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Exercise-induced Fatigue in Severe Hypoxia after an Intermittent Hypoxic Protocol


Medicine & Science in Sports & Exercise: December 2017 - Volume 49 - Issue 12 - p 2422–2432
doi: 10.1249/MSS.0000000000001371
Basic Sciences

Purpose 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.

Methods 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.

Results From pre- to postexercise in TTF-Pre, maximal voluntary contraction (MVC), cortical voluntary activation (VATMS), and potentiated twitch force (Q tw,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.

Conclusions 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.

Supplemental digital content is available in the text.

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

Address for correspondence: Rosie Twomey, Ph.D., Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4; E-mail:

Submitted for publication April 2017.

Accepted for publication June 2017.

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© 2017 American College of Sports Medicine