title: Non-stationarity and power spectral shifts in EMG activity reflect motor unit recruitment in rat diaphragm muscle.
abstract: We hypothesized that a shift in diaphragm muscle (DIAm) EMG power spectral density (PSD) to higher frequencies reflects recruitment of more fatigable fast-twitch motor units and motor unit recruitment is reflected by EMG non-stationarity. DIAm EMG was recorded in anesthetized rats during eupnea, hypoxia-hypercapnia (10% O(2)-5% CO(2)), airway occlusion, and sneezing (maximal DIAm force). Although power in all frequency bands increased progressively across motor behaviors, PSD centroid frequency increased only during sneezing (p<0.05). The non-stationary period at the onset of EMG activity ranged from ∼80 ms during airway occlusion to ∼150 ms during eupnea. Within the initial non-stationary period of EMG activity 80-95% of motor units were recruited during different motor behaviors. Motor units augmented their discharge frequencies progressively beyond the non-stationary period; yet, EMG signal became stationary. In conclusion, non-stationarity of DIAm EMG reflects the period of motor unit recruitment, while a shift in the PSD towards higher frequencies reflects recruitment of more fatigable fast-twitch motor units.
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Yasin B
authors.initials: YB
authors.lastname: Seven
authors.forename: Carlos B
authors.initials: CB
authors.lastname: Mantilla
authors.forename: Wen-Zhi
authors.initials: WZ
authors.lastname: Zhan
authors.forename: Gary C
authors.initials: GC
authors.lastname: Sieck
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003964:Diaphragm / Q000502:physiology*; D004576:Electromyography; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012912:Sneezing / Q000502:physiology; D013057:Spectrum Analysis; D013997:Time Factors