肖曉飛,李旭鴻,劉 宇,3

(1.上海體育學(xué)院運(yùn)動(dòng)科學(xué)學(xué)院，上海 200438；2.浙江體育科學(xué)研究所，浙江 杭州 310004；3.沈陽(yáng)體育學(xué)院，沈陽(yáng) 110102)

體體操落地沖擊負(fù)荷機(jī)制研究進(jìn)展

肖曉飛1,李旭鴻2,劉 宇1,3

(1.上海體育學(xué)院運(yùn)動(dòng)科學(xué)學(xué)院，上海 200438；2.浙江體育科學(xué)研究所，浙江 杭州 310004；3.沈陽(yáng)體育學(xué)院，沈陽(yáng) 110102)

競(jìng)技體操日常訓(xùn)練和比賽中重復(fù)的落地/下法動(dòng)作,致使運(yùn)動(dòng)員承受高頻落地沖擊負(fù)荷,增加了骨骼肌肉系統(tǒng)損傷風(fēng)險(xiǎn)。因此,亟需對(duì)落地沖擊負(fù)荷機(jī)制研究進(jìn)行梳理。傳統(tǒng)對(duì)落地沖擊負(fù)荷機(jī)制的實(shí)驗(yàn)研究備受青睞,但實(shí)驗(yàn)研究的控制方法及離體研究在一定程度上限制了對(duì)體操落地沖擊負(fù)荷機(jī)制的深入理解,人體運(yùn)動(dòng)計(jì)算機(jī)仿真方法提高了對(duì)已有研究成果的理解。隨著落地沖擊負(fù)荷機(jī)制的理論研究的深入,實(shí)驗(yàn)研究獲得的數(shù)據(jù)可以供理論研究使用,對(duì)沖擊負(fù)荷機(jī)制的研究正在整合理論研究及實(shí)驗(yàn)研究的數(shù)據(jù),使得離體研究的局限性逐步降低。本研究對(duì)近年來(lái)體操落地沖擊負(fù)荷機(jī)制的兩種常用方法—實(shí)驗(yàn)研究和建模仿真研究進(jìn)行綜述,加深對(duì)沖擊負(fù)荷機(jī)制的理解,為選擇合適的生物力學(xué)方法研究體操落地沖擊負(fù)荷與損傷風(fēng)險(xiǎn)提供理論依據(jù),并為競(jìng)技體操運(yùn)動(dòng)損傷評(píng)估提供參考。

體操落地;沖擊負(fù)荷;實(shí)驗(yàn)研究;建模仿真

競(jìng)技體操高難度落地或下法動(dòng)作致使運(yùn)動(dòng)員以高速旋轉(zhuǎn)狀態(tài)撞擊體操落地墊,承受自身體重8-14倍[1-4]的地面反作用力。運(yùn)動(dòng)員訓(xùn)練中平均每周需要完成超過(guò)200次[5]的落地/下法,如此短暫、頻繁的沖擊負(fù)荷給人體下肢環(huán)節(jié)的骨骼肌肉系統(tǒng)帶來(lái)嚴(yán)峻的考驗(yàn)。國(guó)際體聯(lián)(FIG,2013)的評(píng)分規(guī)則致使運(yùn)動(dòng)員為追求較高成績(jī),選用的動(dòng)作難度越來(lái)越大,帶來(lái)的落地沖擊力也可能隨之增大,下肢環(huán)節(jié)損傷風(fēng)險(xiǎn)也會(huì)增加[6]。運(yùn)動(dòng)員落地時(shí)多移動(dòng)一步、身體失衡、上臂的多余擺動(dòng)等動(dòng)作將導(dǎo)致0.1-0.5的扣分,運(yùn)動(dòng)員落地時(shí)必須在完美動(dòng)作和損傷風(fēng)險(xiǎn)之間做出選擇。緊張激烈的體操比賽中,運(yùn)動(dòng)員落地時(shí)常常會(huì)出現(xiàn)失誤,產(chǎn)生的瞬時(shí)沖擊負(fù)荷就有可能超過(guò)其身體承受范圍,從而導(dǎo)致?lián)p傷[7]。國(guó)外體操的流行病學(xué)研究報(bào)告指出,體操運(yùn)動(dòng)損傷的發(fā)生率高達(dá)50%,且比賽中的損傷高于訓(xùn)練,并且損傷的主要部位發(fā)生在下肢,而落地是引發(fā)損傷的主要原因[7-10]。流行病學(xué)的調(diào)查只能提供損傷概況的數(shù)據(jù),引起教練員和運(yùn)動(dòng)員在思想觀念上的重視,而要做到合理預(yù)防損傷,就必須較好的理解損傷的發(fā)生機(jī)制[11]。鑒于此,對(duì)體操落地沖擊負(fù)荷機(jī)制進(jìn)行梳理,對(duì)落地沖擊潛在損傷的生物力學(xué)研究方法進(jìn)行評(píng)價(jià),以期能加深對(duì)體操落地沖擊負(fù)荷機(jī)制生物力學(xué)方法的理解,也為損傷風(fēng)險(xiǎn)預(yù)防、損傷后期康復(fù)訓(xùn)練提供參考。

1 落地沖擊負(fù)荷機(jī)制

描述和定量分析沖擊負(fù)荷與損傷風(fēng)險(xiǎn)關(guān)系的生物力學(xué)方法,在確定損傷原因及機(jī)制方面起著重要作用。生物力學(xué)方法將體操落地沖擊負(fù)荷機(jī)制分為內(nèi)在機(jī)制和調(diào)節(jié)機(jī)制[5]。內(nèi)在機(jī)制主要和運(yùn)動(dòng)員先天性的身體條件有關(guān),包含運(yùn)動(dòng)員本身的身體狀況,膝、踝關(guān)節(jié)剛度[12]、下肢肌肉組織力量[13]、足骨骼剛度[14],下肢的神經(jīng)肌肉控制能力和協(xié)調(diào)性[15],膝、踝關(guān)節(jié)承受沖擊后的移動(dòng)范圍和松弛度[16]等。也有研究把性別差異歸于內(nèi)在機(jī)制[13],認(rèn)為不同性別的運(yùn)動(dòng)員落地時(shí)的姿勢(shì)和運(yùn)動(dòng)類型不同,沖擊損傷也存在差異,但運(yùn)動(dòng)員的落地姿勢(shì)是可以自我調(diào)整的。體操運(yùn)動(dòng)員的落地技術(shù)熟練程度[17],落地時(shí)下肢關(guān)節(jié)的彎曲程度,足觸地時(shí)的部位、角度[18-20],空中動(dòng)作所到達(dá)的最大重心高度,同樣高度不同動(dòng)作導(dǎo)致落地時(shí)人體方向不同,落地瞬間身體的垂直和旋轉(zhuǎn)速度[17,21-22],落地表面(落地墊是體操運(yùn)動(dòng)員足所接觸最多的表面)的力學(xué)特性[21]等則屬于調(diào)節(jié)機(jī)制的范疇。

雖然有些機(jī)制(如相同體重運(yùn)動(dòng)員不同環(huán)節(jié)的質(zhì)量不同[23,24],每個(gè)運(yùn)動(dòng)員膝關(guān)節(jié)和踝關(guān)節(jié)剛度不同,完成相同動(dòng)作時(shí)身體姿勢(shì)不同導(dǎo)致承受的沖擊力存在差異[25-26])對(duì)落地沖擊的潛在損傷有貢獻(xiàn),但未被廣泛認(rèn)可。目前,雖然離體研究方法可揭示和定量分析損傷機(jī)制,加上運(yùn)動(dòng)員不同的身體條件、狀態(tài),但所獲得的生物力學(xué)信息十分有限,導(dǎo)致諸如落地頻率、幅度與損傷的關(guān)系[7]無(wú)法確定。用于研究落地沖擊負(fù)荷調(diào)節(jié)機(jī)制的生物力學(xué)方法有實(shí)驗(yàn)研究和建模仿真研究[5]。

2 落地沖擊負(fù)荷機(jī)制的實(shí)驗(yàn)研究

落地沖擊負(fù)荷的生物力學(xué)實(shí)驗(yàn)研究可以加深對(duì)落地沖擊負(fù)荷調(diào)節(jié)機(jī)制的理解。研究顯示,影響沖擊負(fù)荷機(jī)制的主要因素有落地高度、下肢運(yùn)動(dòng)學(xué)特征、沖擊表面力學(xué)特性、性別差異[17,21,24,27-28]等。但具體的實(shí)驗(yàn)研究往往涉及到多種因素,例如落地高度和落地經(jīng)驗(yàn)[21,24,29],落地高度和沖擊表面力學(xué)特性相互作用[24,4],落地高度與性別,性別與下肢運(yùn)動(dòng)學(xué)特征,落地高度與下肢運(yùn)動(dòng)學(xué)特征等。本研究重點(diǎn)對(duì)落地高度、落地表面力學(xué)特征、性別差異和相關(guān)的運(yùn)動(dòng)學(xué)特征進(jìn)行總結(jié)。

2.1 落地高度與沖擊負(fù)荷

隨著落地高度的增加,落地沖擊帶來(lái)的垂直GRF峰值隨之增加,即落地高度與垂直地面反作用力峰值為正相關(guān)[21,30-31](多為三個(gè)不同高度)或者指數(shù)關(guān)系[22,32],并且不論落地高度還是落地墊的力學(xué)特性,影響垂直GRF最主要的因素均包含體操運(yùn)動(dòng)員的膝關(guān)節(jié)運(yùn)動(dòng)學(xué)特征。落地沖擊產(chǎn)生的內(nèi)部和外部負(fù)荷由下肢運(yùn)動(dòng)學(xué)技術(shù)決定[18],運(yùn)動(dòng)員自我選擇的落地技術(shù)對(duì)髖膝踝關(guān)節(jié)的運(yùn)動(dòng)學(xué)調(diào)整,對(duì)減緩沖擊負(fù)荷起著重要作用[26,33],下肢環(huán)節(jié)之間的協(xié)同作用,也可以有效減少落地時(shí)的沖量[21,24]。同樣的高度,膝關(guān)節(jié)屈曲角度不同,關(guān)節(jié)承受的垂直GRF沖擊不同,一般屈曲角度較大,關(guān)節(jié)的反作用力相對(duì)較小,這被不少研究所認(rèn)可,如30cm高度的落地,膝關(guān)節(jié)屈曲較大,柔軟狀態(tài)承受的沖擊力比屈曲較小,僵硬狀態(tài)的沖擊力小55%[34],80cm高度的落地,前者的沖擊力比后者低32%[4]。但受體操規(guī)則限制,比賽中運(yùn)動(dòng)員的落地不能使用較大的膝關(guān)節(jié)屈曲,且?guī)в羞B接動(dòng)作的第一次落地,需要下肢關(guān)節(jié)具有一定的剛度,否則很難完成后面的連接動(dòng)作。此外,在不同的落地高度,由于采取的測(cè)試條件不同,比如:是否裸足、落地墊力學(xué)特性存在差異等,使得測(cè)試結(jié)果存在一定的差異性。大多數(shù)實(shí)驗(yàn)研究,較低落地高度(大約30cm)時(shí)使用測(cè)力臺(tái)或者壓力板獲取GRF,而較大高度(大約60cm),較少采用裸足方式落地,也很少使用測(cè)力臺(tái),尤其是體操正式比賽,無(wú)法獲取GRF數(shù)據(jù)。另外,對(duì)于空翻帶轉(zhuǎn)體、接近200cm[4]以上的高度以及實(shí)際比賽中高難動(dòng)作落地的研究較少,從而導(dǎo)致實(shí)驗(yàn)研究對(duì)體操落地沖擊負(fù)荷調(diào)節(jié)機(jī)制的深度解析仍然存在局限性。

2.2 落地表面力學(xué)特性與沖擊負(fù)荷

相對(duì)于其它體育運(yùn)動(dòng)項(xiàng)目,體操運(yùn)動(dòng)員無(wú)法使用鞋來(lái)減緩落地沖擊,除體操鞋(襪)(僅為美觀或防滑,一般不穿)外,體操落地墊是體操運(yùn)動(dòng)員足與地面接觸的唯一介質(zhì),因此也是致使損傷的風(fēng)險(xiǎn)因素之一, FIG對(duì)體操落地墊的材料和力學(xué)特性有著嚴(yán)格的規(guī)定。落地墊的力學(xué)特性對(duì)減緩運(yùn)動(dòng)員落地沖擊的作用尤為關(guān)鍵,近年來(lái),科研人員試圖通過(guò)更改器械材質(zhì)[3,4,36-37],尤其是落地墊的材料,降低運(yùn)動(dòng)員落地時(shí)的沖擊力,從而降低落地?fù)p傷發(fā)生率[4,29,36]。

由于落地墊的重要性,落地沖擊過(guò)程中下肢環(huán)節(jié)和不同落地墊表面交互作用的研究也相應(yīng)較多。落地墊表面變形的增加可以誘發(fā)運(yùn)動(dòng)員腿和關(guān)節(jié)剛度的增加[38];隨著落地表面剛度的增加,運(yùn)動(dòng)員會(huì)通過(guò)增加膝關(guān)節(jié)屈曲角度[22,39]來(lái)適應(yīng)落地墊較大的變形率,這樣絕大多數(shù)沖擊負(fù)荷得以被肌肉肌腱系統(tǒng)所吸收,從而保護(hù)骨和關(guān)節(jié)組織遭受潛在的破壞性壓力[40]。

落地表面(軟墊、硬墊、無(wú)墊)的剛度系數(shù)不同,落地過(guò)程中運(yùn)動(dòng)員的運(yùn)動(dòng)學(xué)特征和動(dòng)力學(xué)特征不同。軟墊容易引起前腳掌關(guān)節(jié)內(nèi)側(cè)和外側(cè)的外翻,從而導(dǎo)致更高的損傷風(fēng)險(xiǎn)。硬墊表面的沖擊吸收能力較差,會(huì)導(dǎo)致下肢的生物組織(如韌帶、肌肉張力、骨、軟骨等)的負(fù)荷增加,如果超過(guò)了承受極限,可能會(huì)導(dǎo)致跖骨和舟骨骨折。而介于軟硬墊之間且表面為彈性的落地墊,有助于運(yùn)動(dòng)員提高運(yùn)動(dòng)表現(xiàn),可以有效降低關(guān)節(jié)軟骨損傷的風(fēng)險(xiǎn)[4,41-42]。改變體操落地墊材料特性(比如增加阻尼)可以減小GRF、大腿和小腿的彎曲力,同時(shí)可能增加前足部分在跳馬觸地初期的負(fù)荷[43]。

2.3 性別差異與沖擊負(fù)荷

競(jìng)技體操中,落地沖擊負(fù)荷性別差異(見(jiàn)表1)的研究結(jié)果表明,男女運(yùn)動(dòng)員的落地技術(shù)存在明顯差異。女子運(yùn)動(dòng)員的騰空時(shí)間和高度都低于男子,為獲得比賽中的高分,女子不斷嘗試并完成接近男子水平的空翻與轉(zhuǎn)體動(dòng)作,必然會(huì)增加損傷風(fēng)險(xiǎn)。研究表明,女子運(yùn)動(dòng)員下肢承受的沖擊負(fù)荷(體重標(biāo)準(zhǔn)化之后的GRF)分別比男子運(yùn)動(dòng)員高9%(單腳落地)[27]和34% (雙腳落地)[44],膝、踝關(guān)節(jié)所承受的地面反作用力沖擊分別高20%[18]和39%[18,44]。落地時(shí)女子運(yùn)動(dòng)員往往采取直立的落地姿勢(shì),在矢狀面,主要依靠膝、踝關(guān)節(jié)力矩來(lái)減緩沖擊負(fù)荷[12],而男子運(yùn)動(dòng)員往往利用膝、髖關(guān)節(jié)力矩來(lái)減緩矢狀面的沖擊負(fù)荷[18]。但也有研究顯示,落地過(guò)程中腳的不同位置接觸落地墊時(shí),下肢關(guān)節(jié)屈曲角度不存在性別差異[18]。

盡管體操損傷的流行病學(xué)調(diào)查結(jié)果表明,在落地沖擊過(guò)程中女子運(yùn)動(dòng)員的損傷率高于男子運(yùn)動(dòng)員,但是關(guān)于性別的落地技術(shù)和負(fù)荷機(jī)制的研究尚未見(jiàn)確切報(bào)道。因而,針對(duì)不同性別的落地調(diào)節(jié)技術(shù)與沖擊負(fù)荷機(jī)制的生物力學(xué)分析應(yīng)該成為未來(lái)研究趨向之一,在基于性別的落地技術(shù)差異與損傷機(jī)制之間搭建橋梁。

表1 落地高度與性別差異對(duì)沖擊負(fù)荷機(jī)制影響的研究

3 落地沖擊負(fù)荷機(jī)制的建模仿真研究

受學(xué)術(shù)倫理道德和體操比賽規(guī)則的限制,單純的實(shí)驗(yàn)方法很難捕獲高難度體操動(dòng)作落地沖擊(尤其是比賽時(shí))的GRF數(shù)據(jù),因此不少學(xué)者建議使用建模仿真方法,結(jié)合實(shí)驗(yàn)研究的數(shù)據(jù),開(kāi)展進(jìn)一步的研究。

3.1 沖擊負(fù)荷的評(píng)估指標(biāo)

沖擊負(fù)荷分為外部負(fù)荷和內(nèi)部負(fù)荷。對(duì)于外部沖擊負(fù)荷的評(píng)估指標(biāo),多數(shù)研究選取垂直GRF峰值、到達(dá)垂直GRF峰值時(shí)間、水平GRF峰值等。采用GRF指標(biāo)對(duì)外部沖擊負(fù)荷進(jìn)行評(píng)估在文獻(xiàn)中是最常見(jiàn)的,如表1,采用垂直GRF峰值來(lái)評(píng)估落地沖擊過(guò)程中運(yùn)動(dòng)員所承受的沖擊負(fù)荷大小。此外,有研究發(fā)現(xiàn),GRF負(fù)荷率比GRF更適合評(píng)估脛骨負(fù)荷和應(yīng)力性骨折風(fēng)險(xiǎn)[49]。

然而,只有部分研究采用關(guān)節(jié)反作用力、骨彎矩、肌肉力、肌肉功等指標(biāo)對(duì)內(nèi)部沖擊負(fù)荷進(jìn)行評(píng)估[50-52]。如使用肌電圖方法,確定了逆向動(dòng)力學(xué)分析中單個(gè)肌肉對(duì)落地沖擊負(fù)荷減緩的貢獻(xiàn)[20];使用逆向動(dòng)力學(xué)方法對(duì)比分析軟、硬落地過(guò)程中膝關(guān)節(jié)屈曲角度差異后,發(fā)現(xiàn)軟落地可以減緩19%的動(dòng)力學(xué)能量[21];采用肌電圖[12]和逆向動(dòng)力學(xué)[22]的方法,結(jié)合實(shí)驗(yàn)研究收集的運(yùn)動(dòng)學(xué)、人體解剖學(xué)、GRF數(shù)據(jù),對(duì)內(nèi)部沖擊負(fù)荷進(jìn)行評(píng)估[53]。因此,量化產(chǎn)生于踝、膝、髖的關(guān)節(jié)力矩,有利于加深對(duì)身體內(nèi)部沖擊負(fù)荷的理解,有助于更好地理解沖擊負(fù)荷調(diào)節(jié)機(jī)制。

3.2 體操落地墊的建模仿真研究

體操落地墊的力學(xué)特性是沖擊負(fù)荷調(diào)節(jié)機(jī)制的重要外部因素之一,諸多聚焦于體操落地墊力學(xué)特性的研究直接推動(dòng)了FIG對(duì)體操落地墊材料的改進(jìn)。計(jì)算機(jī)建模仿真方法比單純的材料實(shí)驗(yàn)測(cè)試方法有著先天性優(yōu)勢(shì),只需提供材料的主要屬性,如剛度、阻尼、密度、尺寸等數(shù)據(jù),即可迅速構(gòu)建符合要求的體操落地墊模型,然后結(jié)合沖擊器實(shí)驗(yàn)數(shù)據(jù)進(jìn)行仿真模擬,并可方便的調(diào)整落地墊材料參數(shù),尋找最符合體操比賽需求的落地墊力學(xué)屬性值。

常用的體操落地墊模型有簡(jiǎn)單的線性的彈簧阻尼模型、非線性的彈簧阻尼模型以及綜合使用的更復(fù)雜的模型[54-55]。也有研究使用有限元方法進(jìn)行建模,但假如沖擊力大小相同,有限元方法不能處理落地墊泡沫層的能量吸收問(wèn)題,而非線性的彈簧阻尼系統(tǒng)更適合處理能量吸收問(wèn)題[54]。有學(xué)者采用單純算法優(yōu)化落地墊的剛度和阻尼系數(shù),仿真了落地墊剛度和阻尼系數(shù)變化對(duì)GRF和內(nèi)部關(guān)節(jié)力、關(guān)節(jié)力矩的變化[43]。使用不同力學(xué)特性的落地墊模型,仿真了運(yùn)動(dòng)員落地沖擊時(shí)的力-時(shí)間特征,在關(guān)鍵參數(shù)上(如垂直GRF峰值、到達(dá)GRF峰值時(shí)間、最大沖擊負(fù)荷率、初次最小力、到達(dá)初次最小力的時(shí)間等),計(jì)算機(jī)仿真結(jié)果與實(shí)際運(yùn)動(dòng)表現(xiàn)結(jié)果是一致的[36]。此外,采用視頻分析方法,結(jié)合不同力學(xué)特性的體操落地墊,對(duì)落地墊的變形和有效質(zhì)量進(jìn)行計(jì)算,結(jié)合落地墊下面的測(cè)力臺(tái)測(cè)量落地沖擊時(shí)的GRF,使用逆向動(dòng)力學(xué)方法計(jì)算運(yùn)動(dòng)員落地沖擊的內(nèi)部關(guān)節(jié)應(yīng)力[41],但該方法很難用于真實(shí)比賽中對(duì)落地沖擊負(fù)荷的評(píng)估。盡管建模仿真方法優(yōu)勢(shì)明顯,但仍離不開(kāi)實(shí)驗(yàn)方法數(shù)據(jù)的支持,因此體操落地墊的沖擊器實(shí)驗(yàn)測(cè)量結(jié)合體操運(yùn)動(dòng)員真實(shí)的落地表現(xiàn),結(jié)合建模仿真方法開(kāi)展研究,無(wú)疑會(huì)推動(dòng)落地墊對(duì)減緩沖擊負(fù)荷作用的進(jìn)展[3]。

3.3 沖擊負(fù)荷的計(jì)算機(jī)仿真研究

計(jì)算機(jī)仿真的研究提高了對(duì)人體內(nèi)部環(huán)節(jié)的洞察,很難在實(shí)驗(yàn)室的設(shè)置和控制的操作(比如軟組織分布對(duì)沖擊負(fù)荷的影響),也可以通過(guò)計(jì)算機(jī)仿真方法來(lái)實(shí)現(xiàn)。人體運(yùn)動(dòng)的計(jì)算機(jī)仿真方法把人體假設(shè)為剛體模型或顫擺模型,結(jié)合運(yùn)動(dòng)學(xué)數(shù)據(jù)和人體測(cè)量學(xué)數(shù)據(jù),采用逆向動(dòng)力學(xué)方法,對(duì)人體落地沖擊進(jìn)行仿真,并和實(shí)際運(yùn)動(dòng)表現(xiàn)進(jìn)行一致性檢驗(yàn)。

剛體模型把人體假設(shè)為若干單個(gè)剛體環(huán)節(jié),環(huán)節(jié)之間通過(guò)鉸鏈鏈接。使用不同剛體模型開(kāi)展計(jì)算機(jī)仿真研究,對(duì)內(nèi)部關(guān)節(jié)負(fù)荷進(jìn)行評(píng)估已成為研究熱點(diǎn)。創(chuàng)建3環(huán)節(jié)剛體模型對(duì)跳馬中的前空翻和后空翻落地的沖擊力進(jìn)行仿真研究,評(píng)估落地過(guò)程中下肢環(huán)節(jié)的內(nèi)部受力[52]。4環(huán)節(jié)剛體模型的研究結(jié)果發(fā)現(xiàn),落地過(guò)程中,運(yùn)動(dòng)員采用的落地策略和內(nèi)在身體條件對(duì)沖擊負(fù)荷減輕影響較大,尤其是落地策略的選擇對(duì)GRF峰值影響高達(dá)103%[56]。創(chuàng)建7環(huán)節(jié)剛體模型結(jié)合體操落地墊模型,對(duì)GRF和關(guān)節(jié)反作用力進(jìn)行評(píng)估[57,41]。創(chuàng)建8環(huán)節(jié)剛體模型,研究了落地過(guò)程中肌肉共收縮對(duì)地面沖擊力降低的作用[58]。創(chuàng)建體操運(yùn)動(dòng)員骨骼肌肉模型,仿真運(yùn)動(dòng)員在騰空階段如何控制反作用力的影響,如何調(diào)整降低膝關(guān)節(jié)的伸肌力矩,減少落地沖擊的反作用力峰值幅度[59]。

人體是一個(gè)復(fù)雜的生物體,落地沖擊過(guò)程中,除了受GRF外力沖擊外,人體本身的骨骼、肌肉、韌帶等對(duì)沖擊負(fù)荷有重要的緩沖作用[24]。因此,剛體模型對(duì)沖擊負(fù)荷評(píng)估存在一定的局限性,有研究提出使用顫擺模型,把軟組織對(duì)減緩沖擊負(fù)荷的貢獻(xiàn)歸因于軟和硬質(zhì)量調(diào)整的耦合以及對(duì)肌肉活動(dòng)能力和肌肉調(diào)控能力的調(diào)節(jié)[60]。質(zhì)量耦合表示軟組織(如肌肉、皮膚、皮下脂肪等)相對(duì)剛體環(huán)節(jié)(比如大腿或小腿)運(yùn)動(dòng),具有彈性和阻尼。體操落地沖擊中利用顫擺模型研究軟組織對(duì)沖擊負(fù)荷作用的研究已經(jīng)見(jiàn)諸于報(bào)道[6,24,52,61]。體操的落地沖擊過(guò)程中,降低軟組織和剛體環(huán)節(jié)之間的阻尼系數(shù),可以降低0.13BW的沖擊負(fù)荷[23]。利用顫擺模型,獲得的GRF數(shù)據(jù)更接近于測(cè)力臺(tái)測(cè)量值[61]。剛體模型中得到的腳跟和地面接觸的GRF值為顫擺模型計(jì)算結(jié)果的1.5倍;若前腳先接觸地面,隨后腳跟接觸地面,則剛體模型計(jì)算的垂直GRF峰值高估約14%[24]。落地沖擊前期,顫擺模型是有效的,由于體操的落地沖擊過(guò)程需要身體變得剛性化[62],隨著沖擊過(guò)程中肌肉的激活,顫擺模型在消散GRF效果的百分比逐漸下降。采用顫擺質(zhì)量模型和多層落地墊模型聯(lián)合仿真的研究結(jié)果發(fā)現(xiàn),通過(guò)落地策略調(diào)整降低GRF峰值對(duì)減少?zèng)_擊損傷并不合適,因?yàn)榭赡軙?huì)導(dǎo)致骨彎矩、關(guān)節(jié)反作用力、肌肉力等人體內(nèi)部沖擊負(fù)荷的增加[6]。

軟組織對(duì)于衰減沖擊負(fù)荷峰值有明顯作用[24],顛擺質(zhì)量模型的理論應(yīng)用到?jīng)_擊負(fù)荷的調(diào)節(jié)機(jī)制中,雖然會(huì)增加模型復(fù)雜性和仿真時(shí)間[52],且缺乏真實(shí)人體內(nèi)部軟組織和剛體質(zhì)量的真實(shí)信息[63],存在一定的局限性,但在評(píng)估體操落地?fù)p傷風(fēng)險(xiǎn)時(shí),仿真模型可以有效確定人體環(huán)節(jié)之間的真實(shí)的內(nèi)部應(yīng)力。

4 落地沖擊負(fù)荷機(jī)制與潛在損傷預(yù)防的應(yīng)用研究

4.1 落地沖擊負(fù)荷機(jī)制實(shí)驗(yàn)研究的應(yīng)用

實(shí)驗(yàn)研究的易操作和可控性特征為有效應(yīng)對(duì)體操落地潛在損傷提供良好的科學(xué)依據(jù),但缺乏隨機(jī)狀況和比賽環(huán)境變化方面的應(yīng)對(duì),尤其是很難確定有效預(yù)防落地?fù)p傷的落地技術(shù)。有學(xué)者研究提示,運(yùn)動(dòng)員的跳躍能力、轉(zhuǎn)體技術(shù)、落地急停能力[64]、肌肉力量、爆發(fā)力、身體狀態(tài)、精神狀態(tài)與落地沖擊損傷的預(yù)防存在較大關(guān)系。最近的生物力學(xué)研究試圖對(duì)落地?fù)p傷進(jìn)行干預(yù),比如使用生物力學(xué)手段測(cè)量膝關(guān)節(jié)運(yùn)動(dòng)屈曲范圍,結(jié)合臨床醫(yī)生友情提示(Clinician friendly)方法預(yù)防落地可能引發(fā)的ACL損傷[65-67]。雖然對(duì)運(yùn)動(dòng)損傷預(yù)防干預(yù)的應(yīng)用研究較少,但可喜的是,已有研究使用生物力學(xué)方法確定臨床實(shí)踐與落地?fù)p傷潛在因素之間的關(guān)聯(lián)[53],為生物力學(xué)領(lǐng)域?qū)＜覍W(xué)者進(jìn)一步深入研究研究提供了指引。

4.2 落地沖擊負(fù)荷機(jī)制建模仿真研究的應(yīng)用

建模仿真研究可提供沖擊負(fù)荷調(diào)節(jié)機(jī)制的系統(tǒng)改變時(shí)可能出現(xiàn)的情況,沖擊負(fù)荷與落地?fù)p傷之間的“因果關(guān)系”理論已被業(yè)界認(rèn)可。在判斷沖擊負(fù)荷是否會(huì)引發(fā)損傷時(shí),首先要鑒別損傷部位的結(jié)構(gòu)。目前的負(fù)荷對(duì)損傷是比較危險(xiǎn)還是已經(jīng)超過(guò)身體部位的壓力限制,確定各個(gè)身體部位關(guān)鍵的壓力限制,識(shí)別影響壓力的因素,確保壓力低于關(guān)鍵壓力限制位[68]。

在實(shí)驗(yàn)研究中,無(wú)法有效調(diào)整運(yùn)動(dòng)員身體環(huán)節(jié)質(zhì)量和關(guān)節(jié)剛度,因此軟組織特性和質(zhì)量耦合特性的調(diào)節(jié)機(jī)制無(wú)法確定,而建模仿真研究可以有效解決上述問(wèn)題,同時(shí)利用運(yùn)動(dòng)員自己確定的落地技術(shù),達(dá)到有效減輕高速度沖擊的目的。例如,體操的落地沖擊過(guò)程中,改變膝、踝關(guān)節(jié)的運(yùn)動(dòng)時(shí)間,可以導(dǎo)致外部沖擊負(fù)荷(GRF)分別改變1.5BW和3.9BW[69]。

針對(duì)運(yùn)動(dòng)員個(gè)體潛在損傷的預(yù)防,評(píng)估內(nèi)部和外部沖擊負(fù)荷的影響,分析潛在損傷的因素。把有關(guān)損傷風(fēng)險(xiǎn)和損傷機(jī)制的信息放在模型中,通過(guò)建模仿真的方式來(lái)考慮如何調(diào)整與損傷風(fēng)險(xiǎn)相關(guān)的內(nèi)部和外部因素[11]。例如,把姿勢(shì)穩(wěn)定性下降定義為損傷的風(fēng)險(xiǎn)因素[70-71],把GRF作為誘發(fā)落地沖擊過(guò)程中下肢損傷的重要因素[72],落地沖擊的頻率、較高的沖擊力、沖擊的減速、軀干姿勢(shì)、肢體的不對(duì)稱、腿的剛度、關(guān)節(jié)角度和運(yùn)動(dòng)范圍、雙腳落地的評(píng)分規(guī)則等[73]作為下肢損傷風(fēng)險(xiǎn)的因素,也有把肌肉疲勞作為損傷的風(fēng)險(xiǎn)因素[74-86],甚至,有研究提出軟組織的固有頻率和沖擊力的頻率發(fā)生共振是誘發(fā)損傷的另一主要因素[77-78]。

5 結(jié)語(yǔ)

由于體操落地沖擊損傷存在多種因素,目前的研究大多立足于調(diào)節(jié)機(jī)制的研究。實(shí)驗(yàn)研究和建模仿真研究逐步增多,對(duì)應(yīng)的離體機(jī)制研究趨勢(shì)的部分結(jié)果是確定的,但仍然很難確定體操落地沖擊負(fù)荷與潛在損傷的關(guān)系。對(duì)體操落地沖擊負(fù)荷機(jī)制的建模仿真研究需要實(shí)驗(yàn)研究數(shù)據(jù)作為支撐,考慮在建模仿真有采用帶有軟組織特性的顫擺質(zhì)量模型,對(duì)體操落地沖擊負(fù)荷進(jìn)行深入研究,并考慮使用計(jì)算機(jī)圖像技術(shù)獲取骨骼、軟組織質(zhì)量分布的具體數(shù)據(jù),提高對(duì)內(nèi)在機(jī)制和調(diào)節(jié)機(jī)制相互作用的科學(xué)理解,可以增加對(duì)已有的特定損傷預(yù)防策略的理解,為合理預(yù)防落地?fù)p傷提供科學(xué)依據(jù)。

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Research Progress of Im pact Load M echanism Gymnastic Landing

XIAO Xiao-Fei,et all
(Shanghai University of Sport,Shanghai200438,China)

Gymnasts are exposed to a high incidence of impact load due to the execution of repeated dismount performances in daily exercise and competition in gymnastics,which increased the potential injuries of musculoskeletal system.Therefore,it is necessary to sort out the impact load mechanisms during landing.While laboratory-based studies have traditionally been favored,the difficulty in controlling and isolating mechanisms of interest has partially restricted the further understanding of the impact loadmechanisms in gymnastic-style landings.An increase in the use of theoretical approaches,especially the development of computer simulation of human movement,has been evident over the past two decades.Both laboratory-based and theoretical research has successfully enhanced the insight into impact load mechanisms.Theoretical studies have advanced knowledge in impact landing mechanics,but some data from laboratory-based researches can be input into theoretical model.This review examines gymnastic-style impact load mechanisms during landing using biomechanical approaches which include laboratory-based research and modelsimulation research.It is hoped to deepen the understanding of the impact load mechanisms,to provide scientific evidence for selecting the appropriate biomechanical approach to examine the relation between gymnastic-style impact load and potential injuries,and to provide a reference for assessment about potential injuries in gymnastics.

gymnastics-style landing;impact load;inherentmechanisms;regulatorymechanisms;model and simulation

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:A

:1001-9154(2014)09-0058-08

G83

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:1001-9154(2014)09-0058-08

上海市人類運(yùn)動(dòng)能力開(kāi)發(fā)與保障重點(diǎn)實(shí)驗(yàn)室項(xiàng)目(11DZ2261100);上海體育學(xué)院研究生教育創(chuàng)新基金項(xiàng)目(項(xiàng)目編號(hào):xsxr2013027)

肖曉飛(1980-),男,山東榮成人,講師,在讀博士研究生,主要研究方向?yàn)?運(yùn)動(dòng)生物力學(xué)、人體運(yùn)動(dòng)的技術(shù)優(yōu)化與仿真。

2014-06-12