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 hypothesized 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 ofwhichfollowed4 week of inspiratorymuscle training(IMT). The inspiratorymetaboreflex was induced by inspiring against a calibrated flowresistor.We measured torque andEMGduring isometric PF exercise at 85% of maximal voluntary contraction (MVC) torque. Supramaximal twitches were superimposed uponMVC 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 aswhen PF was preceded immediately by fatiguing inspiratory muscle work (6.28±2.24 min; P =0.009). Resting the
inspiratory muscles for 30 min restored the PF Tlim to control. After 4 weeks, IMT, inspiratory muscle work at the same absolute intensity did not influence PF Tlim, but Tlim was significantly shorter at thesamerelative intensity.Thedata are the first toprovide evidence that the inspiratory muscle metaboreflex accelerates the rate of calf fatigue during PF, and that IMT attenuates this effect. |
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