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Received July 20, 2006
Revised August 2, 2006
Accepted after revision September 12, 2006
1 Brunel University
* To whom correspondence should be addressed. E-mail: alison.mcconnell{at}brunel.ac.uk.
The purpose of this study was to assess the influence of the work history of the inspiratory muscles upon the fatigue characteristics of the plantar flexors (PF). We hypothesised that under conditions where the inspiratory muscle metaboreflex has been elicited, PF fatigue would be hastened due to peripheral vasoconstriction. Eight volunteers undertook seven test conditions, two of which followed 4 wk of inspiratory muscle training (IMT). The inspiratory metaboreflex was induced by inspiring against a calibrated flow resistor. We measured torque and EMG during isometric PF exercise at 85% of maximal voluntary contraction (MVC) torque. Supra-maximal twitches were superimposed upon MVC efforts at 1 min intervals (MVCTI); twitch interpolation assessed the level of central activation. PF was terminated (Tlim) when MVCTI was <50% of baseline MVC. PF Tlim was significantly shorter than control (9.93 ± 1.95 min) in the presence of a leg cuff inflated to 140 mmHg (4.89 ± 1.78 min; p = 0.006), as well as when PF was preceded immediately by fatiguing inspiratory muscle work (6.28 ± 2.24 mins; p -= 0.009). Resting the inspiratory muscles for 30 min restored the PF Tlim to control. After 4 wk IMT, inspiratory muscle work at the same absolute intensity did not influence PF Tlim, but Tlim was significantly shorter at the same relative intensity. The data are the first to provide evidence that the inspiratory muscle metaboreflex accelerates the rate of calf fatigue during PF, and that IMT attenuates this effect.
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