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The balance recovery mechanisms against unexpected forward perturbation.
Hwang, Sungjae,Tae, Kisik,Sohn, Ryanghee,Kim, Jungyoon,Son, Jongsang,Kim, Youngho Pergamon Press [etc.] 2009 Annals of biomedical engineering Vol.37 No.8
<P>Falls are one of the main concerns of the elderly. Proper postural adjustments to maintain balance involve the activation of appropriate muscles to produce force and to relocate the center of body mass (CoM). In this study, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles and EMG activations. Thirteen young and healthy volunteers took turns standing on a flat platform, and were directed to move in the forward direction by an AC servo-motor set at two different speeds (0.1 and 0.2 m/s). Joint motions were recorded, and they followed the sequence of ankle dorsiflexion, knee flexion, and then hip flexion during the later acceleration phase (AP) in order to maintain postural balance against forward perturbation. Tibialis anterior for the ankle dorsiflexion and biceps femoris for the knee flexion were activated during the second half of the AP as the primary muscles to recover balance. In addition, gastrocnemius, which was related to ankle plantarflexion, and rectus femoris, which was related to knee extension, were activated to maintain balance. Movements of the center of plantar pressure and ground reaction forces in fast-speed perturbation were significantly larger than those in slow-speed perturbation. As a result, the ankle strategy was used for slow-speed perturbation, but the mixed strategy consisting of both ankles and hip were used for fast-speed perturbation.</P>
The Motion Analysis about the Balance Recovery Mechanisms against the Forward Perturbation
Sungjae Hwang,Hueseok Choi,Kisik Tae,Youngho Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this paper, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles, linear accelerations, EMG activations, CoP movements and ground reaction forces(GRF). The sequence of joint motions due to the forward perturabation was in the order of ankle dorsiflexion, knee flexion and then hip flexion during the second half of the acceleration phase. Forward accerlerations were found both at the heel and the sacrum during the second half of the acceleration phase and the early, constant speed phase. Tibialis anterior(TA) for ankle dorsiflexion and biceps femoris(BF) for knee flexion, the primary muscle to recover balances against the forward perturbation, was activated during the half of acceleration phase. Ankle strategy was used for slow-speed perturbation, but mixed strategy of both ankle and hip used for the fast-speed perturbation. In addition, speed and magnitude of the perturbation influenced the postural response.
Sungjae Hwang,Jongsang Son,Yujin Shin,Jungmi Park,Youngho Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
Many studies have been unsuccessful to classify biomechanical characteristics of pathological gaits in hemiplegic patients using joint motions of the lower extremity. In this paper, we analyzed changes in muscle length of lower limbs for hemiplegic walking by using the 3D motion analysis and the musculoskeletal modeling to determine gait patterns. Twenty young healthy volunteers and three hemiplegic patients participated in this study. 3D motion analyses were performed by using six infra-red cameras and four force plates. The musculoskeletal model was made based on subjects' anthropometric data and 3D motion capture data. The musculoskeletal model included twelve major lower extremity muscles based on the modified Hill-type muscle model in each lower limb. Results showed that insufficient push-off was found during pre-swing in hemiplegic walking, without showing enough contraction of gastrocnemius and soleus. Excessive ankle dorsiflexion was also found due the contracture of tibialis anterior. Semimembranosus was shown to be tighter and thus knee flexion was larger during loading response than those in the normal subjects. Changes in muscle length of extensor muscles were also very similar to joint motions in the sagittal plane. These results could be very useful to classify and to characterize various abnormal gait patterns.
Biomechanical Effects of Heel Wedges on the Knee Varus Torque during Walking
Sungjae Hwang,Imsook Jeong,Sunwoo Park,Ohyoun Kwon,Youngho Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In the present study, knee varus torque and mediolateral accelerations were compared using the threedimensional motion analysis system and a linear accelerometer in order to determine biomechanical effects of heel wedges during walking. Wedges were inclined with 10° and 15° in medial and lateral directions respectively. Both knee varus torques and mediolateral accelerations showed two distinct positive peaks in loading response and pre-swing. Medial wedges resulted in significantly increased both knee varus torque and lateral acceleration in loading response, compared with barefoot walking (p<0.05). On the other hand, lateral wedges decreased them in loading response (p<0.05). This became more significant in more inclined wedges. However, no significant correlations were found between knee varus torque and lateral acceleration in preswing with respect to the wedge angle. From this study, it was found that a lateral wedge would be helpful to treat osteoarthritis, decreasing knee varus torque in loading response. In addition, lateral acceleration of the knee joint might be an alternative to determine the effect of wedges during walking, instead of measuring knee torque by the three-dimensional motion analysis.
Joint Moments and Lumbar Lordosis during Symmetric Lifting
Seonhong Hwang,Sungjae Hwang,Youngeun Kim,Youngho Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this study, contributions of lower extremity joints and lumbar lordotic angles were investigated for two different symmetrical lifting techniques using the three-dimensional motion analysis: squat and stoop. Joint angles and moments were determined when the lumbar curvature changed from kyphosis to lordosis. Thirteen male volunteers lifted boxes weighing 5, 10 and 15㎏ by both squat and stoop lifting techniques. Results showed that extension moments of hip and ankle joints contributed the most to support the body in squat lifting, and the knee flexion moment played an important role in stoop lifting. There were individual differences in lower extremity joint moments when the lumbar lordotic curve appeared. However, the correlations about angles and moments between lumbar and lower extremity joints could confirmed the results from the support moment analysis. In conclusion, there might be some strategy to minimize mechanical stress on the waist by the change of lordotic curvature in the lumbar spine for the safe lifting technique.
마비환자의 보행훈련을 위한 로봇형 보행훈련 시스템 개발
황성재(Sungjae Hwang),김정윤(Jungyoon Kim),손종상(Jongsang Son),손량희(Ryanghee Sohn),김영호(Youngho Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In this study, we developed a robotic gait training system which induces the active gait training based on predefined continuous proper lower extremity joint movements for the paralysis. AC servo motors and linear actuators were used to control hip and knee joints of patients and the weight support system was used to support the patient's weight during the gait training. We also implemented a GUI program to set the gait training pattern with several training parameters and to confirm states of patients and the system through the visual feedback. The effectiveness of the gait training system will be determined by the long-term clinical experiments in the future. We expect that the developed robotic gait training system could be applied very practically to recover gait abilities for persons with gait disorder.