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First published online on December 22, 2005.
 Copyright © 2005 by The Physiological Society
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Received October 5, 2005
Revised October 26, 2005
Accepted after revision December 21, 2005

Effect of inspiratory muscle work on peripheral fatigue of locomotor muscles in healthy humans

Lee M Romer1*, Andrew T Lovering2, Hans C Haverkamp3, David F Pegelow2, and Jerome A Dempsey2

1 Brunel University
2 University of Wisconsin
3 University of Vermont

* To whom correspondence should be addressed. E-mail: lee.romer{at}brunel.ac.uk.

The work of breathing required during maximal exercise compromises blood flow to limb locomotor muscles (QL) and reduces exercise performance. We asked if force output of the inspiratory muscles affected exercise-induced peripheral fatigue of locomotor muscles. Eight male cyclists exercised at ≥90% peak O2 uptake to exhaustion (CTRL). On a separate occasion, subjects exercised for the same duration and power output as CTRL (13.2 ± 0.9 min, 292 W), but force output of the inspiratory muscles was reduced (-56% vs. CTRL) using a proportional assist ventilator (PAV). Subjects also exercised to exhaustion (7.9 ± 0.6 min, 292 W) while force output of the inspiratory muscles was increased (+80% vs. CTRL) via inspiratory resistive loads (IRL), and again for the same duration and work rate with breathing unimpeded (IRL-CTRL). Quadriceps twitch force (Qtw), in response to supramaximal paired magnetic stimuli of the femoral nerve (1-100 Hz), was assessed pre- and at 2.5 through 70 min post-exercise. Immediately after CTRL exercise, Qtw was reduced 28 ± 5% below pre-exercise baseline; this reduction in Qtw was attenuated following PAV exercise (-20 ± 5%; p < 0.05). Conversely, increasing the force output of the inspiratory muscles (IRL) exacerbated exercise-induced quadriceps fatigue (Qtw = -12 ± 8% CTRL-IRL vs. -20 ± 7% IRL; p < 0.05). Repeat studies between days showed that the effects of exercise, per se, and of superimposed inspiratory muscle loading on quadriceps fatigue were highly reproducible. In conclusion, peripheral fatigue of locomotor muscles resulting from high-intensity sustained exercise is, in part, due to the accompanying high levels of respiratory muscle work.


Key words: Exercise • Muscle fatigue • Respiratory muscle




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