title: Experimental muscle pain increases variability of neural drive to muscle and decreases motor unit coherence in tremor frequency band.
abstract: It has been observed that muscle pain influences force variability and low-frequency (<3 Hz) oscillations in the neural drive to muscle. In this study, we aimed to investigate the effect of experimental muscle pain on the neural control of muscle force at higher frequency bands, associated with afferent feedback (alpha band, 5-13 Hz) and with descending cortical input (beta band, 15-30 Hz). Single-motor unit activity was recorded, in two separate experimental sessions, from the abductor digiti minimi (ADM) and tibialis anterior (TA) muscles with intramuscular wire electrodes, during isometric abductions of the fifth finger at 10% of maximal force [maximum voluntary contraction (MVC)] and ankle dorsiflexions at 25% MVC. The contractions were repeated under three conditions: no pain (baseline) and after intramuscular injection of isotonic (0.9%, control) and hypertonic (5.8%, painful) saline. The results showed an increase of the relative power of both the force signal and the neural drive at the tremor frequency band (alpha, 5-13 Hz) between the baseline and hypertonic (painful) conditions for both muscles (P < 0.05) but no effect on the beta band. Additionally, the strength of motor unit coherence was lower (P < 0.05) in the hypertonic condition in the alpha band for both muscles and in the beta band for the ADM. These results indicate that experimental muscle pain increases the amplitude of the tremor oscillations because of an increased variability of the neural control (common synaptic input) in the tremor band. Moreover, the concomitant decrease in coherence suggests an increase in independent input in the tremor band due to pain.
authors.affiliation: Department of Orthobionics, Georg August University, Göttingen, Germany; and Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology, University Medical Center Göttingen, Georg August University, Göttingen, Germany.
authors.forename: Utku Ş
authors.initials: UŞ
authors.lastname: Yavuz
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology, University Medical Center Göttingen, Georg August University, Göttingen, Germany.
authors.forename: Francesco
authors.initials: F
authors.lastname: Negro
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology, University Medical Center Göttingen, Georg August University, Göttingen, Germany.
authors.forename: Deborah
authors.initials: D
authors.lastname: Falla
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology, University Medical Center Göttingen, Georg August University, Göttingen, Germany dario.farina@bccn.uni-goettingen.de.
authors.forename: Dario
authors.initials: D
authors.lastname: Farina
mesh_terms: D000513:Alpha Rhythm; D001611:Beta Rhythm; D004576:Electromyography; D025461:Feedback, Physiological / Q000502:physiology; D005385:Fingers / Q000503:physiopathology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D063806:Myalgia / Q000503:physiopathology*; D012462:Saline Solution, Hypertonic; D012965:Sodium Chloride; D014202:Tremor / Q000503:physiopathology
chemical_list: D012462:Saline Solution, Hypertonic; D012965:Sodium Chloride
keywords: experimental muscle pain; motor unit; motor unit coherence; tremor