tested in this study. After measuring the elasticity of the mattresses, they were sorted into five different classes. Physiological and psychological variables including Electromyography (EMG), heart rates (HR), oxygen saturations (SaO2) were used. In addition, the peak body pressure concentration rate was used to find uncomfortably pressured body part. Finally, the personal factors and subjective satisfaction were also examined. A protocol was made to select the best mattress for individual subject. The selection rule for the protocol considered all the variables tested in this study. Results: The result revealing psychological comfort range of 0.68 to 0.95, dermal comfort range of 3.15 to 6.07, back muscle relaxation range of 0.25 to 1.64 and personal habit range of 2.0 to 3.4 was drawn in this study. Also a regression model was developed to predict biofeedback with the minimal use of biofeedback devices. Moreover results from the proposed protocol with the regression equation and subjective satisfaction were compared with each other for validation. Ten out of twenty subjects recorded the same level of relaxation, and eight subjects showed one-level difference while two subjects showed two-levels difference. Conclusion: The psychophysiological variables and suitability selection process used in this study seem to be used for selecting and assessing ergonomic products mechanically or emotionally. Application: This regression model can be applied to the mattress industry to estimate back muscle relaxation using dermal, psychophysiology and personal habit values.

The Prevalence of Playing-related Musculoskeletal Disorders of Traditional Korean Musical Instrument Player

Objective: This study was performed to investigate the prevalence of musculoskeletal disorders of traditional Korean instrument player using a variety of traditional classical instruments: Gayageum, Geomungo, Ajaeng, Haegeum, Daegeum, Piri and Samul instruments. Background: A large percentage of instrument players have suffered from the musculoskeletal pain of each body parts. However, there is no research on the prevalence of musculoskeletal disorders of traditional Korean musical instrument players. Method: Through the focus group interview, a questionnaire to investigate musculoskeletal disorders was developed. The questionnaire consisted of four parts: demographic factors, performance factors, musculoskeletal disorders symptoms, musculoskeletal disorder experience. For the survey, 118 expert players participated. The data from the survey were analyzed by correlation analysis and chi-square analysis. Results: The symptoms of musculoskeletal disorders and the severe pain from musculoskeletal disorders were observed at neck, shoulder, back and knee. The musculoskeletal experience was statistically related to the factor of body height in Gayageum and Geomungo. In addition, the musculoskeletal experience in Geomungo was related to age and career. However, the musculoskeletal experience in Ajaeng and Haegeum was only related to the factor of hobby. The musculoskeletal experience in Daegeum and Piri was related to stretching. In addition, there was a statistical significance between the musculoskeletal experience and sex in Daegum. In Samul instruments, the statistical significance was observed at age, BMI, career and stretching. Conclusion: The symptoms of playing-related musculoskeletal disorders of traditional Korean musical players were prevalently observed at neck, shoulder, back and knee. In addition, these symptoms were related to the various demographic factors such as age, body height, BMI, career, sex, hobby and stretching. Application: The results of this study can be used as the preliminary data for preventing the musculoskeletal injuries of traditional Korean musical instrument players.