title: Both coordination and symmetry of arm swing are reduced in Parkinson's disease.
abstract: OBJECTIVE
  A recent study reporting significantly reduced symmetry in arm swing amplitude in early Parkinson's disease (PD), as measured during single strides in a gait laboratory, led to this investigation of arm swing symmetry and coordination over many strides using wearable accelerometers in PD.
  
  
  METHODS
  Forearm accelerations were recorded while eight early PD subjects and eight Controls performed 8-min walking trials. Arm swing asymmetry (ASA), maximal cross-correlation (MXC), and instantaneous relative phase (IRP) of bilateral arm swing were compared between PD and Controls. Correlations between arm swing measurements (ASA and MXC) and Unified PD Rating Scale (UPDRS) scores were estimated.
  
  
  RESULTS
  PD subjects demonstrated significantly higher ASA (p=0.002) and lower MXC (p<0.001) than Controls. The IRP probability distribution for PD was significantly different than Controls (p<0.001), with an angular standard deviation of 67.2° for PD and 50.6° for Controls. Among PD subjects, ASA was significantly correlated with the UPDRS score for the limbs (R(2)=0.58, p=0.049), whereas MXC was significantly correlated with the tremor subscore of the limbs (R(2)=0.64, p=0.031).
  
  
  CONCLUSIONS
  The study confirms previously reported higher arm swing asymmetry in PD but also shows there is significantly lower MXC and greater IRP variability, suggesting that reduction in bilateral arm coordination may contribute to clinically observed asymmetry in PD. The differential correlation of clinical measures of motor disability with measurements of arm swing during gait is intriguing and deserves further investigation.
authors.affiliation: Department of Neurology, The Pennsylvania State University - Milton S. Hershey Medical Center, Hershey, PA 17033, USA. xuemei@psu.edu
authors.forename: Xuemei
authors.initials: X
authors.lastname: Huang
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Mahoney
authors.forename: Mechelle M
authors.initials: MM
authors.lastname: Lewis
authors.lastname: Guangwei Du
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Piazza
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Cusumano
mesh_terms: D000054:Acceleration; D000368:Aged; D000704:Analysis of Variance; D001132:Arm / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D005260:Female; D020233:Gait Disorders, Neurologic / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009068:Movement; D010300:Parkinson Disease / Q000503:physiopathology*; D012016:Reference Values; D012720:Severity of Illness Index; D016138:Walking / Q000502:physiology
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