• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.57-64
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• 2007

The purpose of this study was to investigate comparative analysis of the vertical ground reaction force variables during landing from vertical jump blocking in volleyball through GRF analysis system. The subjects participated in this study were 6 male university volleyball player and 6 male acted as a control group. The results are as follows: 1. The skilled group was longer than the unskilled group in flight time during vertical jump blocking. 2. The skilled group was faster than the unskilled group in tFz2 during landing from vertical jump blocking. 3. The skilled group was higher than the unskilled group in Fz2 during landing from vertical jump blocking. 4. The skilled group was higher than the unskilled group in Fz2LR during landing from vertical jump blocking. 5. The skilled group was higher than the unskilled group in impulse during landing from vertical jump blocking. Consequently, during landing from vertical jump, the landing strategy of the skilled group was found as a form of a stiff landing. Therefore, this landing strategy will be required to strengthen of hip and knee extensors and ankle plantar flexors for injury prevention.

• Korean Journal of Applied Biomechanics
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• v.27 no.4
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• pp.257-262
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• 2017

Objective: This study aimed to investigate the differences in skiing time and vertical ground reaction force (vGRF) between the basic parallel turn and short turn. Method: Eleven alpine ski instructors (age: $28.73{\pm}4.29yrs$, height: $172.36{\pm}6.30cm$, body mass: $71.45{\pm}9.16kg$, career: $11.09{\pm}2.70yrs$) participated in this study. Each skier was asked to perform a basic parallel turn and short turn on a $16^{\circ}$ groomed slope. A foot pressure measurement system was used to measure the skiing time and vGRF under the three plantar regions (forefoot, midfoot, rearfoot). Results: Skiing time decreased significantly in all three phases during the short turn (p<.05). In the initiation phase, the vGRF showed a greater decrease on the midfoot and rearfoot during the short turn (p<.05). In the steering phase 1, the vGRF showed a greater increase on the forefoot and decreased on the midfoot during the short turn (p<.05). In the steering phase 2, the vGRF showed a greater increase on the forefoot and rearfoot during the short turn (p<.05). Conclusion: Our findings proved that the skiing time and vGRF changed during the short turn. Consequently, we suggest that recreational skiers should decrease the skiing time of the steering phase compared to that of the initiation phase and increase the vGRF on the forefoot and rearfoot in the steering phase.

• Korean Journal of Applied Biomechanics
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• v.20 no.2
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• pp.213-219
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• 2010

The purpose of this study is developing a method to analyze and evaluate a golf swing motion using the ground reaction force (GRF) data. Proper weight shifting is essential for a successful shot in golf swing and this could be evaluated by means of the forces between the feet and ground. GRF during the swing were measured from 15 low-handicapped male golfers including professionals. Four clubs(driver, iron 3, iron 5, and iron 7) were selected to analyze the differences due to different characteristics of club. Swings of each subject were taken using a high speed video camera and GRF data were taken simultaneously by two AMTI force platforms. To simplify the GRF data, forces of the three major component of GRF(vertical, lateral, anterior-posterior force) at 10 predefined temporal events for each trial were selected and the mean of each event were calculated and evaluated. Analyzed vertical GRF (VGRF) data could be divided into two different styles, one-legged and two legged. One-legged style shows good weight transfer to the target leg and most of the previous study shows this style as a typical pattern of good players. Therefore the data from the iron 5 swing obtained from 10 one-legged style golfers are provided as criteria for the evaluation of a swing.

• Korean Journal of Applied Biomechanics
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• v.24 no.2
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• pp.151-160
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• 2014

The purpose of this study was to investigate the GRF(ground reaction force) parameters according to the shoes's heel heights and ground landing distances during downward stairs on bus. Participants selected as subject were consisted of young and healthy women(n=9, mean age: $21.30{\pm}0.48$ yrs, mean height: $164.00{\pm}3.05cm$, mean body mass: $55.04{\pm}4.41kg$, mean BMI: $20.47{\pm}1.76kg/m^2$, mean foot length: $238.00{\pm}5.37mm$). They were divided into 2-types of shoe's heel heights(0 cm/bare foot, 9 cm) and also were divides into downward stairs with 3 types of landing distance(20 cm, 35 cm, 50 cm). A one force-plate was used to collect the GRF(AMTI, USA) data from the sampling rate of 1000 Hz. The GRF parameters analyzed were consisted of the medial-lateral GRF, anterior-posterior GRF, vertical GRF, loading rate, Center of Pressure(${\Delta}COPx$, ${\Delta}COPy$, COP area) and Dynamic Postural Stability Index(MLSI, APSI, VSI, DPSI) during downward stairs on bus. Medial-lateral GRF and vertical GRF didn't show significant differences statistically according to the shoe's heel heights and landing distance, but 9 cm shoes heel showed higher vertical GRF than that of 0 cm bare foot in landing distance of 50 cm. Also anterior-posterior GRF didn't show significant difference statistically according to the shoe's heel heights, but landing distance of 20 cm showed higher than that of landing distances of 35 cm and 50 cm in anterior-posterior GRF. Loading rate didn't show significant difference statistically according to the landing distance, but 9 cm shoe's heel showed higher than that of 0 cm bare foot during downward stairs. The ${\Delta}COPy$ and COP area didn't show significant differences statistically according to the shoe's heel heights and landing distance, but 0 cm bare foot showed higher than that of 9 cm shoe's heel in ${\Delta}COPx$. Dynamic Postural Stability Index(MLSI, APSI, VSI, DPSI) didn't show significant differences statistically according to the landing distance, but 9 cm shoe's heel showed decreased value than that of 0 cm bare foot in dynamics balance. Considering the above, parameters of GRF showed different characteristics according to the shoe's heel heights and ground landing distances during downward stairs on bus.

• Korean Journal of Applied Biomechanics
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• v.16 no.4
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• pp.153-164
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• 2006

This thesis is focused on kinematical and kinematical analysis of each types(Type #1 : use both swing of arm and reaction of knee, Type #2 : Use only swing of arm, not reaction of knee, type #3 : Neither use of swing of arm nor reaction of knee) of vertical jumps according to gender of High School Students. The subjects of this study is High School Student's male and female, 5 each, for analyzation of actions 3D image analyzing and GRF machines were used. To identify the differences of analyzed variables, an independent T-test on gender, an One-way ANOVA on types were used. Summery of the results are stated below. first of all, female students showed differences on Hip Joint angle and Joint Velocity from male students on Kimentic Variable. So training on hip joint force of flection and extension of female students is needed. Both male and female students showed relatively bigger result of arm's Angular Momentum than thigh's Angular Momentum on Type #1. This is regarded of faster Joint Velocity of Arm. Bigger result of female students of arm's contribution on Type #1 than male students can be said as Female student's weaker hip joint's angular muscle force than male student's, so the dependency of arm is heavier than male students. In Kinetic variable, GRF showed bigger result on male students than female students. So female students need to enhance joint's torque to increase GRF than male students. On vertical Impulse, high numeric data of last two reaction of tiptoe of vertical GRF and antero-posterior GRF helped increasing impulse by extending action time of force.

• Korean Journal of Applied Biomechanics
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• v.27 no.1
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• pp.1-7
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• 2017

Objective: The purpose of this study was to analyze the relationship between ground reaction force (GRF) and attack time according to the position of hand segments during counter attack in Kendo. Method: The participants consisted of 10 kendo athletes (mean age: $21.50{\pm}1.95yr$, mean height: $175.58{\pm}5.02cm$, mean body weight: $70.96{\pm}9.47kg$) who performed standard head strikes (A) and counter attack with a preferred hand position of +10 cm (B), 0 cm (C), and -10 cm (D). One force-plate (AMTI-OR-7., USA) was used to collect GRF data at a sample rate of 1,000 Hz. The variables analyzed were the attack time, medial-lateral GRF, anterior-posterior GRF (AP GRF), peak vertical force (PVF), and loading rate. Results: The total attack time was shorter in types A and C than in types C and D. The AP GRF, PVF, and loading rate had significantly higher forces in types C and D than in types A and C. The attack time (bilateral and unilateral leg support and total) was positively correlated with the GRF variables (vertical GRF and loading rate) during the counter attack in Kendo (r = 0.779 [$R^2=0.607$], p < 0.001). Conclusion: The positions of the hand segments can be changed by various conditions of the opponent in Kendo competitions; however, the position preferred by an individual can promote the successful ratio of the counter attack.

• Korean Journal of Applied Biomechanics
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• v.17 no.3
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• pp.181-188
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• 2007

The purpose of this study was to investigate the biomechanical effects of wearing different type of insole shoes on gait characteristics in patients with knee osteoarthritis. Seven patients with knee osteoarthritis (Grade 3 & 4 by Kellgren & Lawrence) were participated in the study. They wore two different type of shoes (with Gel-type Insole: GIS, with Normal insole: NIS) during gait. Three dimensional cinematography and Ground Reaction Force(GRF) data were used to get the maximal value of horizontal distance between the center of pressure in GRF and knee joint center, GRF in mediolateral direction, peak value of GRF in frontal plane, vertical compressive force and adduction moment in knee joint. The results were as follows: The maximal value of horizontal distance between the center of pressure in GRF and knee joint center was smaller in GIS than NIS. The peak value of GRF in mediolateral direction was found in 30% of gait cycle, five subjects wearing GIS showed lower value of peak GRF in mediolateral direction than wearing NIS. The peak value of GRF in frontal plane and vertical compressive force in knee joint did not show any difference between GIS and NIS. The adduction moment in GIS decreased in the late stance of gait and the mean value of the adduction moment in GIS smaller than that in NIS. GIS may help to move quickly knee joint center to the center of pressure in GRF, therefore it may prevent increasing the adduction moment in knee joint.

• Journal of Biomedical Engineering Research
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• v.28 no.2
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• pp.187-194
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• 2007

The purpose of this study is to determine the characteristics of ground reaction force(GRF) in golf swing for various slopes of flat lie and uphill lies of 5 and 10 degrees. Five right-handed professional golfers were selected for the experiment and the 7 iron club was used. We used four forceplates to measure GRF and synchronized with the three-dimensional motion analysis system. Results showed that slope did not affect the total time for golf swing, but the time until the impact had a tendency to slightly increase for the uphill lie(p<0.05). The medial-lateral GRF of the right foot increased toward the medial direction during back swing, but less increases were found with the angle of uphill lie(p<0.05). The GRF of the left foot increased rapidly toward the medial direction at the uncocking and the impact during down swing, but decreased with the increase in the angle of uphill lie(p<0.05). The anterior-posterior GRF of both feet showed almost the same for different slopes. With the slopes, the vertical GRF of the right foot increased, but the vertical GRF of left foot decreased(p<0.05). Uphill lies would have negative effect to provide the angular momentum during back swing, restricting pelvic and trunk rotations, and to provide the precise timing and strong power during down swing, limiting movements of body's center of mass. The present study could provide valuable information to quantitatively analyze the dynamics of golf swing. Further study would be required to understand detailed mechanism in golf swing under different conditions.

• Korean Journal of Applied Biomechanics
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• v.23 no.3
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• pp.225-233
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• 2013

The purpose of this study was to estimate the potential injury via analyzing ground reaction force components that were resulted from a prolonged-run-induced fatigue. For the present study, passive and active components of the vertical ground reaction force were determined from time and frequency domain. Shear components of GRF also were calculated from time and frequency domain. Twenty subjects with rear foot contact aged 20 to 30, no experience in injuries of the extremities, were requested to run on the instrumented tread-mill for 160 minutes at their preference running speed. GRF signals for 10 strides were collected at 5, 35, 65, 95, 125, and 155 minute during running. In conclusions, there were no significant difference in the magnitude of passive force, impact load rate, frequency of the passive and active components in vertical GRF between running times except the magnitude of active force (p<.05). The magnitude of active force was significantly decreased after 125 minute run. The magnitude of maximum peak and maximum frequency of the mediolateral GRF at heel strike and toe-off have not been changed with increasing running time. The time up to the maximum peak of the anteroposterior at heel-strike moment tend to decrease (p<.05), but the maximum peak and frequency of that at heel and toe-off moment didn't depend significantly on running time.

• Korean Journal of Applied Biomechanics
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• v.21 no.3
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• pp.289-296
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• 2011

The purpose of this study was to quantify the biomechanical characteristics of the ground reaction force(GRF) during the Taekwondo's Apkubi, one of the basic movement in Taekwondo and the walking. The GRF profiles under the stance foot of Apkubi movement and walking were directly measured in sample of 20 healthy older persons. In the anterior-posterior and vertical direction, the GRF of the Apkubi movement reached to the peak braking force at 10% of the normalized stance time percent and the peak driving force at 90% of stance time, but that of the walking reached to the peak braking force at 20% of stance time and the peak driving force at 80% of stance time. In vertical force, the GRF of the walking showed two peak values, but that of the Apkubi movement seemed three peak values. Moreover the first peak vertical force was significantly(t=6.085, p<.001) greater in the walking(about 1.8 times of body weight) than the Apkubi(about 1.4 times of body weight). The walking velocity was affected significantly(over p<.05) by the braking impulse, the peak braking force and the first peak vertical force. Futhermore the peak braking force in the Apkubi showed a significant effect on the Apkubi's stride length(p<.01). So, we concluded that the braking force after the right touch down, the stance foot on the ground contributed to move the leg forward.