Evidence that reduced skeletal muscle recruitment explains the lactate paradox during exercise at high altitude

Noakes, Timothy D.

doi:10.1152/japplphysiol.90410.2008

Cited by 17 publications

(18 citation statements)

References 26 publications

(44 reference statements)

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“…Interestingly, while the present study was performed under moderate hypoxemia (~82% S p O 2 ), cerebral TSI decreased to ~53% in the third sprint and remained low until the end of the protocol. In such conditions of oxygenation, a direct effect of hypoxia in reducing the central motor output to working muscles is possible [33,44]. This requires further experimentation during RSE in particular using circulatory occlusion to better distinguish between peripheral and central influences.…”

Section: Discussionmentioning

confidence: 99%

Interaction of Central and Peripheral Factors during Repeated Sprints at Different Levels of Arterial O2 Saturation

et al. 2013

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PurposeTo investigate the interaction between the development of peripheral locomotor muscle fatigue, muscle recruitment and performance during repeated-sprint exercise (RSE).MethodIn a single-blind, randomised and cross-over design, ten male team-sport athletes performed two RSE (fifteen 5-s cycling sprints interspersed with 25 s of rest; power self-selected) in normoxia and in acute moderate hypoxia (FIO2 0.138). Mechanical work, total electromyographic intensity (summed quadriceps electromyograms, RMSsum) and muscle (vastus lateralis) and pre-fontal cortex near-infrared spectroscopy (NIRS) parameters were calculated for every sprint. Blood lactate concentration ([Lac-]) was measured throughout the protocol. Peripheral quadriceps fatigue was assessed via changes in potentiated quadriceps twitch force (ΔQtw,pot) pre- versus post-exercise in response to supra-maximal magnetic femoral nerve stimulation. The central activation ratio (QCAR) was used to quantify completeness of quadriceps activation.ResultsCompared with normoxia, hypoxia reduced arterial oxygen saturation (-13.7%, P=0.001), quadriceps RMSsum (-13.7%, P=0.022), QCAR (-3.3%, P=0.041) and total mechanical work (-8.3%, P=0.019). However, the magnitude of quadriceps fatigue induced by RSE was similar in the two conditions (ΔQtw,pot: -53.5% and -55.1%, P=0.71). The lower cycling performance in hypoxia occurred despite similar metabolic (muscle NIRS parameters and blood [Lac-]) and functional (twitch and M-wave) muscle states.ConclusionResults suggest that the central nervous system regulates quadriceps muscle recruitment and, thereby, performance to limit the development of muscle fatigue during intermittent, short sprints. This finding highlights the complex interaction between muscular perturbations and neural adjustments during sprint exercise, and further supports the presence of pacing during intermittent sprint exercise.

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Section: Discussionmentioning

confidence: 99%

Interaction of Central and Peripheral Factors during Repeated Sprints at Different Levels of Arterial O2 Saturation

et al. 2013

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“…As a result all forms of exercise are submaximal since there is always a reserve of motor units in the exercising limbs (Amann et al, 2006; Swart et al, 2009b; Marcora and Staiano, 2010; Ross et al, 2010) that is never fully utilized even during maximal exercise (Sloniger et al, 1997a,b; Albertus, 2008) especially when undertaken at altitude (Kayser et al, 1994; Noakes, 2009). Indeed recent studies show that the conventional testing of the maximum oxygen consumption produce submaximal values for oxygen consumption (Beltrami et al, 2012; Mauger and Sculthorpe, 2012), a finding which seriously challenges the foundation finding on which Hill based his model.…”

Section: The Central Governor Model Of Exercise Regulationmentioning

confidence: 99%

Fatigue is a Brain-Derived Emotion that Regulates the Exercise Behavior to Ensure the Protection of Whole Body Homeostasis

Noakes¹

2012

Front. Physio.

368

313

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An influential book written by A. Mosso in the late nineteenth century proposed that fatigue that “at first sight might appear an imperfection of our body, is on the contrary one of its most marvelous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism” so that “muscular fatigue also is at bottom an exhaustion of the nervous system.” It has taken more than a century to confirm Mosso’s idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso’s ideas were supplanted in the English literature by those of A. V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles – “peripheral fatigue” – to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance. This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops. These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop. The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body’s known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance.

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“…These data suggest that hypoxia suppresses flight motivation. Reduced locomotor performance by humans in hypoxia is also believed to be partially explained by hypoxic suppression of central nervous system drive (Amann et al, 2006;Noakes, 2009). In contrast to the relatively strong sensitivity of flight behavior to hypoxia, the CO 2 emission rates of flying dragonflies tended to be quite insensitive to oxygen levels over a broad range (Fig.…”

Section: Fig 5 Total Flight Duration Versus Oxygen Level In Dragonfmentioning

confidence: 99%

Body size effects on the oxygen-sensitivity of dragonfly flight

Henry

Harrison

2014

Journal of Experimental Biology

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One hypothesis for the small size of insects relative to vertebrates, and the existence of giant fossil insects, is that atmospheric oxygen levels constrain insect body sizes because oxygen delivery is more challenging in larger insects. This study tested this hypothesis in dragonflies by measuring the oxygen sensitivity of flight metabolic rates and behavior during hovering for 11 species of dragonflies that ranged in mass by an order of magnitude. We measured flight times and flight metabolic rates in seven oxygen concentrations ranging from 30% to 2.5% to assess the sensitivity of their flight to atmospheric oxygen. We also assessed the oxygen sensitivity of flight in lowdensity air (nitrogen replaced with helium) in order to increase the metabolic demands of hovering flight. Lowered atmospheric densities did induce higher flight metabolic rates. Flight behavior was more sensitive to decreasing oxygen levels than flight metabolic rate. The oxygen sensitivity of flight metabolic rates and behaviors were not correlated with body size, indicating that larger insects are able to maintain an oxygen supply-to-demand balance even during flight.

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Evidence that reduced skeletal muscle recruitment explains the lactate paradox during exercise at high altitude

Cited by 17 publications

References 26 publications

Interaction of Central and Peripheral Factors during Repeated Sprints at Different Levels of Arterial O2 Saturation

Interaction of Central and Peripheral Factors during Repeated Sprints at Different Levels of Arterial O2 Saturation

Fatigue is a Brain-Derived Emotion that Regulates the Exercise Behavior to Ensure the Protection of Whole Body Homeostasis

Body size effects on the oxygen-sensitivity of dragonfly flight

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