Analysis of the Area of Center of Pressure (COP) Trajectories According to Running Speed and Its Correlation with Ankle Joint Motion

Hojong Gil,Sihyun Ryu,Sang-Kyoon Park,Jiseon Ryu 대한인간공학회 2018 大韓人間工學會誌 Vol.37 No.6

Objective: The purpose of this study was to determine the difference of motions using the new calculation method of COP area and to investigate the correlation with the change of the foot eversion. Background: The quantitative analysis process on the data of COP revealed in the process of repetitive gait and running cycle is essentially required and through COP trajectories, the correlations between ground and feet can be effectively examined. Method: Thirty young males participated in this study. They were asked to run on an instrumented treadmill (Bertec, USA) at speeds of 3.5m/s and 4.5m/s for running. A system of motion analysis cameras (Oqus 300, Qualisys, and Sweden) and pedar-X system (Novel GmbH, Germany) were used to collect joint angles and COP trajectories, and Shoelace Formula was used to calculate the area of multiple COP lines from running. The analysis variables were the area of COP, the COP range, the COP velocity, and the ankle joint eversion angle. The Pearson"s correlation coefficient was calculated to investigate the relations between variables. Results: The running at 4.5m/s showed the smaller area of COP and the range of COP, but the greater velocity of COP (p <0.05) in comparison with the running at 3.5m/s. There was a positive correlation between the area of COP and the anteriorposterior range of COP (r =.350). Additionally, there was a negative correlation between the area of COP and the maximum eversion angle of ankle joint (r =-.418). Conclusion: The findings indicate that the method using the Shoelace Formula to calculate the area of COP was able to determine the difference between running speeds and predict the maximum eversion angle of the ankle joint. Application: Based the results, the area of COP trajectories newly presented in this study is judged to be used as a variable to predict running speed and the eversion angle of the ankle joint.

Effects of an 8-week Pilates Core Training on the Stability and Symmetry of the L-sit on Rings

( Hojong Gil ),( Sihyun Yoo ),( Sukhoon Yoon ) 한국운동역학회 2016 한국운동역학회지 Vol.26 No.4

Objective: Gymnastics on rings needs a high level of muscle strength with balance ability for controlling the body. A study on a new balance training program is necessary for elite gymnasts. Therefore, the purpose of this study was to investigate the effects of an 8-week pilates core-muscle training on balance ability and asymmetry index of the L-sit on the rings in male elite gymnasts. Method: Ten elite gymnasts (age: 20.6±0.7 years, height: 169.9±4.9 cm, weight: 65.4±5.6 kg, career duration: 20.6±0.7 years), who are students at K-university, participated in this study. Results: First, the range of the COM tended to decrease in the anterior-posterior direction. Second, the left hip joint angle and knee extension and ankle dorsiflexion angles significantly increased after the pilates training. Third, the ROM also increased. Fourth, the symmetry value increased in the hip angle, while the symmetry index in all joints of the ROM decreased. As a result, the pilates core-muscle training influenced the static balance ability during the L-sit on the rings. Conclusion: Accordingly, the pilates core-muscle training is suitable in enhancing the basic balance ability in gymnastics on rings.

Effects of an 8-week Pilates Core Training on the Stability and Symmetry of the L-sit on Rings

Gil, Hojong,Yoo, Sihyun,Yoon, Sukhoon Korean Society of Sport Biomechanics 2016 한국운동역학회지 Vol.26 No.4

Objective: Gymnastics on rings needs a high level of muscle strength with balance ability for controlling the body. A study on a new balance training program is necessary for elite gymnasts. Therefore, the purpose of this study was to investigate the effects of an 8-week pilates core-muscle training on balance ability and asymmetry index of the L-sit on the rings in male elite gymnasts. Method: Ten elite gymnasts (age: $20.6{\pm}0.7years$, height: $169.9{\pm}4.9cm$, weight: $65.4{\pm}5.6kg$, career duration: $20.6{\pm}0.7years$), who are students at K-university, participated in this study. Results: First, the range of the COM tended to decrease in the anterior-posterior direction. Second, the left hip joint angle and knee extension and ankle dorsiflexion angles significantly increased after the pilates training. Third, the ROM also increased. Fourth, the symmetry value increased in the hip angle, while the symmetry index in all joints of the ROM decreased. As a result, the pilates core-muscle training influenced the static balance ability during the L-sit on the rings. Conclusion: Accordingly, the pilates core-muscle training is suitable in enhancing the basic balance ability in gymnastics on rings.

The Optimization of the Number and Positions of Foot Pressure Sensors to Develop Smart Shoes

Sihyun Yoo,Hojong Gil,Jongbin Kim,Jiseon Ryu,Sukhoon Yoon,Sang Kyoon Park 대한인간공학회 2017 大韓人間工學會誌 Vol.36 No.5

Objective: The purpose of this study was to optimize the number and positions of foot pressure sensors using the reliability analysis of the center of pressure (COP) in smart shoes. Background: Foot pressure can be different according to foot region, and it is important which region of the foot pressure needs to be measured. Method: Thirty adults (age: 20.5±1.8 years, body weight: 71.4±6.5kg, height: 1.76±0.04m) participated in this study. The foot pressure data were collected using the insole of Pedar-X system (Novel GmbH, USA) with a sampling frequency of 100Hz during 1.3m/s speed walking on the treadmill (Instrumented treadmill, Bertec, USA). The intraclass correlation coefficients (ICC) were calculated between the COP positions using 4, 5, 6, 7, 8, and 99 sensors, while one-way repeated measure ANOVA was performed between the standard deviation (SD) of the COP positions. Results: The medio-lateral (M/L) COP position using 99 sensors was positively correlated with the M/L COP positions using 6, 7, and 8 sensors; however, it was not correlated with the M/L COP positions using 4 and 5 sensors during landing phase (1~4%) (p <.05). The antero-posterior (A/P) COP position using 99 sensors was positively correlated with the A/P COP positions using 4, 5, 6, 7, and 8 sensors (p <.05). The SD of the COP position using 99 sensors was smaller than the SD of the M/L COP positions using 4, 5, 6, 7, and 8 sensors (p <.05). Conclusion: Based on our findings, it is desirable to arrange at least 6 sensors in smart shoes. Application: The study of optimizing the number and positions of foot pressure sensors would contribute to developing more effective smart shoes using foot pressure technology.

발바닥 부위별 인솔 소재 및 경도 변화가 착화감과 충격 흡수에 미치는 영향

류시현(Sihyun Ryu),길호종(Hojong Gil),공세진(Sejin Kong),최용석(Yongsuk Choi),류지선(Jiseon Ryu),윤석훈(Sukhoon Yoon),박상균(Sang Kyoon Park) 대한인간공학회 2018 大韓人間工學會誌 Vol.37 No.4

Objective: The purpose of this study was to evaluate the biomechanical effects of insole material and hardness in different plantar regions on the comfort and impact absorption during walking and to analyze the correlations between comfort and impact variables. Background: It is necessary to apply materials tailored to the functionalities of different plantar regions during different phases of the gait cycle: the rearfoot portion should absorb the impact force during the heel-contact phase, the midfoot portion should support the entire arch, and the forefoot portion should enhance the swing efficiency during the toe-off phase. Method: Twenty men in their twenties were recruited for the study (age: 23.4±2.7yrs; height: 175.9±4.1㎝; weight: 72.9±9.4㎏). They wore insoles in random order. Pedar-X system (Novel GmbH, USA) and Treadmill (Instrumented treadmill, Bertec, USA) were used to measure the plantar pressure and ground reaction force. The walking speed was set at 1.3㎧ and 1.7㎧. The sampling rate was set at 50㎐ and 1,000㎐, respectively. For comfort testing, the subjects administered a questionnaire survey using the visual analogue scale (VAS) after walking 1km. Three insole models were tested: Insole A using a mixed material with shock-absorbing and anti-rebound components uniformly spread throughout the insole; Insole B and Insole C using sponge and ethylene vinyl acetate (EVA), respectively, as underlying material and strengthened with shock absorber in the rearfoot portion, high-hardness material in the midfoot portion, and anti-rebound function in the forefoot portion. The impulse, mean impact force, initial peak of ground reaction force, and loading rate were calculated. Results: First, Insole B significantly outscored Insole A in terms of the forefoot cushioning comfort (p <.05), with Insole B and C showing higher overall comfort scores compared with Insole A (p <.05). Second, Insole A showed higher mean impact force, initial and peak vertical ground reaction forces, and loading rate compared with Insoles B and C, but without reaching statistical significance. Third, Insole B and C showed statistically higher mean pressure in the midfoot portion compared with Insole A (p <.05). Conclusion: Positive effects in terms of comfort and impact absorption were demonstrated by the insoles fabricated with different materials and hardness tailored to the functionalities of different plantar regions in comparison with the conventional insoles using the uniform material throughout the insole. In particular, positive effects on overall comfort were found to be ascribable to the enhanced hardness in the midfoot portion, which supported the arch more efficiently and contributed to an even distribution of the overall pressure on the plantar. Application: The study results can be applied to insole development as follows: Insole material and hardness should be varied for different plantar regions, and shock absorber and high-hardness material should be used for the rearfoot and midfoot portions, respectively.

캘리퍼 모드에 의한 디스크 브레이크 스퀼 시험 및 해석

최호일(Hoil Choi),강재영(Jaeyoung Kang),길호종(Hojong Gil) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.12

본 논문은 차량 제동 시 발생하는 소음의 원인을 해석적으로 예측하고, 본 실험실에서 제작한 브레이크 다이나모 메터를 이용하여 실험적으로 검증하였다. 압력 변화에 따른 브레이크 시스템에 대한 주파수 응답 시험 및 유한 요소 해석(FEM)을 실시하여 캘리퍼 및 디스크의 수직 모드(Out-of-plane)의 시스템 주파수를 추적하였다. 이를 제동 시 발생한 스퀼 소음의 주파수와 비교해본 결과 스퀼 주파수는 캘리퍼 및 패드의 변위를 갖는 시스템 모드임을 확인하였다. 또한 유한 요소 해석을 이용한 복소수 고유치 해석 결과 패드의 회전변위를 발생시키는 캘리퍼 모드가 음의 마찰곡선 기울기와 연동하여 불안정하게 됨을 확인하였다. This study numerically simulates brake squeal and validates it experimentally by using a lab-scaled brake dynamometer. The system frequencies of the disc brake are traced with respect to the brake pressure by using a modal test and FEM. Then, the squeal frequencies measured from the brake dynamometer are found to correspond to the brake system mode with the dominant displacement of the caliper and pad. Furthermore, a complex eigenvalue analysis conducted using the finite element model confirms that the caliper mode generating the rotational displacement of the pad becomes unstable owing to the negative friction-velocity slope.

Comparisons of Age-Related Changes in Impact Characteristics Between Healthy Older and Younger Runners

Sang-Kyoon Park,Darren Stefanyshyn,Sihyun Ryu,Hojong Gil,Young-Seong Lee,Jongbin Kim,Ji-Seon Ryu 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.12

The purpose of this study was to investigate whether there are any age-related differences in impact characteristics during running between healthy older and younger men. Ten healthy older (age: 58.7 ± 2.5 years) male and ten healthy younger (age: 22.3 ± 1.6 years) male recreational runners ran on a treadmill at three different running speeds (i.e. 2.2 m/s, 2.8 m/s, and 3.2 m/s). Tri-axial accelerometers (Noraxon, USA) were firmly attached to the tibia and the sternum. Gait parameters, three-dimensional peak tibial accelerations, peak sternum accelerations and shock attenuation were calculated during the stance phase of running. The ANOVA repeated measures was applied at an alpha level of .05. Older runners showed greater impact on the sternum, leading to reduced shock attenuation compared with younger runners (p < .05). In addition, older runners showed a shorter lag between peak resultant accelerations experienced by the upper body and peak acceleration experienced by the lower leg compared with younger runners (p < .05). This study suggests that the intensity (i.e. speed and duration) and types of exercise should be carefully considered for older adults because of lower shock attenuation of the body and changes in coordination strategy between the segments in high-impact activities like running.