• Korean Journal of Applied Biomechanics
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• v.13 no.3
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• pp.293-309
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• 2003

The purpose of this study was to analyze the kinematic variables of the right-straight punch(RSP) in boxing with three-dimensional analysis technical methods. The subjects are boxers who have been playing in national boxing representative team and the RSP is their special favorite technique, The right-straight punches were filmed on 16mm video cameras(30frames/sec.) The kinematic variables were temporal, postural and center of gravity(COG). The mean and the standard deviation of variables have been obtained and used as basic factors for examining characteristics of the RSP by out-boxers. From the data analysis and discussion, the following conclusions have been drawn. 1) Temporal variables It is a significant characteristic that LDJ and KDM s' the amount of elapsed time(EF) needed for both an attack and a defense were similar : ET for stretch-out of attack-arm was $0.52{\pm}0.04\;sec$. and return was $0.54{\pm}0.01\;sec$. Therefore, a defense motion is as important as an attack motion. 2) Posture variables When the subjects performed a RSP, the significant characteristic of the ankle angle was that it wasn't completely returned to the original position after stretching-out. Therefore it is necessary to do supplementary exercises, such as side steps, to move the center of gravity more effectively. The hee angle was not fully stretched either. In regard to the hip angle, it should be rotated with all strength to harmonize with the direction of movement. 3) Center of Gravity(COG) variables When both LDJ and KDM performed a RSP, a significant characteristic was the transformation of sagittal view rather than transverse or frontal views.

• Korean Journal of Applied Biomechanics
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• v.22 no.2
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• pp.183-191
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• 2012

The objective of this study was to evaluate the plantar foot pressure of skilled and unskilled players during a free throw. The experiment performed here in measured the movement route of the mean foot pressure, maximum foot pressure, and center of pressure in four event zones (ready, maximum knee flexion, release event, and maximum knee extension) for both groups while they were wearing the plantar foot pressure measurement equipment under identical conditions. The major findings are as follows. When getting ready (RD) during a free throw, the skilled player group had higher mean and maximum foot pressures, although neither variable showed significant differences statistically. For the maximum knee flexion (MF) during a free throw, the skilled player group had higher mean and maximum foot pressures, but only the mean foot pressure significantly differed statistically. For the release event (RE) during a free throw, the unskilled player group had higher mean and maximum foot pressures, but only the mean foot pressure significantly differed statistically. During the maximum knee extension (ME) of a free throw, the unskilled player group had a higher mean foot pressure, and the skilled player group had a higher maximum foot pressure. No significant correlation was found between the two groups. For the skilled player group, movement towards the center of pressure showed a stable form that moved from the rear to the front and from side to side during a free throw. For the unskilled player group, movement towards the center of pressure was unstable, which made it impossible to move from the rear to the front and from left to right.

• Korean Journal of Applied Biomechanics
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• v.26 no.4
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• pp.333-341
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• 2016

Objective: The purpose of this study was to assess the consistency of the gliding and push-off motion for single leg skating from the first to fourteenth steps. We hypothesized that: 1) there would be no difference in stroke trajectory, step rate, and cycle rate between the left and right steps of gliding; and 2) there would be a difference in the resultant velocity of toe push-off and the horizontal velocity of the center of mass after six step push-offs. Method: The study included five male 500-m speed skaters (mean height, $1.80{\pm}0.02m$; mean weight, $76.8{\pm}3.96kg$; record, $35.83{\pm}0.30sec$; 100-m record, <9.97 sec). Data were collected from the first to fourteenth steps (40 m) and recorded using five digital JVC GR-HD1KR video cameras (Victor Co., Japan) operating at a sampling frequency of 60 fields/sec and shutter speed of 1/500 sec. For each film frame, the joint positions were digitized using the KWON3D motion analyzer. Position data were filtered with low-pass Butterworth $4^{th}$ order at the cut-off frequency of 7.4 Hz. Results: The right toe of the skating trajectories at $2^{nd}$, $5^{th}$, and $7^{th}$ strokes differed from those of the left toe. The angles of the right and left knee demonstrated unbalanced patterns from the flexion and extension legs. The step and cycle rates of the right and left leg differed from the start until 20 m. The resultant velocities of the toe at the push-off phase and of the body mass center diverged before the six push-offs. Conclusion: This study's findings indicate that the toe of skating trajectory on left and right sliding after push-off should maintain a symmetrical trajectory. The resultant velocity of toe push-off and horizontal velocity from the center of body need to be separated after about six step push-offs.

• Korean Journal of Applied Biomechanics
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• v.31 no.2
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• pp.104-112
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• 2021

Objective: This study aimed to analyze the effects of consecutive whole body vibration through heel raise posture on the center of pressure and electromyography of anterior tibial muscle, lateral gastrocnemius and soleus muscles during single-leg stance. Method: The subjects of this study included 30 healthy males in their 20's, with the following inclusion criteria: no history of orthopaedic medical history, no participation in regular exercises, no history of whole body vibration exercise, and right leg being the dominant leg. The experimental procedure involved pretreatment measurement of eye open single-leg stance, application of whole body vibration for 30 seconds, post-treatment measurement (3 measurements in total). Static and dynamic movements have been measured over 2 separate experiments, with 72 hours gap between the experiments. Static movement involved maintaining single-leg heel raise posture for 30 seconds while applying whole body vibration, and dynamic movement involved heel raise (15 repetitions over 30 seconds) while applying whole body vibration. The strength of applied whole body vibration was 35 Hz frequency and 2~4 mm amplitude. Results: As the single-leg posture after static heel raise posture, mediolateral velocity of the center of pressure at post 2 and post 3 were significantly reduced compared to the pre-treatment measurement. In addition, the percentage for reference voluntary contraction in anterior tibial muscle and soleus and median frequency at anterior tibial muscle and lateral gastrocnemius muscle at post 3 were significantly decreased compared to the pre-treatment value. As the single-leg posture after dynamic heel raise posture, the mediolateral 95% edge frequency of the center of pressure and median frequency at anterior tibial muscle, lateral gastrocnemius muscle, and soleus muscle at post 3 were significantly reduced compared to the pre-treatment value. Conclusion: Acute whole body vibration via static and dynamic heel raise posture have positive effect on mediolateral posture control during single-leg stance.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.729-742
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• 2023

It is a recent attraction to the mechanical scientists to investigate state of wave propagation, buckling and vibration in the sport balls to observe the importance of different parameters on the performance of the players and the quality of game. Therefore, in the present study, we aim to investigate the wave propagation in handball game ball in term of mass of the ball and geometrical parameters wit incorporation of the viscoelastic effects of the ball material into account. In this regard, the ball is modeled using thick shell structure and classical elasticity models is utilized to obtain the equation of motion via Hamilton's principle. The displacement field of the ball model is obtained using first order shear deformation theory. The resultant equations are solved with the aid of generalized differential quadrature method. The results show that mass of the ball and viscoelastic coefficient have considerable influence on the state of wave propagation in the ball shell structure.

• Korean Journal of Applied Biomechanics
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• v.20 no.2
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• pp.155-165
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• 2010

The purpose of this study was to analyze kinematic quantitative factors required of a forehand counter drive in table tennis through 3-D analysis. Four national table tennis players participated in this study. The mean of elapsed time for total drive motion was $1.009{\pm}0.23\;s$. At the phase of impact B1 was the fastest as 0.075 s. This may affect efficiency in the initial velocity and spin of the ball by making a powerful counter drive. The pattern of center of mass showed that it moved back and returned to where it was then moved forward. At the back swing, lower stance made wide base of support and a stronger and safer stance. It may help increasing the ball spin. Angle of the elbow was extended up to $110.75{\pm}1.25^{\circ}$ at the back swing and the angle decreased by $93.75{\pm}3.51^{\circ}$ at impact. Decreased rotation range of swinging arm increased linear velocity of racket-head and impulse on the ball. Eventually it led more spin to the ball and maximized the ball speed. Angle of knee joint decreased from ready position to back swing, then increased from the moment of the impact and decreased at the follow thorough. The velocity of racket-head was the fastest at impact of phase 2. Horizontal velocity was $7796.5{\pm}362\;mm/s$ and vertical velocity was $4589.4{\pm}298.4\;mm/s$ at the moment. It may help increase the speed and spin of the ball in a moment. The means of each ground reaction force result showed maximum at the back swing(E2) except A2. Vertical ground reaction force means suggest that all males and females showed maximum vertical power(E2), The maximum power of means was $499.7{\pm}38.8\;N$ for male players and $519.5{\pm}136.7\;N$ for female players.

• 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.26 no.4
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• pp.427-432
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• 2016

Objective: The goal of this study was to systematically investigate the postural stability of dancers by providing unexpected perturbations. Method: Six female dancers and college students participated in this study. Unpredictable wait-pull balance perturbations in the anterior direction were provided to the participants during standing. Three different perturbation intensities (low, moderate, and high intensity) were used by increasing perturbation forces. Spatial and temporal stability of postural control were measured by using margin of stability (MoS) and time to contact (TtC), respectively. Results: Both MoS and TtC at moderate intensity were significantly greater in the dancer group than in the control group, but no significant differences were found at low and high intensities between the groups. Conclusion: The present study showed spatial and temporal stability of dynamic postural control in dancers. We found that the dancers were more spatially and temporally stable than the ordinary participants in response to unexpected external perturbation when the perturbation intensity was moderate at two extreme intensity levels (low and high).

• IMMUNE NETWORK
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• v.16 no.2
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• pp.109-115
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• 2016

To find the relation between exercise and cytokines, we examined the effect of the training intensity on the levels of cytokines, including interferon-gamma (IFN-γ), interlukine-4 (IL-4) and interlukine-4/interferon-gamma ratio (IL-4/IFN-γ ratio) in female Futsal players. Twelve well-trained female college Futsal players aged 19~22 participated in this study. The athletes completed 30-min of running at 60~65% maximal heart rate [moderate-intensity exercise], and 30-min of running at 75~80% maximal heart rate [high-intensity exercise]. peripheral blood samples were collected 24 h before and 24 h and 48 h after each of the exercise bouts. finding showed that The 30-min bout of moderate-intensity exercise induced a significant increase in IFN-γ (p=0.01) and significant decreases in IL-4 (p=0.001) and IL-4/IFN-γ ratio (p=0.003). And also, 30-min of running at 75~80% maximal heart rate induced increase in IFN-γ (p=0.07) and decreased in IL-4 (p=0.01) and IL-4/IFN-γ ratio (p=0.06) that these changes not significantly. In summary, exercise intensity can effect on the magnitude of changes in cytokines. It seems that moderate intensity exercise enhances cytokine pattern in female college Futsal players.

• Korean Journal of Applied Biomechanics
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• v.12 no.2
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• pp.65-75
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• 2002

The study has a goal that produces abundant documents that needed for athletes to teach and progress skills by analyzing 3-dimensional action analysis of C-difficulties Ring jump included in body original elements among techniques constructing Rhythmic Sport Gymnastics. 1. It was the longest applied time delay that E-3 indicates 0.409${\pm}$0.017sec in each event applied time delay. 2. It was the tallest height that E-3 indicates 88.5${\pm}$1.3% in displacement of body's center. 3. It was the fastest velocity in E-2 where the velocity of left foot is 732.4${\pm}$46.1cm/sec, the velocity of right foot is 1958.4${\pm}$25.1cm/sec. 4. the lowest angle was founded at 97.8 degree in the E-3 on the trunk extension angle. 5. The lowest angle of both sides were seen at 92.8${\pm}$14.9degree and 69.2${\pm}$5.7degree in the E-3 on the each displacement of knee joint. 6. The highest angle of both sides were seen at 171.3${\pm}$6.9degree and 167.9${\pm}$8.4degree in the E-3 on the each displacement of ankle joint As a result of these studies, by jumping with ankle joint extension to accomplish the Ring jump action, it is considered to have the time of flexiblity and staying in the air which we can see in a back.