• Journal of International Academy of Physical Therapy Research
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• v.5 no.1
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• pp.641-646
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• 2014

The purpose of this study is to observe how balance exercise on an unstable platform and on a stable platform affects balance ability. The subjects were 35 adults in their 20s and were randomly assigned to a stable platform group and an unstable platform group. They performed balance exercise three times per week for six weeks. Balance exercise introduced by previous research was modified and complemented for use in this study. Balance ability of the subjects was measured through center of pressure(COP) area, medial-lateral displacement, and anterior-posterior displacement using a portable balance platform BT4. There was significant difference in the COP area between the unstable platform exercise group and the stable platform exercise group. In comparison in differences between the unstable platform exercise group and the stable platform exercise group after the exercise, there was significant difference in anterior-posterior movement. Therefore, exercise on an unstable platform is more effective than exercise on a stable platform in strengthening balance ability.

• Journal of the Korean Applied Science and Technology
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• v.40 no.4
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• pp.642-649
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• 2023

The purpose of this study was to analyze the effects of knee joint injury experiences of judo players on kinematic factors and center of pressure factors during uchimata. Among right-handed male college judo players specializing in uchimata, 13 people who had a knee joint injury experience(age, 20.69.1±0.75 years; height, 172.85±4.81 cm; body mass, 74.92±5.51 kg; and career, 8.92±0.95 years) and 13 people who did not have a knee joint injury experience(age, 21.08.1±0.76 years; height, 172.54±6.32 cm; body mass, 76.62±9.09 kg; and career, 9.46±0.94 years) within the last 2 years were divided into two groups and participated as subjects. The two groups were evaluated for differences in ankle, knee, and hip joint angle variables, COP range, and velocity components during uchimata. As a result of the study, the EIG group showed smaller values in the knee joint flexion angle at E3 and the hip joint extension angle at E4 during uchimata than the NIG group. In addition, the EIG group showed lower values in the range of motion of the COP and forward movement velocity of the COP in the one-leg support phase than the NIG group.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.419-425
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• 2019

The objective of this study was to investigate the cooling performance characteristics of a hybrid refrigeration system in a heavy duty vehicle. The tested hybrid refrigeration system had additionally an electric compressor besides the present mechanical compressor for selective use according to the operating conditions. The applied electric compressor was a scroll type and with 18.0 cc displacement. In order to analyze the performance characteristics of the hybrid refrigeration system with respect to the cooling capacity and Coefficient of Performance (COP), other components, including two different types of compressors, were installed and tested under various operating conditions such as compressor speed and air flow rate of the evaporator. When the electric compressor was operated at 4,500 rev/min, the cooling capacity was about 4.0kW and COP was 3.5. When the mechanical compressor was operated, whereas the cooling capacity was higher than the electric controlled compressor, COP was lower due to the larger displacement and higher power consumption. To analyze the hybrid system operating characteristics due to reasonable cooling capacity with electric compressor operation, the mechanical compressor and electric compressor were operated by turns every 10 minutes under certain system operating conditions. Because surge pressure occurred when both compressors were switched on, the operating strategy required some time to balance the system pressure.

• Korean Journal of Applied Biomechanics
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• v.32 no.1
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• pp.9-16
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• 2022

Objective: The purpose of this study was to investigate how the chronic ankle instability affects postural control during forward jump landing. Method: 20 women with chronic ankle instability (age: 21.7 ± 1.6 yrs, height: 162.1 ± 3.7 cm, weight: 52.2 ± 5.8 kg) and 20 healthy adult women (age: 21.8 ± 1.6 yrs, height: 161.9 ± 4.4 cm, weight: 52.9 ± 7.2 kg) participated in this study. For the forward jump participants were instructed to stand on two legs at a distance of 40% of their body height from the center of force plate. Participants were jump forward over a 15 cm hurdle to the force plate and land on their non-dominant or affected leg. Kinetic and kinematic data were obtained using 8 motion capture cameras and 1 force plates and joint angle, vertical ground reaction force and center of pressure. All statistical analyses were using SPSS 25.0 program. The differences in variables between the two groups were compared through an independent sample t-test, and the significance level was to p < .05. Results: In the hip and knee joint angle, the CAI group showed a smaller flexion angle than the control group, and the knee joint valgus angle was significantly larger. In the case of ankle joint, the CAI group showed a large inversion angle at all events. In the kinetic variables, the vGRF was significantly greater in the CAI group than control group at IC and mGRF. In COP Y, the CAI group showed a lateral shifted center of pressure. Conclusion: Our results indicated that chronic ankle instability decreases the flexion angle of the hip and knee joint, increases the valgus angle of the knee joint, and increases the inversion angle of the ankle joint during landing. In addition, an increase in the maximum vertical ground reaction force and a lateral shifted center of pressure were observed. This suggests that chronic ankle instability increases the risk of non-contact knee injury as well as the risk of lateral ankle sprain during forward jump landing.

• Physical Therapy Rehabilitation Science
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• v.8 no.3
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• pp.125-133
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• 2019

Objective: To compare the postural control between non-specific chronic low back pain (NSCLBP) subgroups and healthy people during dynamic balance performance using a modified Star Excursion Balance Test (mSEBT). Design: Cross-sectional study. Methods: Eighteen NSCLBP subjects (9 active extension pattern [AEP], 9 flexion pattern [FP]), and 10 healthy controls were enrolled in this study. All subjects performed mSEBT on their dominant leg on a force plate. Normalized reach distance and balance parameters, including the center of pressure (COP) displacement and velocity, were recorded. Results: There were significant differences in mean reach distances in both posterolateral and posteromedial (PM) reach directions between AEP and healthy subjects (p<0.001) and between FP and healthy subjects (p<0.001). However, there were no significant differences among the three groups in the anterior reach direction. Also, the results showed no significant differences in mean COP variables (velocity and displacement) between pooled NSCLBP and healthy subjects. However, the subjects were reclassified into AEP, FP and healthy groups and the results showed a significant difference in mean COP velocity in the PM direction between AEP and FP subjects (p=0.048), and between AEP and healthy subjects (p=0.024). Conclusions: The findings in this study highlight the heterogeneity of the individuals with NSCLBP and the importance of identifying the homogenous subgroups. Individuals with AEP and FP experience deficits in dynamic postural control compared to healthy controls. In addition, the findings of this study support the concept of the Multidimensional Classification System.

• Korean Journal of Applied Biomechanics
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• v.24 no.1
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• pp.43-50
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• 2014

The purpose of this study was to analyze of the GRF (ground reaction force) parameters according to the change of positions and weights of bag during downward stairs between dominant and non-dominant in upper & lower limbs. To perform this study, participants were selected 9 healthy women (age: $21.40{\pm}0.94yrs$, height: $166.50{\pm}2.68cm$, body mass: $57.00{\pm}3.61kg$, BMI: $20.53{\pm}1.03kg/m^2$), divided into 2 carrying bag positions (dominant arm/R, non-dominant arm/L) and walked with 3 type of bag weights (0, 3, 5 kg) respectively. One force-plate was used to collect GRF (AMTI OR6-7) data at a sample rate of 1000 Hz. The variables analyzed were consisted of the medial-lateral GRF (Fx), anterior-posterior GRF (Fy), vertical GRF (Fz), impact loading rate and center of pressure (COPx, COPy, COP area, COPy posterior peak time) during downward stairs. 1) The Fx, Fy, Fz, COPx, and COP area of GRF were not statistically significant between dominant leg and non-dominant leg, but non-dominant leg, that is, showed the higher COPy, and showed higher impact loading rate than that dominant leg during downward stairs. 2) In bag wearing to non-dominant arm, Fx, Fz, COPx, COPy, impact loading rate and COP area showed increase tendency according to increase of bag weights. Also, against bag wearing to dominant arm, non-dominant showed different mechanism according to increase of bag weights. The Ground Reaction Force parameters showed different characteristics according to the positions and weights of bag during downward stairs between dominant and non-dominant arm.

• Annals of Clinical Neurophysiology
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• v.20 no.1
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• pp.31-35
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• 2018

Background: Although postural instability is one of the major symptoms of Parkinson's disease (PD), dopaminergic treatment is ineffective for treating postural instability. Recent reports have shown that somatosensory deficit is associated with postural instability, and that somatosensory input improved postural instability. The purpose of this study is to evaluate the effects of lateral wedges for quiet standing postural control in people with PD. Methods: Twenty-two patients who were diagnosed with PD were enrolled in this study. The participants stood on a force plate under two conditions (wedge and no wedge) with or without having their eyes open or closed. The center of pressure (COP) range and velocity were analyzed using a two-way repeated-measures analysis of variance. Results: The range and velocity of COP in the anterioposterior and mediolateral (ML) directions were significantly improved after the patients stood on the lateral wedge with their eyes closed (p < 0.05). The range in ML direction and velocity in both directions of COP were significantly decreased when their eyes were open (p < 0.05). Conclusions: Regardless of vision, standing on lateral wedges improved postural sway in people with PD.

• Korean Journal of Applied Biomechanics
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• v.18 no.1
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• pp.159-168
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• 2008

The purpose of this study was to analyze the variables of plantar pressure distribution, the COG between Flying Sit Spin(FSS) and Flying Camel Spin(FCS) during a Figure Skating. In order to investigate the two types of spin mechanism in the Korea national of elite women Figure skaters(N=4), this study investigated the phase time, CA(contact area), MF(maximum force) Mean Force, and PP(peak pressure) Mean Force. The data was collected using PEDAR Mobile System which is the pressure distribution measuring devices. The obtained conclusions were as follow: During the two types of spins(FSS and FCS), the FCS is higher than the FSS on the MF(20%BW), PP(20%BW) variables during P4 phase, but the FSS is larger than the FCS in the CA, MF, and PP during P1, P2, P3 phase. Consequently, depend on the COP and the COG locations about the vertical ground reaction vector, the FCS comparatively excelled control of speed feedback than the FSS in the P4 phase.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.31 no.4
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• pp.146-152
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• 2008

This study was aimed to understand the effects of perturbed floor surface on human postural stability while standing. Ten subjects were asked to stand quietly on the surface with two angles of inclination ($0^{\circ}$ and $5^{\circ}$), two contamination conditions (dry and oil-contaminated), and three commercial floor materials (ceramic tile, coated wood, and vinyl tile). During each trial, a force plate with data acquisition systems was used to collect subject's center of pressure (COP) position. Measured COPs were then converted into the length of postural sway path in both subject's anterior-posterior (AP) and medio-lateral (ML) axis. Results showed that the length of sway path in ML axis was significantly affected by the angle of inclination and the type of floor material. The sway length was increased significantly at the inclination angle of $5^{\circ}$ and on the vinyl tile, respectively. The contamination condition, however, did not significantly affect the postural sway length in both AP and ML axis. The results imply that a proper treatment of floor surface and material is critical to preserving postural balance while standing.

• Journal of the Korean Society of Physical Medicine
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• v.17 no.4
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• pp.103-111
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• 2022

PURPOSE: This study was performed to investigate the effects of the whole-body vibration exercise combined with ankle joint mobilization on the gait and balancing ability in patients with hemiplegic stroke. METHODS: A total of 19 patients at a rehabilitation hospital who had suffered a hemiplegic stroke were randomly assigned to the experimental group (whole-body vibration exercise combined with ankle joint mobilization, n=10) or control group (whole-body vibration exercise, n=9). All participants underwent 30 min of comprehensive rehabilitation therapy (5 × /week for 6 weeks). Additionally, the experimental group performed the whole body vibration exercise and ankle joint mobilization (15 minutes each, 30 minutes total, 3 × / week for 6 weeks). In the control group, only the whole- body vibration exercise was performed in the same manner and not the ankle joint mobilization. The gait and balancing abilities were measured before and after the 6-week training. RESULTS: Significant improvements were observed in the 10-m walk test, timed up-and-go (TUG) test, center of pressure (COP) path length, and COP path velocity in the experimental group (p < .05). The experimental group showed a larger decrease in the COP path length and velocity than the control group (COP path length, -10.27 mm vs. -3.67 mm, p < .05; COP path velocity, -.33 cm/sec vs. -.13 cm/sec, p < .05, respectively). CONCLUSION: The whole-body vibration exercise combined with ankle joint mobilization could be effective in improving the gait and balancing ability of stroke patients and could also be more effective for improving the static balance ability than the general whole-body vibration exercise alone.