Junghwa Hong

Konkuk University, Seoul, Seoul, South Korea

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Publications (8)4.84 Total impact

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    ABSTRACT: Evaluation of motor symptoms in Parkinson's disease (PD) is still based on clinical rating scales by clinicians. Reaction time (RT) is the time interval between a specific stimulus and the start of muscle response. The aim of this study was to identify the characteristics of RT responses in PD patients using electromyography (EMG) and to elucidate the relationship between RT and clinical features of PD. The EMG activity of 31 PD patients was recorded during isometric muscle contraction. RT was defined as the time latency between an auditory beep and responsive EMG activity. PD patients demonstrated significant delays in both initiation and termination of muscle contraction compared with controls. Cardinal motor symptoms of PD were closely correlated with RT. RT was longer in more-affected side and in more-advanced PD stages. Frontal cognitive function, which is indicative of motor programming and movement regulation and perseveration, was also closely related with RT. In conclusion, greater RT is the characteristic motor features of PD and it could be used as a sensitive tool for motor function assessment in PD patients. Further investigations are required to clarify the clinical impact of the RT on the activity of daily living of patients with PD.
    Parkinson's disease. 01/2014; 2014:848035.
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    ABSTRACT: AIM: Reaction times of the hip abductor were reported to be longer in elderly women than in elderly men, and this was suggested to be related to mediolateral balance performance. The aim of the present study was to investigate the effects of age and gender on the reaction performance of ankle muscles, which have predominant roles in anterioposterior balance control. METHODS: A total of 40 elderly subjects and 40 young subjects (even number of men and women) carried out a series of isometric plantarflexions and dorsiflexions, as forcefully and quickly as possible, in response to auditory stimulus. Surface electromyogram at the dorsiflexor and plantarflexor were recorded, together with foot plantar force. Premotor time, motor time and total reaction time derived from the experimental data were compared between age groups and genders by two-way anova. RESULTS: Both dorsiflexor and plantarflexor showed similar reaction performance. Premotor time increased with age with no gender difference. Motor time increased with age in women and not in men, resulting in longer motor time in elderly women than in elderly men. Total reaction time was dominated by premotor time, so that it was longer in the elderly with no gender difference. CONCLUSION: Although age-related elongation of motor time was greater in women, total reaction time was not different between the genders. This may be related to no gender difference in anterioposterior balance performance. Geriatr Gerontol Int 2013; ●●: ●●-●●.
    Geriatrics & Gerontology International 04/2013;
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    ABSTRACT: This study aims to analyze viscoelastic properties of the wrist in patients with Parkinson's disease (PD) in comparison with the clinical score of severity. Forty-five patients with PD and 12 healthy volunteers participated in this study. Severity of rigidity at the wrist was rated by a neurologist just before the experiment. Wrist joint torque resistive to the imposed movement was measured. Three different models, (identical in structure, only different in the number of parameters for extension and flexion phases) were used in identification of viscoelastic properties: 1) one damping constant and one spring constant throughout all phases, 2) two damping constants for each phase and one spring constant throughout all phases, and 3) two damping constants and two spring constants for each phase. Normalized work and impulse suggested in the literature were also calculated. Spring constants of different models and phases showed comparable correlation with rigidity score ( r =0.68-0.73). In terms of the correlation of damping constant with clinical rigidity score, model 1 ( r = 0.90) was better than models 2 and 3 ( r =0.59 - 0.71). These results suggest that the clinical rigidity score is better represented by the mean viscosity during both flexion and extension. In models with two dampers (model 2 and 3), the damping constant was greater during extension than flexion in patients ( p <; 0.001), in contrast that there was no phase difference in normal subjects. This suggests that in contrast with normal subjects, phase-dependent viscosity may be an inherent feature of PD. Although work and impulse were correlated with clinical rigidity score ( r = 0.11 - 0.84), they could not represent the phase-dependent rigidity inherent in PD. In conclusion, the viscosity of model 1 would be appropriate for quantification of clinical ratings of rigidity and that of model 2 for distinction of PD and also for investigation of phase-dependent charact- - eristics in parkinsonian rigidity.
    IEEE Transactions on Neural Systems and Rehabilitation Engineering 05/2011; · 3.26 Impact Factor
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    ABSTRACT: It has been reported that the fall incidence in women is much higher than men and that fallers have worse postural balance performance than non-fallers. However, it is controversial whether any sex difference in postural balance performance exists. The purpose of this study was to investigate the effects of sex and age and their interactions in balance performance during quiet standing with natural stance width. Sixty-three elderly subjects (aged 65-86 years) and 66 young subjects (aged 18-26 years) performed quiet standing with self-selected natural feet distance on a force plate. Four analysis variables - mean distance, mean velocity, 95% power frequency and total power - were derived from the center of pressure (COP) and they were evaluated both in anteroposterior and mediolateral directions. In anteroposterior direction, no sex effect and interaction existed, however, all variables except mean distance showed significant age effects (P < 0.01). In contrast, mediolateral direction variables showed significant sex effect where women had greater but less frequent COP movement than men (P < 0.01). Interactions of age and sex were also significant in mediolateral direction, where age-related changes were significant only in women so that sex differences (faster COP movement with more total power in women than men) existed only in the elderly (P < 0.01) but not in the young. The sex difference in balance performance (some of which are significant only in the elderly) and the sex difference in age-related change of balance performance were demonstrated in mediolateral direction. These sex differences may contribute to the sex difference in balance-related problems, such as falls.
    Geriatrics & Gerontology International 04/2010; 10(2):191-8.
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    ABSTRACT: For accurate analysis in low-speed collisions, roles of muscle in the low extremities are included in a finite element (FE) human model. The impact accelerations were estimated for vehicle-pedestrian collisions with and without muscle activations under 10 km/hour. The predicted acceleration at the medial knee was verified by the actual tests performed at 2.88 km/hour. Then, experiments were performed using a sled to obtain muscle activations, and impact accelerations of the subjects. More analyses were performed using the FE human model at 5 and 10 km/hour to understand effects of muscle activations on impact accelerations. At the lowest impact speed, the reduction of acceleration was 20% when the result with muscle activations was compared to that without muscle activations. The reduction was decreased to 12% at 5 km/hour. At 10 km/hour, the reduction was insignificant but existed to as much as 3%. Therefore, muscle activations in the lower limbs are important when the impact velocity is lower than 10 km/hour.
    International Journal of Vehicle Design - INT J VEH DES. 01/2009; 51.
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    ABSTRACT: This study investigated characteristics of interface pressure distribution of right and left hemiplegia (rt_hemi and lt_hemi), paraplegia (para), quadriplegia (quadric), and normal subjects (normal) during wheelchair seating. A total of 73 subjects were participated in this study. Maximum interface pressure, mean interface pressure, and interface pressure gradient in the right and left sides of buttocks were measured for 30 minutes while minimizing possible movements of participants and using a same manual type wheelchair with a fabric seat. The ANOVA was performed using the data measured at the end of the test. There were substantial differences in the mean interface pressure on the buttocks between rt_hemi and lt_hemi. The maximum interface pressure on the buttocks was significantly high in hemi, para and quadric compared to normal. A statistically significant difference in the maximum interface pressure gradient on the buttocks as found between paralytic patients and normal people. Based on these results, a new approach for developing seat cushion orthosis to prevent decubitus ulcer is required for even distribution of interface pressure considering individual paralytic characteristics. In addition, the maximum interface pressure and gradient on the buttocks could be used as a useful clinical-biomechanical guideline in developing a seat cushion orthosis for preventing decubitus ulcer of paralytic patients.
    Proceedings of the 2nd International Convention on Rehabilitation Engineering & Assistive Technology; 05/2008
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    ABSTRACT: The purpose of this study is to investigate the angular rate during motor examination of Parkinson's disease patients, as a quantitative measure of the severity. 14 Parkinson's disease patients, 36 healthy elderly subjects and 13 healthy young subjects participated in the experiments. Three different movements selected from the motor examination category of UPDRS i. e. Finger Taps, Rapid Alternating Movements of Hands and Leg Agility test were performed. Frequency and peak angular velocity of swing were derived from the experimental angular rate. Both the frequency and peak velocity showed negative correlation with the clinical score. This suggests that the angular rate can be used for a quantitative measurement of severity in Motor Examination.
    Proceedings of the 2nd International Convention on Rehabilitation Engineering & Assistive Technology; 05/2008
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    ABSTRACT: Many studies have reported postural control against support surface translation. However, postural control mechanism against external force perturbation is not clear. Therefore, in this study we investigated the postural recovery against external force (1∼4Kg) applied to the high-back in health young male subjects (24±4 years). Kinematic data and center of pressure of the reaction to an unexpected perturbation were analyzed. Experimental results showed that the hill-lifting strategy with ankle plantarflexion and knee hyperextension was used in all subjects, regardless of the force magnitude. Specifically, maximum ankle plantarflexion and hip flexion increased with the perturbation force magnitude, the heel vertical excursion and anterior COP excursion. The results of this study show that the postural control strategy for the external force perturbation is quite different from that for surface translation and needs further investigation.
    International Journal of Precision Engineering and Manufacturing 10(4):147-151. · 1.59 Impact Factor