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      Dynamic Fatigue Does Not Alter Soleus H-Reflexes Conditioned by Homonymous or Heteronymous Pathways

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          Abstract

          H-reflex depression (diminution of amplitude after a conditioning stimulus) is mediated presynaptically and therefore can help distinguish central versus peripheral mechanisms of fatigue. We examined the effects of a dynamic exercise protocol on H-reflex depression using two conditioning methods: homonymous conditioning (paired-pulse tibial nerve stimulation); and heteronymous conditioning (common peroneal nerve stimulation). Ten subjects performed dynamic contractions of the soleus muscle through 30° ankle range of motion. The concentric phase required a target force of 10% of maximum voluntary isometric contraction (MVIC) and the eccentric phase force target was 80% MVIC. Fatigue persisted for >20 min after cessation of the exercise. Compared with prefatigue values, the dynamic fatigue protocol did not increase presynaptic inhibition after either homonymous or heteronymous conditioning. Peak to peak amplitude of unconditioned H-reflexes was likewise unchanged despite a long term depression of muscle force (long duration fatigue). These results suggest that persistent fatigue after dynamic exercise is attributed to muscle changes and not altered spinal mechanisms.

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          Author and article information

          Contributors
          Journal
          9706297
          20995
          Motor Control
          Motor Control
          Motor control
          1087-1640
          30 August 2017
          13 October 2016
          July 2017
          19 September 2017
          : 21
          : 3
          : 345-358
          Affiliations
          Dept. of Physical Therapy, University of the Pacific, Stockton, CA
          Dept. of Physical Therapy Rehabilitation Science, University of Iowa, Iowa City, IA
          Dept. of Physical Therapy Rehabilitation Science, University of Iowa, Iowa City, IA
          Author notes
          Address author correspondence to Shauna Dudley-Javoroski at shauna-dudley@ 123456uiowa.edu
          Article
          PMC5604332 PMC5604332 5604332 nihpa902497
          10.1123/mc.2016-0030
          5604332
          27736308
          61477741-1613-486f-99b3-e5594ab10c01
          History
          Categories
          Article

          eccentric,presynaptic inhibition,post-activation depression,concentric

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