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Randomized Controlled Trial
. 2007 Jun 15;156(3):353-61.
doi: 10.1016/j.resp.2006.10.008. Epub 2006 Nov 10.

Inspiratory muscles do not limit maximal incremental exercise performance in healthy subjects

Lee M Romer  1 , Jordan D Miller, Hans C Haverkamp, David F Pegelow, Jerome A Dempsey
Affiliations
Randomized Controlled Trial

Inspiratory muscles do not limit maximal incremental exercise performance in healthy subjects

Lee M Romer et al. Respir Physiol Neurobiol. .

Abstract

We investigated whether the inspiratory muscles affect maximal incremental exercise performance using a placebo-controlled, crossover design. Six cyclists each performed six incremental exercise tests. For three trials, subjects exercised with proportional assist ventilation (PAV). For the remaining three trials, subjects underwent sham respiratory muscle unloading (placebo). Inspiratory muscle pressure (P(mus)) was reduced with PAV (-35.9+/-2.3% versus placebo; P<0.05). Furthermore, V(O2) and perceptions of dyspnea and limb discomfort at submaximal exercise intensities were significantly reduced with PAV. Peak power output, however, was not different between placebo and PAV (324+/-4W versus 326+/-4W; P>0.05). Diaphragm fatigue (bilateral phrenic nerve stimulation) did not occur in placebo. In conclusion, substantially unloading the inspiratory muscles did not affect maximal incremental exercise performance. Therefore, our data do not support a role for either inspiratory muscle work or fatigue per se in the limitation of maximal incremental exercise.

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Figures

Fig. 1
Fig. 1
Group mean (n = 5 subjects) diaphragm force output (∫Pdi dt · fr; top panel), total inspiratory muscle force output (∫Pe dt · fr; middle panel), and the relative contribution of the diaphragm to the total inspiratory muscle force output (∫Pdi/∫Pe; bottom panel) for placebo (closed circles) and PAV (open circles). **P < 0.01, significantly different vs. placebo.
Fig. 2
Fig. 2
Group mean data (n = 6 subjects) for ratings of dyspnea (top panel) and limb discomfort (bottom panel) versus exercise intensity for placebo (closed circles) and PAV (open circles). *P < 0.05, significantly different vs. placebo.
Fig. 3
Fig. 3
Individual and group mean (n = 5 subjects) transdiaphragmatic twitch pressure (Pdi,tw) response to supramaximal bilateral phrenic nerve stimulation at 1 Hz (nonpotentiated), 10 Hz, 50 Hz, and 100 Hz before, within 15 min and at 35 min after maximal incremental exercise for placebo condition. *P < 0.05, significantly different vs. pre-exercise (Pre).
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References

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