Dieen, J.H. van [Promotor]Hoozemans, M.J.M. [Copromotor

Lee, Y.J.

DSpace at VU

Control	  of	  trunk	  movement:	  Perturbations	  in	  cart	  pushing	  	  
131.	  
Mechanical	  perturbations	  challenge	  trunk	  stability,	  which	  is	  considered	  a	  risk	  factor	  for	  low-­‐back	  injury.	  Increased	  trunk	  muscle	  activity	  causes	  an	  increase	  in	  trunk	  stiffness,	  which	  enhances	  the	  trunk	  stability	  and	  may	  thus	  prevent	  negative	  effects	  of	  mechanical	  perturbations.	  	  However,	  trunk	  stiffness	  is	  relatively	  low	  during	  low-­‐demand	  tasks,	  such	  as	  pushing	  tasks.	  Pushing	  carts	  has	  therefore	  been	  suggested	  to	  impose	  a	  challenge	  for	  trunk	  muscle	  control	  as	  a	  system	  with	  a	  relatively	  low	  stiffness	  may	  have	  to	  deal	  with	  perturbations	  induced	  by	  an	  object	  with	  high	  inertia.	  This	  might	  cause	  uncontrolled	  trunk	  motions	  and	  inappropriate	  trunk	  muscle	  responses	  could	  further	  increase	  the	  risk	  of	  low-­‐back	  injury.	  	  In	  pushing	  tasks,	  handle	  height	  is	  one	  of	  ergonomic	  factors,	  which	  determines	  trunk	  posture	  and	  affects	  trunk	  muscle	  activity,	  i.e.	  when	  pushing	  at	  low	  handle	  height	  trunk	  inclination	  is	  larger	  and	  trunk	  muscle	  activity	  is	  higher,	  which	  may	  affect	  the	  impact	  of	  perturbations.	  In	  addition,	  expectation	  of	  an	  impending	  perturbation	  may	  lead	  to	  early	  initiation	  of	  trunk	  muscle	  activity,	  which	  may	  also	  reduce	  the	  impact	  of	  the	  perturbations.	  This	  thesis	  focuses	  on	  trunk	  moment	  perturbations	  in	  the	  sagittal	  plane	  and	  transverse	  planes	  in	  combination	  with	  corresponding	  trunk	  muscle	  activity	  in	  response	  to	  perturbations,	  which	  can	  occur	  when	  pushing	  a	  cart.	  The	  principal	  objectives	  of	  the	  studies	  were:	  (1)	  to	  study	  the	  effects	  of	  predictable	  perturbations	  on	  the	  control	  of	  trunk	  muscle	  activity	  and	  trunk	  motion	  before	  the	  actual	  occurrence	  of	  the	  perturbations,	  (2)	  to	  study	  the	  effects	  of	  predictable	  and	  unpredictable	  perturbations	  on	  the	  control	  of	  trunk	  muscle	  activity	  and	  trunk	  motion	  after	  the	  occurrence	  of	  the	  perturbations,	  and	  (3)	  to	  study	  the	  effects	  of	  self-­‐generated	  and	  externally	  generated	  perturbations	  on	  trunk	  motion	  after	  the	  occurrence	  of	  the	  perturbations	  and,	  finally,	  (4)	  to	  study	  differences	  in	  trunk	  muscle	  control	  and	  trunk	  motion	  in	  response	  to	  the	  perturbations	  when	  pushing	  at	  shoulder	  height	  or	  hip	  height.	  In	  chapter	  2,	  we	  studied	  the	  effects	  of	  handle	  height	  and	  the	  expectation	  of	  sudden	  unloading	  during	  the	  transition	  of	  cart	  movement	  from	  static	  to	  dynamic	  friction.	  Subjects	  were	  asked	  to	  push	  a	  cart	  with	  brakes	  (externally	  triggered)	  and	  without	  brakes	  (self-­‐initiated).	  This	  sudden	  drop	  in	  contact	  force	  at	  the	  hands	  associated	  with	  the	  onset	  of	  cart	  movement	  is	  considered	  as	  a	  sudden	  
Summary	  	  
132.	  
unloading	  perturbation.	  Compared	  to	  pushing	  at	  hip	  height,	  lower	  muscle	  activity	  and	  trunk	  stiffness	  at	  shoulder	  height	  before	  onset	  resulted	  in	  a	  higher	  trunk	  inclination	  after	  onset.	  Before	  self-­‐initiated	  cart	  movement,	  trunk	  stiffness	  and	  muscle	  activity	  were	  significantly	  higher	  than	  before	  an	  externally	  triggered	  onset	  at	  a	  comparable	  pushing	  force.	  In	  conclusion,	  higher	  preparatory	  activation	  of	  trunk	  muscles	  serves	  to	  increase	  trunk	  stiffness	  in	  anticipation	  of	  cart	  movement	  and	  may	  reduce	  the	  impact	  of	  the	  perturbation	  associated	  with	  the	  onset	  of	  cart	  movement.	  Change	  in	  contact	  force	  at	  the	  hands	  was	  shown	  to	  cause	  a	  perturbation	  of	  the	  trunk	  in	  the	  previous	  chapter.	  Opposite	  to	  the	  sudden	  unloading	  perturbation	  in	  cart	  pushing,	  sudden	  loading	  was	  studied	  in	  chapter	  3.	  The	  objective	  of	  this	  study	  was	  to	  investigate	  whether	  different	  types	  (self-­‐generated	  &	  externally	  generated)	  of	  sudden	  loading	  perturbations	  due	  to	  sudden	  stops	  while	  pushing	  a	  high	  inertia	  cart.	  Subjects	  were	  instructed	  to	  stop	  a	  cart	  as	  fast	  as	  possible	  after	  an	  auditory	  cue	  (self-­‐induced	  stop)	  or	  the	  wheels	  of	  the	  cart	  were	  unexpectedly	  blocked	  (externally	  induced	  stop).	  Initial	  responses	  in	  both	  stops	  consisted	  of	  flexor	  and	  extensor	  muscle	  cocontraction.	  In	  the	  self-­‐induced	  stops,	  trunk	  extension	  coincided	  with	  an	  internal	  extensor	  moment,	  indicating	  that	  voluntary	  trunk	  extension	  was	  observed.	  In	  the	  externally	  induced	  stops,	  an	  external	  extension	  moment	  caused	  a	  decrease	  in	  trunk	  inclination.	  The	  opposite	  directions	  of	  the	  internal	  moment	  and	  trunk	  motion	  in	  the	  externally	  induced	  stop	  while	  pushing	  at	  shoulder	  height	  may	  indicate	  loss	  of	  control	  over	  trunk	  posture.	  In	  conclusion,	  different	  types	  of	  perturbations	  in	  cart	  pushing	  induce	  voluntary	  (self-­‐generated)	  and	  involuntary	  (externally	  generated)	  trunk	  motions	  and	  particularly	  when	  pushing	  at	  shoulder	  height	  externally	  generated	  perturbations	  may	  put	  the	  low	  back	  at	  risk	  of	  mechanical	  injury.	  The	  horizontal	  component	  of	  the	  hand	  force	  in	  pushing	  also	  affects	  trunk	  moments	  in	  the	  transverse	  plane,	  i.e.	  the	  trunk	  twisting	  moments	  around	  the	  L5S1	  joint.	  These	  moments	  were	  expected	  to	  vary	  cyclically	  when	  pushing	  while	  walking	  and	  the	  objective	  of	  chapter	  4	  was	  to	  investigate	  whether	  cyclic	  oblique	  abdominal	  muscle	  activity	  was	  associated	  with	  cyclic	  pushing	  forces	  when	  pushing	  while	  walking.	  In	  addition,	  we	  hypothesized	  that	  external	  and	  unpredictable	  perturbations	  would	  be	  counteracted	  by	  cocontraction	  of	  the	  
Control	  of	  trunk	  movement:	  Perturbations	  in	  cart	  pushing	  	  
133.	  
oblique	  abdominal	  muscles.	  Subjects	  were	  instructed	  to	  push	  at	  two	  target	  forces	  in	  a	  static	  standing	  position,	  while	  walking	  and	  additionally	  while	  walking	  and	  pushing	  against	  a	  randomly	  perturbed	  target	  force	  to	  simulate	  the	  effect	  of	  non-­‐constant	  rolling	  resistance.	  A	  tonic	  level	  of	  oblique	  abdominal	  muscle	  activity	  (static	  component	  of	  EMG	  amplitudes)	  was	  used	  to	  maintain	  trunk	  posture	  in	  pushing	  while	  walking.	  The	  additional	  dynamic	  activity	  was	  associated	  with	  the	  twisting	  moments,	  which	  were	  actively	  modulated	  by	  the	  pairs	  of	  oblique	  muscles	  as	  in	  normal	  gait.	  In	  line	  with	  the	  hypothesis,	  in	  the	  perturbed	  condition,	  an	  increased	  baseline	  of	  oblique	  abdominal	  muscle	  activity	  reflected	  cocontraction	  of	  the	  antagonistic	  muscle	  pairs	  of	  trunk	  rotator	  muscles,	  which	  was	  associated	  with	  an	  increase	  in	  trunk	  stiffness	  around	  the	  longitudinal	  axis.	  	  The	  small	  asymmetry	  of	  the	  hand	  reaction	  forces	  in	  pushing	  while	  walking	  studied	  in	  chapter	  4	  elicited	  trunk	  oblique	  abdominal	  muscle	  cocontraction.	  More	  asymmetry	  of	  the	  hand	  forces	  is	  expected	  when	  steering	  a	  cart	  to	  make	  a	  turn.	  The	  objective	  of	  chapter	  5	  was	  to	  investigate	  effects	  of	  the	  predictability	  of	  the	  perturbation	  induced	  by	  making	  a	  turn	  while	  pushing.	  Subjects	  were	  instructed	  to	  push	  while	  making	  a	  gradual	  turn,	  a	  sharp	  turn	  and	  an	  unexpected	  sharp	  turn	  (i.e.	  making	  a	  sharp	  turn	  as	  fast	  as	  possible	  after	  an	  auditory	  cue).	  An	  increase	  of	  oblique	  abdominal	  muscle	  activity	  before	  the	  gradual	  and	  sharp	  turns	  indicated	  that	  anticipatory	  activation	  occurred	  when	  a	  turn	  was	  planned,	  which	  was	  however	  not	  directionally	  specific.	  After	  a	  left	  turn,	  trunk	  twisting	  motion	  to	  the	  right	  was	  associated	  with	  a	  twisting	  moment	  in	  the	  same	  direction	  induced	  by	  the	  reaction	  forces	  on	  the	  left	  hand	  and	  presumably	  slowed	  down	  by	  an	  increased	  stiffness	  as	  a	  consequence	  of	  the	  bilateral	  oblique	  abdominal	  muscle	  activity.	  Anticipatory	  activation	  was	  absent	  in	  the	  unexpected	  sharp	  turns	  and	  bilateral	  trunk	  rotator	  muscle	  activity	  increased	  only	  after	  the	  turn.	  Trunk	  rotation	  to	  the	  right	  was	  faster	  than	  in	  the	  planned	  turns.	  In	  conclusion,	  trunk	  motion	  in	  pushing	  while	  turning	  was	  initially	  opposite	  to	  the	  travel	  direction.	  Additionally,	  the	  predictability	  of	  the	  turn	  affected	  the	  control	  of	  this	  trunk	  twisting	  motion.	  In	  the	  unexpected	  turns,	  the	  combination	  of	  an	  uncontrolled	  twisting	  motion	  with	  delayed	  muscle	  activation	  may	  increase	  the	  potential	  risk	  of	  low-­‐back	  injury.	  	  	  
Summary	  	  
134.	  
In	  conclusion,	  this	  thesis	  provides	  evidences	  of	  changes	  in	  contact	  force	  at	  the	  hands	  in	  pushing	  being	  a	  perturbation	  to	  the	  trunk	  that	  may	  impose	  a	  risk	  of	  low-­‐back	  injury.	  In	  cart	  pushing,	  externally	  generated	  unpredictable	  perturbations,	  especially	  while	  pushing	  at	  shoulder	  height,	  induce	  involuntary	  trunk	  motions	  counteracted	  by	  relatively	  late	  responses	  in	  muscle	  activity.	  Prior	  to	  expected	  and	  self-­‐generated	  perturbations,	  anticipatory	  activity	  increased	  trunk	  stiffness,	  but	  did	  not	  completely	  prevent	  displacements	  of	  the	  trunk.	  The	  impact	  of	  perturbations	  in	  pushing	  was	  attenuated	  by	  the	  increase	  in	  trunk	  inclination	  associated	  with	  pushing	  at	  hip	  height.	  When	  generalizing	  the	  findings	  of	  this	  thesis	  to	  other	  situations,	  such	  as	  a	  different	  cart	  mass,	  cart	  speed	  or	  population,	  the	  responses	  of	  trunk	  muscle	  activity	  and	  motion	  should	  be	  considered	  with	  care,	  as	  these	  factors	  may	  affect	  task	  demands	  in	  terms	  of	  external	  moments	  to	  the	  trunk.	  Previous	  studies	  on	  trunk	  control	  mainly	  addressed	  unidirectional	  sudden	  loading	  or	  sudden	  release	  perturbations	  applied	  directly	  to	  the	  trunk.	  In	  functional	  activities,	  perturbations	  may	  be	  multidirectional	  and	  may	  be	  applied	  either	  directly	  at	  the	  trunk	  or	  at	  the	  hands.	  The	  studies	  presented	  highlighted	  differences	  in	  patterns	  of	  trunk	  muscle	  activity	  between	  artificial	  perturbations	  used	  in	  previous	  studies	  on	  trunk	  control	  and	  realistic	  perturbations	  during	  functional	  activities.	  	  	   	  


Control of trunk movement: Perturbations in cart pushing

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VU Research PortalControl of trunk movementLee, Y.J.2011document versionPublisher's PDF, also known as Version of recordLink to publication in VU Research Portalcitation for published version (APA)Lee, Y. J. (2011). Control of trunk movement: Perturbations in cart pushing.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.E-mail address:vuresearchportal.ub@vu.nlDownload date: 14. Sep. 2021Control of trunk Movement: Control of trunk movement:Perturbations in cart pushingYun-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration between researchers of the Faculty of Human Movement Sciences, VU University Medical Center and the Academic Centre for Dentistry Amsterdam. The research of MOVE is related to human movement and health, with an emphasis on prevention and recovery of injury and disorders of the (neuro-)musculoskeletal system, on optimal recovery of tissue and function, and on motor control and coordination. MOVE aims at fundamental, multidisciplinary and translational research, especially in the fields of (oral) regenerative medicine, rehabilitation and sports.www.move.vu.nlYun-Ju Leeperturbations in cart pushingisbn: 978-94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingcontrol of trunk movement:perturbations in cart pushing12-12-2011 09:45@AulaVrije UniversiteitDe Boelenlaan 11051081 HV Amsterdamyun-ju Leeyunju1127.lee@gmail.comParanimfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptieControl of trunk Movement: Control of trunk movement:Perturbations in cart pushingYun-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration between researchers of the Faculty of Human Movement Sci nces, VU Unive sity Medical Center and the Academic Centre for Dentistry Amsterdam. The research of MOVE is related to human movement and health, with an emphasis on prevention and recovery of injury and disorders of the (neuro-)musculoskeletal system, on optimal recovery of tissue and function, and on motor control and coordination. MOVE aims at fundamental, multidisciplinary and translational research, especially in the fields of (oral) regenerative medicine, rehabilitation and sports.ww.move.vu.nlYun-Ju Leeperturbations in cart pushingis -94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingcontrol of trunk movement:perturbations in cart pushing12-12-2011 09:45@AulaVrije UniversiteitDe Boelenlaan 11051081 HV Amsterdamyun-ju Leeyunju1127.lee@gmail.comParanimfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptieControl of trunk Movement: Control of trunk movement:Perturbations in cart pushingYun-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration between researchers of he Faculty of Human Movement Sciences, VU University Medical Center d the Academic Centre for Dentistry Amsterdam. The research of MOVE is related to human movement and health, with an emphasis on prevention and recovery of injury and disorders of the (neuro-)musculoskeletal system, on optimal recovery of tissue and function, and on motor control and coordination. MOVE aims at fundamental, multidisciplinary and translational research, espe ially  the fields of (oral) regenerative medicine, rehabilitation and spor s.www.move.vu.nlYun-Ju Leeperturbations in cart pushingisbn: 978-94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingcontrol of trunk movemen :perturbations in cart pushing12-12-2011 09:45@AulaVrije UniversiteitDe Boelenlaan 11051081 HV Amsterdamyun-ju Leeyunju1127.lee@gmail.comParanimfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptieControl of trunk Movement: Control of trunk movement:Pe turbations in cart pushingY n-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration between researchers of the Faculty of Human Movement Sciences, VU University Medical Center and the Academic Centre for Dentistry Amsterdam. The research of MOVE is related to human ovement and health, with an emphasis on prevention and recovery of injury and disorders f the (neuro-)musculoskeletal system, on optimal recove y of tissue and function, and on motor cont l and oordination. MOVE aims at fundamental, multidisciplinary and translational research, especially in the fields of (oral) regenerative medicine, rehabilitation and sports.www.move.vu.nlYun-Ju Leeperturbations in cart pushingisbn: 978-94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingco trol of trunk movement:perturbations in cart pushing12-12-2011 09:45@AulaVrije UniversiteitDe Boelenl 051081 HV Ayun-ju Leeyunju1127.lee@gmail.comParanimfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptieControl of trunk Movement: Cont l  trunk movement:Pe tions in cart pushingYun-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration between researchers of the Faculty of Human Movement Scie ces, VU University Medical Center and the Academ c C ntr  for D ntistry Amsterd m. The rese rch of MOVE is related to human movement and health, with an emphasis o  prevention and recove y of injury and disorde s of the (ne ro-) usculoskeletal system, on opti al recovery of tissue  function, and on motor control and coordination. MOVE aims at fundam ntal, multidisciplinary and translatio al rese rch, especia ly in the f elds of (oral) regenerative medicine, rehabilitation and sports.www.m ve.vu.nlYun-Ju Leeperturbations in cart pushingisb : 978-94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingcontrol of trunk m ve ent:pertu bations in cart pushing12-12-201  09:45@AulaVrije UniversiteitDe Boelenlaan 11051081 HV Amst rdamyun-ju Leeyunju1127.lee@gmail.comPara imfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptieControl of trunk Movement: Control of trunk movement:Perturbations in cart pushingYun-Ju LeeMOVE TO IMPROVEVU University Research Institute MOVE is a collaboration b tween rese rche s of the Facu ty of Human Movement Sci nces, VU University Medical Center and the Academic Centre for Dentistry Amsterdam. The research of MOVE is el te o human movement and health, with an emphasis on prevention nd recovery of injury and disorders of the ( euro-)musculoskeletal system, on optimal recovery of tissue and function, and on motor control and coo dination. MOVE aims at fundam ntal, multidisciplinary and translatio al research, especially in the fields of (oral) regenerative medicine, rehabilitation and sports.www.move.vu.nlYun-Ju Leeperturbations in cart pushingisbn: 978-94-6191-073-8voor de openbare verdediging van mijn proefschrift:uitnodigingcontrol of trunk movement:perturbations in cart pushing12-12-2011 09:45@AulaVrije UniversiteitDe Boelenlaan 11051081 HV Amsterdamyun-ju Leeyunju1127.lee@gmail.comParanimfenJing-nong LiangJN-Liang@u.northwestern.eduNienke Willigenburgn.w.willgenburg@vu.nlAansluitend receptie

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