• Journal of the Korean Society of Industry Convergence
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• v.17 no.4
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• pp.245-254
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• 2014

In this paper, stable and robust dynamic walking for a biped motion is proposed. To success this objective, the following structures are processed. In this paper, the proposed control method is one that adjusts actual zero moment position to move to the closest possible point in the stable area instead of following desired zero moment position. This minimizes energy consumption with the smallest joint movements. The proposed control method makes mechanical energy that drives lower limb of the bipedal robot efficient. In this paper, walking experiment is carried out with the three control structures mentioned above. The trajectory generated by off-line is illustrated by performing to walking on flat ground. experiment with an obstacle whose height is lower than that of trajectory is executed to validate dynamic motion.

• Sleep Medicine and Psychophysiology
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• v.5 no.1
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• pp.103-110
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• 1998

Objectives : High co-morbidity of periodic limb movements during sleep(PLMS) and obstructive sleep apnea syndrome(OSAS) is well known and their incidences tend to increase in the elderly. Previous studies have inconsistently rep0l1ed increase or no change of periodic limb movement index(PLMI) by nasal continuous positive airway pressure(CPAP) in OSAS without analyzing possible variables affecting PLMI. We attempted to examine PLMI change evoked during CPAP titration and also factors affecting it in OSAS. Methods : Twenty-nine OSAS patients(M:F=26:3, mean age: $51.6{\pm}10.6\;yrs$) without other sleep disorders except for PLMS were selected, based on the nocturnal (baseline) polysomnograhy. Another night of noctumal polysomnography was performed for CPAP pressure titration. We compared between those two nights PLMI, mean and lowest $SaO_2$, and sleep variables. We also calculated PLMI differences between baseline and CPAP nights, named as delta PLMI (value of CPAP night PLMI minus value of baseline night PLMI). Correlations were calculated between delta PLMI and factors such as age, body mass index, applied CPAP pressure, baseline night values of respiratory disturbance index, mean and lowest $SaO_2$, and sleep parameter differences between baseline and CPAP nights. Results : Decrease of RDI(p<.01) and increase in mean and lowest $SaO_2$ (p<.05, p<.01) were observed during CPAP night. No sleep parameters showed significant change except for the decrease of total stage 1 sleep%(p<.01) during CPAP night. Ten out of 29 patients showed PLMI increase, while the other 19 patients showed either no change(n=14) or even PLMI decrease(n=5) during CPAP night. The 10 patients showing PLMI increase during CPAP night showed a significant positive correlation between delta PLMI and baseline night RDI(p<.05), which meant that PLMI increase was found to be more prominent in higher RDI patients than in lower RDI ones. There were no significant correlations between delta PLMI and other factors in the other 19 patients. Conclusions : We suggest that during the baseline night PLMS would have been underscored and/or masked due to the overlapping of PLMS and apneas/hypopneas or the arousals induced by apneas/hypopneas. Despite its still unknown mechanism, the CPAP application may unmask PLMS and increase PLMI in a subgroup of OSAS patients. It needs to be evaluated further whether the chronic CPAP use sustains the above finding.

• The Journal of Korean Physical Therapy
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• v.26 no.6
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• pp.449-452
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• 2014

Purpose: The purpose of this study was to analyze the coordination between trunk flexion and lower limb extension contributing to vertical propulsion during sit-to-stand (STS) at different chair heights in the elderly. Methods: Ten elderly subjects were asked to stand up at their natural speed from different chair heights : (1) $90^{\circ}$ knee flexion; (2) $100^{\circ}$ knee flexion; (3) $110^{\circ}$ knee flexion; and (4) $120^{\circ}$ knee flexion. A standard chair without a backrest or armrests was used in this study. To remove inertial effects of upper limb movements, subjects were asked to stand up from a chair with their arms crossed at the chest. Mean of results of three trials were used in the analysis at different knee flexion angles. Distances moved by the shoulder for compensatory trunk movement was recorded by motion analysis and vertical force was recorded under foot using force plates. Distances moved by the shoulder and vertical ground reaction force measurements were analyzed using repeated ANOVA. Results: Distances moved by the shoulder significantly decreased with higher chair (p<0.05). Vertical forces were not significant difference on chair heights (p>0.05), but results of pairwise comparisons for vertical force revealed significant difference between $90^{\circ}$ knee flexion and $120^{\circ}$ knee flexion (p<0.05). Conclusion: Trunk movement is probably used as a compensatory mechanism at low chair heights to increase lift-off from sitting by the elderly.

• Safety and Health at Work
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• v.12 no.2
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• pp.225-229
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• 2021

Background: The socioeconomic burden of musculoskeletal disorders (MSDs) is significant, and kitchen work is a high-risk occupation for MSDs due to the intensive manual workload and repetitive movements that are involved. However, there are very few studies on MSDs and rest breaks as a workplace intervention among kitchen workers. This study examined the relationship between insufficient rest breaks and increased MSD risk among Korean kitchen workers. Methods: Sociodemographic and occupational factors of 1,909 kitchen workers were collected from the 3rd-4th Korean Working Conditions Survey data. Five items on rest breaks at work were categorized into two groups, "sufficient" and "insufficient." The number of MSDs and work-related MSDs (WMSDs), an outcome variable, was obtained from the sum of MSDs/WMSDs in three anatomical sites (back, neck, and upper limb, lower limb). The association between rest breaks and MSDs was estimated using zeroinflated negative binomial analyses, with adjustments for age, education level, and weekly working hours, and the analyses were stratified by sex. Results: After adjustment, significant associations were found between insufficient rest breaks and an increased risk of MSDs (odds ratio [OR] 1.68 95% confidence interval [CI] 1.11-2.54) and WMSDs (OR 1.40 95% CI 1.01-1.96) among female kitchen workers. Insufficient rest breaks were significantly associated with MSDs in female kitchen workers in all three anatomical sites. Conclusion: This study emphasizes the need for rest breaks as a workplace intervention for preventing MSDs in kitchen workers. Further studies to reveal the causality of this relationship are required.

• Sleep Medicine and Psychophysiology
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• v.24 no.1
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• pp.24-31
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• 2017

Objectives: Periodic limb movement disorder (PLMD) has been debated with regard to its clinical significance and diagnostic criteria. The current diagnostic criterion for PLMD in adults has been changed from periodic limb movement index (PLMI) > 5/hour to PLMI > 15/hour by the International Classification of Sleep Disorders (ICSD). In this study, we aimed to investigate the changes in polysomnographic sleep variables according to PLMI and to determine the relevance of the diagnostic criterion for PLMD. Methods: Out of 4195 subjects who underwent standard polysomnography, we selected 666 subjects (370 males and 296 females, aged $47.1{\pm}14.8$) who were older than 17 years and were not diagnosed with primary insomnia, sleep apnea, narcolepsy, or REM sleep behavior disorder. Subjects were divided into three groups according to PLMI severity: group 1 ($PLMI{\leq}5$), group 2 (5 < $PLMI{\leq}15$), and group 3 (PLMI > 15). Demographic and polysomnographic sleep variables and Epworth sleepiness scale (ESS) were compared among the three groups. Results: There were significant differences among the three groups in age and gender. Sleep efficiency (SE) and stage 3 sleep percentage in group 1 were significantly higher than those in groups 2 and 3. The wake after sleep onset (WASO) score in group 1 was significantly lower than those in groups 2 and 3. However, there were no significant differences in SE, stage 3 sleep percentage, or WASO between groups 2 and 3. Sleep latency (SL) in group 1 was significantly lower than that in group 3, but there was no difference in SL between group 2 and group 3. ESS score in group 1 was significantly higher than that in group 3, but there was no difference between group 2 and group 3. Partial correlation analysis adjusted by age showed that PLMI was significantly related to SE and WASO. Conclusion: This study suggests that PLMI influences polysomnographic sleep variables. In addition, we found the individuals who did not have PLMD but had PLMI > 5 were not different in polysomnographic sleep variables from the individuals who had PLMD according to the current criterion. These results raise questions about the relevance of the current diagnostic criterion of PLMD.

• Journal of the Ergonomics Society of Korea
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• v.30 no.5
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• pp.605-611
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• 2011

Objective: The aim of this study was to investigate the influence of seat heights for optimizing the ingress/egress performance in the elderly people. Background: Recently elderly users have been increasing in number and the ease of ingress/egress of the vehicle becomes an important issue. Method: Seven elderly subjects participated in this study(age: 71.7${\pm}$3.6yr, height: 167.7${\pm}$5.4cm, weight: 68.1${\pm}$11.5kg). Each subject performed the sitting and rising task from comfortable seated position on the chair under the following conditions: (1) with a lumbar support and (2) without a lumbar support. We measured EMG activities of seven muscles(tibialis anterior, soleus, gastrocnemius, vastus lateralis, rectus femoris, biceps femoris and erector supinae) and ranges of motion in lower limb during sitting and standing from three different heights (400mm, 500mm and 600mm from ground) of slide-up seat. Results: Muscle activities and angular movements of hip and knee joints during standing-up and sitting-down with a high seat height(600mm) were reduced mean 30.4% in extensor muscles, 57.11% in flexor muscle, 18.74% in erector muscle and 31.0% in joints compared with a low seat height(400mm). Conclusion: Muscle activities and joint movements in hip and knee were reduced when rising/sitting from a high seat height(600mm) compared with a low seat height(400mm). Application: This study can be used to design vehicle that are easy to get in and out of by older peoples with or without impairments.

• Korean Journal of Applied Biomechanics
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• v.25 no.2
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• pp.191-198
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• 2015

Objective : The purpose of this study was to conduct biomechanical analysis of varying backpack loads on the lower limb movements during downhill walking over $-20^{\circ}$ ramp. Method : Thirteen male university students (age: $23.5{\pm}2.1yrs$, height: $175.7{\pm}4.6cm$, weight: $651.9{\pm}55.5N$) who have no musculoskeletal disorder were recruited as the subjects. Each subject walked over $20^{\circ}$ ramp with four different backpack weights (0%, 10%, 20% and 30% of body weight) in random order at a speed of $1.0{\pm}0.1m/s$. Five digital camcorders and two force plates were used to obtain 3-d data and kinetics of the lower extremity. For each trial being analyzed, five critical instants were identified from the video recordings. Ground reaction force, loading rate, decay rate, and resultant joint moment of the ankle and the knee were determined by the inverse dynamics analysis. For each dependent variable, one-way ANOVA with repeated measures was used to determine whether there were significant differences among four different backpack weight conditions (p<.05). When a significant difference was found, post hoc analyses were performed using the contrast procedure. Results : The results of this study showed that the medio-lateral GRFs at RHC in 20% and 30% body weight were significantly greater than the corresponding value in 0% of body weight. A consistent increase in the vertical GRFs as backpack loads increased was observed. The valgus joint movement of the knee at RTO in 30% body weight was significantly greater than the corresponding values in 0% and 10% body weight. The increased valgus moment of 30% body weight observed in this phase was associated with decelerating and stabilizing effects on the knee joint. The results also showed that the extension and valgus joint moments of the knee were systematically affected by the backpack load during downhill walking. Conclusion : Since downhill walking while carrying heavy external loads in a backpack may lead to excessive knee joint moment, damage can occur to the joint structures such as joint capsule and ligaments. Therefore, excessive repetitions of downhill walking should be avoided if the lower extremity is subjected to abnormally high levels of load over an extended period of time.

• Tuberculosis and Respiratory Diseases
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• v.45 no.5
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• pp.1039-1046
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• 1998

Background: Sleep-related breathing disorders(SRBD) and periodic leg movements disorder(PLMD) are both common, and are considered as separate sleep disorders. However, both disorders show high comorbidity. SRBD and PLMD can result in excessive daytime sleepiness and insomnia due to frequent sleep fragmentation. So, it is very important to consider the presence of PLMD, when we are dealing with the diagnosis and management of SRBD. The objectives of this study were to determine the incidence of PLMD in patients with SRBD, and to describe any differences between patients with and without PLMD. Method: The authors reviewed the sleep recordings of 106 patients with a final diagnosis of SRBD(obstructive sleep apnea or upper airway resistance syndrome), who underwent full nocturnal polysomnography, including the monitoring of the anterior tibialis electromyogram. All sleep records were recorded and scored using the standard criteria. The data was analyzed by the student t-test. Result: 106 patients(M=76, F=30) were included in the analysis. Data revealed a mean age of $49.5{\pm}13.6$ years, a respiratory disturbance index(RDI) of $22.3{\pm}25.4$/hour sleep, a lowest oxygen saturation of $84.9{\pm}11.3%$, a maximal esophageal pressure of $-41.0{\pm}19.1cmH_2O$, and PLM index(PLMI) of $13.1{\pm}22.4$movements/hour sleep. Forty four percent(47 of 106 patients) had a PLMI of greater than 5 on this study. The mean age of the patients with PLMD was significantly higher than that of the patients without PLMD(p<0.005). Female patients with SRBD accompanied more PLMD(p<0.05). The apnea index of the patients with PLMD was significantly lower than that of the patients without PLMD(p<0.01). The percentage of stage 1 sleep in the patients with PLMD was significantly lower than that of the patients without PLMD(p<0.05). Conclusion: The prevalence of PLMD in the patients with SRBD was high at 44.3%. The patients with PLMD were older and had more high RDI in comparison to the patients without PLMD, which was consistent with previous findings. The authors recommend that more careful consideration of PLMD is required when diagnosing and treating SRBD.

• Annals of Clinical Neurophysiology
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• v.10 no.2
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• pp.98-100
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• 2008

Restless legs syndrome (RLS) is a sensorimotor neurological disorder in which the primary symptom is a compelling urge to move the legs, accompanied by unpleasant and disturbing sensations in the legs. Although pathophysiologic mechanism of RLS is still unclear, several evidences suggest that RLS is related to dysfunction in central nervous system involving brain and spinal cord. L-DOPA, as the precursor of dopamine, as well as dopamine agonists, plays an essential role in the treatment of RLS leading to the assumption of a key role of dopamine function in the pathophysiology of RLS. Patients with RLS have lower levels of dopamine in the substantia nigra and respond to iron administration. Iron, as a cofactor in dopamine production, plays a central role in the etiology of RLS. Functional neuroimaging studies using PET and SPECT support a central striatal D2 receptor abnormality in the pathophysiology of RLS. Functional MRI suggested a central generator of periodic limb movements during sleep (PLMs) in RLS. However, to date, we have no direct evidence of pathogenic mechanisms of RLS.

• Journal of KIISE
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• v.42 no.12
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• pp.1544-1550
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• 2015

Recently, the development of practical wearable robot interfaces has resulted in the emergence of wearable robots such as arm prosthetics or lower-limb exoskeletons. In this paper, we propose a novel method of wrist movement intention estimation based on a regression technique using electromyography of human bio-signals. In daily life, changes in user arm position changes cause decreases in performance by modulating EMG signals. Therefore, we propose an estimation method for robust wrist movement intention for arm position changes, combining several movement intention models based on the regression technique trained by different arm positions. In our experimental results, our method estimates wrist movement intention more accurately than previous methods.