• Korean Journal of Mathematics
• /
• 제4권1호
• /
• pp.71-76
• /
• 1996

The purpose of the present paper is to derive the perturbations and jumps of semi-Fredholm operators.

• 한국운동역학회지
• /
• 제25권1호
• /
• pp.39-47
• /
• 2015

Objective : The purpose of this study was to investigate the velocity conversion coefficient and invariance for the optimal phase ratio on the performance of the women's triple jump. Methods : Three-dimensional kinematic data were obtained from the three finalists of the women's triple jumper competition at the 2011 Daegu IAAF World Championships. Computer simulations were performed using the biomechanical model of the triple jump to optimize the phase ratio for the longest actual distance for all athletes with altered velocity conversion coefficients. Results : Top elite triple jumpers showed better technical consistency at the phase ratio. Also, no consistent relationship was observed between the loss in horizontal velocity and the gain in vertical velocity across supporting the three phase. In addition, regardless of the magnitude A1, all athletes were optimized with jump-dominated technique. Finally, as the magnitude of A1 increased, the athletes showed better performance. The obtained overall distance jumped showed the longest actual distance when the optimal phase ratio was transferred from hop-dominated to jump-dominated(the step ratio was 30%~31%), and when the optimal phase ratio was transferred from balanced to jump-dominated(the step ratio was 27%~29%). Conclusion : Future studies need to be conducted in order to explore the active landing motion and the inclination angle of the body with the velocity conversion coefficient simultaneously at each supporting phase.

• 대한정형외과스포츠의학회지
• /
• 제2권1호
• /
• pp.50-55
• /
• 2003

목적: 플라이오메트릭 훈련이 하지 슬관절의 굴곡과신전, 족관절의 배측굴곡과 족저굴곡의 등속성 총일량에 미치는 영향의 정도를알아보며이훈련법의효과검증을위해시도되었다. 대상및방법: 선택된 플라이오메트릭훈련 방식은 7가지로pike jump, double leg hop, double leg bound, single leg hop, stride jump cross over, alternate leg bound, box jump로구성되었다. 연구대상자는20 $\~$22세사이의대학생으로, 훈련시행군(N=5), 대조군(N=4)으로8주간 시행하고 훈련 전후 등속성 장비를 이용하여 슬관절과 족관절의 등속성 총일량을 측정하였다. 결과: 플라이오메트릭 훈련을 시행한군에서 높은 각속도의 슬관절과 족관절 운동의 총일량이 대조군에 비하여 증가하였다(p<0.05) .결론: 결과적으로 플라이오메트릭 훈련은 하지슬관절과족관절의등속성 총일량에 부분적으로영향을미치는것을알수있으며, 더나아가운동수행에도영향을미칠수있는것을의미한다.

• 한국정보통신학회논문지
• /
• 제21권1호
• /
• pp.8-16
• /
• 2017

줄넘기와 같은 반복적인 운동들의 횟수를 측정하는 방법은 다양하다. 그 중 대표적으로 가속도 센서의 가속도 값 또는 자이로스코프 센서의 각속도 값을 이용하여 파형과 데이터의 특징을 추출하고 선택한 후 선택한 특징을 알고리즘에 적용하여 측정하는 방법이 있다. 하지만 고정되지 않고 유동적인 운동들은 다양한 변수가 존재한다. 이러한 경우의 수를 하나의 센서만으로 찾기 쉽지 않으며, 잡음과 진동에 취약한 가속도계와 드리프트 현상이 발생하는 각속도의 문제점으로 인하여 정확한 줄넘기 개수를 세는데 다소 정확도가 떨어지는 현상이 발생한다. 본 논문에서는 기존의 방식인 단일 센서만의 값으로 회전운동을 검출하는 방법의 문제점을 개선하기 위해 가속도와 각속도의 데이터값에 상보 필터를 적용하고, 가속도와 각속도 값이 상호보완 하여 서로의 문제점을 최소화하여 보다 정확한 개수를 측정할 수 있는 방법을 제안한다. 제안하는 방법은 센서 값의 특징만을 보고 판단하는 방법과 비교하여 정확하게 줄넘기 개수를 측정하는 것을 실험 결과를 통해 확인할 수 있다.

• 한국운동역학회지
• /
• 제19권1호
• /
• pp.27-36
• /
• 2009

본 연구에서는 수직점프시 몸통운동의 제약이 수직점프의 수행에 미치는 영향을 알아보기 위해 10명의 성인 남성을 대상으로 몸통을 자유롭게 사용한 일반적인 형태와 몸통동작을 제한한 형태의 수직점프를 비교, 분석하였다. 분석 결과 몸통동작을 제한한 경우 비 제약점프에 비해 10% 정도의 수행 손실이 있었는데, 이는 이지 순간의 중심 높이보다는 이 지속도의 차이에 의해 발생하였다. 몸통의 운동은 엉덩관절의 모멘트 파워를 증가시켜 추진의 초기 시점부터 지면반력의 증가에 기여하였는데 이러한 요인이 수행력 증가의 주요한 요인으로 작용하였다. 반면 몸통운동이 제한된 점프에서는 엉덩관절에서의 역학적 출력의 감소를 보상하는 측면에서 무릎관절의 역할이 증가하였으나 충분치 못하였다. 또한 몸통동작의 제한으로 엉덩관절 무릎관절 발목관절의 순차적인 신전패턴과는 상이하게 추진시점 직후 엉덩관절과 무릎관절이 동시에 신전하는 형태의 점프가 이루어져 협응패턴의 변화가 나타났다. 결국 본 연구의 결과 몸통의 적절한 사용은 수직점프의 수행 향상에 효과적으로 기여하는 것으로 나타났다.

• Physical Therapy Rehabilitation Science
• /
• 제4권1호
• /
• pp.22-27
• /
• 2015

Objective: Jump training helps increase the muscle power by improving the muscle strength and reaction time of the muscle in operation. The purpose of this study was to identify the effects of strengthening, stretching exercise and meditation on electromyographic (EMG) onset timing of rectus femoris and gastrocnemius muscle during vertical jump performance. Design: Cross-sectional study. Methods: Ten healthy adults (5 male and 5 female) who were familiar with the vertical jumping task and had no lower extremity injuries or any bone or joint disorders, were recruited for this study. Muscle onset timing was measured by surface EMG. After EMG onset timing were measured during performing three baseline vertical jump trials, strengthening and stretching exercises of the rectus femoris and gastrocnemius, and meditation were performed in random order. EMG onset timing was measured during vertical jump after intervention, respectively. EMG value was averaged for the three trials and analyzed using one-way repeated ANOVA. Results: During vertical jump, EMG onset timing of gastrocnemius was a significant difference after intervention (p<0.05), and then there was significantly faster in strengthening exercise than meditation (p<0.05). Conclusions: These results indicate the potential positive effect of performing strengthening exercise of the gastrocnemius before a jumping event. Future research is required to identify the effects of intervention over a long period.

• PNF and Movement
• /
• 제13권3호
• /
• pp.135-143
• /
• 2015

Purpose: The purpose of this study was to assess the effect of the proprioceptive neuromuscular facilitation (PNF) relaxation technique (hold relax; HR, contract relax; CR) and static stretch (SS) on hamstring flexibility and vertical jump performance in healthy adults over a four-week period. Methods: Twenty-four healthy adults volunteered to participate in PNF and static stretch sessions. The subjects were divided into three groups as follows: 8 subjects in the SS group, 8 subjects in the HR group, and 8 subjects in the CR group. In the HR and CR groups, contractions lasted 15 seconds per trial and consisted of 5 sets of 15 seconds of hamstring contraction immediately followed by 15 seconds of passive static hamstring stretching. For the static group, the participants were asked to stretch by hanging a leg over a table for 30 seconds. Subjects in all groups performed the exercises three days per week for 4 weeks. The active straight leg raising (ASLR) test, active knee extension (AKE) test, and vertical jump test were performed before the intervention and after 1, 2, and 4 weeks. Results: The SS, HR, and CR techniques effected positive improvement in hamstring flexibility and vertical jump performances but neither of the stretching methods had any statistically significant different effects according to group, although there were interactions (between group and time) in the ALSR group from 1 week to 2 week and in the AKE test from pretest to 1 week. Conclusion: Based on the results of the current study, SS, HR, and CR were shown to affect hamstring flexibility and vertical jump performance in healthy adults. In particular, it was determined that within a short period, hamstring flexibility could be attributed more to CR than to SS.

• Coupled systems mechanics
• /
• 제8권4호
• /
• pp.339-350
• /
• 2019

A numerical simulation of the incompressible multiphase hydraulic jump flow was performed to compare the interface prediction through the use of the three RANS turbulence models: $k-{\varepsilon}$, $RNGk-{\varepsilon}$ and SST $k-{\omega}$. A three dimensional no submerged hydraulic jump and a two dimensional submerged hydraulic jump were modeled. Both the geometry and the mesh were created using the open source Gmsh code. The project's geometry consists of a rectangular channel with length and height differences between the two dimensional and three dimensional simulations. Uniform hexahedral cells were used for the mesh. Three refining meshes were constructed to allow to verify simulation convergence. The Volume of Fluid (abbr. VOF) method was used for treatment of the air-water surface. The turbulence models were evaluated in three distinct set up configurations to provide a greater accuracy in the flow representation. In the two-dimensional analysis of a submerged hydraulic jump simulation, the turbulence model RNG RNG $k-{\varepsilon}$ provided a better interface adjust with the experimental results than the model $k-{\varepsilon}$ and SST $k-{\omega}$. In the three-dimensional simulation of a no-submerged hydraulic jump the k-# showed better results than the SST $k-{\omega}$ and RNG $k-{\varepsilon}$ capturing the height and length of the ledge with a better fit with the experimental results.

• 한국운동역학회지
• /
• 제32권2호
• /
• pp.43-48
• /
• 2022

Objective: The purpose of this study was to verify the effectiveness among simulating ski jumping trainings by comparing with actual ski jump. Method: Three healthy youth national athletes were recruited for this study (age: 13.70 ± 0.9 yrs, height: 169.30 ± 0.9 cm, jumping caree: 5.3 ± 0.9 yrs). Participants were asked to performed ski jumping with 3 simulating and one actual situation. A 3-dimensional motion analysis with 5 channels of EMG was performed in this study. Muscle activations of Rectus Femoris [RF], Tibialis Anterior [TA], Thoracis [TH], Gluteus maximus [GM], and Gastronemius [GL] were achieved with sampling rate of 2,000 Hz during each jump. Results: In the case of S1 in the actual jumping motion, the deviation of the muscle activity peak did not appear each trial, and the jump timing was consistent. For S2, the timing of the muscles peak activation which can maintain the posture of the upper body and ankles appeared at the beginning. In the case of S3, the part maintaining the ankle posture at the beginning appeared, but it could be expected that it would progress in the vertical direction due to the activation of GL at the time of jumping. Conclusion: The muscle activation peak before the take-off point showed a different pattern for each athlete, and individual differences were large. In addition, it was attempted to confirm the actual jump with simulation jump, and it was found that not only the difference in patterns but also the fluctuations in the timing of each muscle activation peak were large.

• 한국운동역학회지
• /
• 제32권1호
• /
• pp.9-16
• /
• 2022

Objective: The purpose of this study was to investigate how the chronic ankle instability affects postural control during forward jump landing. Method: 20 women with chronic ankle instability (age: 21.7 ± 1.6 yrs, height: 162.1 ± 3.7 cm, weight: 52.2 ± 5.8 kg) and 20 healthy adult women (age: 21.8 ± 1.6 yrs, height: 161.9 ± 4.4 cm, weight: 52.9 ± 7.2 kg) participated in this study. For the forward jump participants were instructed to stand on two legs at a distance of 40% of their body height from the center of force plate. Participants were jump forward over a 15 cm hurdle to the force plate and land on their non-dominant or affected leg. Kinetic and kinematic data were obtained using 8 motion capture cameras and 1 force plates and joint angle, vertical ground reaction force and center of pressure. All statistical analyses were using SPSS 25.0 program. The differences in variables between the two groups were compared through an independent sample t-test, and the significance level was to p < .05. Results: In the hip and knee joint angle, the CAI group showed a smaller flexion angle than the control group, and the knee joint valgus angle was significantly larger. In the case of ankle joint, the CAI group showed a large inversion angle at all events. In the kinetic variables, the vGRF was significantly greater in the CAI group than control group at IC and mGRF. In COP Y, the CAI group showed a lateral shifted center of pressure. Conclusion: Our results indicated that chronic ankle instability decreases the flexion angle of the hip and knee joint, increases the valgus angle of the knee joint, and increases the inversion angle of the ankle joint during landing. In addition, an increase in the maximum vertical ground reaction force and a lateral shifted center of pressure were observed. This suggests that chronic ankle instability increases the risk of non-contact knee injury as well as the risk of lateral ankle sprain during forward jump landing.