唐玉成 吳卅
1 深圳大學師范學院體育系(廣東 深圳 518060)
2 北京體育大學研究生院
人口老齡化是我國未來半個世紀所面臨的重大問題。衰老往往導致老年人日?;顒幽芰θ缗罉翘?、步行、起立、搬運重物等衰退或喪失。功率訓練作為一種新興及重要的抗衰老運動手段,在國外越來越受到重視。功率等于力量和速度的乘積,表現(xiàn)為肌肉快速用力的能力,其單位為瓦(W)。功率訓練作為一種較新的老年人抗阻運動方式,與傳統(tǒng)力量訓練相比,功率訓練要求用最快速度完成動作,在提高肌肉功率和日?;顒幽芰Ψ矫娴臐摿Ω蟆N覈壳皩iT針對發(fā)展老年人骨骼肌質(zhì)量、力量、功率以及日?;顒幽芰Φ南嚓P研究較少。為了促進我國抗衰老運動的相關研究,本文綜述了國外老年人功率訓練成果,著重闡述了老年人功率訓練的研究歷程,功率訓練與力量訓練的效果比較,功率訓練的安全性和設計方案,以及未來研究需要解決的主要問題。
骨骼肌是人體最先衰老的組織之一。美國運動醫(yī)學學會(ACSM)認為[1],肌肉從30歲開始衰老,橫切面積和密度減小。40歲時肌肉質(zhì)量丟失顯著,丟失速率約為每年0.5~1%[2]。50歲以后,肌肉質(zhì)量的丟失率為每年1~2%[3]。肌肉質(zhì)量丟失不僅與衰老有關,廢用性萎縮也是重要原因[4,5]。50歲至70歲之間,肌肉力量下降的速率約為每10年15%;70歲以后,還要增加[6,7]。力量下降在50歲之前并不明顯,但肌肉功率下降的初始時間卻相對較早,多始于30~40歲[8],速率也較高,每年下降3%,而力量下降速率只有1~2%[9]。60歲以后,肌肉力量的下降速率為每年1.4~2.5%,而肌肉功率的下降速率為 3~5%[10,11]。
衰老骨骼肌的力量和收縮速度下降,主要是因為II型肌纖維減少,尤其是IIB型肌纖維減少[12],運動神經(jīng)元的募集和沖動頻率減少[13,14],以及肌肉非收縮成份增加和協(xié)調(diào)性下降[15]。從青年到老年,人體的最大無氧功率每10年下降8.3%,其中速度每10年下降4.3%[16]。速度丟失的主要原因是II型肌纖維的減少,II型肌纖維的收縮速度是I型肌纖維的2~4倍[17]。功率丟失速率通常高于力量或速度。例如,老年人經(jīng)歷50%的肌肉力量和速度丟失,其力量可保持原來的50%,但功率卻只有原來的25%。
由于肌肉組織存在衛(wèi)星細胞和肌源干細胞[18],在機械應力刺激下,老年人骨骼肌依然保持著壯大的能力,即使90多歲的老年人也不例外[19]??棺栌柧毮茉黾永夏耆思∪饧∏虻鞍字劓湲悩嬻w的基因表達及IIB型肌纖維的比例,但與年輕人不同,老年人Ⅰ型肌纖維肌球蛋白重鏈的基因表達也增加[20,21]。此外,力量或功率訓練都能增加老年人的肌肉力量、肌肉橫切面積、神經(jīng)肌肉協(xié)調(diào)性,以及雄性激素及生長激素的分泌[22-27]。
1945年,Delorme首次對力量訓練進行了研究[28]。1961年,Perkins等首次對老年人進行力量訓練研究[29]。20世紀60年代至80年代,受有氧運動抗衰老熱潮的影響,關于老年人力量訓練的研究并不多,多數(shù)研究采用低強度力量訓練,受試者多為男性,結果普遍認為力量訓練不能增加老年人肌肉質(zhì)量,只能引起神經(jīng)的適應和改變[30]。20世紀80年代末,F(xiàn)rontera[31]和Fiatarone[32]的研究改變了這一觀念。Fiatarone發(fā)現(xiàn),即使是長期臥床的年齡偏大的老年人,通過短期力量訓練后也能獲得的肌肉質(zhì)量增加(9%)。隨后,有關老年人力量訓練的研究出現(xiàn)幾何增長。一些研究表明[33-38],大強度力量訓練在增加老年人肌肉質(zhì)量和力量方面的效果優(yōu)于低強度力量訓練,大強度力量訓練的方案也被寫入了ACSM的官方建議[39],70~85%1RM的負荷成為老年人力量訓練中被廣泛采用的強度。
上世紀90年代初,Bassey 等[40]進行了早期的老年人功率訓練研究,發(fā)現(xiàn)伸膝肌群功率可以預測體弱老年人爬樓梯和坐姿站起能力。后來的研究[41]確認了這一結論,并認為伸膝肌群的功率比力量能更準確預測日常活動能力。早期研究[42-45]主要關注功率訓練發(fā)展肌肉力量和功率的效果,以及功率對日常活動能力的預測功能。
2000年以后,一些研究開始關注功率訓練對日?;顒幽芰Φ闹苯佑绊?,以及功率訓練與力量訓練在提高日常活動能力上的效果比較。Earles的研究最早,出于安全考慮,Earles對受試者進行了篩選,只留下功能測試成績較好的老年人,導致訓練前后的日?;顒幽芰ψ兓療o顯著性差異[46]。后續(xù)研究吸取了相關教訓,接納了日常功能受損和體弱的老人,或至少沒有排除這部分老人。
2004年以前,通常使用傳統(tǒng)力量訓練采用的器械和動作進行功率訓練。2004年,以Bean為首的哈佛醫(yī)學院團隊突破了這一限制,設計了10種模擬日常活動的功率訓練動作[47]。2007年,Manini也設計出5種日常功能性功率訓練動作,并建立了這些動作的訓練晉級模式[48]。近來,邁阿密大學的Signorile等提出用日常活動能力測試[49,50],如爬斜坡、30秒坐凳起立替代傳統(tǒng)的器械功率測試,并證明這些測試的成績能較好預測身體局部的最大功率??傮w看來,功率訓練在動作設計上有從突破傳統(tǒng)器械訓練模式向不斷模擬和接近日?;顒觿幼鞯内厔?,以期能將功率訓練成果更好地轉(zhuǎn)換為日常活動能力,彌補傳統(tǒng)力量訓練和功率訓練在提高日?;顒幽芰ι系牡托栴}[51]。老年人功率訓練研究也從注重發(fā)展功率和速度向注重發(fā)展和全面提高日?;顒幽芰D(zhuǎn)移。
一些研究認為[52-54],力量訓練和功率訓練在提高老年人力量方面的差別不大,但功率訓練提高功率的效果明顯好于力量訓練。如Fielding等發(fā)現(xiàn),16周的功率訓練將老年人腿舉動作的峰值功率提高了97%,而力量訓練僅提高45%。Marsh等的研究也發(fā)現(xiàn),在提高下肢功率的效果方面,功率訓練比力量訓練幾乎高出1倍。日?;顒幽芰Ρ憩F(xiàn)為功率或速度,而不是純粹的力量,日?;顒訉αα康囊笠驳陀趯λ俣群凸β实囊骩55-57]。
日?;顒幽芰p弱是老年人面臨的最大問題之一。老年人的基本活動能力如行走、爬樓梯等均逐年減弱[58]。日常活動能力是獨立生活和人身安全的基礎和保障,以行走為例,77%(n>5000)的老年人步速在0.77m/s及以下,80歲老人步速在1 m/s以上的不足8%,而要讓老年人安全通過城市交通路口,步速需要保持在1.35 m/s以上[59,60]。
跌倒是老年人面臨的重大問題。為重新站起,老年人需要用更大的身體前傾角度作為補償[61],站起速度更慢,也更容易跌倒。功率比力量能更好地預測跌倒的幾率[62],功率訓練比力量訓練能更有效地減少老年人跌倒的風險[63]。老年人的步態(tài)有所改變,表現(xiàn)為腳踝和膝關節(jié)的支撐時間減少,步長縮短,而足與地面接觸的時間增加,姿態(tài)穩(wěn)定性減弱[64]。而功率訓練,尤其是低負荷高速度的功率訓練,有助于改善身體穩(wěn)定性[65]。Metter等的一項長達40年的研究表明,肌肉功率(而不是力量)與死亡率呈高度相關,快速運動(如快速站起、快速步行)次數(shù)的減少導致肌肉質(zhì)量和功率丟失加劇,顯著增加老年人的死亡率[66]。
在提高日?;顒幽芰Ψ矫?,功率訓練效果或顯著優(yōu)于力量訓練[67,68],或與力量訓練差異不大[69-71]。從目前的研究來看[72-74],即使功率訓練增加肌肉力量和質(zhì)量的效果與力量訓練近似,但與肌肉力量相比, 肌肉功率與日常活動能力的關系更密切。因此,在提高日?;顒幽芰Ψ矫?,功率訓練比力量訓練的潛力可能更大一些。僅有兩項研究[46,75]認為,功率訓練不能顯著提高老年人的日?;顒幽芰Α5@兩項研究的受試者在測試之前就表現(xiàn)出較高的日?;顒幽芰?,如能在4分鐘內(nèi)完成400米行走,步速在1.3 ~ 1.5 m/s之間等。
除了能有效發(fā)展功率和日?;顒幽芰ν猓c力量訓練相比,功率訓練還有一些額外的優(yōu)勢。Stenglel等[76]對老年絕經(jīng)期婦女進行了功率訓練和力量訓練效果的對比,經(jīng)過12個月的訓練,力量訓練組腰椎和骨盆骨密度顯著下降,而功率訓練組能夠保持或有一定提高(P > 0.05 )。Sayers等[77]的研究發(fā)現(xiàn),與80%1RM的力量訓練相比,40%1RM功率訓練帶來的主觀疲勞感更低,功率訓練老人的自發(fā)訓練頻率和量也顯著高于力量訓練。傳統(tǒng)力量訓練的高要求可能對老年人的心理造成不利影響,導致其主動鍛煉的行為減少。還有研究表明[78-80],訓練的持續(xù)性與辛苦程度有關,快速運動能帶來更多的愉悅感和輕松感,中等負荷的快速功率訓練比高強度的力量訓練更利于堅持。在美國只有10%的老年人主動進行力量訓練[81],考慮到環(huán)境和文化的影響,在國內(nèi)這一比例可能還要小。因此,對于老年人而言,選擇便于堅持的訓練方式尤為重要。
Henwood[75]對老年人分別采用遞增強度功率訓練(45%1RM、60%1RM、75%1RM)以及恒定強度力量訓練(75%1RM),負荷量均為3組8次,發(fā)現(xiàn)兩者提高力量和功率的效果相差不大,但在提高老年人生活質(zhì)量滿意度方面,功率訓練的效果好于力量訓練。Henwood認為功率訓練可以用較小的負荷,獲得與力量訓練同樣的訓練效果。Katula的研究[82]也證實,功率訓練在提高老年人自信心、日常活動的滿意度、生活滿意度三個方面均優(yōu)于力量訓練。
老年人功率訓練的安全性問題一直受到關注。傳統(tǒng)力量訓練要求老年人慢速完成動作,以減少損傷。雖然對老年人力量訓練的研究較多,但力量訓練本身的危險性并未明確,只顯示骨骼肌損傷的幾率高于心血管損傷[83]。在功率訓練的研究中,也有報道因各種傷病退出的情況,如疝氣、后背痛、骨性關節(jié)炎、肌肉疼痛、肌腱炎等[84],但這些損傷多為個例,多數(shù)研究沒有報道副作用或者省略相關報道。甚至在身體虛弱及患有慢性疾病老人參與的研究中,也沒有報道出現(xiàn)損傷[85]。
de Vos[86]重點關注了功率訓練的安全問題,對112名受試老人進行了每周一次的健康調(diào)查,未發(fā)現(xiàn)心血管疾病,但有17人出現(xiàn)了20次損傷。其中16次發(fā)生在測試過程中,4次發(fā)生在80%1RM負荷的訓練過程中,測試受傷率為0.34%,而訓練受傷率為0.25%,表明功率訓練受傷幾率并不高,但所有損傷都出現(xiàn)在80%1RM及以上負荷的訓練或測試過程中,值得注意。Hazell的研究則提示[87],加速過程中產(chǎn)生的末端慣性力是導致老年人受傷的重要原因,可通過改進器械減小末端慣性力來降低損傷幾率。
隨著年齡的增長,肌肉功率丟失可能更多與速度丟失有關,而不是力量[88]。力量和速度的關系提示[89-91],在功率恒定的情況下,負重越低,收縮速度越快;負重越高,則收縮速度越慢。當負荷阻力適中時,功率較大,從40%1RM負荷開始增加,到約70%1RM時達到最大。
對于年輕人,無論是重負荷、慢速,還是輕負荷、快速的訓練方式都能有效發(fā)展肌肉功率[92]。對于老年人,ACSM認為[93],應采用40~60%1RM的中等負荷進行快速功率訓練,組數(shù)為1~3組,可從固定器械練習逐漸過渡到自由力量練習。ACSM的上述觀點由Kraemer等在2002年發(fā)表,當時老年人功率訓練的研究成果并不多,對訓練方案設計具體問題的認識還不夠深入。
de Vos等[86]對比了三種不同負荷的功率訓練(20%1RM、50%1RM、80%1RM),發(fā)現(xiàn)三者提高功率的效果相似(增幅為14 ~ 15%),但在發(fā)展力量與耐力方面,80%1RM負荷更好。Orr等[94]則認為,相對于50%1RM、80%1RM負荷的功率訓練,20%1RM的負荷能更好地提高老年人的平衡能力。Cuoco等的研究表明[95],與1RM相比,腿部40%1RM以及70%1RM負荷的最大功率與老年人日常活動能力(爬樓梯、站起、步行)的相關度較高;而與70%1RM的負荷相比,40%1RM負荷的功率與日?;顒幽芰Φ南嚓P度更高。此外,Miszko也針對老年人功率訓練的最佳負荷和收縮速度進行了分析[96]。但這些研究并未對最佳訓練方案達成一致,也沒有闡明某項訓練方案是否對發(fā)展某種特定的日?;顒幽芰Ω行?。
Clemencon等發(fā)現(xiàn)[97],老年人的日?;顒幽芰梢杂眉∪夤β屎妥畲笏俣冗M行預測,不同的日?;顒樱? km走、爬樓梯、坐姿站起)與功率和速度的關系不同。Signorile也認為[98],不同部位的功率訓練應有不同的速度要求,才能讓功率訓練成果最優(yōu)化。Harris等認為[99],大負荷功率訓練有利于提高對力量要求較高和對速度要求較低的日?;顒?,如爬樓梯、坐姿站起;小負荷功率訓練有利于提高對力量要求較低和對速度要求較高的日?;顒樱缧凶?。如果這種推論能得到進一步證實,將增加功率訓練設計的針對性和有效性。
研究認為[100,101],在老年人進行功率訓練前,應先進行兩周左右的力量訓練,目的是為了掌握技巧和建立自信。雖然多數(shù)研究使用的重復次數(shù)為6~10次,但Baker的研究認為[102],最大功率通常出現(xiàn)在第2次或第3次動作,可以保持到第5次動作,從第6次開始顯著下降,建議酌情減少動作次數(shù)。每次動作的向心收縮階段,速度應盡量快,而離心收縮階段速度應較慢,以最大程度地提高功率。
多數(shù)研究采用器械或者自由力量的形式發(fā)展功率,其它形式的功率訓練還不多,主要包括負重服、氣動訓練器械及阻力帶。穿上負重服可以直接進行各種日?;顒?發(fā)展下肢功率的效果好于傳統(tǒng)力量訓練,但負重服通常負荷較小,且不便增加負荷,對體弱或功能喪失的老年人比較適用[103]。氣動訓練器械用氣壓代替負重作為阻力,能減少加速時的慣性作用力,安全系數(shù)高,還可省去調(diào)整負荷的時間,能有效增加老年人的肌肉力量、功率和日常功能[104,105],并逐漸開始普及。但受試者通常需要固定身體,且固定運動軌跡,不利于有效發(fā)展平衡和協(xié)調(diào)能力。Hruda等首次將阻力帶應用于老年人功率訓練[106],發(fā)現(xiàn)其能顯著增強老年人30秒坐姿站起、6分鐘行走等能力。阻力帶便于進行多關節(jié)運動,還可結合使用啞鈴,便于調(diào)節(jié)運動強度,而且隨著阻力帶長度的變化,阻力也會變化,可以減少末端慣性力,防止拉傷。Webber等的最新研究表明[107],阻力帶功率訓練比傳統(tǒng)功率訓練能更好地提高日常活動能力。
盡管越來越多的研究證實,發(fā)展老年人肌肉功率和速度能帶來諸多益處,但在為老年人選擇運動處方時,忽視功率訓練仍比較普遍。一些日常活動能力更依賴于肌肉功率而不是力量,作為一種提高日?;顒幽芰Φ氖侄?,功率訓練不僅可以應用于健康的老年人,而且已成功應用于體弱及機能受損的老年人,研究前景廣闊。未來的功率訓練應重點關注幾個問題:
(1)力量訓練和功率訓練的效果比較。將功率訓練和力量訓練進行對比分析,并同時進行三項指標測試(力量、功率和日常活動能力)的研究并不多,一共才9項,且大多樣本量少于20,女性受試者多于男性[108]。因此,在提高日?;顒幽芰Ψ矫?,功率訓練是否優(yōu)于力量訓練,目前還不能做出最終判斷。此外,多數(shù)研究提供了實驗室條件下的步速、坐姿起立和爬樓梯等數(shù)據(jù),在實驗室外進行的測試并不多[109],這似乎還不足以說明功率訓練優(yōu)于傳統(tǒng)力量訓練,有必要進行一些非實驗室條件下的日?;顒幽芰y試,測試難度應便于區(qū)分效果。后續(xù)研究還應注重增加樣本量,平衡性別比例,系統(tǒng)監(jiān)控損傷,對受試者退出的原因進行跟蹤調(diào)查等。
(2)目前還缺乏不同身體狀態(tài)老年人功率訓練效果的對比研究,無法證明身體情況對功率訓練效果的影響;多數(shù)研究注重下肢功率與日?;顒幽芰Φ年P系,專門針對上肢的研究較少。而上肢功率對于一些日?;顒尤绨徇\、舉起、拖拽重物等較為重要,對下肢功能也會產(chǎn)生一定影響。
(3)提高日?;顒幽芰Φ淖罴沿摵杉白罴褎幼?。不同日常活動對肌肉速度和力量的要求不一致,對最佳負荷的要求也會有所差別。由于目前研究數(shù)量較少,不同動作、不同負荷的功率訓練與不同日?;顒幽芰χg的關系如何還有待進一步研究。功率訓練提高肌肉力量和功率的幅度通常大于提高日?;顒幽芰Φ姆?,后續(xù)研究還需要創(chuàng)新訓練動作,力爭減少這種幅度差。一些研究設計了模擬日?;顒幽芰Φ墓β视柧殑幼鱗110-113],認為模擬日?;顒拥膭幼髂芨行У貙⒐β视柧毘晒D(zhuǎn)化成日?;顒幽芰?,但目前還缺少這些動作優(yōu)于傳統(tǒng)功率訓練動作的對比研究。
(4)不同于年輕人,一些老年人常患有各種慢性疾病。目前,將功率訓練應用于慢性疾病老年人的研究還不多,疾病種類也僅限于骨性關節(jié)炎等少數(shù)疾病[114]。慢性疾病通常導致老年人日常功能喪失或殘疾[115],對患有慢性疾病的老年人,可否用功率訓練替代傳統(tǒng)力量訓練進行康復,以獲得更好的效果,也是值得關注的問題。
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