title: Effects of homosynaptic depression on spectral properties of H-reflex recordings.
abstract: The purpose of this study was to determine the effects of homosynaptic depression (HD) on spectral properties of the soleus (SOL) H-reflex. Paired stimulations, separated by 100 ms, were used to elicit an unconditioned and conditioned H-reflex in the SOL muscle of 20 participants during quiet standing. Wavelet and principal component analyses were used to analyze features of the time-varying spectral properties of the unconditioned and conditioned H-reflex. The effects of HD on spectral properties of the H-reflex signal were quantified by comparing extracted principal component scores. The analysis extracted two principal components: one associated with the intensity of the spectra and one associated with its frequency. The scores for both principal components were smaller for the conditioned H-reflex. HD decreases the spectral intensity and changes the spectral frequency of H-reflexes. These results suggest that HD changes the recruitment pattern of the motor units evoked during H-reflex stimulations, in that it not only decreases the intensity, but also changes the types of motor units that contribute to the H-reflex signal.
authors.affiliation: Department of Physical Therapy, Marquette University, Milwaukee, WI 53201, USA. kristof.kipp@marquette.edu
authors.forename: Kristof
authors.initials: K
authors.lastname: Kipp
authors.forename: Samuel T
authors.initials: ST
authors.lastname: Johnson
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hoffman
mesh_terms: D000328:Adult; D001703:Biophysics; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D036881:Long-Term Synaptic Depression / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D013057:Spectrum Analysis; D018709:Statistics, Nonparametric; D013997:Time Factors; D055815:Young Adult