Twomey Rosie, Wrightson James, Fletcher Hannah, Avraam Stephanie, Ross Emma, Dekerle Jeanne
1Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, CANADA; 2Centre for Sport and Exercise Science and Medicine, University of Brighton, Eastbourne, UNITED KINGDOM; and 3English Institute of Sport, Bisham Abbey National Sports Centre, Marlow, UNITED KINGDOM.
Med Sci Sports Exerc. 2017 Dec;49(12):2422-2432. doi: 10.1249/MSS.0000000000001371.
Exercise-induced central fatigue is alleviated after acclimatization to high altitude. The adaptations underpinning this effect may also be induced with brief, repeated exposures to severe hypoxia. The purpose of this study was to determine whether (i) exercise tolerance in severe hypoxia would be improved after an intermittent hypoxic (IH) protocol and (ii) exercise-induced central fatigue would be alleviated after an IH protocol.
Nineteen recreationally active men were randomized into two groups who completed ten 2-h exposures in severe hypoxia (IH: partial pressure of inspired O2 82 mm Hg; n = 11) or normoxia (control; n = 8). Seven sessions involved cycling for 30 min at 25% peak power (W˙peak) in IH and at a matched heart rate in normoxia. Participants performed baseline constant-power cycling to task failure in severe hypoxia (TTF-Pre). After the intervention, the cycling trial was repeated (TTF-Post). Before and after exercise, responses to transcranial magnetic stimulation and supramaximal femoral nerve stimulation were obtained to assess central and peripheral contributions to neuromuscular fatigue.
From pre- to postexercise in TTF-Pre, maximal voluntary contraction (MVC), cortical voluntary activation (VATMS), and potentiated twitch force (Qtw,pot) decreased in both groups (all P < 0.05). After IH, TTF-Post was improved (535 ± 213 s vs 713 ± 271 s, P < 0.05) and an additional isotime trial was performed. After the IH intervention only, the reduction in MVC and VATMS was attenuated at isotime (P < 0.05). No differences were observed in the control group.
Whole-body exercise tolerance in severe hypoxia was prolonged after a protocol of IH. This may be related to an alleviation of the central contribution to neuromuscular fatigue.
适应高海拔环境后，运动诱发的中枢性疲劳会得到缓解。这种效应背后的适应性变化也可能由短暂、反复暴露于严重低氧环境诱导产生。本研究的目的是确定：（i）间歇性低氧（IH）方案后，严重低氧环境下的运动耐力是否会提高；（ii）IH方案后，运动诱发的中枢性疲劳是否会得到缓解。
19名有运动习惯的男性被随机分为两组，分别在严重低氧环境（IH组：吸入氧分压82 mmHg；n = 11）或常氧环境（对照组；n = 8）下完成10次每次2小时的暴露。七次训练中，IH组以25%的峰值功率（W˙peak）进行30分钟骑行，对照组以匹配的心率进行骑行。参与者在严重低氧环境下进行基线恒定功率骑行至任务失败（TTF - 预）。干预后，重复骑行试验（TTF - 后）。运动前后，通过经颅磁刺激和超强股神经刺激获得反应，以评估中枢和外周对神经肌肉疲劳的影响。
在TTF - 预中，从运动前到运动后，两组的最大自主收缩（MVC）、皮质自主激活（VATMS）和增强的抽搐力（Qtw,pot）均下降（所有P < 0.05）。IH后，TTF - 后得到改善（535 ± 213秒对713 ± 271秒，P < 0.05），并进行了额外的等时试验。仅在IH干预后，等时情况下MVC和VATMS的降低有所减轻（P < 0.05）。对照组未观察到差异。
IH方案后，严重低氧环境下的全身运动耐力得以延长。这可能与中枢对神经肌肉疲劳的影响减轻有关。
