Effects of respiratory muscle unloading on exercise-induced diaphragm fatigue

Babcock, Mark A.; Pegelow, David F.; Harms, Craig A.; Dempsey, Jerome A.

doi:10.1152/japplphysiol.00612.2001

Cited by 135 publications

(113 citation statements)

References 20 publications

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“…Previous investigations demonstrated that respiratory muscle unloading during high-intensity exercise can prevent respiratory muscle fatigue and the reflex vasoconstriction within active locomotor muscles, and can ultimately lead to increased limb blood flow (Babcock et al 2002;Chiappa et al 2009;Harms et al 1997;Romer et al 2006). Although in normal subjects, this phenomenon may not happen during submaximal exercise (Wetter et al 1999), it could occur in obese patient population characterized by a substantially higher work of breathing and increased metabolic demands.…”

Section: Discussionmentioning

confidence: 99%

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

et al. 2014

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Section: Discussionmentioning

confidence: 99%

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

et al. 2014

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“…Expiration becomes active which requires larger muscle recruitment, and a larger amount of oxygen demanding an increase in blood flow (Babcock et al, 2002;Johnson et al, 1993;Witt et al, 2007). Evidence suggests that the demand for an increase in blood flow to the respiratory muscles during maximal or heavy exercise "steals" blood flow from the other exercising muscles through sympathetically mediated vasoconstriction (Harms et al, 1998;St.…”

Section: Discussionmentioning

confidence: 99%

Effects of high-intensity interval training on pulmonary function

Dunham

Harms

2011

Eur J Appl Physiol

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High-intensity interval training (HIT) has been utilized as a time-efficient strategy to induce numerous physiological adaptations and improve performance usually associated with "traditional" endurance training (ET). It is not known however, if HIT might lead to improvements in pulmonary function. Therefore we hypothesized that HIT would increase respiratory muscle strength and expiratory flow rates. Fifteen healthy subjects were randomly assigned to an ET group (n = 7) and a HIT group (n = 8).All subjects performed an incremental test to exhaustion (VO 2 max) on a cycle ergometer prior to and after training. Standard pulmonary function tests, maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax), and maximal flow volume loops, were performed pre training and after each week of training. HIT subjects performed a four week training program on a cycle ergometer at 90% of their VO 2 max final workload while the ET subjects performed exercise at 60-70% of their VO 2 max final workload. All subjects trained three days/ week. The HIT group performed five one-minute bouts with three minute recovery periods and the ET group cycled for 45 minutes continuously at a constant workload. A five-mile time trial was performed prior to training, after two weeks of training, and after four weeks of training. Both groups showed similar (p<0.05) increases in VO 2 max (~8-10%) and improvements in time trials following training (HIT 6.5 ± 1.3%, ET 4.4 ± 1.8%) with no difference (p>0.05) between groups. Both groups increased (p<0.05) PImax post training (ET ~25%, HIT ~43%) with values significantly higher for HIT than ET. There was no change (p>0.05) in expiratory flow rates with training in either group. These data suggest that whole body exercise training is effective in increasing inspiratory muscle strength with HIT leading to greater improvements than ET. Also, HIT offers a time-efficient alternative to ET in improving aerobic capacity and performance.iv

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“…Thus future studies are needed to determine the role these factors may play in the loss of function associated with fatigue. a mechanical ventilator (11). However, other factors besides respiratory muscle work must also be responsible for exerciseinduced respiratory muscle fatigue, because fatigue did not occur when the resting subject mimicked the magnitude and duration of diaphragmatic work incurred during exercise (13).…”

Section: Exercise-induced Respiratory Muscle Fatiguementioning

confidence: 99%

Exercise-induced respiratory muscle fatigue: implications for performance

Romer

Polkey²

2008

Journal of Applied Physiology

256

212

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Romer LM, Polkey MI. Exercise-induced respiratory muscle fatigue: implications for performance. J Appl Physiol 104: 879 -888, 2008. First published December 20, 2007 doi:10.1152/japplphysiol.01157.2007.-It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O 2 and CO2 transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exerciseinduced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles. respiratory muscles; exercise; diaphragm; abdominals; magnetic stimulation; metaboreflex THE PURPOSE OF THIS MINIREVIEW is to address the question of whether the respiratory demands of exercise contribute significantly toward exercise limitation, either directly through limitations of the respiratory muscle pump or indirectly through effects on limb blood flow and locomotor muscle fatigue. We describe the mechanical and metabolic costs of meeting the ventilatory requirements of exercise. We then ask whether the respiratory muscles fatigue with exercise, what factors contribute to any such fatigue, and what the implications of these factors are for exercise tolerance. Finally, we deal with the potential mechanisms by which respiratory muscle fatigue could compromise exercise tolerance and whether it is possible to overcome this potential respiratory limitation. Our review focuses on the healthy young adult exercising near sea level. However, we also consider special circumstances that determine the balance between metabolic demand and respiratory system capacity in the highly trained endurance ...

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Effects of respiratory muscle unloading on exercise-induced diaphragm fatigue

Cited by 135 publications

References 20 publications

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

Effects of high-intensity interval training on pulmonary function

Exercise-induced respiratory muscle fatigue: implications for performance

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