New physiological insights into exercise-induced diaphragmatic fatigue

Kabitz, Hans-Joachim; Walker, David; Schwoerer, Anja; Sonntag, Florian; Walterspacher, Stephan; Röecker, Kai; Windisch, Wolfram

doi:10.1016/j.resp.2007.04.011

Cited by 17 publications

(17 citation statements)

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“…Diaphragmatic fatigue has been shown to occur in response to exercise at 80% to 85%V o 2 max, whereas there is limited evidence that it occurs at lower intensities [see Romer and Polkey (454) for review]. Recent studies (261,262) claim that diaphragmatic fatigue manifests after rather than during exercise. Specifically, stimulated P di was shown to increase progressively during exercise but fell immediately upon the cessation of exercise.…”

Section: Nerve Stimulation Applied To Exercisementioning

confidence: 99%

Ventilation and Respiratory Mechanics

Sheel

Romer

2012

Comprehensive Physiology

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During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.

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Section: Nerve Stimulation Applied To Exercisementioning

confidence: 99%

Ventilation and Respiratory Mechanics

Sheel

Romer

2012

Comprehensive Physiology

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“…In a somewhat related study, Kabitz et al 28 have reported that electrically stimulated diaphragmatic force output increased progressively during exercise but fell immediately exercise terminated, but only when whole-body exercise was performed 29. The authors concluded that diaphragmatic fatigue develops after , not during exercise, so that “the conventional understanding of fatigue might be flawed because it does not distinguish between the sensation itself and the physical expression of that sensation26”.…”

mentioning

confidence: 99%

“…Although the mechanisms explaining the unexpected findings of Kabitz et al 28 29 need to be determined, those studies should encourage exercise physiologists to re-evaluate the implications of studies showing that skeletal muscle contractile function does not necessarily fall during exercise but may sometimes increase.…”

mentioning

confidence: 99%

“…Importantly, the studies of Kabitz et al 28 29 raise the possibility that the use of electrical stimulation to detect the presence of “peripheral fatigue” in skeletal muscle might theoretically produce contrasting results if tested during exercise rather than after the termination of exercise. Indeed, it is clear that electrical stimulation overestimates the degree of “peripheral fatigue” that may be present at the end of exercise.…”

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confidence: 99%

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Testing for maximum oxygen consumption has produced a brainless mode of human exercise performance

Noakes

2008

Br J Sports Med

101

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The measurement of the maximum oxygen consumption (VO2max) is probably the most widely used test in the applied sports sciences. Yet this test includes three features that are foreign to the manner in which humans usually exercise. First, the tested subject does not know the expected duration of the exercise bout when it begins. Second the intensity of the imposed exercise increases progressively, sometimes rapidly from low to “maximal” work rates. Third the imposed work rate is predetermined and immutable, beyond the control of the experimental subject’s brain. As a result the tested subject’s brain merely responds to changes in work rate imposed by the experimenter and is therefore the controlled variable in the experiment. In contrast when subjects are informed beforehand of either the expected exercise duration or the distance to be covered, they will choose to run at different paces depending on the known exercise duration. The brain achieves this by recruiting the exactly appropriate number of motor units in the exercising muscles. The goal of this strategy is to complete the activity without homeostatic failure whilst still allowing an increase in pace near the end of exercise, the “endspurt”. Since the tested subject’s brain is the controlled variable during the VO2max test merely responding passively to the externally-directed changes in work rate, so it has been assumed that the brain plays no part in “limiting” maximal exercise performance. This has in turn developed a “brainless” model of human exercise performance in which the “limiting” factors are described almost exclusively in terms of cardiovascular function. But the outstanding feature of effective human exercise performance is the adoption of the optimum pacing strategy that will avoid, not cause, homeostatic failure and profound skeletal muscle failure. Since the VO2max test does not evaluate the athlete’s ability to choose and sustain the optimum pace during exercise of different durations, it cannot be the optimum test either to evaluate a subject’s athletic potential or to understand the biological basis of superior athletic performance.

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“…Muscle fatigue is a complex phenomenon [20]. Most tests are suitable for detecting the presence of only one component of muscle fatigue [42,47], so complete characterization of fatigue requires a complex series of assessments.…”

Section: Introduction Introduction Introductionmentioning

confidence: 99%