• Korean Journal of Applied Biomechanics
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• v.21 no.5
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• pp.551-560
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• 2011

The purpose of this study was to perform the kinematic analyses of the men's pole vault skills in IAAF World Championships Daegu 2011. Subjects were the 1st through 8th place finishers in the pole vault. The kinematic analyses were divided into four phases: two dimensional run up analysis, and three dimensional analyses for the remaining plant, swing up, and extension phases. Run-up variables consisted of run up distance, number of steps, average step length, the ratio of step length to his height, average velocity at the final 6~11 m, approach position. Three variables were analyzed during plant: pole angle, center of gravity (COG) velocity, and takeoff angle of COG. Swing up phase variables included: pole flexion angle, COG velocity (horizontal, vertical, resultant), COG trajectory and bar approach angle of COG. Compared to the 2009 World Championships in Berlin, the average vault height, run up velocity and approach position increased. However, horizontal velocity during the last two steps of the final approach decreased dramatically compared to speeds from 1990. These results reflect the change in both technique and improved physical fitness in pole vaulters. During extension, the peak height of COG averaged 0.3m higher then COG height when the pole was released. These specific results can help coaches and athletes modify training and improve performance.

• Korean Journal of Applied Biomechanics
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• v.27 no.2
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• pp.109-116
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• 2017

Objective: This study aimed to investigate the relationship between leg stiffness and kinematic variables according to load while running. Method: Participants included eight healthy men (mean age, $22.75{\pm}1.16years$; mean height: $1.73{\pm}0.01m$; mean body weight, $71.37{\pm}5.50kg$) who ran with no load or a backpack loaded with 14.08% or 28.17% of their body weight. The analyzed variables included leg stiffness, ground contact time, center of gravity (COG) displacement and Y-axis velocity, lower-extremity joint angle (hip, knee, ankle), peak vertical force (PVF), and change in stance phase leg length. Results: Dimensionless leg stiffness increased significantly with increasing load during running, which was the result of increased PVF and contact time due to decreased leg lengths and COG displacement and velocity. Leg length and leg stiffness showed a negative correlation (r = -.902, $R^2=0.814$). COG velocity showed a similar correlation with COG displacement (r = .408, $R^2=.166$) and contact time (r = -.455, $R^2=.207$). Conclusion: Dimensionless leg stiffness increased during running with a load. In this investigation, leg stiffness due to load increased was most closely related to the PVF, knee joint angle, and change in stance phase leg length. However, leg stiffness was unaffected by change in contact time, COG velocity, and COG displacement.

• The Journal of Korean Physical Therapy
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• v.31 no.5
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• pp.273-278
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• 2019

Purpose: The purpose of this study was to investigate the effects of three-dimensional virtual reality horse riding simulator training using a head-mounted display on gait and balance in children with cerebral palsy. Methods: Ten children with cerebral palsy were randomly assigned to the horse riding simulator (HRS) group (n=5) or the horse riding simulator with virtual reality (HRSVR) group (n=5). To evaluate balance, center of gravity (COG) sway velocity and total sway distance of each group were assessed using the Wii balance board, and gait speed and stride length of each group were assessed using a gait analysis system. Results: Intra-group comparisons between pre- and post-intervention measures revealed that there were significant changes in all gait and balance variables such as stride length, gait velocity, COG sway velocity and COG sway distance in the HRSVR group (p<0.05). In the HRS group, there were significant changes in all variables except stride length (p<0.05). In addition, inter-group comparisons showed significant differences between the two groups in stride length, gait velocity and COG sway distance except COG sway velocity (p<0.05). Conclusion: The findings of this study suggest that horse riding simulator training combined with 3D virtual reality can be a new positive therapeutic approach for improving functional performance in children with cerebral palsy.

• Journal of Korean Institute of Industrial Engineers
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• v.11 no.2
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• pp.87-99
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• 1985

The purpose of this study is to analyze the changes in centers-of-gravity (COG), acceleration and body posture and their associated effects both on EMG and on the maximum capability of weight lifting during Clean & Jerk and Snatch motions. Displacement, velocity, acceleration of joints were obtained from film analysis. Also levels of exertions on 11 major muscle groups were obtained from EMG analysis during a lifting cycle. The EMG data were measured from Telemetry System which is useful in field experiments. Magnitude and direction of force, change in center-of-gravity were extracted from COG data which were measured from force platform. The results of this study can be to be useful both to coaches and to athletes in weight-lifting.

• PNF and Movement
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• v.16 no.2
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• pp.267-273
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• 2018

Purpose: Leg length discrepancy (LLD) is one of the risk factors for postural imbalance. This study aimed to investigate the effect of induced leg length discrepancy on the limitation of stability (LOS) and static postural balance. Methods: Thirteen adults (males, 7; females 6) participated in this study. The LOS and static postural balance [sway length, sway area, and sway velocity of center of gravity (COG) displacement] were measured by the balance trainer system. The subjects were asked to move the COG for the anterior, posterior, and left and right directions maximally and to keep standing on the platform with and without induced LLD for 30 s in the open and closed eyes conditions, respectively. The LLD was artificially induced to 2 cm using insole. Wilcoxon test was used to compare the LOS and the static postural balance between with and without induced LLD. Results: The anterior and posterior LOS significantly decreased in induced LLD (p<0.05), and the left and right LOS were not significantly different between with and without LLD (p>0.05). Sway length, sway area, and sway velocity of the COG displacement significantly decreased in induced LLD (p<0.05). Conclusion: This study suggests that induced LLD could decease the antero-posterior LOS and increased the static postural balance. Therefore, the LLD could disturb the postural balance.

• Korean Journal of Applied Biomechanics
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• v.23 no.1
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• pp.19-24
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• 2013

The aim of the study was a quantitative analysis of elite athlete's $540^{\circ}$ Dwihuryeochagi and effects of ground movements to the jumping height and kicking velocity. Eleven elite players(Taekwondo demonstration team) participated in this study. In order to get the kinetic and kinematic variables, ten Vicon cameras and a force plate were used. Foot segment velocity(FSV), vertical ground reaction force(GRF), impulse, ground time(GT) in phase 1, trunk angular velocity(TAV), vertical center of gravity(COG), flight time(FT) in phase 2 and kicking leg segment velocity(KSV) in phase 3 were measured and analyzed. Results indicated that there were similar patterns of variables among phases between subjects. Non-significant correlation(r=.145) between flight time(FT) and impulse was found. Also non-significant correlation(r=.119) between center of gravity(COG) and impulse was found. In conclusions, there were similar strategies in phase 1, phase 2, and phase 3 between subjects.

• Korean Journal of Applied Biomechanics
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• v.21 no.5
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• pp.561-571
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• 2011

The purpose of this study was to perform the kinematic analyses of the women's pole vault skills in IAAF World Championships Daegu 2011. Subjects were the 1st through 8th place finishers in the pole vault. The kinematic analyses were divided into four phases: two dimensional run up analysis, and three dimensional analyses for the remaining plant, swing up, and extension phases. Run-up variables consisted of run up distance, number of steps, average step length, ratio of step length to height, average velocity at the final 5~10 m, approach position. Three variables were analyzed during plant: pole angle, center of gravity (COG) velocity, and COG takeoff angle. Swing up phase variables included: pole flection angle, COG velocity (horizontal, vertical, resultant), COG trajectory and bar approach angle of COG. Compared to the 2009 World Championships in Berlin, the average vault height increased, while run up velocity and approach position were almost unchanged. However, horizontal velocity during the last two steps of the final approach decreased noticeably compared to speeds from 1990. These results reflect the change in both technique and physical fitness in pole vaulters. During extension, the peak height of COG surpassed the clearance height by an average of 0.11m. These specific results can help coaches and athletes modify training and improve performance.

• Korean Journal of Applied Biomechanics
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• v.15 no.1
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• pp.237-257
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• 2005

It was to study as a following-research of "A Case Study on Center of Gravity(COG) Analysis when Performing Uchimata(inner thigh reaping throw) by Posture and Voluntary Resistance Levels(VRL) of Uke in Judo[I]". The purpose of this study was to analyze the COG variables when performing uchimata(inner thigh reaping throw) by two postures and voluntary resistance levels(VRL) of uke(reciver) in Judo. The subjects, who were one male judoka(YH) for 1992 Barcelona Olympic Games Olympian(silver medalist), and one male trainee; Y.I.University representative member (SDK), and were filmed on two S-VHS 16mm video cameras(60fields/sec.) through 3-dimensional motion analysis methods, that postures of uke were shizenhontai (straight natural posture) and jigohontai(straight defensive posture), VRL of uke were 0% and 100%, respectively. The kinematical variable was COG variable, distance of COG, and distance of resultant COG between uke and tori(the thrower), velocity and acceleration of COG. The data of this study collection were digitized by SIMI Motion Program computed the mean values and the standard deviation calculated for each variables. When performing uchinmata according to each posture and VRL of uke and classifying. From the data analysis and discussion, the conclusions were as follows : 1. Displacement of COG Subject YH, COG was the highest in kuzushi(balance -breaking), vertical COG was low when following in tsukuri(positioning; set-up), kake(application; execution), and COG was pattern of same character each postures and resistance, respectively. Subject SDK, COG was low from kumikata(engagement positioning) to kake, and COG was that each postures and resistance were same patterns, respectively. Subject YH, SDK, each individual, postures and resistance, vertical COG was the lowest in kake phase, when performing. 2. Distance of COG between uke and tori The distance of COG between uke and tori when performing, subject YH was $0.64{\sim}0.70cm$ in kumikata, $0.19{\sim}0.28cm$ in kake, and SDK was $0.68{\sim}0.72cm$ in kumikata, $0.30{\sim}0.42\;cm$ in kake. SDK was wider than YH. 3. Distance of resultant COG between uke and tori The distance of resultant COG between uke and tori when performing, subject YH was $0.27{\sim}0.73cm$ from kumikata to kake. and SDK was $0.14{\sim}0.34cm$ in kumikata, $0.28{\sim}0.65cm$ in kake. Jigohontai(YH:$0.43{\sim}0.73cm$,SDK:$0.59{\sim}0.65cm$) was more moved than shizenhontai(YH:$0.27{\sim}0.53cm$, SDK: $0.28{\sim}\;0.34cm$). 4. Velocity of COG The velocity of COG when performing uchimata, subject YH was fast anterior-posterior direction in kuzushi, ant.-post. and vertical direction fast in tsukuri and kake. SDK was lateral, ant.-post. and vertical direction in kuzushi, ant.-post. and vertical direction in tsukuri and ant.-post. direction in take, respectively. 5. Acceleration of COG The acceleration of COG when performing uchimata, The trend of subject YH was showed fast vertical direction in kuzushi and tsukuri, ant.-post. and vertical direction fast in kake. The trends of SDK showed lateral direction in kuzushi, lateral and ant.-post. direction in tsukuri and ant.-post. direction in kake, respectively.

• Korean Journal of Applied Biomechanics
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• v.17 no.3
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• pp.41-49
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• 2007

This study was to investigate the kinematical analysis using ski simulator. Twelve people(six skilled, six unskilled) participated in the experiment. Each phase of motion time was slight differences between the skilled group and the unskilled group but not significant difference in statistics. In displacement of vertical on COG(Center of Gravity), left and right down motion showed significant difference between group. In velocity of horizontal on COG, both left and right down motion showed significant difference between group, and up motion of between down motion showed significant difference. In displacement of angle on ankle, knee, hip joint almost showed significant difference between group. Almost in body position was lower skilled group than unskilled group.

• Korean Journal of Applied Biomechanics
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• v.19 no.3
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• pp.425-433
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• 2009

The purpose of this study was to investigate relation between fastball motion and longtoss motion, and the kinematical analysis using APAS(Ariel Performance Analysis System). Eight people(age: $21.2{\pm}3.6years$, height: $177.1{\pm}3.1cm$, weight $68.6{\pm}2.5kg$) participated in the experiment. Followings are the conclusion. In displacement of fore-aft on COG(Center of Gravity), fastball motion moved more forward than longtoss motion. In displacement of vertical on COG(Center of Gravity), fastball motion was lower than longtoss motion In velocity of right hand, greater release velocity was measured for fastball motion than for longtoss motion. In displacement of elbow and shoulder joint, more extended displacement was exhibited in fastball motion than longtoss motion. In displacement of trunk tilt, fastball motion showed foreward tilt, longtoss motion showed backward tilt. In stride, fastball showed longer than longtoss.