title: Single motor unit firing rate after stroke is higher on the less-affected side during stable low-level voluntary contractions.
abstract: Muscle weakness is the most common outcome after stroke and a leading cause of adult-acquired motor disability. Single motor unit properties provide insight into the mechanisms of post-stroke motor impairment. Motor units on the more-affected side are reported to have lower peak firing rates, reduced discharge variability and a more compressed dynamic range than healthy subjects. The activity of 169 motor units was discriminated from surface electromyography in 28 stroke patients during sustained voluntary contractions 10% of maximal and compared to 110 units recorded in 16 healthy subjects. Motor units were recorded in three series: ankle dorsiflexion, wrist flexion and elbow flexion. Mean firing rates after stroke were significantly lower on the more-affected than the less-affected side (p < 0.001) with no differences between dominant and non-dominant sides for healthy subjects. When data were combined, firing rates on the less-affected side were significantly higher than those either on the more-affected side or healthy subjects (p < 0.001). Motor unit mean firing rate was higher in the upper-limb than the lower-limb (p < 0.05). The coefficient of variation of motor unit discharge rate was lower for motor units after stroke compared to controls for wrist flexion (p < 0.05) but not ankle dorsiflexion. However the dynamic range of motor units was compressed only for motor units on the more-affected side during wrist flexion. Our results show that the pathological change in motor unit firing rate occurs on the less-affected side after stroke and not the more-affected side as previously reported, and suggest that motor unit behavior recorded in a single muscle after stroke cannot be generalized to muscles acting on other joints even within the same limb. These data emphasize that the less-affected side does not provide a valid control for physiological studies on the more-affected side after stroke and that both sides should be compared to data from age- and sex-matched healthy subjects.
authors.affiliation: Neuroscience Research Australia Sydney, NSW, Australia ; School of Medical Sciences, UNSW Australia Sydney, NSW, Australia.
authors.forename: Penelope A
authors.initials: PA
authors.lastname: McNulty
authors.affiliation: Neuroscience Research Australia Sydney, NSW, Australia.
authors.forename: Gaven
authors.initials: G
authors.lastname: Lin
authors.affiliation: Neuroscience Research Australia Sydney, NSW, Australia ; School of Medical Sciences, UNSW Australia Sydney, NSW, Australia.
authors.forename: Catherine G
authors.initials: CG
authors.lastname: Doust
keywords: hemiparesis; motor unit firing rate; motor unit firing variability; stroke; torque control
references.citation: Annu Int Conf IEEE Eng Med Biol Soc. 2008;2008:3562-5
references.pmid: 19163478
references.citation: J Physiol. 1992 Mar;448:397-412
references.pmid: 1593472
references.citation: Stroke. 2000 Mar;31(3):672-9
references.pmid: 10700503
references.citation: J Biomech. 2011 Nov 10;44(16):2741-6
references.pmid: 21945568
references.citation: Clin Physiol Funct Imaging. 2008 Jul;28(4):251-61
references.pmid: 18355344
references.citation: J Neurol Sci. 2006 Dec 1;250(1-2):27-32
references.pmid: 16904126
references.citation: Pflugers Arch. 1996;431(6 Suppl 2):R211-2
references.pmid: 8739339
references.citation: J Neurol Sci. 1986 Aug;75(1):89-103
references.pmid: 3746341
references.citation: J Electromyogr Kinesiol. 2004 Jun;14(3):369-77
references.pmid: 15094150
references.citation: Muscle Nerve. 1997 Aug;20(8):938-47
references.pmid: 9236783
references.citation: Eur Neurol. 1993;33(2):109-14
references.pmid: 8467816
references.citation: Electroencephalogr Clin Neurophysiol. 1969 Jul;27(1):66-72
references.pmid: 4182892
references.citation: J Rehabil Med. 2008 Apr;40(4):298-303
references.pmid: 18382826
references.citation: J Neurol Neurosurg Psychiatry. 1973 Apr;36(2):183-93
references.pmid: 4350702
references.citation: Muscle Nerve. 2013 Jul;48(1):85-92
references.pmid: 23605647
references.citation: Electroencephalogr Clin Neurophysiol. 1997 Dec;105(6):438-50
references.pmid: 9448645
references.citation: Stroke. 2009 Feb;40(2):545-50
references.pmid: 19109543
references.citation: Arch Phys Med Rehabil. 2002 Dec;83(12):1703-7
references.pmid: 12474173
references.citation: Muscle Nerve. 2005 Apr;31(4):475-80
references.pmid: 15617094
references.citation: J Exp Biol. 1985 Mar;115:125-36
references.pmid: 4031760
references.citation: Neuroimage. 2005 Dec;28(4):940-6
references.pmid: 16084737
references.citation: Stroke. 1998 Apr;29(4):785-92
references.pmid: 9550512
references.citation: Neurorehabil Neural Repair. 2006 Sep;20(3):380-9
references.pmid: 16885424
references.citation: Stroke. 1986 Sep-Oct;17(5):817-30
references.pmid: 3532434
references.citation: Brain. 2007 Jan;130(Pt 1):170-80
references.pmid: 17148468
references.citation: Clin Neurophysiol. 2005 Jul;116(7):1566-70
references.pmid: 15905127
references.citation: Brain. 2004 Oct;127(Pt 10):2247-58
references.pmid: 15342360
references.citation: Clin Neurophysiol. 2004 Jan;115(1):97-103
references.pmid: 14706475
references.citation: J Neurol Sci. 1970 Dec;11(6):537-50
references.pmid: 5490728
references.citation: Brain. 1989 Jun;112 ( Pt 3):749-63
references.pmid: 2731028
references.citation: Stroke. 1993 Oct;24(10):1462-7
references.pmid: 8378947
references.citation: J Neurophysiol. 2010 Dec;104(6):3168-79
references.pmid: 20861443
references.citation: J Rehabil Res Dev. 2008;45(2):261-72
references.pmid: 18566944
references.citation: Neurorehabil Neural Repair. 2009 Sep;23(7):641-56
references.pmid: 19531606
references.citation: J Physiol. 2007 Jun 15;581(Pt 3):927-40
references.pmid: 17363389
references.citation: Brain. 1990 Dec;113 ( Pt 6):1843-56
references.pmid: 2276047
references.citation: Clin Neurophysiol. 2008 Nov;119(11):2555-8
references.pmid: 18809353
references.citation: Neurorehabil Neural Repair. 2008 May-Jun;22(3):298-304
references.pmid: 17916658
references.citation: Muscle Nerve. 2005 Aug;32(2):119-39
references.pmid: 15880485
references.citation: J Neuroeng Rehabil. 2009 Mar 17;6:8
references.pmid: 19292910
references.citation: Arch Phys Med Rehabil. 2000 Apr;81(4):418-23
references.pmid: 10768529
references.citation: Clin Neurophysiol. 2009 Aug;120(8):1539-42
references.pmid: 19564129
references.citation: Physiol Rev. 1980 Jan;60(1):90-142
references.pmid: 6766557
references.citation: Bone. 2001 Jun;28(6):655-9
references.pmid: 11425655
references.citation: Exp Brain Res. 2013 Jul;228(1):9-24
references.pmid: 23652723
references.citation: J Neurol Neurosurg Psychiatry. 2010 Jul;81(7):788-92
references.pmid: 20392975
references.citation: Muscle Nerve. 2011 Jan;43(1):112-9
references.pmid: 20928907
references.citation: J Neurophysiol. 2013 Jun;109(12):2947-54
references.pmid: 23554434
references.citation: Brain. 2012 Jul;135(Pt 7):2277-89
references.pmid: 22581799
references.citation: PLoS One. 2013;8(1):e52228
references.pmid: 23349681
references.citation: J Electromyogr Kinesiol. 2006 Oct;16(5):469-76
references.pmid: 16311042
references.citation: J Neurol Sci. 1982 Jun;54(3):401-12
references.pmid: 7097310
references.citation: J Neurophysiol. 2001 May;85(5):1907-13
references.pmid: 11353007
references.citation: J Neurol Sci. 1991 Sep;105(1):49-56
references.pmid: 1795169
references.citation: Neurorehabil Neural Repair. 2013 Mar-Apr;27(3):219-29
references.pmid: 23077145
references.citation: Stroke. 2014 Jan;45(1):205-10
references.pmid: 24178916
references.citation: Annu Int Conf IEEE Eng Med Biol Soc. 2012;2012:4116-9
references.pmid: 23366833
references.citation: Clin Neurophysiol. 2008 Dec;119(12):2813-8
references.pmid: 18848803
references.citation: Scand J Rehabil Med. 1992 Sep;24(3):115-9
references.pmid: 1411356
references.citation: Muscle Nerve. 1995 Oct;18(10):1101-14
references.pmid: 7659104
references.citation: IEEE Trans Inf Technol Biomed. 2011 Jul;15(4):505-12
references.pmid: 21478079
references.citation: Ann Neurol. 2004 Mar;55(3):400-9
references.pmid: 14991818
references.citation: Clin Orthop Relat Res. 1985 Oct;(199):159-68
references.pmid: 4042473
references.citation: Can J Appl Physiol. 1998 Feb;23(1):1-22
references.pmid: 9494737
references.citation: Annu Int Conf IEEE Eng Med Biol Soc. 2012;2012:3580-3
references.pmid: 23366701
references.citation: Annu Int Conf IEEE Eng Med Biol Soc. 2011;2011:8243-6
references.pmid: 22256256
references.citation: Brain. 1993 Apr;116 ( Pt 2):369-82
references.pmid: 8461971
references.citation: Acta Neuropathol. 1984;62(4):324-31
references.pmid: 6730908
references.citation: Eura Medicophys. 2006 Sep;42(3):241-56
references.pmid: 17039223
references.citation: Brain. 2012 Aug;135(Pt 8):2527-35
references.pmid: 22689909
references.citation: Res Sports Med. 2009 Jan-Mar;17(1):17-27
references.pmid: 19266390
references.citation: Motor Control. 2013 Jul;17(3):283-97
references.pmid: 23761424
references.citation: J Neurophysiol. 2009 Oct;102(4):2026-38
references.pmid: 19587321
references.citation: Brain. 1990 Oct;113 ( Pt 5):1563-81
references.pmid: 2245311
references.citation: J Neurophysiol. 2005 Nov;94(5):3112-25
references.pmid: 16000517
references.citation: Neurorehabil Neural Repair. 2010 Jun;24(5):413-9
references.pmid: 20516488
references.citation: Muscle Nerve. 2004 Aug;30(2):209-15
references.pmid: 15266637
references.citation: J Neurol Neurosurg Psychiatry. 1980 Oct;43(10):907-16
references.pmid: 7441270