魏 佳,李 博,楊 威,王欣欣,馮連世,黎涌明,
(1.上海體育學(xué)院 體育教育訓(xùn)練學(xué)院,上海200438;2.國家體育總局體育科學(xué)研究所,北京100061)
人體肌肉質(zhì)量在30歲后以每 10年3%~8%的速率下降(Cruz-Jentoft et al.,2010),肌肉質(zhì)量的下降可能會導(dǎo)致一系列健康問題,并可能增加跌倒、殘疾,甚至死亡的風(fēng)險(xiǎn)(Visser et al.,2005)。力量訓(xùn)練被認(rèn)為是提高肌肉質(zhì)量和力量、延緩肌肉萎縮、預(yù)防跌倒和損傷、改善健康的有效方法(Fleck, 1988; Kraemer et al.,2017),近年來,力量訓(xùn)練在中國乃至全球范圍內(nèi)都是健身領(lǐng)域的熱門健身趨勢(黎涌明 等,2018,2019; Thompson,2017)。美國運(yùn)動(dòng)醫(yī)學(xué)學(xué)會(American College of Sports Medicine,ACSM)建議使用≥70% 1RM(1RM表示只能完成一次的最大重量)的重量進(jìn)行訓(xùn)練可以有效引起肌肉肥大(Ratamess et al.,2009)。然而,對于康復(fù)人群(包括受傷的運(yùn)動(dòng)員)和老年人群而言,進(jìn)行大強(qiáng)度力量訓(xùn)練難度較大,且對于無訓(xùn)練經(jīng)驗(yàn)的普通人群,進(jìn)行大強(qiáng)度力量訓(xùn)練可能會增加損傷風(fēng)險(xiǎn)和引起主觀不適。
血流限制訓(xùn)練(blood flow restriction training,BFRT)又稱加壓訓(xùn)練(KAATSU①KAATSU為日文加壓一詞的羅馬音。training),是指在運(yùn)動(dòng)期間通過特殊加壓裝置(一般為氣動(dòng)袖帶或彈性繃帶)對肢體(上肢和或下肢最近端)進(jìn)行外部加壓,使靜脈血流閉塞的同時(shí)部分阻塞動(dòng)脈血流以提高訓(xùn)練效果的訓(xùn)練方法(Loenneke et al.,2014b; Sato,2005)。近年來,由于實(shí)驗(yàn)證明BFRT可以以較小的運(yùn)動(dòng)強(qiáng)度產(chǎn)生與大強(qiáng)度力量訓(xùn)練相似的訓(xùn)練效果(Loenneke et al.,2012c),越來越受到訓(xùn)練實(shí)踐和科學(xué)研究領(lǐng)域的關(guān)注,其應(yīng)用也逐漸由健身領(lǐng)域拓展到競技體育和醫(yī)療康復(fù)領(lǐng)域。在競技體育領(lǐng)域,我國將 BFRT作為備戰(zhàn)東京奧運(yùn)會和北京冬奧會科技助力過程中的一種新方法進(jìn)行推廣和應(yīng)用。然而,眾多教練員和運(yùn)動(dòng)員在嘗試使用BFRT的過程中,對該訓(xùn)練方法的應(yīng)用效果和作用機(jī)制缺少客觀、全面的認(rèn)識,嚴(yán)重制約了 BFRT在我國奧運(yùn)備戰(zhàn)過程中作用的有效發(fā)揮,并可能導(dǎo)致對這一訓(xùn)練方法被片面、盲目甚至是錯(cuò)誤地使用。為此,本研究試圖從應(yīng)用效果和作用機(jī)制兩方面對 BFRT進(jìn)行綜述,旨在為科學(xué)地認(rèn)識和應(yīng)用該訓(xùn)練方法提供理論支撐和實(shí)踐指導(dǎo)。
1966年,Sato(2005)在參加佛教活動(dòng)時(shí),發(fā)現(xiàn)長時(shí)間跪坐后引起的腿部腫脹和不適感與提踵訓(xùn)練后的感覺相似,由此獲得了BFRT的靈感,于1983年開發(fā)出了最早的BFRT裝置,開始在大眾人群中推廣使用,并在 1997年6月獲得了專利。1997年,Shinohara等(1997)首次報(bào)道了使用血流限制裝置進(jìn)行訓(xùn)練可提升肌肉力量的現(xiàn)象。目前,BFRT已被醫(yī)療、私人訓(xùn)練和體育俱樂部等機(jī)構(gòu)用于提高肌肉質(zhì)量和力量、抗衰老、促進(jìn)康復(fù)以及提升運(yùn)動(dòng)表現(xiàn)等(Yasuda et al.,2017)。
在中國知網(wǎng)體育類全部期刊以“血流限制訓(xùn)練”和“加壓訓(xùn)練”為檢索詞進(jìn)行主題檢索(截至 2018年3月30日),共檢索到8篇文獻(xiàn),除去不相關(guān)文獻(xiàn)3篇,得到5篇相關(guān)文獻(xiàn),其中僅 1篇為實(shí)驗(yàn)性研究。以“KAATSU training”和“blood flow restriction training”為檢索詞,在Google Scholar、Web of Science和Ebsco體育運(yùn)動(dòng)全文數(shù)據(jù)庫對國外關(guān)于血流限制的研究進(jìn)行檢索(截至2018年3月30日),通過參考文獻(xiàn)進(jìn)行補(bǔ)充,共得到 419篇文獻(xiàn),經(jīng)刪選最終得到相關(guān)文獻(xiàn) 364篇。國外關(guān)于 BFRT的發(fā)文量較大且自2009年起逐年大幅增加,研究主要集中在應(yīng)用效果和生理機(jī)制兩個(gè)方面,而反觀國內(nèi)相關(guān)文獻(xiàn)較少,對BFRT關(guān)注不足。
關(guān)于限制血流進(jìn)行訓(xùn)練的研究可追溯到 20世紀(jì) 60年代(Fales et al.,1962),然而直到外部加壓血流限制設(shè)備的問世,血流限制(BFR)的應(yīng)用才開始被人們所關(guān)注。過去 20多年對 BFRT效果的研究證明,將 BFR與低強(qiáng)度運(yùn)動(dòng)相結(jié)合可以產(chǎn)生有益的肌肉適應(yīng),并在提高肌肉質(zhì)量和力量、提高有氧能力、促進(jìn)康復(fù)治療和預(yù)防廢用性肌萎縮方面有良好的效果。
肌肉質(zhì)量和力量的維持或提高是保證日常生活質(zhì)量(Md et al.,2002)、降低受傷風(fēng)險(xiǎn)(Visser et al.,2005)的重要基礎(chǔ),也是運(yùn)動(dòng)員提升競技能力的重要影響因素,而實(shí)現(xiàn)這一目的往往需要通過大強(qiáng)度力量訓(xùn)練。對于無力量訓(xùn)練經(jīng)驗(yàn)人群、老年人和康復(fù)人群等而言,大強(qiáng)度力量訓(xùn)練可能會增加訓(xùn)練的損傷風(fēng)險(xiǎn),但 BFRT為此類人群提供了一種替代方法。研究表明,BFRT即使在低至20% 1RM的運(yùn)動(dòng)強(qiáng)度下也顯示出有益的訓(xùn)練效果(Abe et al.,2005b)。Shinohara等(1997)于 1997年進(jìn)行了第一例使用加壓裝置的研究。該研究對 5名無訓(xùn)練經(jīng)驗(yàn)受試者的兩側(cè)下肢(僅單側(cè) BFR)進(jìn)行了為期 4周的單腿伸膝訓(xùn)練,阻力為40%最大自主收縮力(MVC),結(jié)果發(fā)現(xiàn),BFR側(cè)腿在2周和4周后的MVC增幅顯著高于無BFR腿。此后相關(guān)研究開始驗(yàn)證 BFRT的效果。Takarada等(2000c)將無力量訓(xùn)練經(jīng)驗(yàn)受試者分為低強(qiáng)度BFR組(LIBFR組,50% 1RM)、高強(qiáng)度組(HI組,80% 1RM)和低強(qiáng)度對照組(LI組,50% 1RM),經(jīng)過16周的坐姿屈肘訓(xùn)練后發(fā)現(xiàn),LIBFR和HI組的力量增長分別為 18.4%和 22.6%(二者間無顯著差異),均顯著大于 LI組(1.04%)。此外,盡管 LIBFR、HI和LI組都顯著增加了肱二頭肌和肱肌的橫截面積(CSA),但 LIBFR組(20.3%和 17.8%)的增幅顯著高于 LI組(6.9%和3.8%),且與HI組無顯著差異。另外,針對無力量訓(xùn)練經(jīng)驗(yàn)的年輕男性(Abe et al.,2005b)和老年人群(Patterson et al.,2011; Yasuda et al.,2016)的其他研究也有類似發(fā)現(xiàn)。
BFRT不僅在普通人群中顯示出良好的訓(xùn)練效果,在運(yùn)動(dòng)員訓(xùn)練中也有益處。Luebbers等(2017)對 3組高中舉重運(yùn)動(dòng)員進(jìn)行了 6周的深蹲訓(xùn)練,研究發(fā)現(xiàn),低強(qiáng)度BFR組(30% 1RM)的最大深蹲力量顯著提高,而低強(qiáng)度組(≤30% 1RM)和高強(qiáng)度組(≥65% 1RM)相比訓(xùn)練前無顯著變化。舉重運(yùn)動(dòng)員的力量本身就處于較高的水平,進(jìn)一步發(fā)展其肌肉質(zhì)量和力量較為困難(Ahtiainen et al.,2003),而 BFR的加入似乎為訓(xùn)練提供了一個(gè)額外刺激。Yamanaka等(2012)對36名NCAA I級足球運(yùn)動(dòng)員進(jìn)行了4周20% 1RM的臥推和深蹲訓(xùn)練,發(fā)現(xiàn)上下肢BFR組最大臥推和深蹲力量以及上下胸圍的增幅均顯著大于對照組。此外,研究還發(fā)現(xiàn),BFRT除了有助于運(yùn)動(dòng)員肌肉肥大和力量增長外(Luebbers et al.,2017; Yamanaka et al.,2012),還可以提高運(yùn)動(dòng)員在相關(guān)測試中的運(yùn)動(dòng)表現(xiàn),如短距離沖刺(Abe et al.,2005a; Cook et al.,2014; Manimmanakorn et al.,2013)、反向跳功率(Cook et al.,2014)、505敏捷測試(Manimmanakorn et al.,2013)、垂直跳(Manimmanakorn et al.,2013)和多級20 m往返跑測試(Manimmanakorn et al., 2013)。
傳統(tǒng)觀點(diǎn)認(rèn)為,有氧運(yùn)動(dòng)不會導(dǎo)致肌肉肥大(Kraemer et al.,1995),甚至在與力量訓(xùn)練進(jìn)行同期化訓(xùn)練時(shí)還會削弱力量訓(xùn)練的肌肥大效果(Bell et al.,2000)。然而BFRT相關(guān)研究發(fā)現(xiàn),BFR與低強(qiáng)度有氧運(yùn)動(dòng)(步行或自行車)相結(jié)合可以引起肌肉肥大和力量增長(盛菁菁 等,2019; Abe et al.,2010; Ozaki et al.,2011; Sakamaki et al.,2011)。Abe 等(2010)對19名普通男性進(jìn)行了8周40% V?O2max的自行車訓(xùn)練,結(jié)果顯示,BFR組(每次 15 min)大腿肌肉CSA和伸膝MVC顯著增大,而對照組(每次45 min)相較于訓(xùn)練前無顯著變化。同樣,Ozaki等(2011)對23名老年人進(jìn)行了 10周 45%儲備心率(HRR)的步行訓(xùn)練,研究發(fā)現(xiàn),BFR組最大等速伸膝扭矩和屈膝扭矩及大腿肌肉CSA顯著增大,而對照組并未出現(xiàn)類似的效果。這種運(yùn)動(dòng)強(qiáng)度較小且技術(shù)單一的運(yùn)動(dòng)方式對于不適宜進(jìn)行大強(qiáng)度訓(xùn)練的人群來說具有重大意義。除此之外,還有研究將BFR與其他訓(xùn)練形式相結(jié)合,如神經(jīng)肌肉電刺激(NEMS)(Natsume et al.,2015; Ozaki et al.,2015)、水阻訓(xùn)練(Araújo et al.,2015)、彈力帶訓(xùn)練(Thiebaud et al.,2013; Yasuda et al.,2014b)和自重訓(xùn)練(Ishii et al.,2005; Kang et al.,2015),上述研究均發(fā)現(xiàn),BFR可引起肌肉質(zhì)量和力量的顯著增加。
然而在 BFRT中需要注意的是,雖然受試者的絕對最大力量出現(xiàn)明顯增長,但其相對力量(最大力量/肌肉CSA)并沒有顯著變化(Fujita et al.,2008; Yasuda et al.,2010c),并且,低強(qiáng)度 BFRT也沒有產(chǎn)生與傳統(tǒng)高強(qiáng)度訓(xùn)練相似的肌肉激活增加(Cook et al.,2013; Manini et al.,2009)。因此,與傳統(tǒng)大強(qiáng)度力量訓(xùn)練(神經(jīng)適應(yīng)和肌肉肥大)提升力量的機(jī)制不同,BFRT提升肌肉力量可能是肌肉肥大所致。而對于運(yùn)動(dòng)員來說,僅通過肌肉肥大增加肌肉力量是遠(yuǎn)遠(yuǎn)不夠的。Yasuda等(2011)發(fā)現(xiàn),低強(qiáng)度BFRT(30% 1RM)結(jié)合傳統(tǒng)高強(qiáng)度力量訓(xùn)練(75% 1RM)(2天 BFRT+1天高強(qiáng)度力量訓(xùn)練)進(jìn)行 6周的訓(xùn)練后,結(jié)合組最大臥推力量增長與傳統(tǒng)高強(qiáng)度組相似(分別為15.3%和 19.9%),顯著高于單獨(dú)使用 BFR組(8.7%)。此外,傳統(tǒng)高強(qiáng)度訓(xùn)練組和組合組的肱二頭肌相對力量都顯著增加(分別為 10.5%和 6.7%),但單獨(dú) BFR組卻未顯著增加。相比于單獨(dú)BFR組,高強(qiáng)度訓(xùn)練組和組合組產(chǎn)生的訓(xùn)練效果可以歸因于神經(jīng)適應(yīng)(Yamanaka et al.,2012)。鑒于此,有研究將BFRT作為NCAA II級橄欖球運(yùn)動(dòng)員高強(qiáng)度力量訓(xùn)練后的增補(bǔ)訓(xùn)練(即在高強(qiáng)度力量訓(xùn)練完成后進(jìn)行 BFRT),并發(fā)現(xiàn),采用 BFRT增補(bǔ)方案組力量增長效果顯著大于單獨(dú)高強(qiáng)度力量訓(xùn)練組和單獨(dú) BFRT組(Kriley,2014; Luebbers et al.,2014)。因此,運(yùn)動(dòng)員可通過BFRT與傳統(tǒng)高強(qiáng)度力量訓(xùn)練相結(jié)合來實(shí)現(xiàn)對肌肉形態(tài)和神經(jīng)的有效刺激。
綜上所述,現(xiàn)有研究已反復(fù)證明,BFRT可有效引起肌肉肥大和力量增長(徐飛 等,2013; 吳旸 等,2019; Pope et al.,2013),較無 BFR的相同低強(qiáng)度運(yùn)動(dòng)方案更加有效(Abe et al.,2009; Yasuda et al.,2012),且效果與高強(qiáng)度訓(xùn)練相似(Sousa et al.,2017; Yasuda et al.,2010b)。BFRT對普通人群、康復(fù)人群和運(yùn)動(dòng)員都能產(chǎn)生有效的訓(xùn)練效果。低強(qiáng)度 BFRT在降低訓(xùn)練中的機(jī)械應(yīng)力和減緩訓(xùn)練導(dǎo)致的肌肉損傷的同時(shí)(魏佳 等,2019; Loenneke et al.,2014a),可以達(dá)到高強(qiáng)度力量訓(xùn)練類似的效果。運(yùn)動(dòng)員可在力量訓(xùn)練周期中適當(dāng)插入 BFRT,如每周進(jìn)行 2次大強(qiáng)度力量訓(xùn)練和 1次低強(qiáng)度 BFRT,在獲得有效肌肉形態(tài)和神經(jīng)適應(yīng)(力量)的同時(shí)減少運(yùn)動(dòng)員所承受的機(jī)械負(fù)荷。
良好的有氧能力水平對于一些項(xiàng)目運(yùn)動(dòng)員的競技能力至關(guān)重要(黎涌明, 2015)。最大攝氧量(?O2max)是反映有氧能力的重要指標(biāo),一般認(rèn)為中高運(yùn)動(dòng)強(qiáng)度(60%~90%O2max)的耐力訓(xùn)練是提高O2max的主要訓(xùn)練方法(Garber et al.,2011; Swain et al.,2002)。然而BFR相關(guān)研究發(fā)現(xiàn),BFR結(jié)合低強(qiáng)度有氧運(yùn)動(dòng)(步行和自行車)除了可以引起有益的肌肉適應(yīng)外,還可以提高受試者的O2max。Abe等(2010)對19名普通男性進(jìn)行了8周 40%O2max的自行車訓(xùn)練。盡管對照組每次的訓(xùn)練時(shí)間是 BFR組的3倍(45 min vs.15 min),但只有BFR組出現(xiàn)O2max的顯著提高。與此類似,Park等(2010)對14名大學(xué)生籃球運(yùn)動(dòng)員進(jìn)行了2周4~6 km/h的步行訓(xùn)練,研究發(fā)現(xiàn),只有BFR組的O2max出現(xiàn)顯著提高。綜合其他類似文獻(xiàn),除了一項(xiàng)步行研究未觀察到O2max提高外(De Oliveira et al.,2014),其余低強(qiáng)度 BFR步行或自行車運(yùn)動(dòng)后均發(fā)現(xiàn)O2max 的顯著提高(Abe et al.,2010; Park et al.,2010;Ursprung et al.,2017)。這種既可以引起有效的肌肉適應(yīng),也可以改善人體心肺功能的BFR有氧運(yùn)動(dòng)對于老年人和康復(fù)人群來說可能是一種改善身體功能的良好選擇。
提高肌肉質(zhì)量和力量,恢復(fù)骨骼肌肉的功能是康復(fù)治療優(yōu)先考慮的重點(diǎn)。然而,患有骨骼肌肉損傷的康復(fù)人群由于肢體功能退化、疼痛和損傷風(fēng)險(xiǎn)等原因很難進(jìn)行大強(qiáng)度的力量訓(xùn)練(Hoyt et al.,2015),而 BFRT為這類人群提供了恢復(fù)肌肉功能的新途徑。Hylden等(2015)對 7名表現(xiàn)為股四頭肌和腘繩肌肌無力的有過外傷性下肢損傷的患者進(jìn)行了為期2周的BFR低強(qiáng)度(20%~30% 1RM)力量訓(xùn)練,發(fā)現(xiàn)受試者伸膝和屈膝平均扭矩提高了13~37%,平均功率提高了 42%~81%,等速運(yùn)動(dòng)次數(shù)測試增加了 35%~55%。此外,在一項(xiàng)前交叉韌帶(ACL)重建手術(shù)后的康復(fù)研究中,Ohta等(2003)將44名ACL術(shù)后重建患者分為常規(guī)康復(fù)組和 BFR康復(fù)組(兩組康復(fù)訓(xùn)練內(nèi)容相同)。16周訓(xùn)練后,僅在 BFR康復(fù)組發(fā)現(xiàn)膝關(guān)節(jié)力量和伸膝肌CSA顯著提高。其他文獻(xiàn)也報(bào)道了類似的積極康復(fù)效果(Giles et al.,2017; Tillma, 2017; Yow et al.,2018)。
除此之外,還有研究發(fā)現(xiàn),BFR結(jié)合低強(qiáng)度運(yùn)動(dòng)不僅可以引起B(yǎng)FR部位肢體肌肉的有益適應(yīng),還可引起非BFR部位肢體的有益適應(yīng)(Abe et al.,2012)。Abe等(2005b)對年輕男性受試者進(jìn)行了 2周的下肢加壓深蹲和屈腿訓(xùn)練(20% 1RM)發(fā)現(xiàn),BFR組不僅出現(xiàn)了股四頭肌和股二頭肌體積的顯著增大,還出現(xiàn)臀大肌體積的顯著增大。與此類似,Yasuda等(2010b)的研究發(fā)現(xiàn),經(jīng)過2周30% 1RM的臥推訓(xùn)練后,BFR組不僅出現(xiàn)肱三頭肌厚度的顯著增加,還出現(xiàn)胸大肌厚度的顯著增加。此外,研究還發(fā)現(xiàn)BFRT具有遠(yuǎn)程效應(yīng)。May等(2018)將受試者分為下肢BFR組和下肢無 BFR組,進(jìn)行了 7周的上下肢力量訓(xùn)練(3組50% 1RM的單側(cè)屈肘+4組30% 1RM的雙側(cè)屈膝和伸膝)后發(fā)現(xiàn),下肢BFR組的單側(cè)運(yùn)動(dòng)上肢的最大力量提升幅度顯著大于下肢無 BFR組,即下肢 BFR對上肢力量升幅度顯著大于下肢無 BFR組,即下肢 BFR對上肢力量的提升具有遠(yuǎn)程效應(yīng)。此發(fā)現(xiàn)給患側(cè)部位無法進(jìn)行大強(qiáng)度運(yùn)動(dòng)的人群提供了治療的新視角。
與此同時(shí),一些個(gè)案研究還發(fā)現(xiàn),BFRT對老年人和慢性病患者具有積極的治療效果,包括改善老年人的血管功能(降低血管僵硬度和提高靜脈順應(yīng)性)(Fahs et al.,2014; Ozaki et al.,2011; Shimizu et al.,2016),促進(jìn)微血管生成(Evans et al.,2010; Larkin et al.,2012),降低運(yùn)動(dòng)后血壓(Maior et al.,2015; Neto et al.,2015),提高癡呆患者的日?;顒?dòng)能力(Fukuda et al.,2011),降低無腦回畸形的頸部不穩(wěn)定性(Iwashita, 2015),減緩帕金森引起的活動(dòng)功能下降(Douris et al.,2018),治療股骨頭壞死和股骨內(nèi)側(cè)髁骨壞死(Hiraizumi et al.,2016; Nakajima et al.,2015)、病態(tài)竇房結(jié)綜合癥(Satoh, 2006)和腦白質(zhì)軟化(Iwashita et al., 2014)。Loenneke等(2012a)也提出了 BFR康復(fù)訓(xùn)練的漸進(jìn)模型,認(rèn)為康復(fù)人群可以循序漸進(jìn)地進(jìn)行以下4種訓(xùn)練:1)在臥床休息或肢體固定期間單獨(dú)使用 BFR;2)BFR結(jié)合低強(qiáng)度步行;3)BFR結(jié)合低強(qiáng)度力量訓(xùn)練;4)BFR低強(qiáng)度力量訓(xùn)練結(jié)合高強(qiáng)度力量訓(xùn)練。
人體的肌肉質(zhì)量和力量一方面隨著年齡的增長逐漸下降(Frontera et al.,2000),另一方面,在長期無負(fù)荷狀態(tài)下會出現(xiàn)廢用性肌萎縮(Yasuda et al.,2005)。有研究證明,BFR可以有效防止傷病臥床或肢體固定期間由于長期處于無負(fù)荷狀態(tài)造成的廢用性肌萎縮(Clark et al.,2006; Kubota et al.,2008; Takarada et al.,2000b)。Kubota等(2008)對15名健康受試者進(jìn)行 2周的左腳踝固定并保持無負(fù)荷狀態(tài),將其分為BFR組和下肢等長力量練習(xí)組,結(jié)果發(fā)現(xiàn),只有BFR組未出現(xiàn)屈膝肌和跖屈肌肌力和下肢圍度的顯著下降。另外,Takarada等(2000b)對 ACL重建患者術(shù)后第3~14天進(jìn)行了 BFR,發(fā)現(xiàn)相比于對照組(正??祻?fù)訓(xùn)練),BFR組在手術(shù)14天后膝伸肌CSA的下降幅度小于對照組(9.4% vs.20.7%),并且后續(xù)康復(fù)期間BFR顯著縮短了患者的康復(fù)時(shí)間。當(dāng)然,不同的研究在這方面的結(jié)論并不一致。Iversen等(2016)針對ACL重建運(yùn)動(dòng)員進(jìn)行了2周的 BFR和正常康復(fù)訓(xùn)練,發(fā)現(xiàn)兩組患者股四頭肌 CSA都顯著減少,且相互間無顯著差異,作者認(rèn)為這可能是由于所采用的運(yùn)動(dòng)強(qiáng)度小于10% 1RM(肌肉肥大所需最小強(qiáng)度)和受試者實(shí)驗(yàn)前肌肉萎縮程度存在顯著差異(-8.5% ~22.8%)所致。
綜上所述,BFRT可有效引起肌肉肥大和力量增長,BFR結(jié)合低強(qiáng)度有氧運(yùn)動(dòng)還有利于提升有氧能力,并且BFR的單獨(dú)使用和/或與康復(fù)訓(xùn)練相結(jié)合可以有效防止由于長期無負(fù)荷狀態(tài)期間導(dǎo)致的廢用性肌萎縮和肌無力,有利于促進(jìn)損傷康復(fù)或術(shù)后康復(fù)進(jìn)程。BFRT對于普通人群、老年人群、康復(fù)人群和運(yùn)動(dòng)員而言是一種低損傷風(fēng)險(xiǎn)的肌肉增長方法。
BFR對肢體的主要影響是動(dòng)脈血流流入減少和靜脈血液聚集,這一影響導(dǎo)致肢體進(jìn)入一個(gè)相對缺血和缺氧的狀態(tài)(Yasuda et al.,2010a),由于乳酸等代謝產(chǎn)物在這一過程中無法得到有效清除(Teixeira et al.,2017; Yasuda et al.,2014a),使得代謝壓力水平隨之顯著增加?;诖耍煌瑢W(xué)者從不同角度對 BFRT作用機(jī)制進(jìn)行了解釋,這些解釋涉及激素分泌、蛋白質(zhì)合成和抑制合成調(diào)節(jié)、肌纖維募集和細(xì)胞腫脹等方面。
力量訓(xùn)練后生長激素(GH)和類胰島素增長因子 1(IGF-1)等合成代謝激素的濃度增加有利于肌肉的生長(Kraemer et al.,2005)。有學(xué)者認(rèn)為,在BFRT后引起肌肉肥大的機(jī)制可能是由于合成代謝激素分泌的增加(Takarada et al.,2000a)。由于血流被限制的運(yùn)動(dòng)中代謝產(chǎn)物大量累積(Kraemer et al.,2017; Yasuda et al.,2014a),導(dǎo)致內(nèi)環(huán)境pH值降低并通過 III和 IV組傳入神經(jīng)的化學(xué)感受性反射刺激垂體釋放 GH(Gosselink et al.,1998)。Takarada等(2000a)發(fā)現(xiàn),在20% 1RM的BFR伸膝訓(xùn)練后GH濃度顯著增加,達(dá)到靜息時(shí)的 290倍。此外,GH的分泌可刺激肝臟中 IGF-1的釋放(Scott et al.,1985),研究同樣在BFRT運(yùn)動(dòng)后發(fā)現(xiàn)IGF-1濃度的顯著提高(Madarame et al.,2010; Seo et al.,2016)。當(dāng)然,也有研究不支持這一觀點(diǎn)。Mitchell等(2013)并未發(fā)現(xiàn) BFRT后 GH、IGF-1和睪酮濃度的變化,并且認(rèn)為運(yùn)動(dòng)后 IGF-1濃度的提高不是 GH的分泌所致。還有研究將 IGF-1濃度變化歸因于血漿濃度的變化(Madarame et al.,2010)。
理論上,任何有利于蛋白質(zhì)平衡趨于正向的機(jī)制都有利于肌肉的生長。哺乳動(dòng)物雷帕霉素靶蛋白(mammalian Target of Rapamycin,mTOR)被認(rèn)為是調(diào)節(jié)骨骼肌生長的主網(wǎng)路(Bodine et al.,2001),可參與調(diào)節(jié)mRNA翻譯起始和蛋白質(zhì)合成(Wang et al.,2006)。在運(yùn)動(dòng)中蛋白激酶(Akt)被 IGF-1激活進(jìn)而誘導(dǎo) mTOR以刺激蛋白質(zhì)翻譯(Bodine et al.,2001),并在促進(jìn)肌肉生長中發(fā)揮重要作用。mTOR信號通路已被發(fā)現(xiàn)在BFRT中被其下游效應(yīng)物核糖體S6激酶1(SK61)磷酸化刺激,進(jìn)而促進(jìn)蛋白質(zhì)生成和抑制蛋白質(zhì)水解 (Fry et al.,2010; Fujita et al.,2007; Gundermann et al.,2014),同時(shí)SK61磷酸化有利于翻譯的起始和延長(Wang et al.,2006),這都有利于肌肉生長。此外,熱休克蛋白(HSP)在正常狀態(tài)下作為分子伴侶有助于蛋白質(zhì)的組裝與轉(zhuǎn)運(yùn)(Kiang et al.,1998),并對維持細(xì)胞穩(wěn)態(tài)起到一定的作用(Simar et al.,2007),可在缺氧、缺血再灌注和酸中毒的環(huán)境中被誘導(dǎo)(Kregel, 2002),這表明,在缺血、缺氧和代謝產(chǎn)物累積增大的 BFRT中,HSP活性可能發(fā)生改變。Kawada等(2005)對大鼠進(jìn)行了2周BFRT后,發(fā)現(xiàn)跖肌中的HSP72顯著增加。
與此相反,F(xiàn)ry等(2010)的研究中并沒有發(fā)現(xiàn)HSP70的增加,因此,可能只有某種 HSP(HSP72)才對肌肉肥大產(chǎn)生作用。此外,由于 HSP72具有抑制肌肉萎縮信號通路的作用(Dodd et al.,2009; McClung et al.,2008),可在肌肉收縮活動(dòng)減少期間防止蛋白質(zhì)的降解(Naito et al.,2000)。因此,HSP增加可能是 BFRT引起肌肉肥大和預(yù)防肌肉萎縮的潛在機(jī)制之一。
研究還發(fā)現(xiàn),BFR運(yùn)動(dòng)中由于細(xì)胞內(nèi) Ca2+濃度升高或血流再灌注可激活神經(jīng)型一氧化氮合酶( NOS-1)并產(chǎn)生一氧化氮(NO)(Uematsu et al.,1995)。一方面,NO 可直接激活 mTOR信號通路以促進(jìn)蛋白質(zhì)的合成(Ito et al.,2013);另一方面,NO在運(yùn)動(dòng)中可能通過合成肝細(xì)胞生長因子(HGF)激活衛(wèi)星細(xì)胞,并導(dǎo)致衛(wèi)星細(xì)胞的增殖(Anderson,2000)。隨后衛(wèi)星細(xì)胞不斷分化并相互融合形成新的肌纖維和/或融合現(xiàn)有的肌纖維,使肌纖維肥大(Snijders et al.,2015)。已有研究在BFRT后觀察到NOS表達(dá)顯著增加(Kawada et al.,2005; Larkin et al.,2012)。因此,NO對BFRT產(chǎn)生的肌肉適應(yīng)可能具有重要作用。
除了促進(jìn)蛋白質(zhì)合成外,抑制肌肉生長蛋白表達(dá)的降低對蛋白質(zhì)平衡趨于正向合成也可能產(chǎn)生一定作用。肌肉生長抑制素可調(diào)節(jié)衛(wèi)星細(xì)胞的活性和自我更新(McCroskery et al.,2003),這一蛋白的缺失將引起肌肉組織的過度生長(McCroskery et al.,2003; Mesires et al.,2002),其主要通過受體調(diào)節(jié)型 Smad蛋白(Smad2/3)的磷酸化來抑制成肌細(xì)胞和肌管的分化(McCroskery et al.,2003; McPherron et al.,1999;Rebbapragada et al.,2003),進(jìn)而負(fù)調(diào)節(jié)肌肉生長(Lin et al.,2002; Trendelenburg et al.,2009)。已有研究發(fā)現(xiàn),BFRT中肌肉生長抑制素表達(dá)的降低(Drummond et al.,2008;Laurentino et al.,2012)。Laurentino等(2012)將29名年輕男性受試者分為BFRT組(20% 1RM)、高強(qiáng)度訓(xùn)練組(HI組,80% 1RM)和低強(qiáng)度訓(xùn)練對照組(LIT組,20%1RM),8周的伸膝訓(xùn)練后,僅在 BFRT和 HI組發(fā)現(xiàn)肌肉生長抑制素表達(dá)顯著降低(分別下降45%和41%),而LIT組未見顯著變化。這表明,肌肉生長抑制素表達(dá)降低也可能對BFRT引起肌肉肥大具有一定的作用。
肌纖維募集的增加也可能是引起肌肉增長的一種機(jī)制。早期研究證明,高閾值運(yùn)動(dòng)單位除了與肌肉收縮的力和速度相關(guān),還與運(yùn)動(dòng)中的氧濃度有關(guān)(Katz et al.,1987;Moritani et al.,1992)。BFRT中代謝產(chǎn)物累積的增大可以通過 III和 IV組傳入神經(jīng)的代謝刺激(Krogh-Madsen et al.,2010)或橫橋循環(huán)抑制(Kubota et al.,2011)更快地引起神經(jīng)肌肉疲勞。根據(jù)肌纖維募集的大小原則(size principle),肌肉在運(yùn)動(dòng)中首先募集慢肌纖維,但隨著運(yùn)動(dòng)強(qiáng)度的增加,肌肉不斷增加對高閾值快肌纖維的募集(Henneman et al.,1965),而 BFRT被認(rèn)為可對更多數(shù)量的肌纖維進(jìn)行刺激。運(yùn)用肌電圖對 BFRT的研究表明,低強(qiáng)度 BFRT組的肌肉放電頻率和幅度顯著大于低強(qiáng)度對照組(Kim,2009;Loenneke et al.,2011),并由此證明了該機(jī)制在 BFRT中產(chǎn)生作用的可能。然而,學(xué)者對此機(jī)制的觀點(diǎn)并不一致,如Cook等(2013)未發(fā)現(xiàn) BFRT組肌肉激活較對照組顯著更大。
Loenneke等(2012b)提出,因運(yùn)動(dòng)中細(xì)胞水合作用增加的細(xì)胞腫脹反應(yīng)(Cell Swelling)可能是 BFRT引起肌肉肥大適應(yīng)的潛在機(jī)制。由于BFR運(yùn)動(dòng)中代謝產(chǎn)物大量累積所產(chǎn)生的壓力梯度,使血液流進(jìn)肌纖維并引起細(xì)胞腫脹,這種反應(yīng)不僅可以促進(jìn)蛋白質(zhì)合成,還有助于減少細(xì)胞中的蛋白質(zhì)水解(Lang et al.,1998)。雖然的確已有研究在BFR運(yùn)動(dòng)后發(fā)現(xiàn)了肌肉腫脹的現(xiàn)象(Yasuda et al.,2015;Yasuda et al.,2012),但是目前對這一機(jī)制研究較少,還沒有研究證明由于細(xì)胞腫脹引起的蛋白質(zhì)水解減少是否有利于BFRT后肌肉的生長。
綜上所述,盡管目前已經(jīng)提出多種 BFRT的可能作用機(jī)制,但支持 BFRT產(chǎn)生肌肉適應(yīng)的機(jī)制尚不統(tǒng)一。有限的證據(jù)表明代謝應(yīng)激可能起主導(dǎo)作用,其通過激素分泌、肌纖維募集和肌細(xì)胞腫脹,最終影響了蛋白質(zhì)合成和抑制過程。
盡管作為一種高強(qiáng)度力量訓(xùn)練的替代方法,BFRT對于健身人群、醫(yī)療康復(fù)人群和競技運(yùn)動(dòng)員顯示出了其特有優(yōu)勢,但作為一種新型的負(fù)荷刺激方法,BFRT還存在眾多有待解決的問題,需要未來更多的實(shí)踐應(yīng)用和科學(xué)研究。
1)文獻(xiàn)中BFRT的應(yīng)用人群目前還以無訓(xùn)練經(jīng)驗(yàn)或康復(fù)人群為主,以高水平運(yùn)動(dòng)員為對象的研究相對有限。高水平運(yùn)動(dòng)員在保持現(xiàn)有訓(xùn)練形式(內(nèi)容、強(qiáng)度、量、課次頻率等)的前提下如何合理運(yùn)用 BFRT替代部分現(xiàn)有高強(qiáng)度訓(xùn)練,并且最終促進(jìn)運(yùn)動(dòng)成績的提升,還有待更多的研究。
2)現(xiàn)有研究主要證明低強(qiáng)度BFRT能夠達(dá)到甚至超過無 BFR限制的低強(qiáng)度訓(xùn)練,但 BFRT的劑量效應(yīng)尚未確定,即如何根據(jù)練習(xí)人群的特征在合適的訓(xùn)練階段選擇合適的 BFRT運(yùn)動(dòng)方式、強(qiáng)度、量、間歇、組數(shù)、周課次頻率等。
3)一些影響B(tài)FRT的方法學(xué)問題還有待進(jìn)多地關(guān)注,這些問題包括:BFRT器材(材質(zhì)、寬度、松緊)、BFRT的交互效果(即BFR部位對其他部位的影響)、BFRT的營養(yǎng)補(bǔ)充等。
4)BFRT的安全性問題。BFR對代謝壓力的增加是否在個(gè)體(尤其是老年人群和康復(fù)人群)的安全承受范圍內(nèi)還有待進(jìn)一步研究。
5)BFRT可能存的負(fù)面效果(如是否影響神經(jīng)沖動(dòng)和肌肉收縮速度)和長期訓(xùn)練效應(yīng)還尚不明確。
肌肉質(zhì)量和力量是改善健康、預(yù)防跌倒和損傷、提升運(yùn)動(dòng)表現(xiàn)的重要保障,≥70% 1RM被認(rèn)為是發(fā)展肌肉質(zhì)量的有效強(qiáng)度。然而對于包括運(yùn)動(dòng)員在內(nèi)的損傷康復(fù)人群和沒有大強(qiáng)度訓(xùn)練(包括力量訓(xùn)練在內(nèi))經(jīng)驗(yàn)的健身人群來說,大強(qiáng)度力量訓(xùn)練可能會增加損傷風(fēng)險(xiǎn)和主觀不適。BFRT以低強(qiáng)度達(dá)到高強(qiáng)度訓(xùn)練效果的優(yōu)勢受到了健身人群、醫(yī)療康復(fù)人群和競技運(yùn)動(dòng)員的歡迎?,F(xiàn)有研究表明,BFRT可以有效地引起肌肉肥大和力量增長,BFR結(jié)合低強(qiáng)度有氧運(yùn)動(dòng)有利于提升有氧能力,BFR的單獨(dú)使用和/或與康復(fù)訓(xùn)練相結(jié)合使用,可以有效防止由于長期無負(fù)荷狀態(tài)期間導(dǎo)致的廢用性肌萎縮和肌無力,有利于促進(jìn)損傷或術(shù)后康復(fù)進(jìn)程。BFRT產(chǎn)生效果的主要作用機(jī)制為代謝壓力(缺血缺氧和乳酸堆積)增加,并主要涉及激素分泌(GH和 IGF-1)、蛋白質(zhì)合成(mTOR、HSP和 NO)和抑制(肌肉生長抑制素)調(diào)節(jié)、肌纖維募集和細(xì)胞腫脹等過程。
在競技體育領(lǐng)域,我國在備戰(zhàn)東京奧運(yùn)會和北京冬奧會的科技助力過程中將 BFRT作為一種新的訓(xùn)練方法進(jìn)行推廣和使用,一些運(yùn)動(dòng)項(xiàng)目的教練員和運(yùn)動(dòng)員在摸索的過程中也感受到了 BFRT的訓(xùn)練優(yōu)勢。但需要注意的是,競技體育的訓(xùn)練是一個(gè)綜合應(yīng)用各種方法的過程,只有從項(xiàng)目特征和需求出發(fā),合理搭配應(yīng)用各種方法才能真正有助于競技能力的提升。
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