股関節脱臼骨折及び大腿骨骨幹部骨折は，転落や交通外傷などの高エネルギー外傷が原因となるものが多い．今回我々は中に受傷した下肢外傷の2例を経験したので報告する．【症例1】37歳，男性．でジャンプした際に着地に失敗し受傷．単純X線にて右大腿骨骨幹部骨折を認め，受傷5日目に髄内釘による骨接合術を行った．【症例2】39歳，男性．中にバランスを崩して転倒し受傷．単純X線にて左股関節脱臼骨折を認め，静脈麻酔下に徒手整復を行った．整復後の単純CTでは骨頭窩付近と臼蓋後壁に骨折を認めたが，保存的に加療を行った．

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This paper describes the propulsion mechanism of a skateboard. We observed the behavior of a rider on a skateboard and built experimental apparatuses. Further we analyze the characteristic by using a two dimensional analytical model. Comparing experimental and analytical results we show that primary propulsion of a skateboard is given by twisting motion of a rider. Propulsion is influenced considerably by the phase difference between twisting motion and tilting the front and rear wheel axles, that is, torque acting on a skateboard and angle of the two axles.

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腓骨が脛骨後方に転移し脛骨後面に固定されるBosworth型足関節脱臼骨折の1例を経験したので報告する．症例は27歳男性．原付バイクで走行中に大型トラックと接触しバイクに左足を巻き込まれる形で転倒し受傷．近医にて非観血的脱臼整復困難であり，シーネ固定されて当院搬送となった．当院にて単純X線で左足関脱臼骨折を認め，CTにて腓骨近位骨片が腓骨切痕から後方に脱臼しておりBosworth型脱臼骨折と診断し，同日観血的整復固定術を行った．Bosworth型脱臼骨折は非観血的整復が困難であるため，受傷後可及的早期に観血的整復固定術が必要となる．本骨折は単純X線側面像で距骨が後方脱臼しているにも関わらず，腓骨骨片間の解離が少ないという特徴がある．この特徴的X線所見を知っておくことが早期診断に有用である．また，本骨折を疑った場合にはCT精査を追加することでより正確な診断へとつながる．

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The skateboard has the feature that it weigh light, is easy to carry and its width is very narrow. In order to develop a portable mobile robot based on the electric skateboard, authors analyzed the steering mechanism of skateboard. The mathematical relationship between the turning radius and the center of gravity of the load was derived, and was verified by experiments of the real electric skateboard.

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The skateboard has the feature; easily carriable light weight, and the narrow width to path the movement. In order to develop a portable mobile robot based on the electric skateboard, authors describe the relationship between the lateral motion of the C.O.G. and steering angle to control the driving path. Authors designed the lateral motion mechanism of the load to change the C.O.G..

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アクションスポーツはエクストリームスポーツとも呼ばれ，速度や高さ，派手さ，危険さなどの過激な要素を持った，離れ業を特徴とするスポーツの総称である．スノーボードハーフパイプやビッグエアはオリンピック種目として採用され，

も選考中である．本研究ではハーフパイプ，ビッグエアランプでのなどの滑走を，複数のGPS付き慣性センサで動作計測および，時系列データ分析にもとづく，種目・技能レベルの判定や，段階的トレーニング指針の提案例を報告する．

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The skateboard has the feature; easily carriable light weight, and the narrow width to path the movement. In order to develop a portable mobile robot based on the electric skateboard, authors describe the relationship between the lateral motion of the C.O.G. and steering angle to control the driving path. Authors manufactured the lateral motion mechanism of the load to change the C.O.G and experimented with it.

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This paper describes the experimental results and the numerical results to investigate the mechanism of production of propulsion force that provides the motion of skateboard. Consequently, it is clarified that turnings of the human's body and motions of the tilt angle of wheels produce the propulsion. The best phase difference between the turning motion and tilt angle of wheels are also clarified to production of propulsion force.

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This paper aims to clarify the development process of a public skateboarding park in Himeji city. In 1999, the delinquent behavior of youths became a social problem in Himeji city, and the youths would often gather at a spot around Himeji station. Since skateboarding-on and around the central shopping street-was also viewed as a problem, the police would reprimand the skateboarders. A young woman "A" hoped for a solution for the conflict between the skateboarders and the police. She began a signature campaign on the street for the development of a skateboarding park. A group of high school students and several skateboarders joined her movement; they established a group named "sports park-wo-tukuroukai" and made a petition with over 10,000 signatures to the Himeji city council through an alderperson of the Communist Party. Initially, the council rejected this petition; however, a Diet member of the Liberal Democratic Party supported the "sports park-wo-tukuroukai" in order to win the Lower House election. Subsequently, the council considered the petition. At the same time, a "kitaizoku-regulation" was placed by the city executives. This regulation aimed to put an end to the delinquent behavior of the youths around Himeji station. Since the council required the executives to finance the skateboarding park, this regulation was accepted. The city executives agreed to this request, and both the regulation and the budgeting of the park were accepted by the council. In 2001, the municipal administration set up a skateboarding park in the public area reserved for the construction of the hall within a duration of two years. As is evident from above, the youths' petition was used as a political tactic. However, at the moment, the skateboarding park still exists in this place because the public hall construction was terminated and the plan was rejected by the present mayor, owing to the financial crisis faced by the city. In the meantime, the skateboarding park is being utilized by many people, and now, it has become one of the important places for skateboarders in Himeji city. It is not exactly known how long such a situation will persist. Well, we could say that the youths' hope led to the establishment of the skateboarders' whereabouts in Himeji city.

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This study focuses on the mechanics of skateboarding. Skateboard has become so popular that it has been officially certified at the 2020 Tokyo Olympics. There are many “tricks” in skateboarding. However, the tricks are acquired by the riders empirically. Its mechanical principle and conditions to succeed have not been clarified theoretically yet. In the present study, the mechanical principle and conditions to succeed of “Ollie”, which is one of the basic tricks, were clarified theoretically. For this purpose, the simulation model of skateboarding based on the multibody dynamics analysis was constructed. The motion of the rider was acquired by using a motion capture system. By inputting the acquired motions of the feet, Ollie was reproduced in the simulation. In addition, a parameter study was conducted to investigate the conditions to succeed. Regarding the principle, it was clarified that the upward momentum given to the skateboard by the kicking down of the right foot is preserved, and it is realized by switching the rotation direction of the skateboard with the left foot. In terms of conditions, it was found that more technical control is required when the kick angle is large, that the track mounting position has little effect, and that there are conditions in the movement of the left and right feet.

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