• Title/Summary/Keyword: eccentric

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Analysis of the Differences of the Shock Absorption Strategy between Drop-Landing and Countermovement-Jump (드롭 착지와 착지 후 점프 시 충격흡수 기전의 차이 분석)

  • Cho, Joon-Haeng;Kim, Kyoung-Hun;Koh, Young-Chul
    • Korean Journal of Applied Biomechanics
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    • v.22 no.4
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    • pp.379-386
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    • 2012
  • The aim of this study was to investigate and identify the differences in lower extremity energy dissipation strategies between drop-landing and countermovement-jump maneuvers. Fourteen recreational athletes(Age : $23.3{\pm}2.1years$, Height : $172.3{\pm}4.0cm$, Weight : $69.2{\pm}4.7kg$) were recruited and instructed to perform drop-landing from 45 cm height and countermovement-jump from 45 cm to 20 cm height. The landing phase was taken as the time between initial contact and peak knee flexion. A motion-capture system consisting of eight infra-red cameras was employed to collect kinematics data at a sampling rate of 200 Hz and a force-plate was used to collect GRF data at a sampling rate of 2000 Hz. Paired t-test was performed to determine the difference in kinematics and kinetics variables between each task. During the countermovement-jump task, all of lower extremity joint ROM and the hip joint eccentric moment were decreased and the ankle joint plantarflexion moment was increased than drop-landing task. In the eccentric work during countermovement-jump task, the ankle joint displayed greater while knee and hip joint showed lesser than drop-landing. Therefore, the knee joint acted as the key energy dissipater during drop-landing while the ankle joint contributed the most energy dissipation during countermovement-jump. Our findings collectively indicated that different energy dissipation strategies were adopted for drop-landing and countermovement-jump.

The Effect of Transient Eccentric Propeller Forces on Shaft Behavior Measured Using the Strain Gauge Method During Starboard Turning of a 4,700 DWT Ship (스트레인 게이지법을 이용한 4,700 DWT 선박의 우현 전타시 프로펠러 편심추력이 축 거동에 미치는 영향 연구)

  • Lee, Jae-ung;Kim, Hong-Ryeol;Rim, Geung-Su
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.4
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    • pp.482-488
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    • 2018
  • Generally, after stern tube bearing shows a significant increase in local load due to propeller load, which increases the potential adverse effects of bearing failure. To prevent this, research on regarding shaft alignment has been carried out with a focus on reducing the relative slope between the shaft and support bearing(s) under quasi-static conditions. However, for a more detailed evaluation of a shafting system, it is necessary to consider dynamic conditions. In this context, the results revealed that eccentric propeller force under transient conditions such as a rapid rudder turn at NCR, lead to fluid-induced instability and imbalanced vibration in the stern tube. In addition, compared with NCR condition, it has been confirmed that eccentric propeller forces given a rapid rudder starboard turn can lift a shaft from the stern tube bearing in the stern tube, contributes to load relief for the stern tube bearing.

The Effect of Ginseng on Muscle Injury and Inflammation

  • Alvarez A.I.;Oliveira A. C. Cabral de;Perez A.C.;Vila L.;Ferrando A.;Prieto J.G.
    • Proceedings of the Ginseng society Conference
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    • 2002.10a
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    • pp.159-175
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    • 2002
  • The effect of Panax ginseng administration in muscle inflammatory process induced after eccentric exercise, that causes myofibrillar disruption, was studied. Changes in lipid peroxidation, inflammation, glycogen levels in muscle and release of myocellular proteins to blood were measured. The analyses were performed immediately after eccentric exercise and over week since this period are necessary for the muscle damage-repair cycle. The ginseng extract $(100\;mg\;kg^{-1})$ was orally administered to rats for three months, before the eccentric exercise performance. The results showed the protective role of ginseng against skeletal muscle damage. This effect could be associated with their membrane stabilising capacity since creatine kinase (CK) activity was significantly decreased 96 h post-exercise from $523{\pm}70\;to\;381{\pm}53$ and 120 h post-exercise from $443{\pm}85\;to\;327{\pm}75$ in treated animals. ${\beta}-glucuronidase$ activity, as indicator of inflammation, showed a significant reduction of about $15-25\%$ in soleus, vastus and triceps in these post-exercise times. The lipid peroxidation, measured by malondyaldehyde levels, was significantly decreased in the 24 h postexercise period in soleus and vastus intermedius muscles and on the recovery period. Finally ginseng administration reduced significantly the decrease of the glycogen levels immediately after exercise and when the regenerative process took place (72-168 h post exercise). Collectively, the results have showed that ginseng did not inhibit the vital inflammatory response process associated with the muscle damage-repair cycle but presumably ameliorate the injury.

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The Immediate Effects of Hamstring Eccentric Exercise and Static Stretching on Trunk Forward Bending (즉각적인 뒤넙다리근 편심성 운동과 정적 스트레칭이 몸통 전방 굽힘에 미치는 영향)

  • Kim, Tae-eun;Choi, Bo-ram
    • Physical Therapy Korea
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    • v.26 no.3
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    • pp.32-41
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    • 2019
  • Background: Limitations in hip flexion caused by tight hamstrings lead to excessive lumbar flexion and low back pain. Accordingly, many studies have examined how to stretch the hamstring muscle. However, no study has focused on the effect of hamstring eccentric exercise for tight hamstrings on trunk forward bending. Objects: We compared the short-term effect of hamstring eccentric exercise (HEE) and hamstring static stretching (HSS) on trunk forward bending in individuals with tight hamstrings. Methods: Thirty individuals with tight hamstrings participated in the study. The subjects were randomly allocated to either a HEE or HSS group. To determine whether the hamstrings were tight, the active knee extension (AKE) test was performed, and the degree of hip flexion was measured. To assess trunk forward bending, subjects performed the fingertip to floor (FTF) and modified modified Schober tests, and the degree of trunk forward bending was measured using an inclinometer. We used paired t-tests to compare the values before and after exercise in each group and independent t-tests to compare the two groups on various measures Results: The FTF test results were improved significantly after the exercise in both groups, and AKE for both legs increased significantly in both groups. There was no significant difference in the hip angles, mmS test results, or degree of trunk forward bending between groups after the exercise. No test results differed significantly between the two groups at baseline or after the exercise. Both groups increased hamstring flexibility and trunk forward bending. Conclusion: HSS and the HEE groups increased hamstring flexibility and trunk forward bending. However, HEE has additional benefits, such as injury prevention and muscle strengthening.

Seismic behavior of non-seismically designed eccentric reinforced concrete beam-column joints

  • Liu, Ying;Wong, Simon H.F.;Zhang, Hexin;Kuang, J.S.;Lee, Pokman;Kwong, Winghei
    • Earthquakes and Structures
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    • v.21 no.6
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    • pp.613-625
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    • 2021
  • Non-seismically designed eccentric reinforced concrete beam-column joints were extensively used in existing reinforced concrete frame buildings, which were found to be vulnerable to seismic action in many incidences. To provide a fundamental understanding of the seismic performance and failure mechanism of the joints, three 2/3-scale exterior beam-column joints with non-seismically designed details were cast and tested under reversed cyclic loads simulating earthquake excitation. In this investigation, particular emphasis was given on the effects of the eccentricity between the centerlines of the beam and the column. It is shown that the eccentricity had significant effects on the damage characteristics, shear strength, and displacement ductility of the specimens. In addition, shear deformation and the strain of joint hoops were found to concentrate on the eccentric face of the joint. The results demonstrated that the specimen with an eccentricity of 1/4 column width failed in a brittle manner with premature joint shear failure, while the other specimens with less or no eccentricity failed in a ductile manner with joint shear failure after beam flexural yielding. Test results are compared with those predicted by three seismic design codes and two non-seismic design codes. In general, the codes do not accurately predict the shear strength of the eccentric joints with non-seismic details.

Physiotherapy Approaches for Chronic Subacromial Impingement Syndrome : Comparison of Effects of Eccentric Training and General Exercise (만성 봉우리 밑 충돌증후군을 위한 물리치료적 접근법 : 편심성 훈련과 일반적 운동의 효과 비교)

  • Choo, Yeon-Ki;Bae, Won-Sik;Kim, In-Seob
    • Journal of The Korean Society of Integrative Medicine
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    • v.10 no.1
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    • pp.61-72
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    • 2022
  • Purpose : This study was to verify the effect of eccentric training and suggest a specific application method by comparing the effects of acromohumeral distance (AHD), supraspinatus tendon thicknees (STT), pain intensity and functional performance after MWM and eccentric training (MWM-ET) or general exercise (MWM-GE) in chronic subacromial impingement syndrome (SAIS) patients. Methods : A total of 55 participants were randomly assigned to each group, and according to the intervention method, "MWM-ET group (n=28)" vs. "MWM-GE group (n=27)" was divided into two groups. AHD, STT, pain intensity, and functional performance were measured before intervention, and both groups were re-measured 3 times a week after 6 weeks of intervention in the same way. Results : The AHD was significantly increased in MWM-ET group compared to MWM-GE group. No significant difference was observed between the groups in the STT, but Pain intensity was significantly lower in MWM-ET group than in MWM-GE group, and functional performance was significantly increased in MWM-ET group compared to MWM-GE group. Conclusion : As a result of MWM-ET intervention that further increases AHD compared to MGE, it can be clinically presented as a more effective intervention method for faster recovery from injury due to pain reduction and smooth return to daily life due to improved functional performance.

Wave load resistance of high strength concrete slender column subjected to eccentric compression

  • Jayakumar, M.;Rangan, B.V.
    • Structural Engineering and Mechanics
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    • v.50 no.3
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    • pp.287-304
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    • 2014
  • A computer based iterative numerical procedure has been developed to analyse reinforced high strength concrete columns subjected to horizontal wave loads and eccentric vertical load by taking the material, geometrical and wave load non-linearity into account. The behaviour of the column has been assumed, to be represented by Moment-Thrust-Curvature relationship of the column cross-section. The formulated computer program predicts horizontal load versus deflection behaviour of a column up to failure. The developed numerical model has been applied to analyse several column specimens of various slenderness, structural properties and axial load ratios, tested by other researchers. The predicted values are having a better agreement with experimental results. A simplified user friendly hydrodynamic load model has been developed based on Morison equation supplemented with a wave slap term to predict the high frequency non-linear impulsive hydrodynamic loads arising from steep waves, known as ringing loads. A computer program has been formulated based on the model to obtain the wave loads and non-dimensional wave load coefficients for all discretised nodes, along the length of column from instantaneous free water surface to bottom of the column at mud level. The columns of same size and material properties but having different slenderness ratio are analysed by the developed numerical procedure for the simulated wave loads under various vertical thrust. This paper discusses the results obtained in detail and effect of slenderness in resisting wave loads under various vertical thrust.

Experimental study on long-term behavior of RC columns subjected to sustained eccentric load

  • Kim, Chang-Soo;Gong, Yu;Zhang, Xin;Hwang, Hyeon-Jong
    • Advances in concrete construction
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    • v.9 no.3
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    • pp.289-299
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    • 2020
  • To investigate the long-term behavior of eccentrically loaded RC columns, which are more realistic in practice than concentrically loaded RC columns, long-term eccentric loading tests were conducted for 10 RC columns. Test parameters included concrete compressive strength, reinforcement ratio, bar yield strength, eccentricity ratio, slenderness ratio, and loading pattern. Test results showed that the strain and curvature of the columns increased with time, and concrete forces were gradually transferred to longitudinal bars due to the creep and shrinkage of concrete. The long-term behavior of the columns varied with the test parameters, and long-term effects were more pronounced in the case of using the lower strength concrete, lower strength steel, lower bar ratio, fewer loading-step, higher eccentricity ratio, and higher slenderness ratio. However, in all the columns, no longitudinal bars were yielded under service loads at the final measuring day. Meanwhile, the numerical analysis modeling using the ultimate creep coefficient and ultimate shrinkage strain measured from cylinder tests gave quite good predictions for the behavior of the columns.

Nonlinear Rotating Flows in Eccentric Cylinders (편심환내의 비선형 회전 유동)

  • Sim, U-Geon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.1 s.173
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    • pp.16-28
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    • 2000
  • The steady rotating flows in eccentric annulus has been studied by a numerical method based on the spectral collocation method. The inner cylinder has a constant angular velocity while the outer on e is stationary. Flow between eccentric cylinders is of considerable technical importance as it occurs in journal bearings. In the present work, the governing equations for laminar flow are expressed as Navier-Stokes equations, including the non-linear convection terms. The solutions were utilized i, estimate the effects of the nonlinear terms on the load acting on the rotating cylinder. Based on the half and the full Sommerfeld methods, the load on the rotating cylinder is evaluated with eccentricity, by integrating the pressure and skin friction around the cylinder. The attitude angle and Sommerfeld reciprocal are calculated from the load. Also, the torque on the rotating inner cylinder was calculated. considering the skin friction. The attitude angle and Sommerfeld reciprocal are decreased with eccentricity. Viscous damping coefficient due to the skin friction becomes larger with decreasing the annular space. It is found the non-linear effects of the convection terms on the flow and the load are important. especially on the attitude angle, for relatively wide annular configurations however, the effects on those are minor for very narrow annular ones.

Analysis of Muscle Activities of Lower Extremity in Jumping Pattern (점프유형에 따른 하지의 근 활동 형태연구(근전도 데이터 표준화 방법을 중심으로))

  • Lee, Sung-Cheol;Hwang, In-Seong;Cho, Young-Jae;Kim, Sun-Jung
    • Korean Journal of Applied Biomechanics
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    • v.15 no.2
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    • pp.155-165
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    • 2005
  • The purpose of this study was to compare the muscle activities of Double Legged Jump (DLJ) and Single Legged Jump (SLJ) by the normalization of muscle activity. Eight college students without the lower extremity injuries were selected as subjects for collecting EMG data of vastus medialis and gastrocnemius. The entire section of motion was established as eccentric and concentric contractions, and each of the contractions was divided into three sections with equal timing intervals, which becomes a total of 6 phases. The EMG data of each phase was integrated and normalized. The muscle activities of the vastus medialis for both eccentric and concentric contractions were significantly different between DLJ and SLJ(p<.05). The increase in overall muscle activity of SLJ was 33.6%. Approximately, there was an increase of 25.9% in eccentric contraction and 40% in concentric contraction. Moreover, the data of the muscle activity of gastrocnemius was similar to the data of the muscle activity of vastus medialis. In conclusion, this research suggests muscle activity of a certain motion can be normalized for an analysis of another motion.