• Journal of Life Science
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• v.33 no.3
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• pp.242-251
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• 2023

The purpose of this study was to investigate the effects of 8-week β-hydroxybutyrate (β-HB) administration with and without endurance exercise training on endurance exercise performance and skeletal muscle protein synthesis and degradation using a mouse model. Forty-eight male wild-type ICR mice (8 weeks old) were randomly divided into four groups: sedentary control (Sed+Con), (Sed+Con), sedentary β-HB (Sed+β-HB), exercise control (Exe+Con), and exercise β-HB (Exe+β-HB). β-HB was dissolved in PBS (150 mg/ml) and injected subcutaneously daily (250 mg/kg) for 8 weeks. Mice performed 5 days/week of a 20 min treadmill running exercise for 8 weeks. The running exercise was carried out at a speed of 10 m/min at a 10° incline for 5 min, and then the speed was increased by 1 m/min for every 1 min of the remaining 15 min. Following 8 weeks of treatments, visceral fat mass and skeletal muscle mass, blood parameters, and the markers for autophagy and protein synthesis were analyzed. The data were analyzed with one-way ANOVA (p<0.05) using the SPSS 21 program. Eight weeks of Exe+β-HB treatment significantly lowered blood lactate levels compared with the other three groups (Sed+Con, Sed+β-HB, and Exe+β-HB) Exe+β-HB) (p<0.05). Eight weeks of Exe+β-HB significantly increased maximal running time (time to exhaustion) compared with the Sed+Con and Exe+Con groups (p<0.05). Eight weeks of β-HB administration significantly decreased autophagy flux and autophagy-related proteins in the skeletal muscle of mice (p<0.05). Conversely, the combined treatment of β-HB and endurance exercise training increased protein synthesis (mTOR signaling and translation) (p<0.05). The 8-week β-HB treatment and endurance exercise training had synergistic effects on the increase in endurance performance, increase in protein synthesis, and decrease in protein degradation in the skeletal muscle of mice.

• Journal of Life Science
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• v.23 no.1
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• pp.116-124
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• 2013

The aim was to examine resistance exercise-related genes after 8 weeks of resistance training. Thirty-two male Sprague-Dawley rats were divided into four groups: 4 weeks sedentary (4 wks CON, n=8), 8 weeks sedentary (8 wks CON, n=8), 4 weeks exercise training (4 wks REG, n=8), and 8 weeks exercise training (8 wks REG, n=8). The rats were trained to climb a 1-m vertical incline (85-degree), with weights secured to their tails. They climbed 10 times, 3 days per week, for 8 consecutive weeks. Skeletal muscle was taken from the flexor halucis longus after the exercise training. After separating the total RNA, large-scale gene expression was investigated by beadarray (Illumina RatRef-12 Expression BeadChip) analysis, and qPCR was used to inspect the beadarray data and to analyze the RNA quantitatively. The detection p-value for the genes was p<0.01, the M-value {M=$log_2$(condition)-$log_2$(reference)} was >1.0, and the DiffScore was >20. In total, the expression of 30 genes significantly increased 4 weeks after the exercise training, and the expression of six genes decreased. At 8 weeks, the expression of five genes significantly increased and that of 12 decreased. Several genes are potentially involved in resistance exercise and muscle hypertrophy, including 1) regulation of cell growth (IGFBP1, PLA2G2A, OKL38); 2) myogenesis (CSRP3); 3) tissue regeneration and muscle development (MUSTN1, MYBPH); 4) hypertrophy (CYR61, ATF3, NR4A3); and 5) glucose metabolism (G6PC, PCK1). These results may help to explain previously reported physiological changes of the skeletal muscle and suggest new avenues for further investigation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.590-599
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• 2009

In this paper, a method of modeling seat belts on crew seat during dynamic seat testing was studied. The body segments of the occupant were modeled with joints. The joints consisted with various stiffnesses, dampings, and frictions. Three types of seat belt restraint systems were investigated. The analysis for on the injury assessment of helicopter's crew under drop impact was conducted. The effectiveness of the seat belt system for crashworthiness and safety was evaluated. As the results of impact analysis, head, neck and spine of the crew can be easily damaged in the vertical direction more than the longitudinal direction. Based on the verified model, behavior of human body was studied with three-point restraint systems. The displacement and injury level of the 12-point restraint system was the smallest.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.764-776
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• 2007

On the human-rifle system, the human body is affected by the firing impact. The firing impact will reduce the firing accuracy and change the initial shooting posture. Therefore the study of biomechanical characteristics using human-rifle modeling and numerical investigation is needed. The musculoskeletal model is developed by finite element method using beam and spar elements. In this study structural analysis has been performed in order to investigate the human body impact by firing of 5.56mm small caliber machine gun. The firing experiments with the standing shooting postures were performed to verify analytical results. The result if this study shows analytical displacements of the human-rifle system and experimental displacements of the real firing. As the results, the analytical displacement and stress of human body are presented.

• Journal of Biosystems Engineering
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• v.35 no.3
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• pp.206-213
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• 2010

The purpose of this study is to analyze musculoskeletal injuries in combine harvesting operation using a digital human model. In order to analyze problems in combine harvesting operation, the operations were broken into 5 work processes and then we preformed ergonomic and biomechanical analyses such as RULA test, Comfort Assessment and joint kinetic analysis for the each process. As a result, there was a clear need to change the combine operating environment, as the RULA score ranged from 4 to 7. In addition, we could find two major musculoskeletal injury factors which are the standing posture with upperbody forward tilting and inappropriate location of operating levers.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.611-613
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• 1998

A structure of musculotendon model with a fatigue profile is investigated. The Hill-type musculotendon model can predicts the decline in muscle force for a given fatigue profile. It consists of nonlinear activation and contraction dynamics based on the physiological concepts. It is normalized for generalization to deal with the various muscles. Muscle force generated by continuous tetanic electrical monophasic pulsewidth modulation stimulation is decreased in time. A fatigue profile is expressed by a function of intramuscular acidification and applied to the relationship between muscle force and shortening velocity in contraction dynamics. The results of computer simulation are well matched with data in a literature which are isometrically performed for knee extension muscles. Also change in optimal fiber length has an effect only on muscle time, constant not on the steady-state tetanic force.

• Proceedings of the ESK Conference
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• 1997.10a
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• pp.23-30
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• 1997

근골격계 질환은 부적절한 작업 자세, 중량물의 무리한 취급, 과도한 작업 부하 등과 같은 작업 환경 에서 기인한다. 현장의 대부분의 공구사용작업에 있어서, 쪼그려앉아서 작업하는 경우가 매우 빈번하게 발생한다. 본 연구에서는 쪼그려 앉은자세에서 사용하는 공구를 설계하는데 필요 요소인 악력의 최대치 를 조사하는 것을 목적으로 한다. 23세-29세의 남자 8명을 피실험자로 실험하였다. 실험모델로는 쪼그려 앉기에서 1) 0 .deg. 외전된 어깨와 정위치의 손목에서 어깨 굴곡이 180 .deg. , 135 .deg., 90 .deg. 와 45 .deg. 의 조합된 자세에서의 악력, 2) 0 .deg. 외전된 어깨와 정위치의 손목에서 팔꿈치 굴곡이 135 .deg. , 90 .deg. 와 45 .deg. 조합된 자세에서의 악력을 조사하였다. 조사결과 쪼그려 앉은 자세에서 어깨굴곡이 45 .deg. 인 자세에서 최대의 악력이 발휘되는 것으로 나타났으며, 인체부위 중에서 손너비, 손목둘레, 팔길이, 손두께, 팔꿈치-손목까지의 길이 등이 쪼그려 앉은자세와 깊은 상관관계가 있는 것으로 나타났다.

• The Korean Journal of Zoology
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• v.35 no.3
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• pp.287-294
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• 1992

배양 중의 골격근 세포는 증식을 거쳐 세포융합을 통해 다핵세포로 분화되므로 세포분화의 연구에 좋은 모델로서 이용되고 있다. 이전 실험에서 근원세포 융합을 억제하는 단일클론항체(MII-3J31)가 제작되었으며(Kim et al., 1992)이 항체에 대한 항원은 분자량이 약 35 kDa인 세포막 단백질로 추정되었다. 본 실험에서는 13일 계배와 성체의 근섬유 mRNA에서 CDNA라이브러리를 제작하여 근원세포 분화에 특이적으로 나타나는 유전자를 추적하였다. 근원세포 융합에 관여하는 단백질에 대한 CDNA는 계배 13일 째의 근원세포 CDNA라이브러리에서 단일클론항체를 사용한 immunoscreening 방법을 이용하여 확인하였다. 이 CDNA의 크기는 약 1.5 kb였다. 한편 13일 계배와성체 근섬유 CDNA 라이브러 리를 이용하여 13일 계배에만 특이하게 유전자 발현 이 일어 나고 성체에서는 나타나지 않는 약 0.8 kb의 CDNA플 찾았다.

• Journal of Biomedical Engineering Research
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• v.22 no.2
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• pp.151-156
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• 2001

A computer model of the musculoskelotal system that provides accurate prediction of muscle force and body movement trom the stimulation input is desired for the effective control system design in FES. This paper aims to investigate the fundamental properties of the gradual muscle force potentiation that was not included in the previous muscle models, for future development of a model that provides vetter prediction of FES-induced muscle force and body movement. Specifically, hou the muscle length was investigated. The experimental results showed that both the force increment ratio and the time-to-peak during electrical stimulation decreased with stimulatino frequency. When the muscle potentiation state was saturated by preceding stimulation. the force did not increase any more during additive stimulation. Muscle length significantly affected the force potentiation in such a way that the force increment ratio decreased with muscle length. A new model of the muscle potentiation based on these results is desired in the future.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1243-1248
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• 2011

The purposes of this study were to develop a dynamic model of a human and to investigate the effect of a walker on an elderly subject's motions, such as sit-to-stand (STS) motion and normal gait, by using this model. A human model consisting of 15 segments and 14 joints was developed, embedded in $RecurDyn^{TM}$, and connected through a Simulink$^{(R)}$ interface with collected motion data. The model was validated by comparisons between joint kinematic results from inverse dynamics (Matlab$^{(R)}$-based in-house program) and from $RecurDyn^{TM}$ simulation during walking. The results indicate that the elderly walker induced a longer movement time in walking, such that the speed of joint flexion/extension was slower than that during a normal gait. The results showed that the muscle activities of parts of the ankle and hamstring were altered by use of the elderly walker. The technique used in this study could be very helpful in applications to biomechanical fields.