Central Command Increases Muscle Sympathetic Nerve Activity More to Contracting than Non‐Contracting Muscle during Unloaded Rhythmic Exercise in Humans

Abstract

We have previously shown that the increase in muscle sympathetic nerve activity (MSNA) to contracting muscle during sustained isometric exercise is due primarily to central command, and that the contracting muscle does not exhibit a metaboreflex. Here, we tested the hypothesis that MSNA increases to the contracting muscle also during rhythmic isotonic exercise, in which muscle metabolites will not accumulate because the contraction is performed without external load. MSNA was recorded from the common peroneal nerve in 10 participants and negative‐going sympathetic spikes extracted during 50 cycles of sinusoidal (0.15 Hz) isotonic dorsiflexions of the ipsilateral or contralateral ankle. Electromyographic activity (EMG) was recorded from the tibialis anterior muscle on both sides. Cross‐correlation analysis between the MSNA and EMG revealed a marked cyclic modulation of MSNA to the contracting (ipsilateral) muscle. This modulation, in which MSNA increased during the contraction phase, was three times greater than that to the non‐contracting muscle (modulation index = 27.4 ± 3.2 vs 9.2 ± 1.5 %; P<0.001). There were no differences in either the intensity or magnitude of modulation of EMG during ipsilateral and contralateral contractions. We conclude that, in addition to static isometric exercise, central command increases MSNA to the contracting muscle during rhythmic isotonic exercise.Support or Funding InformationThis work was supported by the National Health & Medical Research Council (Grants 1029782 and 1100040).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.