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This Article Full Text Full Text (PDF) All Versions of this Article: 571/2/425    most recent jphysiol.2005.099697v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Romer, L. M. Articles by Dempsey, J. A. Search for Related Content PubMed PubMed Citation Articles by Romer, L. M. Articles by Dempsey, J. A. Related Collections Integrative

¹ John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, Medical Sciences Center, 1300 University Avenue, University of Wisconsin, Madison, WI 53706, USA
² Centre for Sports Medicine and Human Performance, Brunel University, Middlesex UB8 3PH, UK
³ University of Vermont, Department of Medicine, 149 Beaumont Avenue, HSFR 226, Burlington, VT 05405, USA

The work of breathing required during maximal exercise compromises blood flow to limb locomotor muscles 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%versus 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%versus CTRL) via inspiratory resistive loads (IRLs), and again for the same duration and power output with breathing unimpeded (IRL-CTRL). Quadriceps twitch force (Q_tw), in response to supramaximal paired magnetic stimuli of the femoral nerve (1–100 Hz), was assessed pre- and at 2.5 through to 70 min postexercise. Immediately after CTRL exercise, Q_tw was reduced –28 ± 5% below pre-exercise baseline and this reduction was attenuated following PAV exercise (–20 ± 5%; P < 0.05). Conversely, increasing the force output of the inspiratory muscles (IRL) exacerbated exercise-induced quadriceps muscle fatigue (Q_tw=–12 ± 8% IRL-CTRL versus–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.

(Received 5 October 2005; accepted after revision 21 December 2005; first published online 22 December 2005)
Corresponding author L. M. Romer: Centre for Sports Medicine and Human Performance, Brunel University, Middlesex UB8 3PH, UK. Email: lee.romer{at}brunel.ac.uk

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