title: Eccentric exercise inhibits the H reflex in the middle part of the trapezius muscle.
abstract: The objectives of this study were to (1) investigate the modulation of the H reflex immediately after and 24 h after eccentric exercise in the presence of delayed-onset muscle soreness (DOMS) and (2) test the reproducibility of the H reflex in trapezius across days. H reflexes were recorded from the dominant middle trapezius muscle by electrical stimulation of the C3/4 cervical nerve in ten healthy subjects. DOMS was induced by eccentric exercise of the dominant shoulder. H reflexes were obtained in four sessions: "24 h before", "Pre", "Post", and "24 h after" eccentric exercise. Ratios of maximal H reflex and M wave responses (H (max)/M (max)) were compared between sessions. In addition, a between session comparison was done for the ratios of H reflex amplitudes (H (i_75)/M (max), and H (i_50)/M (max)) obtained from the stimulus intensity needed to obtain 75 and 50 % of H (max) at "24 h before". No ratio changes were found when comparing "24 h before" and "Pre" recordings. A decrease in H (i_50)/M (max) was found at "Post" (P < 0.05) and decreases in both H (i_75)/M (max) and H (i_50)/M (max) were observed at "24 h after" (P < 0.05). This study presented evidence that an acceptable day-to-day reproducibility of the H reflex could be obtained with the applied experimental setup. Furthermore, immediately after and 24 h after exercise a stronger stimulus intensity was needed to reach the same magnitude of the H reflex reflecting that the recruitment curve was shifted to the right. This modulation of the stimulus-response relationship could be caused by presynaptic inhibition of Ia afferent fibres' input to the motoneuron by group III and IV afferents.
authors.affiliation: Department of Health Science and Technology, Laboratory for Ergonomics and Work-related Disorders, Center for Sensory-Motor Interaction, Aalborg University, Fredrik Bajers Vej 7, Bldg. D-3, 9220 Aalborg, Denmark.
authors.forename: Steffen
authors.initials: S
authors.lastname: Vangsgaard
authors.forename: Lars T
authors.initials: LT
authors.lastname: Nørgaard
authors.forename: Brian K
authors.initials: BK
authors.lastname: Flaskager
authors.forename: Karen
authors.initials: K
authors.lastname: Søgaard
authors.forename: Janet L
authors.initials: JL
authors.lastname: Taylor
authors.forename: Pascal
authors.initials: P
authors.lastname: Madeleine
mesh_terms: D000328:Adult; D012090:Cumulative Trauma Disorders / Q000503:physiopathology*; D005260:Female; D006181:H-Reflex; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000293:injuries* / Q000503:physiopathology*; D012782:Shoulder / Q000503:physiopathology*