Browsing by Author "Kim, Jemin"
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Item A biomechanical comparison of successful and unsuccessful triple-turn pirouette en dehors trials in ballet(1/9/2019) Kim, Jemin; Kwon, Young-HooPirouette en dehors is a turn in which the dancer's body rotates and completes at least one full revolution with one foot on the floor. It is considered difficult to learn and perform in classical ballet. The purpose of this study was to identify biomechanical kinetic differences between the successful- and unsuccessful-trials groups in triple turn pirouette en dehors motion. It was hypothesized that the successful trials group would have larger longitudinal whole body angular momentum (AM), pivoting moment (PM) and ground reaction force moment (GRFM) than the unsuccessful trials group. Forty skilled collegiate or professional classic ballet dancers (11 males and 29 females) were recruited for this study. The participants were divided into two groups based on their successful and unsuccessful trials. Selected variables were computed through a seven-camera (Qualisys-three-dimensional) motion capture system (250 Hz) and two force-plates (Kistler-2500Hz), with 48 reflective markers. The data was imported into the Kwon3D (5.0) motion analysis software for subsequent data processing. Three MANOVA (SPSS 25.0) were used to compare the dependent variables between successful trials group and unsuccessful trials group conditions (each MANOVA was set p < .025). The first MANOVA was completed to compare all primary variables. The second MANOVA was performed to compare expannatory variables. The peak longitudinal AM, AM generation rate, and peak combined PM, gesture foot PM at TPM (time of peak PM) and gesture foot horizontal GRF at TPM were significantly different between the successful- and unsuccessful-trials groups. The successful trials group was characterized by larger whole body longitudinal AM, AM generation rate and peak PM, meaning this group demonstrated superiority in the generation of angular motion. The unsuccessful trials group had an inefficient double-to-single stance phase for the kinetic variables which caused unsuccessful triple turn pirouette en dehors motion. While peak PM is lower for the unsuccessful trials group, a loss of whole body AM and AM rate creates a failed motion. Kinetics plays a major role in the performance of the triple-turn pirouette en dehors. Further investigation to compare kinematic variables for successful- and unsuccessful- trials group is warranted.Item Effects of pelvis-shoulders torsional separation style on kinematic sequence in golf driving(Taylor & Francis, 2019) Han, Ki Hoon; Como, Christopher; Kim, Jemin; Hung, Cheng-Ju; Hasan, Mohammad; Kwon, Young-HooThe golfer’s body (trunk/arms/club) can be modeled as an inclined axle-chain system and the rotations of its parts observed on the functional swing plane (FSP) can represent the actual angular motions closely. The purpose of this study was to investigate the effects of pelvis-shoulders torsional separation style on the kinematic sequences employed by the axle-chain system in golf driving. Seventy-four male skilled golfers (handicap ≤ 3) were assigned to five groups based on their shoulder girdle motion and X-factor stretch characteristics: Late Shoulder Acceleration, Large Downswing Stretch, Large Backswing Stretch, Medium Total Stretch, and Small Total Stretch. Swing trials were captured by an optical system and the hip-line, thorax, shoulder-line, upper-lever, club, and wrist angular positions/velocities were calculated on the FSP. Kinematic sequences were established based on the timings of the peak angular velocities (backswing and downswing sequences) and the backswing-to-downswing transition time points (transition sequence). The backswing and transition sequences were somewhat consistent across the groups, showing full or partial proximal-to-distal sequences with minor variations. The downswing sequence was inconsistent across the groups and the angular velocity peaks of the body segments were not significantly separated. Various swing characteristics associated with the separation styles influenced the motion sequences.Item Effects of the golfer–ground interaction on clubhead speed in skilled male golfers(Taylor & Francis, 2019) Han, Ki Hoon; Como, Christopher; Kim, Jemin; Lee, Sangwoo; Kim, Jaewoong; Kim, Dae Kyoo; Kwon, Young-HooThe purposes of this study were to characterise the golfer–ground interactions during the swing and to identify meaningful associations between the golfer–ground interaction force/moment parameters and the maximum clubhead speed in 63 highly skilled male golfers (handicap ≤ 3). Golfers performed shots in 3 club conditions (driver, 5-iron and pitching wedge) which were captured by an optical motion capture system and 2 force plates. In addition to the ground reaction forces (GRFs), 3 different golfer–ground interaction moments (GRF moments, pivoting moments and foot contact moments) were computed. The GRF moment about the forward/backward (F/B) axis and the pivoting moment about the vertical axis were identified as the primary moments. Significant (p < 0.05) correlations of peak force parameters (all components in the lead foot and F/B component in the trail foot) and peak moment parameters (lead-foot GRF moment and trail-foot pivoting moment) to clubhead speed were found. The lead-foot was responsible for generating the GRF moment, while the trail foot contributed to the pivoting moment more. The instant the lead arm becomes parallel to the ground was identified as the point of maximum angular effort, and the loading onto the lead-foot near this point was critical in generating both peak moments.