title: Effects of whole body vibration on motor unit recruitment and threshold.
abstract: Whole body vibration (WBV) has been suggested to elicit reflex muscle contractions but this has never been verified. We recorded from 32 single motor units (MU) in the vastus lateralis of 7 healthy subjects (34 ± 15.4 yr) during five 1-min bouts of WBV (30 Hz, 3 mm peak to peak), and the vibration waveform was also recorded. Recruitment thresholds were recorded from 38 MUs before and after WBV. The phase angle distribution of all MUs during WBV was nonuniform (P < 0.001) and displayed a prominent peak phase angle of firing. There was a strong linear relationship (r = -0.68, P < 0.001) between the change in recruitment threshold after WBV and average recruitment threshold; the lowest threshold MUs increased recruitment threshold (P = 0.008) while reductions were observed in the higher threshold units (P = 0.031). We investigated one possible cause of changed thresholds. Presynaptic inhibition in the soleus was measured in 8 healthy subjects (29 ± 4.6 yr). A total of 30 H-reflexes (stimulation intensity 30% Mmax) were recorded before and after WBV: 15 conditioned by prior stimulation (60 ms) of the antagonist and 15 unconditioned. There were no significant changes in the relationship between the conditioned and unconditioned responses. The consistent phase angle at which each MU fired during WBV indicates the presence of reflex muscle activity similar to the tonic vibration reflex. The varying response in high- and low-threshold MUs may be due to the different contributions of the mono- and polysynaptic pathways but not presynaptic inhibition.
authors.affiliation: Centre of Human and Aerospace Physiological Sciences, King's College London, UK. ross.pollock@kcl.ac.uk
authors.forename: Ross D
authors.initials: RD
authors.lastname: Pollock
authors.forename: Roger C
authors.initials: RC
authors.lastname: Woledge
authors.forename: Finbarr C
authors.initials: FC
authors.lastname: Martin
authors.forename: Di J
authors.initials: DJ
authors.lastname: Newham
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004576:Electromyography / Q000379:methods; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D009044:Motor Cortex / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D014732:Vibration
references.citation: J Physiol. 1975 Dec;253(2):429-42
references.pmid: 1214220
references.citation: J Strength Cond Res. 2003 Aug;17(3):621-4
references.pmid: 12930196
references.citation: J Neurol Neurosurg Psychiatry. 1976 Aug;39(8):719-28
references.pmid: 134135
references.citation: J Physiol. 1975 Oct;251(2):333-61
references.pmid: 1185668
references.citation: J Neurophysiol. 1963 Jan;26:177-90
references.pmid: 13968075
references.citation: J Neurol Neurosurg Psychiatry. 1966 Feb;29(1):1-11
references.pmid: 5910574
references.citation: J Physiol. 1976 Oct;261(3):695-711
references.pmid: 135841
references.citation: Neurosci Lett. 1998 Dec 24;258(3):147-50
references.pmid: 9885952
references.citation: J Neurol Sci. 1973 Jan;18(1):111-29
references.pmid: 4120482
references.citation: Neuroimage. 2006 Feb 1;29(3):923-9
references.pmid: 16253525
references.citation: Eur J Appl Physiol Occup Physiol. 1988;57(5):558-62
references.pmid: 3396572
references.citation: Arch Phys Med Rehabil. 2009 Dec;90(12):2131-4
references.pmid: 19969180
references.citation: Exp Brain Res. 1982;47(2):177-90
references.pmid: 6214420
references.citation: J Physiol. 1967 Oct;192(3):773-800
references.pmid: 4293790
references.citation: J Physiol. 1991 Dec;444:645-67
references.pmid: 1822565
references.citation: J Appl Physiol (1985). 2002 Sep;93(3):1093-103
references.pmid: 12183507
references.citation: Clin Physiol. 2000 Mar;20(2):134-42
references.pmid: 10735981
references.citation: J Physiol. 1969 Nov;205(2):329-39
references.pmid: 5357239
references.citation: Clin Biomech (Bristol, Avon). 2010 Feb;25(2):181-6
references.pmid: 19944501
references.citation: Muscle Nerve. 2007 Jul;36(1):21-9
references.pmid: 17471568
references.citation: Int J Sports Med. 2002 Jul;23(5):374-9
references.pmid: 12165890
references.citation: Exp Brain Res. 1990;81(1):35-45
references.pmid: 2394229
references.citation: J Physiol. 1976 Oct;261(3):673-93
references.pmid: 135840
references.citation: Exp Neurol. 1966 Sep;16(1):80-92
references.pmid: 5923486
references.citation: Br J Sports Med. 2005 Nov;39(11):860-5
references.pmid: 16244199
references.citation: J Physiol. 1973 Dec;235(2):371-408
references.pmid: 4271734
references.citation: Brain Res. 1996 Apr 15;716(1-2):84-90
references.pmid: 8738223
references.citation: Exerc Sport Sci Rev. 2003 Jan;31(1):3-7
references.pmid: 12562163
references.citation: Jpn J Physiol. 1972 Aug;22(4):367-77
references.pmid: 4346104
references.citation: J Strength Cond Res. 2009 Jul;23(4):1309-15
references.pmid: 19568035
references.citation: Exp Brain Res. 1990;82(1):227-30
references.pmid: 2257911
references.citation: Neuroimage. 2002 Sep;17(1):421-30
references.pmid: 12482095
references.citation: Aviat Space Environ Med. 1980 Nov;51(11):1227-33
references.pmid: 7213269
references.citation: J Physiol. 1990 Apr;423:15-26
references.pmid: 2388149
references.citation: Exp Brain Res. 1989;76(1):213-22
references.pmid: 2753103
references.citation: J Neurol Neurosurg Psychiatry. 1976 Aug;39(8):729-41
references.pmid: 956859
references.citation: Eur J Appl Physiol. 2010 Mar;108(5):877-904
references.pmid: 20012646
references.citation: Eur J Appl Physiol. 2010 Jan;108(2):311-9
references.pmid: 19795130
references.citation: Brain Res. 1986 Apr 2;370(1):171-5
references.pmid: 3708319
references.citation: Exp Physiol. 2009 Jan;94(1):103-16
references.pmid: 18658234
references.citation: Clin Physiol Funct Imaging. 2002 Mar;22(2):145-52
references.pmid: 12005157
references.citation: Clin Biomech (Bristol, Avon). 2010 Oct;25(8):840-6
references.pmid: 20541297
references.citation: J Physiol. 1978 Dec;285:197-207
references.pmid: 154563
references.citation: Med Sci Sports Exerc. 2007 Sep;39(9):1642-50
references.pmid: 17805098
references.citation: J Physiol. 1990 Apr;423:1-14
references.pmid: 2388146
references.citation: Brain Res. 1993 Jan 29;602(1):32-40
references.pmid: 8448656
references.citation: J Electromyogr Kinesiol. 2009 Aug;19(4):710-8
references.pmid: 18495492