title: Old adults preserve motor flexibility during rapid reaching.
abstract: OBJECTIVE
  Our ability to flexibly coordinate the available degrees of freedom allows us to perform activities of daily living under various task constraints. Healthy old adults exhibit subclinical peripheral and central nervous system dysfunctions, possibly compromising the flexibility in inter-joint coordination during voluntary movements and the ability to adapt to varying task constraints.
  
  
  METHODS
  We examined how healthy old (75.4 ± 5.2 years, n = 14) compared with young adults (24.3 ± 2 years, n = 15) make use of the available motor flexibility to adapt to physical and dexterity constraints during a rapid goal-directed reaching task. We manipulated physical and dexterity demands by changing, respectively, external resistance and target size. Motor flexibility was quantified by an uncontrolled manifold (UCM) analysis.
  
  
  RESULTS
  We found that healthy young and old adults employ similar motor flexibility as quantified by the ratio between goal equivalent and non-goal equivalent variability (VRatio) and were similarly able to adapt to increases in physical and dexterity demands during goal-directed rapid reaching (VRatio: p = .092; young: 0.548 ± 0.113; old: 0.264 ± 0.117). Age affected end-effector kinematics. Motor flexibility and end-effector kinematics did not correlate.
  
  
  CONCLUSIONS
  The data challenge the prevailing view that old age affects movement capabilities in general and provide specific evidence that healthy old adults preserve motor flexibility during a reaching task. Future studies applying UCM analysis should examine if experimental set-ups limit movement exploration, leaving possible age differences undetected.
authors.affiliation: Center for Human Movement Science, University of Groningen, University Medical Center Groningen, Hanzeplein 1, HPC CB41, Postbus 30.001, 9700 RB, Groningen, The Netherlands. c.greve@umcg.nl.|Department of Rehabilitation Medicine, Center for Rehabilitation, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. c.greve@umcg.nl.
authors.forename: Christian
authors.identifier: http://orcid.org/0000-0003-2906-3753
authors.initials: C
authors.lastname: Greve
authors.affiliation: Center for Human Movement Science, University of Groningen, University Medical Center Groningen, Hanzeplein 1, HPC CB41, Postbus 30.001, 9700 RB, Groningen, The Netherlands.
authors.forename: Tibor
authors.initials: T
authors.lastname: Hortobágyi
authors.affiliation: Center for Human Movement Science, University of Groningen, University Medical Center Groningen, Hanzeplein 1, HPC CB41, Postbus 30.001, 9700 RB, Groningen, The Netherlands.
authors.forename: Raoul M
authors.initials: RM
authors.lastname: Bongers
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009048:Motor Skills; D018482:Muscle, Skeletal / Q000254:growth & development / Q000502:physiology*; D016059:Range of Motion, Articular; D011930:Reaction Time
keywords: Ageing; Motor control; Motor flexibility; Reaching; Task demand; Uncontrolled manifold