Research article summary (published 20 Feb 2007):

Severity of arterial hypoxaemia affects the relative contributions of peripheral muscle fatigue to exercise performance in healthy humans.

Full Abstract

We examined the effects of hypoxia severity on peripheral versus central determinants of exercise performance. Eight cyclists performed constant-load exercise to exhaustion at various fractions of inspired O2 fraction (FIO2 0.21/0.15/0.10). At task failure (pedal frequency < 70% target) arterial hypoxaemia was surreptitiously reversed via acute O2 supplementation (FIO2 = 0.30) and subjects were encouraged to continue exercising. Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force (DeltaQ(tw,pot)) as measured pre- versus post-exercise in response to supramaximal femoral nerve stimulation. At task failure in normoxia (haemoglobin saturation (SpO2) approximately 94%, 656 +/- 82 s) and moderate hypoxia (SpO2) approximately 82%, 278 +/- 16 s), hyperoxygenation had no significant effect on prolonging endurance time. However, following task failure in severe hypoxia (SpO2) approximately 67%; 125 +/- 6 s), hyperoxygenation elicited a significant prolongation of time to exhaustion (171 +/- 61%). The magnitude of DeltaQ(tw,pot) at exhaustion was not different among the three trials (-35% to -36%, P = 0.8). Furthermore, quadriceps integrated EMG, blood lactate, heart rate, and effort perceptions all rose significantly throughout exercise, and to a similar extent at exhaustion following hyperoxygenation at all levels of arterial oxygenation. Since hyperoxygenation prolonged exercise time only in severe hypoxia, we repeated this trial and assessed peripheral fatigue following task failure prior to hyperoxygenation (125 +/- 6 s). Although Q(tw,pot) was reduced from pre-exercise baseline (-23%; P < 0.01), peripheral fatigue was substantially less (P < 0.01) than that observed at task failure in normoxia and moderate hypoxia. We conclude that across the range of normoxia to severe hypoxia, the major determinants of central motor output and exercise performance switches from a predominantly peripheral origin of fatigue to a hypoxia-sensitive central component of fatigue, probably involving brain hypoxic effects on effort perception.

Author information

Author/s: Amann, Markus (M); Romer, Lee M (LM); Subudhi, Andrew W (AW); Pegelow, David F (DF); Dempsey, Jerome A (JA);

Affiliation: University of Wisconsin Medical School, John Rankin Laboratory of Pulmonary Medicine, Madison, WI, USA. amann(-atsign-)wisc.edu

Grants: HL-15469 (Agency:NHLBI NIH HHS)

Journal and publication information

Publication Type: Clinical Trial; Journal Article; Research Support, N.I.H., Extramural

Journal: The Journal of physiology (J Physiol), published in England. (Language: eng)

Reference: 2007-May; vol 581 (issue Pt 1) : pp 389-403

Dates: Created 2007/05/15; Completed 2007/07/23; Revised 2008/11/21;

PMID: 17317739, status: MEDLINE (last retrieval date: 2/18/2009, IMS Date: )

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

Comments and Corrections

CommentIn: J Physiol. 2007 Dec 15;585(Pt 3):919-21; author reply 923-4. (PMID: 17962324)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adult Anoxia - blood; physiopathology Bicycling - physiology Brain - physiology Electromyography Exercise - physiology Heart Rate - physiology Humans Lactates - blood

Lactates - blood Magnetics Male Muscle Fatigue - physiology Muscle, Skeletal - physiopathology Oxygen - administration & dosage; metabolism Physical Endurance - physiology Physical Exertion - physiology Severity of Illness Index

Associated Chemicals: Lactates (0) ; Oxygen (7782-44-7)

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