Effect of acute hypoxia on central fatigue during repeated isometric leg contractions

Abstract

To determine whether hypoxia has a direct influence on the central command independently of the working muscles, 16 subjects performed intermittent isometric unilateral knee extensions until exhaustion either in normobaric hypoxia (inspired O(2) fraction=0.11, arterial oxygen saturation approximately 84%) or in normoxia while the knee extensor muscles were exposed to circulatory occlusion with a 250 mmHg cuff. Among the subjects, 11 also performed the tests in hypoxia and normoxia without occlusion. Single electrical stimulations were regularly delivered to the femoral nerve to measure the changes in the knee extensor peak twitch force. With the cuff, the average slope of decrease in peak twitch did not depend on the inspired oxygen fraction. Performance was slightly but significantly lower during hypoxia than in normoxia (8.2+/-2.6 vs 9.4+/-3.1 repetitions, P<0.05) with the cuff on. The number of repetitions was much higher during hypoxia with maintaining leg blood flow (15.6+/-4.5 repetitions) than with circulatory occlusion in normoxia. In conclusion, this study showed that a direct effect of hypoxia in reducing the motor drive to the working muscles exists but this effect is moderate.

Resistance Training Using Different Hypoxic Training Strategies: a Basis for Hypertrophy and Muscle Power Development

“…Literature describes a direct but moderate influence of the inspired O 2 fraction on the central nervous system. This conclusion was reached by Millet et al [62] after studying the response of intermittent isometric unilateral knee extensions to failure with and without blood flow restriction (BFR, via a cuff), in N and while breathing a reduced O 2 air (NH of 11% FiO 2 and 84% SaO 2 ). Both, hypoxia and the occlusion cuff, affected the number of repetitions.…”

The interactive effect of cooling and hypoxia on forearm fatigue development

“…However, increases in muscle fatigue during prolonged exercise in hypoxia have been observed during both whole-body (Amann & Calbet 2007) and repeated contractions of isolated muscle groups (Fulco 1994;Katayama et al 2007;Perrey & Rupp 2009;Millet et al 2008;Christian et al 2014a). The rise in muscle fatigue during hypoxia can be largely attributed to a shift of the relative exercise intensity, higher muscle fibre recruitment, and thereby increased intramuscular metabolic disturbance (Edwards 1981;Fulco et al 1996;Amann et al 2006a;2006b;2007a;2007b;Fulco et al 1994, Katayama et al 2007Christian et al 2014a).…”

“…In cold conditions (C, HC) T a was 5°C (50% RH) and participants wore the same clothing, minus any upper body insulation (t-shirt). 5°C T a was selected in an attempt to reduce average skin temperature (T sk ) by approximately 5-10°C, which in turn was assumed to change forearm muscle temperature and cause an increase in fatigue (Oksa et al 2002) equivalent attitude = ~4000m) aiming to reduce peripheral arterial oxygen saturation (SpO 2 ) to approximately 85%, a moderate level assumed high enough to influence fatigue during isolated muscle exercise (Millet et al 2008;Perrey & Rupp 2009;Christian et al 2014a). The selection of temperature and F I O 2 also aimed to balance severity with ecological validity, in order to maintain relevance for those working or exercising at altitude.…”

“…Specifically, the increase in inorganic phosphate, reactive oxygen species and hydrogen ion production and their interference with the contractile proteins and sarcoplasmic Ca 2+ release mechanisms are thought to be a major factor behind the increase in muscle fatigue development Hogan et al 1999;Amann & Calbet 2007;Perrey & Rupp 2008). In hypoxia, evidence also suggests increased afferent feedback and decreased cerebral oxygenation can reduce voluntary drive to the muscle, exacerbating net fatigue Amann et al 2006a;2007b;Goodall et al 2010;Millet, 2008;. However, the relative contributions of afferent feedback and cerebral oxygenation, as well as the sense of effort, to changes in central drive during 4 fatiguing exercise in hypoxia remains subject to on-going investigations (Millet et al 2008;Goodall et al 2010;Amann et al, 2013;Christian et al 2014a;Christian et al 2014b).…”

Cerebral perturbations during exercise in hypoxia

“…To separate the central and peripheral effects of hypoxia, including the potential inhibitory effect of sensory feedback from working muscles, Millet et al (64) induced ischemia of the exercising muscles, therefore maintaining a similar metabolic state within the working muscle independent of changes in FI O 2 . Subjects performed an intermittent isometric knee extension protocol (at 50% MVC) in normoxia or hypoxia (FI O 2 ϭ 0.11), with or without leg circulation occlusion (with a 250-mmHg cuff inflated proximally on the thigh).…”