高温环境中训练和比赛的共识性建议
2016-10-15翻译徐金成高璨审校赵杰修
翻译:徐金成高璨审校:赵杰修
1国家体育总局体育科学研究所运动生物科学中心(北京100061)
2国家体育总局运动医学研究所(北京100061)
高温环境中训练和比赛的共识性建议
翻译:徐金成1高璨2审校:赵杰修1
1国家体育总局体育科学研究所运动生物科学中心(北京100061)
2国家体育总局运动医学研究所(北京100061)
译文通信作者:赵杰修,Email:zhaojiexiu1@163.com
高温环境中运动会引起体温调节和其它生理压力,继而可导致耐力运动能力的损害。本共识性声明的目的是提供最新的建议以使热环境中体育活动时的运动能力最优化。可用于降低热应激压力和优化运动能力的最重要干预方式是热习服,其应包括1~2周以上反复的运动—高温环境暴露。此外,运动员应在正常水合状态下开始比赛和训练,并将运动中的脱水最小化。随着商用降温系统(如降温背心)的发展,在高温环境中训练或比赛前,运动员可以采取降温策略来促进热的散发或提高蓄热能力。而且,赛事组织者应该设计大面积的遮阳区域,并提供降温和补水设施,按照最小化运动员的健康风险来安排赛事,尤其是在大众参与的赛事中及一年之中炎热天气开始之初。以最近的2008年奥运会和2014年国际足联世界杯为例,当比赛在高温环境中举行时,赛事主管机构应考虑在比赛中或比赛之间允许额外的(或更长的)恢复期以提供补水和降温的时机。
1 目标和范围
大多数重要的国际性赛事,例如夏季奥运会、国家足联世界杯和环法自行车赛——以电视观众而言,也是世界范围内最受欢迎的三项赛事——均在北半球的夏季月份举行,通常也是在热环境中进行。2014年3月23日、24日,在卡塔尔多哈ASPETAR骨科与运动医学医院举办的一个主题会议上,专家小组回顾和讨论了“高温环境中训练和比赛”这个专题。会议以圆桌讨论的形式结束,并达成了本共识性建议。
本文旨在为热环境中运动时的运动能力最佳化提供最新的建议。热环境中运动时,考虑到短时运动能力(如跳跃和冲刺)仅受到最轻微的影响,或甚至还能得到提高[1],但长时间运动能力显著受损[2],因此本共识性声明中的建议主要针对长时类运动项目。有关“高温环境中训练和比赛”的更多信息,读者可在《斯堪的纳维亚运动医学与科学杂志》(Scandinavian Journal of Medicine and Science in Sports)的专刊上获取,包括针对性综述和原创性研究[3]。
2 前言
高温环境中运动时,皮肤血流量和出汗率增加以利于机体向周围环境散热。但是,这些体温调节的调整会增加生理压力,可能会导致长时间运动时的脱水。当体温过高发生时,热应激可单独损害有氧运动能力[2,4-6]。因此,高温环境中运动时,运动员从事耐力性项目、持拍类项目及团队项目的工作效率较温和环境中低[7-12]。此外,高温环境运动中的脱水加剧了热调节和心血管压力[13-18],并进一步损害有氧运动能力[2,17,19]。本文中所含建议和策略可被用于维持/改善高温环境中训练和比赛时的运动能力,也可以使运动性中暑(Exertional heat illness)的风险最小化。如本文第1部分所述,能用于降低生理压力和优化运动能力的最重要干预方式是热习服。考虑到脱水可损害运动能力及加剧运动性热应激压力,本共识性声明的第2部分提供了关于补水的建议。第3部分强调了通过皮肤降温服装,如冰袋、冷毛巾、降温背心,以及冷水浸泡(Cold water immersion,CWI)或冰浆饮料的应用,在运动前或运动中可能降低核心和皮肤温度的方法。
考虑到缺乏实际比赛中的数据,国际奥委会(IOC)强调了各专项运动协会、队医和科研工作者共同合作收集优秀运动员这一特定人群在具有挑战性环境中运动时数据的必要性[20]。有几个国际性运动协会,如国际足联(FIFA)、国际泳联(FINA)、国际排联(FIVB)、国际田联(IAAF)和国际网联(ITF),已经启用监控系统评估比赛时的环境条件及相关不良后果,开展这项具有挑战性的工作[12,21-23]。许多运动协会也已修改了他们的指导原则以进一步降低运动性中暑的风险。这些指导原则在本共识性建议的第4部分进行了综述。本文还针对在高温环境中赛事期间如何最好地保护运动员的健康和维持/改善运动能力,向赛事组织者和运动主管机构提供了建议。
3 热习服
尽管温和环境中的规律运动会引发部分的热习服[24],但其并不能取代高温环境中连续多日训练所引发的效益[24-27]。热习服可改善温热条件下的热舒适感与次最大和最大强度下的有氧运动能力[11,28,29]。热习服的益处通过以下途径获得:增加汗液分泌和皮肤血流反应,血浆容量扩张从而改善心血管功能稳定性(即维持血压和心输出量的能力更佳)和体液—电解质平衡[19,30,31]。因此,运动性热习服对于备战温热环境中比赛的运动员来说是必不可少的[30]。本部分描述了如何实施热习服方案和使其对运动员的效益最优化。
3.1热习服的诱导
3.1.1持续时间
大多数适应性改变(即心率、皮肤和肛门温度的降低,出汗率和工作能力的提高)在热习服的第1周内发生,在随后2周内进展较为缓慢[32-34]。与未经训练的个体相比,这些适应性变化在训练有素的运动员中发展更为迅速(时间可相当于前者的一半)[24,35]。因此,运动员在热习服的前几天即可受益[36-38],但需要6~10天才能获得近乎完整的心血管和泌汗运动神经的适应性变化[28,29,39],因而需要2周才能使热环境中的有氧运动能力(即自行车计时测试)最优化[11]。
3.1.2训练
任何热习服方案的根本原理是体温(核心和皮肤)的升高以诱导大量出汗和增加皮肤血流量[19,30]。最初,研究显示高温环境中反复的100米运动训练有效诱导了上述反应[40]。另据报道,热环境中(40℃,10%RH)每天以60%最大摄氧量(VO2max)强度运动到力竭,持续9-12天,可将运动能力从48 min提升到80 min[28]。适应性变化的幅度最终取决于强度、持续时间、频率和热暴露的次数[30,31]。例如,Houmard等[41]报道中等强度短时间(30-35 min,75%VO2max)和低强度长时间(60 min,50%VO2max)运动后出现了相似的生理适应性变化。
随着热习服的进展,恒定负荷的运动方案可能导致一个逐渐降低的训练刺激(即相对运动强度的减小)。相应地,如果高温环境中运动训练课的持续时间和/或强度不对应增加,就可能会限制适应性变化的幅度[42]。在可能的情况下,可采用等温方案(例如核心温度至少在38.5℃的受控高体温)以使适应性变化最优化[43,44]。尽管如此,等温方案可能需要更强的控制及使用人工实验室条件,因此可能会限制其在场地中的实用性。或者,最近有人提出利用基于心率的受控强度方案来实现习服过程中增加绝对强度和维持相似相对强度的需求[31]。最后,运动员可通过高温环境中的户外训练进行适应(即习服),可以是自我调控的运动或维持原有的常规训练方案。该练习的功效已在团队项目运动员中得到证实[45,46],且不会干扰他们的训练方案。
3.1.3环境
干热环境中的热习服可改善湿热环境中的运动能力[48,49],反之亦然[49]。但是,湿热环境中的习服较干热环境产生更高的皮肤温度和循环适应,可能增加最大皮肤湿润度,因此增大从皮肤蒸发性散热的最大速率[30,31,50]。尽管该做法依然缺乏科学支持,但是在干热环境中热习服训练的末期让运动员转移到湿热环境中进行训练,进一步刺激心血管和体温调节系统,对于运动员来说可能是有益的。然而,尽管不同环境中的习服存在迁移效应,但有些适应性变化是特定于气候(沙漠或热带)和体力活动水平的[51]。因此,建议运动员主要针对即将比赛的环境进行习服。
不能到自然热环境中(所谓的自然气候习服(Acclimatisation))的运动员可以在人工室内热环境中进行训练习服(所谓的实验室习服(Acclimation))。然而,虽然实验室习服和自然气候习服有相似的生理适应性变化,但户外训练对于比赛环境更具特异性,因为它可以让运动员体验到热应激的实质[52-54]。
3.2短期热习服的衰退和周期
热适应以不同的速度衰退,最快的适应性变化衰退也更快[35]。然而,热习服的衰退速率通常是慢于其诱导速率的,这就允许热习服的大多数效益(例如心率、核心温度)可维持2~4周[34,55-58]。而且在此期间,个体的再习服要快于第一个习服期[57](表1)。但是这些研究主要基于热习服的生理指标,竞赛运动能力的衰退仍有待进一步的阐释。
表1 热习服策略示例
3.3个体化热习服
热习服可明显减弱生理应激压力[59,60]。然而,个体的习服反应可能有所不同,因此应该使用一些简易的指标进行监控,例如标准次最大强度运动时心率增加幅度的减少[33,61-63]。监控热习服的其它较难与较不敏感指标包括出汗率和钠含量[64],核心温度[33]和血浆容量[65]。热习服中,血浆容量扩张的作用仍然存在争议,因为人为地增加血浆容量似乎并没有改善体温调节能力[66,67],但是在短期热习服之后的热应激反应测试中,红细胞压积(Hct)的变化与个体运动能力相关[45,46]。这就提示血浆容量变化可能代表了一个有价值的指标,即使其可能并非是改善高温环境中运动能力的生理机制。重要的是,适宜温和环境中的测量方法并不能用于替代热环境中的测试[45,46,68]。
如同热习服的诱导一样,热习服的衰减在不同个体间也存在差异[32]。因此,我们建议运动员在重大高温赛事前数月进行一个习服练习以确定他们个体化的适应与衰减速率[20,45](表1)。
3.4热习服作为训练刺激
最近几项实验室或未加环境控制的场地研究已报告指出适宜温和环境中的身体运动能力在高温环境中训练后得到改善[29,46,62,69,70]。因此,赛季前和赛季中,运动员可考虑采用热环境中的集训来改善身体运动能力[46](表1)。需要谨记的是,训练质量不应该被损害,从中获益最多的运动员可能是那些需要新异训练刺激的有经验的运动员[46],而对于训练有素而又需有限体温调节需求(如冷环境中的自行车运动)的运动员来说,益处可能更多地视情况而定[71]。
3.5热习服主要建议的总结
—计划到热环境中进行比赛的运动员应进行热习服(即高温环境中的反复训练)以获得生物适应性变化,继而降低高温环境中的生理应激压力和改善高温环境中的运动能力。
—热习服训练课应持续至少60分钟/天,应诱导核心和皮肤温度的升高,还应刺激出汗。
—运动员应在与比赛场地相同的环境中进行训练,或如不可能的话,则应在室内热环境房内进行训练。
—早期适应性变化在最初几天即可获得,但是主要的生理适应性变化直到1周后才能完整获得。理想条件下,为了最大化所有的效益,热习服阶段应超过2周。
4 补水
热环境中运动时,体温过高的发展与出汗率的升高有关,如果体液的丢失未通过增加液体摄入而最小化,则可导致渐进性脱水。运动性脱水,导致机体处于缺水状态,与血浆容量的降低和血浆渗透压的升高相关,后两者与体内总水分含量的降低成比例[19]。血管舒张相关核心体温阈值的升高和运动起始的排汗与随后产生的高渗透压和血容量过低紧密联系在一起[72,73]。运动时,血浆高渗会降低任何给定核心体温的出汗率,减少蒸发散热[74]。此外,脱水还会减少心脏充盈,给血压调节带来挑战[75-77]。因此,机体的热蓄积率和心血管压力加剧,高温环境中的运动耐受能力则降低[78-80]。
尽管该领域的研究已有数十年[81],脱水损害竞技运动中有氧能力这一观点并未得到普遍接受,似乎存在一个两极化的争议[82-84]。大量研究报告指出如果运动是在温热环境中进行且水分的缺失已至少超过体重的2%时,脱水会损害该情况下的有氧运动能力[13,49,81,85-90]。另一方面,一些最近的研究认为在真实自然生态条件下,达体重4%的脱水并未改变自行车运动表现[82,83,91]。然而,对上述研究结果的解读必须结合研究背景:训练有素的自行车运动员是在高达33℃、60%RH的环境中通常进行60 min运动,且开始运动时身体处在水分充足状态。尽管如此,还是有人提出了一个观点,即脱水的不良后果被运动饮料公司过分强调了[92]。正因如此,有人认为应根据口渴感饮水[82,83,91]。但是,许多研究(通常是在运动饮料被发明和市场化之前进行)已经反复观察到当出汗率高及在温热环境中运动时,根据口渴感饮水往往导致机体水的缺失,其可能超过体重的2%~3%[13,47,49,93-98]。总之,根据口渴感饮水可能在很多环境中适用,但不适用于可预期到严重脱水的情况中(如铁人三项)[84]。
在比赛环境中,补水取决于几个因素,包括液体的可获得性和赛事的特异性。例如,由于比赛中暂停休息的频次,网球运动员可定期补液,其它运动员,如马拉松运动员,则只有较少的机会进行补水。不同选手之间也存在区别。最快的马拉松选手在比赛中不会摄取大量的液体及脱水,相反地,较慢的选手可能补水过度[99],且伴随着水中毒(即低钠血症)的相关风险[100]。马拉松比赛中产生低钠血症的相关易感因素包括体重大量增加、比赛时间长于4小时、女性及低身体质量指数(BMI)[101,102]。因此,尽管下文中针对竞技运动员的建议解释了如何最小化与显著脱水和体重丢失(即≥2%)相关的运动能力损害,但参加长时间运动的业余运动员应注意不要在运动中补水过度。
4.1运动前补水
静止休息及营养充足人群通常是处在充足水合状态,每日的身体总水分含量差异在体重的0.2%到0.7%之间波动[93,104]。然而,当比赛前几天暴露于热应激条件下时,提醒运动员充分地饮水和补充电解质以确保身体充分水合状态的维持可能是明智的。一般而言,在此期间每隔2~3小时或高温环境中训练或比赛前2~3小时,以每千克(kg)体重6毫升(mL)的量饮水是适当的。
目前,有几个方法可用于评测身体的水合状态,鉴于体液丢失的方式和时间,每个方法都有其局限性[105,106]。最被广泛接受和推荐的方法包括监控体重变化,测量血浆渗透压和尿比重。基于这些方法,如果每日体重变化维持在<1%、血浆渗透压<290 mmol/kg及尿比重<1.020,即被认为是正常水合状态。这些技术方法可应用于持续多天的间歇性赛事中(如自行车分段赛,网球/团队项目的锦标赛),以监控水合状态。由于体重可能发生每日波动,设定基准体重是重要的。基准体重最好通过测量连续数日清晨排空后的裸体重来获得,测试前一晚摄取1~2 L的液体[81]。此外,因为运动、饮食和早前的饮水会影响尿液浓度的测量,第一次晨尿是评价水合状态的首选评定时间点[81]。如果不能获取第一次晨尿,尿液采集前的数小时应只有最小量的体力活动、液体摄入和进食。
4.2运动中补水
鉴于代谢速率、环境条件和热习服状态,高温环境中运动时的出汗率差异显著[107]。虽然对于热环境中进行剧烈运动的运动员来说,范围1.0 L/h-1.5 L/h的出汗率值是常见的,但是某些个体可超过2.5 L/h[108-111]。在过去的数十年中,不同的数学模型已被发展用于预测广泛环境条件中的汗液丢失[112-117]。虽然其已被证明在公共健康、军事、职业及运动医学领域中是有用的,但是这些模型仍需进一步的完善和针对运动员群体的个性化,尤其是优秀运动员。
汗液中丢失的主要电解质是钠(20~70毫克当量/升(mEq/L))[118-119],对于出汗严重且汗液中含较多盐分的人,运动中需要进行补充,以维持血浆中的钠平衡。严重出汗者可能还需要在炎热天气中的训练和比赛前后注意增加钠(即盐分)的摄入量以维持钠平衡(如在0.5 L糖-电解质饮料中加入3.0 g的盐)。为此,美国医学研究所(Institute of Medicine)[103]已经强调有关钠摄入的公共健康建议不适用于汗液中丢失大量钠的个体,如高温环境中训练或比赛的运动员。盐分的摄入如果不能代偿汗液中钠的丢失就会导致体内钠的缺失,钠缺失达到体内可交换性钠盐池的20%~30%时,就可能导致肌肉痉挛[120]。因此,持续时间超过1小时的运动中,运动员应力求摄入一份含0.5~0.7 g/L钠的溶液[121-123]。对于出现肌肉痉挛的运动员,建议将液体中钠的补充增加到1.5 g/L[124]。对于超过1小时的运动,运动员在其补水方案中还应力求包括30-60 g/h量的糖摄入;运动时间超过2.5小时的赛事,糖的摄入量可达90 g/h[125];上述建议可通过液体和固体食物的组合来实现。4.3运动后补水
高温环境中训练或比赛后,水分的再补充对促进优化恢复尤为重要。如果体液的缺失迫切地需要得到补充,那么建议在运动停止后的1小时内补充体重丢失量的150%[123,126],其中包含电解质的补充,以维持体内总水分含量。从实际角度来看,由于各种原因(例如时间、肠胃不适),上述建议并不是所有运动员都能实现的。因此,更实际的是补充体重丢失量的100%~120%。运动后补水的首选方式是通过液体和食物(例如咸食)的摄入。
考虑到高温环境中运动会增加糖的代谢[127,128],耐力运动员应确保不仅水和钠的丢失得到补充,而且糖存储也应得到补充[129]。为确保肌肉糖原再合成的最高速率,糖的摄取应该在运动结束后的1小时内[130]。而且,含蛋白质的饮品(例如牛奶)较标准的糖-电解质运动饮料可能更好地实现运动后的体液平衡恢复[131]。有报告指出结合蛋白质(0.2~0.4 g/kg/h)和糖(0.8 g/kg/h)的摄入可最大化蛋白质的合成率[132]。因此,运动员在运动后应该考虑摄取如巧克力牛奶样的饮料,其含有4:1的糖-蛋白质比例,同时还含有钠[133]。
4.4补水主要建议的总结
—高温环境中训练和比赛前,运动员应每隔2~3小时以6 ml/kg体重的量饮水,以便开始运动时处在正常水合状态。
—高温环境中长时间大强度运动时,身体水分的丢失应该被降低到最小(不出现体重增加)以降低生理应激压力及帮助维持最佳运动能力。
—高温环境中训练的运动员较一般人群有更高的每日钠(即盐分)需求。运动中钠的补充也可能是有必要的。
—对于持续多日的比赛(如自行车分段赛,网球/团队项目锦标赛),简便的监测方法,如监测每日晨起体重和尿比重,可有助于深入了解运动员的每日水合状态。
—通过提供充足的液体和食物来实现运动-高温应激后的充分补水是必要的。如果需要积极快速的补充,那么摄入液体和电解质来补偿体重丢失量的100%~150%就可实现充分补水。
—恢复性补水方案应包含钠、糖和蛋白质。
5 降温策略
皮肤降温会降低高温环境中运动时的心血管压力,而全身降温可降低器官和骨骼肌的温度。数项在受控实验室条件下(如不可代偿的热应激)的研究,运动中大多数伴随或未伴随降低通风强度的情况,已报告指出预冷降温可改善耐力[134-140]与高强度[141]及间歇冲刺或重复冲刺运动能力[142-145]。但是,其它几个研究报告指出未见预冷降温对高温环境中间歇冲刺或重复冲刺运动能力的改善效益[142,146-148]。在单次冲刺或涉及重复冲刺运动的最初几次练习中,全身降温(包括运动肌的降温)甚至不利于运动能力的发挥[149,150]。
因此,虽然数篇综述得出降温干预可延长高温环境中运动能力的结论[151-158],但必须承认,基于实验室的降温干预研究与户外空气流动的环境相比可能高估了预冷降温的效应[159],或者未考虑到赛前热身的需求。因此,比赛环境中的降温效应依然是不清晰的,下文中的建议限于无气流运动或有限气流运动热环境中的长时间运动。
5.1冷水浸泡
有众多的冷水浸泡(Cold water immersion,CWI)方案可以利用(综述可见本文参考文献[156,160-162]),但最常用的方法是在22~30℃水温中全身CWI 30 min,或肢体节段(如腿部)在更低的水温中(10~18℃)浸泡[156]。然而,腿部/肌肉的冷却降温会降低神经传导和肌肉收缩速度[1],因此运动员在比赛前可能需要再次热身。所以,包含降温服在内的其它技术方法就被发展用于选择性地对运动员躯干进行降温,这就可能防止活动肌群的过度降温,同时降低总热应激和心血管压力。
5.2降温服
在为实现降温目的而应用冰毛巾的早期实践基础上,一些厂商设计了用于运动员运动前或运动中降温的冰夹克[137,142,163,164]。与CWI或混合降温法相比[158],使用降温背心时的核心温度降低更少,但是降温服体现了降低皮肤温度这一优势,继而减小心血管压力,最终可降低热蓄积[165]。降温服的实用性在于可在不降低肌肉温度的情况下降低皮肤温度,且运动员可在热身或恢复间歇时穿着。
5.3冷液的摄取
在运动前[166,167]而非运动中[168,169]摄取冷液,可能会促进耐力性运动能力的发挥。实际上,有人指出运动中摄取冷液的一个负面作用是可能减少出汗从而减少皮肤表面的蒸发[170],其应归因于可能位于腹部的温度感受器的激活[171]。
5.4冰浆饮料
根据热力学焓理论,与升高水温所需的能量(4 J/g/℃)相比,冰需要更多的热能(334 J/g)才能引起从固态到液态(0℃时)这样一个相变。因此,在使运动员降温方面,冰浆可能较冷水摄入更有效。但是,尚不清楚与运动中冷水摄入成比例降低的汗液分泌[170]是否在摄取冰浆时发生。有几项近期研究报告支持冰浆饮料的摄入,因为无论运动前[140,172,173]抑或运动中[174]摄取冰浆饮料后(~1 L碎冰,≤4℃),耐力运动或间歇冲刺运动的运动能力均得到改善。但是在另一项研究中,在两回合运动的恢复间歇摄取冰浆,并无明显的效益[175]。因此,冰浆的摄取可作为外用降温法的一个实用补充或替代方法[155],但其在真实户外比赛中的应用仍需更多的研究。
5.5混合方法的降温策略
混合方法(即同时使用体内和体外降温策略)较相同方法的单独使用有着更高的降温能力,这就使得在运动能力上可获得更多的益处[158]。实际上,混合法降温应用于热带环境中比赛的足球运动员[176]、热环境中训练的网棒球运动员[177](译者注:又称长曲棍球)及实验室模拟比赛环境中的自行车运动员[139]时,已经被证明是有益的。在运动场景中,混合法降温可通过组合简便的方法来实现,例如饮用冰浆、穿戴降温背心及提供风扇。
5.6连续运动回合间降温以改善运动能力
有证据支持在高温环境中剧烈运动的组间恢复期(如15 min)可使用CWI(5~12min,水温14℃)来改善后续的运动能力发挥[178,179]。该做法的益处可能与血流从皮肤到中心循环的重新分布[180]及心理(即安慰剂)效应相关[181]。就体内降温而言,恢复期冷水[182]或冰浆[175]的摄入可能会减轻次回合运动的热应激压力,但并不一定显著提高运动能力[175]。这些研究结合到一起提示在不可代偿的实验室热应激环境中,降温可能会帮助剧烈运动后的恢复,而且在某些情况下,还可能提高后续剧烈运动回合中的运动能力发挥。积极降温与现场热环境或更凉爽环境中简单休息的效果比较还有待比赛条件下(例如团体项目中的中场休息)的验证。
5.7降温策略主要建议总结
—降温方法包括体外(例如冰服、毛巾、水浸泡或风扇的应用)和体内(例如冷液或冰浆的摄入)降温法。
—预冷降温可能有益于热环境中持久运动(例如中长距离跑、自行车、网球和团体项目)的体育活动。体内降温法(即冰浆)可在运动中使用,而网球和团体项目运动员也可在暂停休息间歇采用混合降温法。
—对于相似环境中进行的爆发力或较短时项目(例如冲刺、跳跃、投掷)来说,降温策略可能是不可行的。
—使用风扇和商用降温冰背心可能是湿热环境中的一个实用方法,它们可提供有效的降温而不损害肌肉温度。无论如何,降温方法应该在训练中进行测试和个性化,以将对运动员的干扰减至最小程度。
6 给赛事组织者的建议
赛事组织者调整或取消一项赛事所遵循的一系列最常见建议建立在湿球温度(Wet bulb global temperature,WBGT)指数基础上,该指数由美国军队均凭经验发展而来并被美国运动医学学会在运动医学中进行推广[183],而且被不同的运动协会所采纳(表2)。但是,当汗液蒸发受到限制时(即高湿度和/或较低的空气流动),WBGT可能低估了热应激的风险[184]。因此,有学者提出了修正性建议[185](表3)。此外,WBGT是一个气候指数且不能说明代谢产热或穿衣着装,因此不能预测热量的散失[19]。所以,下文中的建议为不同体育活动提供了指南而非基于WBGT指数的固定边界点。
表2 不同运动管理机构基于WBGT的建议措施示例
表3 基于WBGT的运动性中暑风险的校正估计——将WBGT低估高湿度下的热应激考虑在内
6.1取消赛事抑或采取对策?
关于预期环境中任何赛事的适当安排,当叠加的外源性和内源性热负荷不能被生理代偿时,为保护运动员健康,可能需要停止比赛。生理代偿极限被超越的环境条件取决于几个因素,例如代谢产热(取决于工作负荷和效率/经济性),运动员身体形态(例如体表面积-体重比),习服状态(例如出汗率)与着装。因此,不同运动项目建立统一的边界值(Cut-off values)是不科学的。环境指标应被赛事组织者视为采取预防性对策以抵消中暑潜在风险的建议。建议的对策包括考虑到降温间歇和液体补充可能性(时间和地点)而修改规则,此外还包括在休息期提供主动降温。还建议应将应对运动性中暑的医疗响应方案和设施准备就绪。
6.2建议的特异性
6.2.1运动项目间的差异
热环境会损害耐力运动能力,如马拉松[7],但可能改善短时运动项目能力,如跳跃和冲刺[1]。很多运动中,运动员会根据环境条件来调整他们的活动。例如,与较凉爽的环境相比,当在高温环境中(WBGT~34℃)运动时,足球运动员会减少比赛中的总跑动距离或高强度跑动距离,维持他们的冲刺活动/能力[9,12,186],而网球运动员会减少每分的得分时间[8]及增加每分之间的间歇时间[10]。因此,赛事组织者和国际协会应通过相应地修改规则和判罚来承认和支持这样的行为性体温调节策略。
6.2.2给定运动项目中个体间的差异
当比较两项在墨尔本举办的铁人三项比赛时,两项比赛的环境条件相似(即每项比赛中WBGT均从22℃上升到27℃),比赛间隔2个月,Gosling等[187]在第一项比赛中观察到15例运动性中暑(包括3例热射病(Heat stroke),其在夏初不合时令的炎热天气中举行,但在第二项比赛中未见任何病例。该研究表明中暑的风险在那些可能未经季节性热习服的运动员中增加[187],且支持了许多关于夏初或炎热天气时中暑风险增加的早期研究[188]。尽管如此,运动性热射病也可能发生在良好热习服及之前已进行过几次相似活动的个体中,因为他们可能在之前罹患了病毒感染或类似的疾病[19]。在极少数结合WBGT和运动员疾病的流行病学研究中,Bahr等[22]在3年时间中调查了48场沙滩排球比赛(包括世界巡回赛和锦标赛)。他们仅报告了1例与高温相关的医疗退赛,其与一名因3天急性肠胃炎导致体液平衡受损的运动员相关[22]。而且,虽然健康的跑者也能完成温湿环境中的半程马拉松而不发生中暑[189],凉爽环境中的马拉松赛时,运动性热射病已被证实可发生在正从病毒性感染中恢复的跑者上[190]。
事实上,先前的病毒感染正成为热损伤/热射病的潜在重要风险因素[19,191]。因此,赛事组织者应该对可能处于较大风险的所有人群给予特别的医疗关注,包括正在生病或正从近期感染中恢复的参赛者、腹泻者、近期免疫接种者、由于身体状况(如残奥会运动员)而散热能力受限者或因规则限制了散热能力(例如保护性的服装/装备)的运动项目参与者。未经环境习服的参赛者也存在风险。尽管在大型赛事中筛查每个运动员是不切实际的,但是赛事组织者应当提供相关信息以告知运动员在不同的机体受损状态下参赛时的相关风险及建议对策,这些信息可包含在注册时发送的用品中。
6.3给赛事组织者的主要建议总结
—WBGT是一个环境热应激指数,并不代表人体的热应激压力。因此,跨越不同运动项目为不同运动员建立绝对的参赛分界值是非常困难的,当制订极限高温环境策略时,我们更愿意推荐采取预防性对策或评价运动的专项需求。
—对策包括根据气候模式安排赛事的开始时间,修改规则和判罚以允许额外的暂停休息或更长的恢复期,制定医疗响应方案与开发降温设施。
—赛事组织者应特别关注所有的“风险”人群。考虑到未经气候习服的参赛者(主要在大众参与的赛事中)面临中暑的高风险,赛事组织者应适当告知参赛者比赛相关的风险,或考虑在意外或反常炎热天气条件下取消赛事。
7 总结
我们当前有关热应激的知识主要来源于军事和职业研究领域,而运动科学方面的知识补充则是源于近期研究资料。基于本文,运动员应至少训练1周,理想情况下2周,来进行环境的习服,并使用与目标赛事类似热应激程度的环境条件。运动员还应注意,以在正常水合状态下从事运动,并通过运动中的适当补水使身体水分的缺失(通过体重丢失的监控)最小化。运动员还可采取专门的对策(例如降温方法)来降低比赛和训练中的热蓄积和生理应激压力,尤其是当环境条件不可代偿时。赛事组织者和运动主管机构可通过允许高温环境比赛中的额外(或更长)恢复期以促进补水和提供降温时机来支持运动员。
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Consensus Recommendations on Training and Competing in the Heat
Original Authors:Sébastien Racinais,Juan-Manuel Alonso,Aaron J.Coutts,Andreas D.Flouris,Olivier Girard,José González-Alonso,Christophe Hausswirth,Ollie Jay,Jason K.W.Lee,Nigel Mitchell,George P. Nassis,Lars Nybo,Babette M.Pluim,Bart Roelands,Michael N.Sawka,Jonathan Wingo,Julien D.Périard.
Sébastien Racinais,Email:sebastien.racinais@aspetar.com
国家自然科学基金(31371195);国家体育总局重点领域课题(委14-08);国家科技部公益性研究院所专项基金项目(基本14-03)
注:本译文的发表已获得原文作者的许可。该共识性建议原文于2015年5月或6月已免费开源(Open Access)发表在《运动医学》(Sports Medicine;http://link.springer.com/article/10.1007/s40279-015-0343-6)、《英国运动医学杂志》(British Journal of Sports Medicine;http://bjsm.bmj.com/content/49/18/1164. long)、《斯堪的纳维亚运动医学与科学杂志》(Scandinavian Journal of Medicine and Science in Sports;http://onlinelibrary.wiley.com/doi/10.1111/sms.12467/full)。