Si-Hyun Yoo

Comparisons between Skilled and Less-Skilled Players` Balance in Hakdariseogi

The purpose of this study was to investigate the balance differences between skilled players and less-skilled players during Hakdariseogi motion of Keumgang Poomsae in Taekwondo. To achieve the study goal, total of 10 Taekwondo athletes; 5 skilled players(S, body mass: kg, height: cm, age: yrs) and 5 less-skilled players(LS, body mass: kg, height: cm, age: yrs) participated in this study. A three-dimensional motion analysis with 8 infrared cameras and one force plate whose sampling frequency as 30 Hz and 300 Hz, respectively, were performed. Participants` motion were divided into three phases which were preparation phase(P1), performing phase(P2) and maintaining phase(P3). The range and velocities of COP, the range and RMS of ground reaction torque and displacement between COM and center of BOS of each phase were computed. In this study, at P1 and P3 which were double and single stance, respectively, the range and M-L velocities of COP revealed significantly higher in LS compared with those of S(p

Comparison between the Balance of Skilled and Less-Skilled Players during Successful and Failed Front Kick and Turning Side Kick Motions

The aim of this study is to identify the appropriate movement for maintaining postural balance during Front Kick and Turning Side Kick motions. To do so, ten Taekwondo athletes: five skilled players(S, body mass: , height: , age: , career: ) and five less-skilled players(LS, body mass: , height: , age: , career: ) participated in this study. A three-dimensional motion analysis was performed on the participants using eight infrared cameras and two force plate(sampling frequency of 200 Hz and 2000 Hz for S and LS players, respectively). The participants` motions were divided into: a front-kick phase(P1) and a turning-side-kick phase(P2). For P2(p

Comparisons of Foot Pressure Patterns between Experienced Skiers and Intermediate Skiers during Alpine Skiing

This study investigated foot pressure patterns between experienced skiers and intermediate skiers during alpine skiing. Five experienced skiers and five intermediate skiers participated in this study. Foot pressure measurement system was used to measure vertical ground reaction force (vGRF) and contact area under the six plantar regions. Each participant was asked to perform basic parallel turns and carved turns on a 18o groomed slope. Each right turn was divided into the initiation phase, the steering phase 1 and 2. For the initiation phase of the basic parallel turns, significantly greater contact area was found on the LRF and RRF of the intermediate skiers (p<.05) and significantly greater vGRF was found on the LRF of the intermediate skiers (p<.05). Also significantly greater vGRF and contact area were found on the LRF and RRF of the intermediate skiers at the steering phase 1 (p<.05) and on the LRF of the intermediate skiers at the steering phase 2 (p<.05). For the carved turns, significantly greater vGRF and contact area were found on the LRF and RRF of the intermediate skiers at all three phase (p<.05). On the other hand, significantly greater vGRF was found on the RFF of the experienced skiers at the steering phase 1 (p<.05). Also significantly greater vGRF and contact area were found on the RMF of the experienced skiers at the steering phase 2 (p<.05). In order to increase performance, we suggest that the intermediate skiers should be unweighted at the initiation phase and shift the body weight to the forefoot of the outer foot at the steering phase 1. Also, the outer ski should be loaded more than the both skis at the steering phase 1 and 2.

The Kinematic Analysis of Upper Extremities for Badminton Smash and Drop Motions depends on the Player's Level

The aim of this study was to investigate badminton smash and drop motion depends on players level. To perform this study, ten male badminton players were participated: five skilled players (SG, age: 21.6±1.1 yrs, height: 181.4±6.8 cm, body mass: 72.4±5.7 kg, career: 11.2±1.1 yrs) and five less-skilled players (LSG, age: 21.2±1.1 yrs, height: 180.2±5.6 cm, body mass: 73.6±6.7 kg, career: 10.6±0.9 yrs). Three-dimensional motion analysis with 7 infrared cameras was performed with a sampling frequency as 200 Hz. Players swing motion was divided into four events: starting motion (E1), backswing (E2), impact (E3), following (E4). For all upper joints, LSG showed greater angle differences between drop and smash motions than that of SG at E3 (p<.05). For all upper joints, greater angular velocities were found in SG than that of LSG. For both groups, significantly smaller angular veloc- ities were found in drop motion than that of smash motion (p<.05). The greater sequential angular velocities (proximal to distal) were found in SG than LSG during smash motion. Based on our findings, performing the same motion between drop and smash would be related to enhance performance at badminton competition. It is expected that these results will be useful in developing a training program for enhancing performance of badminton athletes.

Comparisons of Center of Mass and Lower Extremity Kinematic Patterns between Carved and Basic Parallel Turn during Alpine Skiing

This study investigated the center of mass and lower extremity kinematic patterns between carved and basic paralell turn during alpine skiing. Six experienced skiers (age: 20.67±4.72 yrs, body mass: 72.67±7.15 kg, height: 171.00±5.51 cm) participated in this study. Each skier were asked to perform carved and basic paralell turn on a 22.95° groomed slope. Each turn was divided into the initiation phase, steering phase 1 and 2. The results of this study show that the carved turn spent significantly less running time than basic paralell turn at all three phases (p<.05). Also vertical displacement of the center of mass was significantly greater in carved turn at all three phases, whereas inward leaning angle of the center of mass was significantly greater in carved turn at the steering phase 1 and 2 (p<.05). Bilateral knee and hip joint angle were significantly greater in basic paralell turn at the initiation phase and the steering phase 2 (p<.05). On the other hand, left knee and hip joint angle were significantly greater in basic paralell turn at the steering phase 1 (p<.05). In order to perform successful carved turn, we suggest that skiers should coordinate bilateral knee and hip joint angles to adjust the center of mass, depending on three ski turn phases.

Kinematic Analysis of Cornering with Different Radius of Curve Course in Short Track Speed Skating

본 연구는 쇼트트랙 스피드 스케이팅 곡선주로를 작은 반경으로 활주하는 집단과 큰 반경으로 활주하는 집단 간 곡선주로 마지막 구간에서 나타나는 밀기동작에 대한 운동학적 요인의 차이를 살펴보고자 하였다. 우선, 작은 반경 집단이 큰 반경 집단에 비해 오랜 시간 곡선주로 밀기동작을 수행하며, 양발의 스트록 길이가 큰 폭으로 움직이는 것은 곡선주로의 회전반경을 최소화하기 위한 전략으로 판단되며(Jun, 2001), 그 결과로 곡선주로의 원 중심부터 신체중심까지 거리를 작게 유지하는 것으로 나타났다. 이것은 작은 반경 집단이 큰 반경 집단에 비해 곡선주로에서 효율적인 활주 동작을 수행하고 있음을 알 수 있다. 이때 빠른 선속도로 곡선주로를 활주하는 작은 반경 집단이 큰 반경 집단에 비해 신체중심을 링크 안쪽으로 많이 기울이는 경향을 보였다. 이것은 빠른 속도를 유지하기 위한 보상 작용으로써, 곡선주로 원 중심에 대한 구심력을 증가시키고 곡선주로 활주 동작의 안정성을 높이기 위한 전략으로 판단된다(Jun, 2001). 곡선주로 활주 시 나타나는 하지 관절각의 움직임은 회전반경의 크기와 속도를 결정하는 중요한 요소이다. 무릎 관절각의 굴곡·신전 움직임이 두 집단 간에 통계적으로 유의한 차이를 보였다. 특히, push off 동작이 시작될 때, 작은 반경 집단이 큰 반경 집단에 비해 왼 무릎관절이 8o, 오른 무릎관절이 19o 정도 더 굴곡되어 있는 것으로 나타났으며, 움직임 범위에서는 각각 14o, 22o로 나타났다. 이것은 스피드 스케이팅 선수들의 운동역학적 특성을 연구한 De Boer, Schermerhorn, Gademan, De Groot와 Van Ingen Schenau (1986), Hyun (1996)의 선행연구에서 보듯이, 쇼트트랙 곡선주로 활주 시 push off 동작을 효율적으로 수행하기 위해서는 무릎관절을 최대한 굴곡한 후, 신전하는 것이 회전반경의 크기와 속도에 큰 영향을 주는 것으로 판단된다. 이와 더불어 왼 고관절의 굴곡·신전 움직임 범위에서 작은 반경 집단이 큰 반경 집단에 비해 크게 나타났다. 이것은 Jun (2001)의 쇼트트랙 곡선주로 동작의 운동학적 특성 분석을 통하여 곡선주로에서는 자세를 최대한 낮추었다가 push off 구간에서 자세를 높이는 동작이 효율적이라고 주장과 일맥상통한 내용이다. 또한, 하지 관절의 내측·외측 회전은 곡선주로를 마무리하면서 직선주로로 접어드는 구간에서 회전반경의 크기에 영향을 미치는 움직임이라 판단된다. 특히, 왼 무릎관절각의 내측·외측 회전에서 최소값은 작은 반경 집단이 -8.54±7.60°, 큰 반경 집단이 17.89±5.78°, 그 범위는 각각 22.55±5.68°, 5.98±1.34°로 나타남으로써, 두 집단 간에 큰 차이를 보였다. 곡선주로 탈출 시 왼 무릎관절의 외측 회전 움직임이 크게 일어나면서 왼발을 곡선주로 안쪽으로 강하게 push off함으로써 회전반경을 작게 유지하는 역할을 한다(De Boer, Ettema, Van Gorkum, De Groot, & Van Ingen Schenu, 1987). 마지막으로 두 집단 간 하지 관절의 각속도는 통계적으로 유의한 차이가 나타나지는 않았으나, De Boer, Schermerhorn, 등 (1986), De Boer, Ettema, Van Gorkum, De Groot와 Van Ingen Schenu (1988) 등의 선행연구와 같이 작은 반경 집단이 큰 반경 집단에 비해 무릎관절 신전 움직임의 각속도가 빠르게 나타났으며, 이것은 곡선주로에서의 속도를 증가시키고 회전반경을 줄이는데 영향을 미치는 것으로 판단된다. 이상 살펴본 바와 같이 쇼트트랙 곡선주로를 작은 반경으로 효율적으로 활주하기 위해서는 push off 동작을 실시할 때, 양발의 스트록 길이를 최대한 벌리면서 빙면을 밀어내야 하고 고관절과 무릎관절을 최대한 굴곡시킨 후, 빠르게 신전시키는 능력이 요구된다. 또한 곡선주로를 마무리하며 직선주로로 접어드는 구간에서 왼발을 크게 외측 회전시켜 작은 반경으로 유지하려는 노력이 필요할 것으로 사료된다.

Successful Factor Analysis of 540° Dwihuryeochagi to Apply Free Style Poomsae of Taekwondo

The purpose of this study was to provide fundamental information for success factors of techniques through kinematic analysis including coordination of lower extremities and landing stability according to the success and failure of 540o Dwihuryeochagi in Taekwondo. Twenty Taekwondo athletes: ten success group (S, age: 22.3±1.8 yrs, height: 172.1±5.4 cm, body mass: 64.4±4.2 kg) and ten failure group (F, age: 22.3±1.8 yrs, height: 172.1±5.4 cm, body mass: 64.4±4.2 kg) participated in this study. Three-dimensional motion analysis using a system of 3 video cameras with a sampling of 60 fields/s was performed during the competition of 540o Dwihuryeochagi. Motions were divided into five events: pivot foot landing (E1), pivot foot toe off (E2), COM max height (E3), kick impact (E4) and landing (E5). At E1, the stride width was greater for S than for F (p<.05) while the time was greater for S than for F during P4 (p<.05). At E4, knee angle was greater for S than for F (p<.05). At E5, hip angle was greater for S than for F (p<.05) while kick distance was greater for S than for F (p<.05). Furthermore, at P3, the time would be related to kicking velocity (p<.05), while at P4, the time, range of hip angle and knee angle would be related to kick distance (p<.05). At P1, COM horizontal velocity would be related to COM vertical velocity of P1 and P2 (p<.05). Based on the findings, success factors of 540°ý Dwihuryeochagi were COM horizontal velocity of P1, COM vertical velocity of P2, the time, kick distance, velocity, angle of lower extremities and coordination of P3-P4.

Comparative Analysis of Gait Parameters and Symmetry between Preferred Walking Speed and Walking Speed by using the Froude Number

Walking is the most basic mode of transportation of humans. It is a complex motion produced by the coordination and control of the upper and lower limb joints. Gait varies depending on the physical traits, habits, walking speed, and personality (Shin, Lee, & Kwon, 2008; Tirosh & Sparrow, 2005; Whittle, 1990). So far, the symmetrical movements of both legs have been regarded as normal gait. However, even non-handicapped individuals can develop asymmetrical gait because of physical traits or differences in function between both feet (Sadeghi, Allard, Prince, & Labelle, 2000). Echeverria, Rodriguez, Velascol, and Alvarez-Ramirez (2010) reported that around 10% of cases of asymmetrical gait could be observed in nonhandicapped individuals. Improper gait and habits can cause diseases in body structure such as bones and muscles (Moon, 2005; Scott & Winter, 1990). In particular, asymmetrical gait can cause body fatigue and can directly cause disabilities or diseases because abnormal loads during gait can travel all the way to the brain (Nigg, De Boer, & Fisher, 1995). Asymmetry produced while walking is used to evaluate gait. In their study, Perttunen, Anttila, Sodergard, Merikanto, and Komi (2004) examined the asymmetrical gait of patients with lower limb length discrepancies and reported that weight bearing was higher on the longer leg. In another study, Lugade, We, Jewett, Collis, and Chou (2010) reported that surgery improved asymmetrical gait in patients with hip osteoarthritis. Hyun and Ryew (2014) investigated the correlation between heel height and gait in young female adults and reported that heel height was directly proportional to asymmetry and observed bilateral asymmetry. Roth, Mervitz, Mroczek, Dugan, and Suh in 1997; Patterson et al. in 2008; and Nam, Kim, and An in 2010 reported that bilateral asymmetry increases with decreased walking speed in stroke KJSB Korean Journal of Sport Biomechanics 2016; 26(2): 221-228 http://dx.doi.org/10.5103/KJSB.2016.26.2.221 http://e-kjsb.org eISSN 2093-9752 ORIGINAL

Effects of Combined Exercise on Injury Risk Factors of Lower Extremity during Landing

【The purpose of this study was to investigate the effect of combined exercise on injury risk factors of lower extremity during landing. Ten sports talented athletes participated in this study. Sports talented athletes participated in a combined exercise (sports talented exercise, coordination) for 16 weeks. A three-dimensional motion analysis was performed using eight infrared cameras (sampling rate of 100 Hz), one force plate, and electromyography system (sampling rate of 1000 Hz) during landing. Kinetic, and kinematics analysis including average impulsive force, angle of lower extremity, vertical stiffness, onset of muscle activation were calculated by Matlab2009a software. Paired t-test was performed at alpha=.05. The average impulsive force in landing phase was not statistically significant (t=-.748, p=.474). The hip joint angle was more decreased in post test compared to pre test (E1: t=2.682, p=.025, E2: t=5.609, p=.000, E3: t=2.538, p=.032). The knee joint (E1: t=-.343, p=.739, E2: t=1.319, p=.220, E3: t=.589, p=.570) and ankle joint (E1: t=.081, p=.937, E2: t=.784, p=.453, E3: t=.392, p=.704) angle were tended to decrease after combined exercise. The vertical stiffness was tended to decrease after combined exercise (t=1.972, p=.080). Onset of quadriceps femoris (t=.698, p=.503) and medial gastocnemius (t=1.858, p=.096) were tended to be faster than biceps femoris (t=-.333, p=.747) after combined exercise. Although thses findings were not statistically significant except on a hip joint angle, risk factors of lower extremity such as joint angle, vertical stiffness and onset of quadriceps femoris, medial gastrocnemius were positively changed after the combined exercise but an additional training for improved onset of biceps femoris would be required in the future.】