Mechanical Alterations to Repeated Treadmill Sprints in Normobaric Hypoxia

PURPOSECompelling evidences suggest larger performance decrements during hypoxic vs. normoxic repeated sprinting, yet the underlying mechanical alterations have not been thoroughly investigated. Therefore, we examined the effects of different levels of normobaric hypoxia on running mechanical performance during repeated treadmill sprinting. METHODSThirteen team-sport athletes performed eight, 5-s sprints with 25-s of passive recovery on an instrumented treadmill in either normoxia near sea level (SL; FiO2 = 20.9%), moderate (MH; FiO2 = 16.8%; corresponding to ~1800 m altitude) or severe normobaric hypoxia (SH; FiO2 = 13.3%; ~3600 m). RESULTSNet power output in the horizontal direction did not differ (P>0.05) between conditions for the first sprint (pooled values13.09±1.97 W.kg) but was lower for the eight sprints in SH, compared to SL (-7.3±5.5%, P<0.001) and MH (-7.1±5.9%, P<0.01), with no difference between SL and MH (+0.1±8.0%, P=1.00). Sprint decrement score was similar between conditions (pooled values-11.4±7.9%, P=0.49). Mean vertical, horizontal and resultant ground reaction forces decreased (P<0.001) from the first to the last repetition in all conditions (pooled values-2.4±1.9%, -8.6±6.5% and -2.4±1.9%). This was further accompanied by larger kinematic (mainly contact time+4.0±2.9%, P<0.001 and +3.3±3.6%, P<0.05; respectively; and stride frequency-2.3±2.0%, P<0.01 and -2.3±2.8%, P<0.05; respectively) and spring-mass characteristics (mainly vertical stiffness-6.0±3.9% and -5.1±5.7%, P<0.01; respectively) fatigue-induced changes in SH compared with SL and MH. CONCLUSIONIn severe normobaric hypoxia, impairments in repeated-sprint ability and in associated kinetics/kinematics and spring-mass characteristics exceed those observed near sea level and in moderate hypoxia (i.e., no or minimal difference). Specifically, severe hypoxia accentuates the RSA fatigue-related inability to effectively apply forward-oriented ground reaction force and to maintain vertical stiffness and stride frequency..

Medienart:	Artikel

Erscheinungsjahr:	2016
Erschienen:	2016

Enthalten in:	Zur Gesamtaufnahme - year:2016
Enthalten in:	Medicine and science in sports and exercise - (2016)

Sprache:	Englisch

Beteiligte Personen:	Brocherie, Franck [VerfasserIn] Millet, Grégoire P [Sonstige Person] Morin, Jean-Benoit [Sonstige Person] Girard, Olivier [Sonstige Person]

Links:	Volltext

doi:	10.1249/MSS.0000000000000937

funding:
Förderinstitution / Projekttitel:

PPN (Katalog-ID):	OLC1972598708