title: Assessment of the H-reflex at two contraction levels before and after fatigue.
abstract: The aim of the present study was to compare the H-reflex evoked at rest and at 20% maximal voluntary contraction (MVC) prior to and after fatiguing the lateral gastrocnemius (LG). The maximal H-reflex and M-wave were recorded in the LG, and soleus (SOL). Electrical evoked potentials were delivered to the posterior tibial nerve when muscles were inactivated and at 20% MVC. After fatigue, the Hmax/Mmaxratio of the fatigued LG was increased for both contraction levels (rest and 20% MVC) and remained unaltered for non-fatigued SOL. Before fatigue, the Hmax/Mmaxratio of SOL was enhanced at rest compared with the Hmax/Mmaxratio at 20% MVC. No differences were observed for LG. Fatigue of a single muscle leads to increased spinal reflex activity of the homonymous muscle. Contrary to previous recommendations in the literature, there appears to be no benefit with regard to the H-reflex amplitude in evoking electrical potentials during constant voluntary contractions at 20% MVC compared with inactivated muscles. The observed difference in SOL prior to fatigue was most likely due to hyperpolarization of the muscle fiber membrane.
authors.affiliation: Department of Exercise Science, Institute of Sport- and Movement Science, University of Stuttgart, Stuttgart, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Stutzig
authors.affiliation: Department of Exercise Science, Institute of Sport- and Movement Science, University of Stuttgart, Stuttgart, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Siebert
mesh_terms: D004558:Electric Stimulation; D004576:Electromyography; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology*; D055815:Young Adult
keywords: 
  NMES
  ; Spinal reflex activity; neuromuscular electrical stimulation; triceps surae; voluntary contractions vs rest