行走技巧 – 理論學習篇

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行走技巧 – 理論學習篇

文章 #1  未閱讀文章PoP » 2007-05-21 17:40

本文是從科學角度分析平衡技巧背後的物理法則:重心栘動
文件狀態:初稿


能用兩腿走路的不一定懂得行走
能用兩腿平穩行走的不一定懂得平衡技巧背後的科學原理!



運動生物力學 (資料來源:http://203.72.198.245/web/Content.asp?ID=4301)

背景資料
  • 運動生物力學的發展早在15世紀﹐義大利科學家L.達‧芬奇就對人體運動發生了濃厚的興趣。他用人的屍體研究解剖學﹐並提出了人體服從於力學定律的觀點。
  • 17世紀﹐義大利醫生A.博雷利發表了運用槓桿定律測定人體重心位置的實驗材料。他還把人體和動物的位移運動進行了分類﹐
  • 19世紀﹐德國生理學家W.韋貝爾和E.H.韋貝爾兄弟發表了對人的基本位移形式──走的研究。俄國的解剖學家列斯加夫特﹐..在探討人體運動器官的形態和機能之間的關係方面作了大量工作﹐寫了《理論解剖學基礎》和《人體運動理論》等著作。
萌芽時期的運動生物力學基本上沒有和解剖學分開﹐多是應用屍體解剖材料分析人體運動﹐闡述動作原理。

照相機﹑電影機的發明﹐對於研究體育動作起了巨大作用。
  • 20世紀60年代以後﹐由於電子工業的發展﹐為運動生物力學的研究提供了新的手段。目前﹐美國﹑德意志民主共和國﹑ 德意志聯邦共和國﹑蘇聯﹑瑞士﹑芬蘭﹑捷克斯洛伐克﹑日本和加拿大等國家都十分重視運動生物力學的研究工作﹐許多國家體育院校都開設運動生物力學課程。
近 20年來﹐運動生物力學的國際學術交流活動頻繁。

運動生物力學在中國還相當年輕。民國時期﹐一些體育工作者曾作過這方面的理論建設工作﹐一些師範院校體育系科開設過“人體機動學”課。吳蘊瑞曾為師範院校的體育系科講授過“運動學”。
  • 1958年以後﹐中國陸續在體育院系設運動生物力學課﹐國家體委體育科學研究所也成立了運動生物力學研究室。
  • 1976年以來 ﹐中國體育科學工作者又研製了游泳速度遙測儀﹑激光計時儀﹑標槍光電測速儀﹑三維測力儀和連續閃光機等一批測試儀器﹐為定量研究運動生物力學創造了條件。
  • 1979~1980年間﹐中華全國體育總會邀請當時的國際生物力學學會主席﹑美國賓夕法尼亞大學生物力學實驗室主任R.C.納爾遜博士及日本﹑德意志聯邦共和國的生物力學專家來華講學。
  • 1980年12月﹐中國體育科學學會宣告成立﹐同時成立了中國運動生物力學學會﹐並舉行了學術報告會。
學術分類
  1. 人體結構材料力學﹕運動生物力學把人體骨骼看作支撐器官﹐研究它的力學性能及安全強度﹔把兩骨通過關節的連接看作是運動偶﹐把依次連接起來的運動偶看作是運動鏈﹔把骨骼﹑關節和肌肉構成的整體視為骨槓桿系統﹔分析在肌肉的拉力下骨骼圍繞關節所進行的轉動﹔探討肌肉在運動鏈中的各種作用。同時也涉及呼吸﹑血液循環等器官的力學特性。
  2. 人體靜力學﹕主要是研究人體從事體育活動時的平衡問題。運動生物力學把人體看作是組合物體﹐分別由頭﹑軀幹﹑上臂﹑前臂﹑手﹑大腿﹑小腿和足這些環節組成。用一定的方法確定人體各環節重心﹐並求得人體重心﹐一般來說﹐人體重心的水平位置在兩臂下垂的對稱站立姿勢中位於第 1至第 5椎之間﹐略高於髖關節的額狀軸﹔它的左右位置﹐在接近人體正中面內﹐稍偏向右﹔它的前後位置﹐在骨和恥骨之間。由於每個人的身體各部分質量大小不一﹐人體重心位置也因人而異。各項運動員的體型不同﹐重心位置也不一樣。人體重心位置不是固定的﹐在呼吸和血液循環的影響下﹐在身體姿勢發生變化的情況下﹐重心位置也隨著發生變化。人體從事平衡運動時﹐根據重心和支點的關係﹐分為支點在重心上方的上支撐平衡和支點在重心下方的下支撐平衡﹔根據人體在外力作用下﹐失去原來平衡位置以後繼續保持平衡的情況﹐分為隨意平衡﹑穩定平衡和不穩定平衡。對下支撐平衡穩度的大小﹐用穩定角及穩定力矩表述。
  3. 人體運動學﹕人體除平衡運動外﹐還有位移運動﹑旋轉運動和複雜的空間運動。這是以人的整體運動的主要特徵進行的分類﹐是相對的。在這相對的分類中﹐多見的是複雜的空間運動。人體運動學是從空間和時間的觀點描述人體的運動﹐探討人體位置的變化和時間的關係﹐求得平動和轉動中的位移﹑時間﹑ 速度和加速度﹐也研究跳躍和投擲的合理角度等問題﹐它抓住運動的外形﹐分析運動的現象和過程(見運動動作的解剖學分析)。
  4. 人體動力學﹕以力學定律為基礎﹐探討力和人體運動的關係。當把人體當做一個力學對象研究其受力情況時﹐將影響人體運動的力分為外力和內力兩類。外力是人體以外別的物體的作用﹐是使人體產生加速度或發生變形的原因﹐它包括人體重力﹑支撐反作用力﹑摩擦力和流體阻力等。內力是人體各部分之間的相互作用﹐只使人體發生變形﹑產生局部加速度﹐它包括組織器官的被動阻力和肌肉拉力等﹐其中肌肉拉力是制約人體運動的主導力。一般﹐人體運動是人體與外界環境之間的相互作用引起的。
最後由 PoP 於 2009-03-04 16:17 編輯,總共編輯了 2 次。
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肌肉力量的物理特性

文章 #2  未閱讀文章PoP » 2007-05-21 18:36

人體運動學 – 解剖學部分 (資料來源:http://203.72.198.245/web/Content.asp?ID=4290)

運動形態學的一個組成部分﹐也是人體運動學的解剖學部分(見運動生物力學)﹐其目的是從人體結構的角度分析運動動作的規律性﹐為學習和提高動作質量提供理論依據

運動動作雖然有多種多樣﹐但從人體結構角度分析﹐它具有一定的規律性。任何動作都是以肌肉收縮為動力﹐牽引骨骼﹐圍繞關節而運動的。骨與關節是運動的被動部分﹐肌肉則是主動部分。肌肉在人體運動中處於重要位置。分析運動動作時﹐其重點為肌肉。因此﹐在進行動作分析之前﹐必須先瞭解肌肉的功能。

肌肉由許多肌纖維構成。在做動作時﹐肌纖維可以縮短﹐也可以被動地伸長﹐還可以處於既不縮短也不伸長的狀態。肌纖維處於縮短狀態時所做的工作叫做克制工作 ﹐這是運動動作中較常見者﹐如三角肌纖維收縮就可使兩臂側平舉。肌纖維處於伸長狀態時所做的工作叫退讓工作﹐在負重的情況下緩慢地屈肘關節﹐使上臂後面之肱三頭肌纖維被拉長時所做的工作﹐就屬此類。做克制工作和退讓工作時﹐肢體是處於運動的狀態﹐所以這種產生運動的工作又稱為動力工作。與此相反的另一種工作為靜力工作﹐即肌纖維長度不變﹐既不縮短也不伸長﹐可是肌肉的緊張程度(張力)增加﹐如兩臂保持側平舉時﹐三角肌纖維長度不變﹐但其張力增加﹐以克服兩臂下垂的重力﹐就屬此類。

每個關節的運動﹐都不是單純地由一塊肌肉來完成﹐而是由一群肌肉完成的。而在這一肌群中各個肌肉所起的作用又不完全一樣﹐其中直接完成動作的肌肉叫原動肌 ﹐與其作用相反的肌肉叫對抗肌。例如屈肘時﹐上臂前面的肱二頭肌﹑肱肌和前臂外側的肱橈肌是屈肘的原動肌﹐而上臂後面的肱三頭肌是屈肘的對抗肌﹐其肌纖維被拉長﹐但保持一定的緊張度﹐使屈肘時的原動肌在收縮過程中免於因動作過猛而受傷。有時在做某個動作時﹐只需一個關節運動﹐要求鄰近的關節固定不動。以便使活動這個關節的肌肉能充分發揮力量。這種使鄰近關節固定不動的肌肉﹐叫固定肌。如用力屈肘時要求肩關節固定﹐所以肩關節周圍的肌肉則稱為固定肌。

在分析運動動作時除了要注意肌肉收縮力以外﹐還要注意重力和摩擦力等。這些力產生於身體外部﹐因而稱為外力。肌肉收縮力產生於身體內部﹐所以稱為內力或肌力。內力和外力往往同時作用於人體﹐其作用的方向可以相同﹐也可以相反。

如果在肢體上兩種力的方向相反﹐肌力大於外力時﹐肢體則朝著與外力相反的方向運動。例如作高抬腿跑時﹐大腿於髖關節處做向上屈的動作﹐其原動肌就是與重力相反的一側的髂腰肌﹑股直肌(圖1 顯示圖片)等﹐若負重蹲起時﹐身體需由蹲位伸直向上﹐這時為了克服槓鈴和身體各部分向下運動﹐則蹲起的原動肌主要為臀大肌﹑股四頭肌和小腿三頭肌(圖2 顯示圖片)﹐ 如果作用於肢體的兩種力的方向一致﹐肢體運動速度則快﹐其原動肌則是位於肢體運動方向同一側的肌群。例如﹐排球運動員在跳起正面扣球時﹐上肢在肩關節處作伸與內收動作﹐其重力也有使上肢向下的作用﹐所以上肢內收和伸的速度要超過重力向下的速度。這時扣球動作的原動肌﹐就是使上臂在肩關節處伸和內收的肌群﹐ 即胸大肌﹑背闊肌和三角肌(圖3 顯示圖片) 等。如果作用於肢體時兩種力的方向相同﹐而肢體運動速度慢於重力﹐則原動肌是位於肢體運動方向相反的一側的肌群。例如在雙槓上做雙臂屈伸慢落下時﹐上臂在肩關節處外展和伸﹐重力也是使上臂在肩關節處外展和伸﹔為了提高訓練效果﹐使身體下落速度小於重力速度﹐原動肌就是位於與肢體運動方向相反的一側﹐即使上臂在肩關節處內收和屈的胸大肌和背闊肌。

瞭解肌肉的工作以後﹐就可著手對運動動作進行解剖學分析。運動動作比較複雜﹐又因有連貫性﹐動作過程較快﹐所以用眼睛觀察往往不易發現問題。若要做確切的分析﹐最好能用電影或錄相將動作記錄下來﹐然後製成連續電影圖片﹐這樣才可以對動作進行詳細的觀察分析。

為了便於分析﹐可將動作劃分成幾個階段。如單槓上的引體向上動作﹐可劃分為懸垂﹑引體向上和還原3個階段等。然後﹐根據圖片描述各階段身體各部分的動作姿勢﹐說明各個階段動作中肢體在關節處的運動方向﹐這樣才能分析出在關節處運動的原動肌。例如﹐引體向上的開始姿勢﹐即懸垂階段﹐上肢伸直﹐懸於單槓上﹐兩手距離與肩同寬﹐手掌面向身體﹐拇指與其他四指相對。引體向上階段﹕上臂在肩關節處伸﹐原動肌為胸大肌﹑大圓肌﹑背闊肌與三角肌後部﹐做動力工作﹔肩胛骨下回旋和內收﹐原動肌為斜方肌﹑菱形肌與胸小肌﹐做動力工作﹔上臂在肘關節處屈﹐其原動肌為肱二頭肌﹑肱肌與肱橈肌﹔橈尺關節保持外旋位置﹔腕關節保持微屈﹐原動肌為屈腕肌群﹐做靜力工作﹔指關節保持微屈﹐原動肌為屈指肌群﹐做靜力工作﹔第一掌指關節﹐保持內收姿勢﹐原動肌為拇指內收肌﹐做靜力工作。還原階段﹕肩關節由伸到屈﹔肩胛骨由下迴旋變為上迴旋﹐內收變為外展﹔橈尺關節﹑腕關節﹑指關節和第一掌指關節保持靜力工作。

除了分析原動肌以外﹐還應分析妨礙動作完成的一些消極因素﹐如重力﹑對抗肌﹑韌帶等。例如﹐在引體向上階段﹐原動肌主要用來克服身體下垂的重力。最後﹐根據分析結果﹐對動作進行總結和討論。從分析可以確認﹐引體向上是發展肩關節伸肌﹑肘關節屈肌和使肩胛骨下迴旋﹑內收的肌群力量的一種簡易的練習。為了進一步發展這些肌肉力量﹐在做動作時可以在身體上增加一定負荷(沙袋槓鈴片等)﹐或加大兩手握槓距離。通過動作分析﹐可以找出動作的積極因素(原動肌)和消極因素(重力﹑對抗的肌力和韌帶阻力等)。在做動作時﹐如能充分利用這些積極因素﹐克服消極因素﹐就可以提高動作質量﹐並可避免發生損傷。
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平衡與重心的力學原理

文章 #3  未閱讀文章PoP » 2007-05-21 19:16

重心的定義 (資料來源:http://www.epsport.idv.tw/epsport/board/show.asp?repno=3535&page=6)
  • 重心為任何物體的平衡點,而且是物體質量與重量平均分配的點。
  • 物體將作用在它身上的力量(包括地心引力)反應在一點上,彷彿所有它的質量都集中在這點上一般。重心不一定在物體的內部。
人體重心的位置
  • 以人體靜止站立時,人體的重心大約在地板量起的身高55%處,大約在肚臍下方約3公分處,而且,人體重心大約在前後的正中央,男人重心比女人高約1至 2%。小孩身體重心比一般成年人高約5%。
  • 手臂與腿部的移動可以改變重心位置約達10公分以上,透過這種重心位置的移動可以改變人體活動時的旋轉狀態,例如跳遠時空中動作的挺身以及落地動作時的身體與雙手下壓與後擺,使得身體在飛程時的身體旋轉產生不同的影響。跳高選手的空中動作改變,可以使得選手增加身體能夠躍過的高度。
  • 其實每一個人的身體重心位置都不同,而不同動作下的重心也會改變
    需要經過計算才能得到真正的重心位置。
重心栘動 (資料來源:http://www.geocities.com/jacquesmak/posture.htm)
  • 人體重心的前後位置取決於骨盆的態勢。如重心位置前移,則骨盆前傾腰部前凸,脊柱的彎曲幅度變大;如重心位置後移,則骨盆直立腰部前凸減小或消失,脊柱姿態顯得挺拔。
  • 重心位置的調整,是人體力學狀態的重大調整。這種調整也是一種能力,要通過相當的、經常性訓練才能提高的。
  • 雙腳打開時,重心會不自覺的前傾,落在的腳的內緣
重心線 (資料來源:http://wushu.ws/redirect.php?tid=223&goto=lastpost)
  • 重心線是將複雜的力學作用概念化的表述方法 (PoP 註解:力學上一般採用力距線 (Force vector) 圖來表達物體栘動的四維空間)
  • 直立运动中的人体由两腿支撑全身的重量,并通过换步移动维持身体的平衡。也就是说要始终以重心线为中轴保持对称与平衡。
  • 由于两腿在运动中支撑全身重量的方式不同,则重心线的位置也有所不同。
  • 当人体双腿并立时,两腿承重均匀,重心线与中心线相吻合。
  • 当人体的双腿承受压力不均时,即成为虚实步时,这时中心线与重心线相分离
    一般来讲我们称那个承受大部分重量的腿为实腿 ,承受少部分重量的腿为虚腿。
  • 按照力学原理,身体重量的重心线若位于两脚间距离偏虚脚约三分之一强的地方,就可以使双足踏地有力 (这个"约三分之一强"准确些可以用"黄金分割法"来度量:即从实脚到虚脚约0、618的地方;从虚脚到实脚约0、382的地方。如果重心线位置超出了这个范围,即重心线位置小于了0、618或者说大于了0、382,就会出现虚腿过虚,实腿倾斜的现象)
  • 当一条腿支撑全部身体的重量时,这时的重心线自然是沿这条承重腿垂直向上。
小結

維持人體身體平衡的重心點
男女各有不同
也因身高各有不同
更會因身體動作姿勢而有所改變
最後由 PoP 於 2007-05-22 00:43 編輯,總共編輯了 1 次。
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重心栘動的六個自由度

文章 #4  未閱讀文章PoP » 2007-05-21 19:35

人體重心栘動特性

  • 三維空間限制物體只能於 X、Y、Z 軸栘動。
  • 在特定的參考點,觀察到的基本栘動模式為:前、後、左、右、上、下,就是所謂的六個自由度(李小龍的截拳道武術基礎就是採用這個理論)。
  • 人體直立時存在穩定的重心這概念是錯誤的!事實上靜止不動時,人體重心會隨著呼吸動作而出現輕微晃動現像。
磨擦力是穩定行走的關鍵

  • 磨擦力是力學中物體間接觸性水平(對應重力線 90 度)栘動的法則。當上文提及的重力線偏離超出三分一時,磨擦力對穩定行走的作用變得明顯。
  • 物體的磨擦系數取決於表面微結構、物料硬度和彈性等物理特性。
  • 實際磨擦力强度取決於磨擦系數、接觸面應力埸和有効接觸面積。
  • 正常行走動作中,有効接觸面積和接觸面應力埸兩項是能夠控制的,而當中數值變化最廣的是有効接觸面積,就是穩定行走的要點。
行走的基礎 – 足踝活動

  • 套用在單一開節上,六個自由度的栘動因應關節、肌肉結構而受到限制。
  • 突破單一開節限制的途徑,就是運用接近關節的肢體協調來減少受到限制的範圍(通常是同時運用遠離關節的身體微調動作補償失去的自由度)。
  • 足踝關節相對膝、髖、肘關節的六個自由度最少(每個關節的自由度不多說,觀察自身關節活動情況就是)。
  • 行走時踝關節栘動配合著地點的傾斜度,儘量將足底緊貼地面、讓接觸地面的面積到達上限。
影嚮行走穩定的裝備選擇
  • 能夠貼近踝關節自由度上限的裝備,依次序遞減為:赤足 -> 軟底短筒鞋 -> 硬底短筒鞋 -> 軟底高筒鞋 -> 硬底高筒鞋
  • 赤足除了沒有外加的自由度限外,亦有整個接觸面的狀況感應優點。這個優點能夠讓人對整個接觸期間進行連續的、微細的調節。
  • 鞋筒高於足踝的鞋,對踝關節做成額外的限制。這一點需要身體其他部份作出額外的補償動作。
  • 鞋底的硬度對有効接觸面積做成額外的限制。這一點要視乎物料特性、坑紋深度和鞋底的幾何設計。
  • 最重要的一點,是對應行程主要的路面地質情況,選擇最適用的鞋。
長時間、穩定、高效率的步行姿勢
(山野活動安全概論 (v0.2),1.2.2 步行方法)

  1. 頭微俯、頸稍微向前,挺胸
    這樣以頸部有效吸收行走時的震盪,也有利觀察三米範圍內的地形環境。
  2. 隨走動節奏水平搖擺肩膊及擺動雙臂
    這樣可以將上身重心保持在脊椎骨中軸範圍內,有利縮短緊急調整重心的反應時間。
  3. 挺腰收腹
    腰部是連接下身、支撐上身重量的位置,是穩定重心的關鍵。
    挺腰是強化左右搖擺、收腹是強化前後搖擺,這樣保証了重心及能量的有效轉移。
  4. 保持膝部彎曲
    這樣是將腳底傳回的反作用力分散到大、小腿肌肉吸收,保護膝蓋軟組織之外、也間接提昇腿部移動速度。
  5. 調整腳踝來配合落點
    這樣腳底和落點間獲得最大接觸面積,增強行走的穩定、減輕腳掌疲勞。
  6. 進行重心轉移
    程序:落腳(touch down)時腳尖向下傾斜、腳趾稍微放鬆
    ---> 接觸地面時腳趾稍為用力向下抓住
    ---> 緊貼是腳前掌接觸地面
    ---> 腳跟緩慢往下落
    ---> 膝部隨腳跟下落緩慢伸展
    ---> 腿完全伸展後運用腰腹肌肉進行重心轉移
    ---> 重心轉到前腳後跨出另一腳
    ---> 另一腳踏上的同時,重心腳往後撐將身體往前推
    ---> 重覆程序
參考文件:靜力學
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文章 #5  未閱讀文章PoP » 2007-05-23 02:47

全文完

版權聲明

part 4 (標題:重心栘動的六個自由度)的文件版權為 Creative Commons-NonCommercial-ShareAlike 3.0,其餘部份版權歸來源所有
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Robot unravels mystery of walking

文章 #6  未閱讀文章PoP » 2007-07-13 14:11

Source: http://news.bbc.co.uk/2/hi/technology/6291746.stm

[right]圖檔[/right]Roboticists are using the lessons of a 1930s human physiologist to build the world's fastest walking robot.

Runbot is a self-learning, dynamic robot, which has been built around the theories of Nikolai Bernstein.

"Getting a robot to walk like a human requires a dynamic machine," said Professor Florentin Woergoetter.

Runbot is a small, biped robot which can move at speeds of more than three leg lengths per second, slightly slower than the fastest walking human.

Bernstein said that animal movement was not under the total control of the brain but rather, "local circuits" did most of the command and control work.

The brain was involved in the process of walking, he said, only when the understood parameters were altered, such as moving from one type of terrain to another, or dealing with uneven surfaces.

The basic walking steps of Runbot, which has been built by scientists co-operating across Europe, are controlled by reflex information received by peripheral sensors on the joints and feet of the robot, as well as an accelerometer which monitors the pitch of the machine.

These sensors pass data on to local neural loops - the equivalent of local circuits - which analyse the information and make adjustments to the gait of the robot in real time.

Information from sensors is constantly created by the interaction of the robot with the terrain so that Runbot can adjust its step if there is a change in the environment.

As the robot takes each step, control circuits ensure that the joints are not overstretched and that the next step begins.

But if the robot encounters an obstacle, or a dramatic change in the terrain, such as a slope, then the higher level functions of the robot - the learning circuitries - are used.

The latest findings of the robot research study are presented in the Public Library of Science Computational Biology journal.

Four other scientists - Poramate Manoonpong, Tao Geng, Tomas Kulvicius and Bernd Porr - are also involved in the project, which has been running for the last four years.

Professor Woergoetter, of the University of Gottingen, in Germany, said: "When Runbot first encounters a slope these low level control circuits 'believe' they can continue to walk up the slope without having to change anything.

"But this is misguided and as a consequence the machine falls backwards. This triggers the other sensors and the highest loop we have built into Runbot - the learning circuitry - and from that experience of falling the machine knows that something needs to be changed."

Dynamic process

He said human walking was a dynamic process.

"About half of the time during a gait cycle we are not doing anything, just falling forward. We are propelling ourselves over and over again - like releasing a spring.

"In a robot, the difficulty lies in releasing the spring-like movement at the right moment in time - calculated in milliseconds - and to get the dampening right so that the robot does not fall forward and crash.

"These parameters are very difficult to handle," he said.

[right]圖檔[/right]Runbot walks in a very different way from robots like Asimo, star of the Honda TV adverts, said Prof Woergoetter.

"They are kinematic walkers - they walk step by step and calculate every single angle, every millisecond.

"That can be handled through engineering but it is very clumsy. No human would walk like that. All these big machines stomp around like robots - we want our robot to walk like a human."

The first step in building Runbot was creating a biomechanical frame that could support passive walking patterns.

Passive walkers can walk down a slope unaided, propelled by gravity and kept upright and moving through the correct mechanical physiology.

Prof Woergoetter said: "Passive walking looks pretty realistic - but that's level one. On top of this we have local circuits, nested neural loops, which operate between the muscles (the joints of the robot) and the spinal cord (the spinal reflex of Runbot)."

He said Runbot learned from its mistakes, much in the same way as a human baby.

"Babies use a lot of their brains to train local circuits but once they are trained they are fairly autonomous.

"Only when it comes to more difficult things - such as a change of terrain - that's when the brain steps in and says 'now we are moving from ice to sand and I have to change something'.

"This is a good model because you are easing the load of control - if your brain had to think all the time about walking, it's doubtful you could have a conversation at the same time."

Nervous system

The principle was first discussed in the human nervous system by Russian physiologist Nikolai Bernstein.

Prof Woergoetter said: "He said it made sense that local agents, local networks, do the basic job, but the brain exerted control whenever necessary."

So using the information from its local circuits Runbot can walk on flat surfaces at speeds of more than three leg lengths per second.

Prof Woergoetter said Runbot was able to learn new walking patterns after only a few trials.

"If walking uphill, the gait becomes shorter, the robot's upper body weight shifts forward," he said.

The key lesson from the study, he said, was that the nested loop design first proposed by Bernstein more than 70 years ago "worked and was efficient".

He said the challenge was now to make Runbot bigger, more adaptive and to better anticipate situations like change of terrain.
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文章 #7  未閱讀文章PoP » 2007-07-13 14:15

Highlights

"About half of the time during a gait cycle we are not doing anything, just falling forward"

Prof Florentin Worgotter

[tab]圖檔
  • Frames 1 - 3: The robot's momentum causes the robot to rise on its standing leg and a motor moves the swinging leg into position
  • Frame 3: The stretch sensor of the swinging leg is activated, which triggers the knee joint to straighten
  • Frames 3-6: The robot falls forward naturally, with no motor functions being used, and catches itself on the next standing leg
  • Frame 6: As the swinging leg touches the ground, the ground contact sensor in the foot triggers the hip extensor and the knee joint of the standing leg and the hip and knee joints of the swinging leg to swap roles
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Energy use 'drove human walking'

文章 #8  未閱讀文章PoP » 2007-07-17 23:01

Source: http://news.bbc.co.uk/2/hi/science/nature/6902379.stm

Humans evolved to walk upright because it uses less energy than travelling on all fours, according to researchers.

A US team compared the energy used by humans and by chimpanzees in walking.

The human bipedal gait is about four times more efficient than chimps getting around on either two or four legs, the researchers found.

Writing in Proceedings of the National Academy of Sciences (PNAS), they say this may explain why we walk bipedally, and some of our anatomical features.

Other research groups have proposed alternative explanations for our two-legged gait.

Some suggest it evolved because early humans needed to reach upwards to collect food or pass it to a mate, while others maintain it predates four-legged locomotion in primates, citing the often upright posture of orangutans as they move across slim branches.

On the treadmill

A study from 1973 found little difference in efficiency between two-legged and four-legged walking in primates, but its conclusions had been disputed because only juvenile chimpanzees were used.

So David Raichlen from the University of Arizona in Tucson and colleagues set up a study in which five adult chimps were trained to use a treadmill, either on two legs or four.

The subjects were fitted with masks to collect exhaled air so that parameters such as oxygen use could be measured. Blobs of white paint on critical parts of the body such as elbows and knees allowed researchers to analyse the gait using video.

The results were compared with four human subjects using the same treadmill.

Generally, the humans were about four times more efficient than the chimps.

Three of the chimps found bipedal walking used more energy than going on all fours. But one of the others showed the opposite pattern; and intriguingly, she was the only chimp to lengthen her stride.

"We were able to tie the energetic cost in chimps to their anatomy," noted Dr Raichlen.

"We were able to show exactly why certain individuals were able to walk bipedally more cheaply than others."

The hypothesis, then, is that early humans began to evolve in a direction which allowed for easy bipedal travel.

David Raichlen suggests that early humans should show adaptations such as a longer leg length, and that there are indications of this in fossils of the genus Australopithecus, such as the famous "Lucy" specimen discovered in Ethiopia in 1974.
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Barefoot running injury concern

文章 #9  未閱讀文章PoP » 2013-05-17 00:54

Source: http://www.bbc.co.uk/news/health-22528387

The trend for barefoot running could lead to injuries in some runners, a small study suggests.

The way you run is more important than whether you wear running shoes or not, say scientists in Taiwan.

The rationale behind barefoot running is to move in a more natural way, with the front of the foot hitting the ground first.

But not all runners manage to adopt this style, putting added strain on muscles, scientific data suggests.

Claims that human feet are naturally designed to run bare on the ground, not in modern cushioned running shoes, have led to many runners trying out barefoot running.

A study, published in Gait & Posture, looked at the effects of different striking patterns for both styles of running, to assess the likely impact on running injuries.

Sports scientists at National Taiwan Normal University tested 12 male runners on a treadmill.

After a warm-up they were assessed while running in one of four ways - barefoot landing heel first, barefoot landing forefoot first, and the same styles while wearing trainers.

Tests were carried out to look at their gait, muscle activity and the likely impact on running injuries.

The scientists found that runners can gain more shock absorption by changing their striking pattern to a forefoot strike, either in shoes or without.

Runners who are used to wearing shoes may, however, be more susceptible to injuries when they run barefoot if they carry on running with the heel hitting the ground first.

Yo Shih and colleagues write: "Habitually shod runners may be subject to injury more easily when they run barefoot and continue to use their heel strike pattern."

Alex Bliss, a sports scientist at the University of Brighton, said the study suggested thatchanging the mechanics of your stride - from heel strike to toe strike - alters the demands placed on the muscles in the calf and shin.

"This would perhaps suggest that foot strike pattern plays a critical role in muscular activation of the lower leg musculature, regardless of footwear or barefoot," he told BBC News.

"However, the study does have limitations in that it employs small subject numbers of [unreported] cardiovascular fitness and training background, and also comprises of running at a single speed of 9km/h [5mph]."
當流赤足蹋澗石,水聲激激風吹衣。
人生如此自可樂,豈必局束為人鞿?
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Ape-like feet 'found in study of museum visitors'

文章 #10  未閱讀文章PoP » 2013-06-01 18:01

Source: http://www.bbc.co.uk/news/science-environment-22728014

Scientists have discovered that about one in thirteen people have flexible ape-like feet.

A team studied the feet of 398 visitors to the Boston Museum of Science.

The results show differences in foot bone structure similar to those seen in fossils of a member of the human lineage from two million years ago.

It is hoped the research, published in the American Journal of Physical Anthropology, will establish how that creature moved.

Apes like the chimpanzee spend a lot of their time in trees, so their flexible feet are essential to grip branches and allow them to move around quickly - but how most of us ended up with more rigid feet remains unclear.

Jeremy DeSilva from Boston University and a colleague asked the museum visitors to walk barefoot and observed how they walked by using a mechanised carpet that was able to analyse several components of the foot.

Floppy foot

Most of us have very rigid feet, helpful for stability, with stiff ligaments holding the bones in the foot together.

When primates lift their heels off the ground, however, they have a floppy foot with nothing holding their bones together.

This is known as a midtarsal breakand is similar to what the Boston team identified in some of their participants.

This makes the middle part of the foot bend more easily as the subject pushes off to propel themselves on to their next step.

Dr DeSilva told BBC News how we might be able to observe whether we have this flexibility: "The best way to see this is if you're walking on the beach and leaving footprints, the middle portion of your footprint would have a big ridge that might show your foot is actually folding in that area."

圖檔
Here A. sediba is compared with a modern human (L) and a chimp (R)

Another way, he added, was to set up a video camera and record yourself walking, to observe the bones responsible for this folding motion.

Most with this flexibility did not realise they had it and there was no observable difference in the speed of their stride.

In addition, Dr DeSilva found that people with a flexible fold in their feet also roll to the inside of their foot as they walk.

The bone structure of a two-million-year old fossil human relative, Australopithecus sediba, suggests it also had this mobility.

"We are using variation in humans today as a model for understanding what this human creature two million years ago was doing," added Prof De Silva.

Tracy Kivell, a palaeoanthropologist from the Max Planck Institute for Evolutionary Anthropology, said: "The research has implications for how we interpret the fossil record and the evolution of these features.

"It's good to understand the normal variation among humans before we go figure out what it means in the fossil record," Dr Kivell told BBC News.
當流赤足蹋澗石,水聲激激風吹衣。
人生如此自可樂,豈必局束為人鞿?
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How do muscles work?

文章 #11  未閱讀文章PoP » 2017-09-08 11:42

Source: http://www.medicalnewstoday.com/articles/319322.php

Muscles move our bodies. To do so, they contract, which then generates movement.

Muscles allow us to consciously move our limbs, jump in the air, and chew our food.

But they are also responsible for many more processes that we cannot actively control, such as keeping our hearts pumping, moving food through our guts, and even making us blush.

Our muscles need signals from our brains and energy from our food to contract and move.

To build new muscles through exercise, we make use of their remarkable ability to repair themselves when damaged.

Contraction gets muscles moving

There are two types of muscle: striated and smooth. The former have regular stripes, or striations, when observed under a microscope. These striations are due to the arrangement of muscle fibers, which form parallel lines.

The muscles that move our body parts are called skeletal muscles, and they are a type of striated muscle. We can actively control these with our brain. Another type of striated muscle are those that keep our hearts pumping, which we are unable to actively control.

Specific molecules within the muscle fibers allow striated muscles to contract rapidly, allowing us to move. The main players in this intricate process are molecules called actin and myosin.

Scientists continue to disagree on what allows actin and myosin work together to make an entire muscle contract. What is known, however, is that this process depends on energy generated from the food that we eat.

The contractions that smooth muscles produce tend to be more gradual than those produced by striated muscle. An example is the slow and controlled movement of food through the digestive system.

Smooth muscles do not have striations and we cannot actively control what they do.

Calcium stimulates contraction

The pathways that regulate contraction in striated and smooth muscles are very different. But they do have one thing in common: calcium is the key molecular messenger in the process.

Striated muscles receive their triggers from the brain via motor neurons. This results in calcium rushing into the muscle, allowing actin and myosin to spring into action.

Smooth muscle cells can be activated by neuronal signaling or by hormones. Both mechanisms lead to a change in calcium levels in the muscle cells. This leads to activation of myosin, and, in turn, muscle contraction.

Some smooth muscles are in a permanent state of contraction, and the muscles that line our blood vessels are in this category. A constant supply of calcium allows these muscles to regulate blood flow. For example, when the muscles that line the blood vessels in our face relax, we blush.

Muscle repair

When we exercise, we damage our muscles. Afterward, stem cells repair the damage and the muscles get stronger.

New research led by George Washington University School of Medicine and Health Sciences in Washington, D.C. - published this week in the journal Science Signaling - challenges a common assumption about this process.

Cell generate reactive oxygen species (ROS) as a byproduct, especially when energy consumption is high, such as during exercise. ROS can be very toxic to cells and were, until now, thought to hinder muscle repair.

"It is still a common belief within the fitness community that taking antioxidant supplements after a workout will help your muscles recover better," explains lead study author Adam Horn.

But the team's research showed that muscles tightly control ROS levels after injury, and that ROS are essential for repair.

If you are among those who look to antioxidants to speed up muscle repair after your workout, it might be worth letting your muscles do their own thing.
當流赤足蹋澗石,水聲激激風吹衣。
人生如此自可樂,豈必局束為人鞿?
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理大研究:跑步「輕着地」減受傷風險 腳踭重踏傷關節 全掌着地可免勞損

文章 #12  未閱讀文章PoP » 2018-03-21 00:25

來源: https://news.mingpao.com/pns/dailynews/ ... 0964109413

近年不少港人愛上跑馬拉松,然而若跑姿不當,健身不成反受傷。理工大學康復治療科學系收集 320 名跑友數據,發現跑步時「輕着地」能減受傷風險 62%。負責研究的學者說,九成長跑新手慣腳踭「重着地」,腿部關節及腳掌肌肉承受過大撞擊力,可引發關節痛或足底筋膜炎,提醒跑友注意跑姿,如落地時應全腳掌着地,膝蓋保持微曲,可避免勞損。

研究團隊於 2016 年挑選 320 名 18 至 50 歲長跑新手,分成「步姿訓練組」及「對照組」。理大康復治療科學系副教授張子熙說,參加者跑齡少於兩年、每周約跑 18 至 19 公里,平均重 60 至 61 公斤等。當中 166 人為「步姿訓練組」,其餘 154 人為「對照組」。

「訓練組」跑手在實驗室接受兩周、共 8 次跑步訓練,每次會在跑步機跑 5 分鐘,儀器會顯示雙腳着地承受的撞擊力,研究人員會提醒落地力度重的跑手「跑輕一點」。「對照組」跑手同在實驗室跑步,但不會有提醒。

研究發現「對照組」之後一年內有 61 宗受傷,傷者比例佔該組 38%;「訓練組」則有 28 宗受傷,傷者比例佔該組 16%。張子熙稱,整體而言,「輕着地」跑手受傷風險較「對照組」低逾六成。

兩組跑手因跑姿不同,受傷類型各異。輕步跑者有 10 宗小腿受傷,「對照組」則無此情况。張分析,雖有提醒跑手「跑輕一點」,但形式屬自行調節,估計有人改用前腳掌着地,過分拉扯小腿肌肉,導致拉傷或炎症。

不過,「對照組」則較多出現髕股(前膝部位)關節痛及足底筋膜炎,分別有 18 宗及 23 宗;「訓練組」只有 4 宗及 2 宗。張子熙表示,「對照組」跑手慣以腳跟重力着地,令足弓(即腳跟內側)勞損,引發足底筋膜炎,而「重着地」時步幅容易過大及着地一刻伸直膝蓋,均會加劇關節勞損,引發痛症。

正確跑姿﹕身體前傾膝微曲落地

張提醒,正確的跑姿應保持身體前傾,落地時膝蓋微曲,前腳掌及腳跟盡量同時着地,避免關節及足部肌肉因長期受壓勞損,「若在健身室練跑,可用手機拍下跑姿,留意腳部着地方式及力度有否不當」,若一時間難改跑姿,可以較密的步頻跑步,也可減少關節受壓。
當流赤足蹋澗石,水聲激激風吹衣。
人生如此自可樂,豈必局束為人鞿?
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註冊時間: 2006-12-06 03:42


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