title: Knee extensor strength, dynamic stability, and functional ambulation: are they related in Parkinson's disease?
abstract: OBJECTIVE
  To evaluate the relationship between knee extensor strength, postural stability, functional ambulation, and disease severity in Parkinson's disease (PD).
  
  
  METHODS
  A cohort study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Patients (N=44) with idiopathic PD.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  Participants were evaluated on their isokinetic knee extensor strength. Additionally, participants completed an assessment of their postural stability (Functional Reach Test for static stability and a dynamic postural stability assessment as measured by the center of pressure-center of mass moment arm during gait initiation). Participants also underwent an evaluation of their functional ambulation as measured by a 6-minute walk test. Lastly, participants were evaluated by a neurologist specially trained in movement disorders to assess neurologic status and disease severity using the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr disability score.
  
  
  RESULTS
  Knee extensor strength positively correlated with dynamic postural stability and negatively correlated with disease severity. Further, dynamic postural stability was negatively correlated to disease severity and positively correlated with functional ambulation in this cohort of patients with PD (P<.05). The results also suggest that the Functional Reach Test may be a valuable assessment tool to examine postural stability in PD.
  
  
  CONCLUSIONS
  These findings suggest a malleable relationship between knee extensor strength, dynamic stability, and disease severity in PD. Although strength is only one piece of the puzzle in the functional outcome of PD, these findings may assist clinicians in designing appropriate interventions aimed at increasing function and decreasing fall risk in PD.
authors.affiliation: Brain Rehabilitation Research Center, Malcom Randall Veterans Affairs Medical Center, Gainesville, FL, USA. jnocera@ufl.edu
authors.forename: Joe R
authors.initials: JR
authors.lastname: Nocera
authors.forename: Thomas
authors.initials: T
authors.lastname: Buckley
authors.forename: Dwight
authors.initials: D
authors.lastname: Waddell
authors.forename: Michael S
authors.initials: MS
authors.lastname: Okun
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Hass
mesh_terms: D000368:Aged; D015331:Cohort Studies; D006801:Humans; D007717:Knee; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000503:physiopathology; D010300:Parkinson Disease / Q000503:physiopathology*; D026741:Physical Therapy Modalities; D004856:Postural Balance; D012720:Severity of Illness Index; D016138:Walking
references.citation: Brain. 2002 Sep;125(Pt 9):2100-14
references.pmid: 12183355
references.citation: Mov Disord. 2003 Feb;18(2):157-62
references.pmid: 12539208
references.citation: Neurorehabil Neural Repair. 2007 Mar-Apr;21(2):107-15
references.pmid: 17312085
references.citation: Mov Disord. 1997 Mar;12(2):206-15
references.pmid: 9087979
references.citation: Gerontology. 2001 Sep-Oct;47(5):277-81
references.pmid: 11490147
references.citation: Am J Phys Med Rehabil. 2004 Dec;83(12):898-908
references.pmid: 15624568
references.citation: Neurorehabil Neural Repair. 2009 Sep;23(7):657-61
references.pmid: 19336530
references.citation: Arch Phys Med Rehabil. 2000 Jan;81(1):45-8
references.pmid: 10638875
references.citation: Phys Ther. 2008 Mar;88(3):323-32
references.pmid: 18187494
references.citation: J Gerontol A Biol Sci Med Sci. 2007 Nov;62(11):1259-65
references.pmid: 18000146
references.citation: Mov Disord. 2008 Jul 15;23(9):1274-80
references.pmid: 18464285
references.citation: J Gerontol. 1990 Nov;45(6):M192-7
references.pmid: 2229941
references.citation: J Gerontol A Biol Sci Med Sci. 2005 Feb;60(2):224-31
references.pmid: 15814867
references.citation: Arch Phys Med Rehabil. 2004 Jan;85(1):129-37
references.pmid: 14970980
references.citation: Gerontology. 2005 Mar-Apr;51(2):116-21
references.pmid: 15711078
references.citation: Phys Ther. 1999 Dec;79(12):1177-85
references.pmid: 10630286
references.citation: Parkinsonism Relat Disord. 2009 Dec;15(10):742-5
references.pmid: 19640769
references.citation: J Neurophysiol. 1996 Jun;75(6):2380-96
references.pmid: 8793751
references.citation: Arch Phys Med Rehabil. 2009 Jun;90(6):1004-8
references.pmid: 19480877
references.citation: J Neurol. 2009 May;256(5):742-9
references.pmid: 19240961
references.citation: Arch Phys Med Rehabil. 1999 Mar;80(3):262-9
references.pmid: 10084433
references.citation: Med Sci Sports Exerc. 2000 Oct;32(10):1679-84
references.pmid: 11039637
references.citation: BMC Public Health. 2005 Aug 26;5:90
references.pmid: 16124871
references.citation: Gait Posture. 1999 Sep;10(1):10-20
references.pmid: 10469937
references.citation: Arch Phys Med Rehabil. 2005 Nov;86(11):2172-6
references.pmid: 16271566
references.citation: Medicina (Kaunas). 2003;39(2):122-8
references.pmid: 12626864
references.citation: Arch Gerontol Geriatr. 2004 Sep-Oct;39(2):163-77
references.pmid: 15249153
references.citation: J Gerontol A Biol Sci Med Sci. 2001 May;56(5):M281-6
references.pmid: 11320107
references.citation: Phys Ther. 2002 Jun;82(6):566-77
references.pmid: 12036398
references.citation: Chest. 2003 Feb;123(2):387-98
references.pmid: 12576356
references.citation: J Bone Miner Metab. 2004;22(6):602-11
references.pmid: 15490272
references.citation: Age Ageing. 2005 Jan;34(1):21-4
references.pmid: 15591480
references.citation: J Neurol Sci. 2000 Apr 1;175(1):57-70
references.pmid: 10785258
references.citation: J Neurol Sci. 1992 Aug;111(1):46-58
references.pmid: 1402997
references.citation: Parkinsonism Relat Disord. 2009 Dec;15(10):776-80
references.pmid: 19560392
references.citation: Arch Phys Med Rehabil. 2004 Oct;85(10):1593-8
references.pmid: 15468016
references.citation: Am J Phys Med Rehabil. 2007 Aug;86(8):621-32
references.pmid: 17667192
references.citation: Med Sci Sports Exerc. 2003 Dec;35(12):1962-71
references.pmid: 14652489
references.citation: Knee. 2002 Feb;9(1):55-63
references.pmid: 11830382
references.citation: J Athl Train. 2005 Oct-Dec;40(4):305-9
references.pmid: 16404452
references.citation: Phys Ther. 2008 Jun;88(6):733-46
references.pmid: 18356292
references.citation: J Neurol Neurosurg Psychiatry. 2002 Jun;72(6):721-5
references.pmid: 12023412
references.citation: Arch Phys Med Rehabil. 1999 May;80(5):490-4
references.pmid: 10326909
references.citation: NeuroRehabilitation. 2000;14(3):165-174
references.pmid: 11455079
references.citation: Arch Phys Med Rehabil. 1998 Dec;79(12):1582-9
references.pmid: 9862305
references.citation: Am J Hum Biol. 2005 Nov-Dec;17(6):746-51
references.pmid: 16254902
references.citation: J Appl Physiol (1985). 2000 Apr;88(4):1321-6
references.pmid: 10749826