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How do anticipatory phenomena during gait initiation develop for children?
Abstracts-InternationalSocietyof BiomechanicsXIV Congress1993 HOW DO ANTICIPATORY PHENOMENA DURING GAIT INITIATION DEVELOP FOR CHILDREN ? Anmck Ledebt, Yvon Breniereand BlandineBril L&o Physiologie du Mouvement, URA-CNRS 631, Univ. PARIS XI, ORSAY, France. Anticipatory postural adjustmentsduring gait initiation was analysed for children aged 4, 6 ans 8 by meansof a force plateform. Spatial and temporalanticipatoryparametersand gait velocity were computedfrom the forceplatedata. In the three age groups,velocity generatedwithin the first step is almost that of steady-state velocity of the forthcoming sequenceof steps as for adults. The anticipatory parameters display a clear developmental trend with age, but more interesting are changesin the correlations between parameters.At 4 years, all children display anticipatory spatial behavior (anticipatory backward shift of the center of foot pressure)even if not consistently.However it is only at 6 yearsthat a positive correlation is found betweenthis backward shift and the forthcoming velocity, as it is the case in adults. Concerning the temporal aspect of anticipation, the covariation betweenthe duration of the anticipatory phaseand the forthcoming velocity fail to be significant in all groups, but a positive trend exists. The results clearly establish that internal anticipatory behavior in gait initiation is not innate and that, once present,it still unfolds toward more elaborateforms. The development of anticipatory behavior in relation to the forthcoming gait velocity is explicitly viewed in this study as indexing the construction of feedforward control of gait. It is during the anticipatory phase of the movement that the conditions of the forthcoming movementare set up. In gait initiation anticipatory behavior has to create the conditions of steady-statevelocity. This meansthat one has not only to predict disequilibrium, due to the shift of bipedal to unipedal stanceand to a move forward, but one has to createthe conditions for the first step as well. This twofold design could be one reasonwhy the developmentof anticipatory behavior takes so long.
PRACTICE-RELATED CHANGES IN LOWER EXTREMITY JOINT COORDINATION DURING PULLS MADE WHILE STANDING Wynne A. Lee and Aileen M. Russo Programsin Physical Therapy and The NorthwesternInstitute for Neuroscience NorthwesternUniversity Medical School, Chicago,IL USA This study evaluatedBernstein’shypothesisthat novicesto a motor task restrict joint motion and minimize their kinematic degreesof freedom(DFs), but after practiceusefewer tightly coupledmotions (more DFs). We evaluatedhow five subjects’ankle, knee and hip joint angle coordinationchangedover three days’ practiceon a task where they attemptedto make accuratebilaterally symmetrical,impulse-like pulls to a force *aget qual to 55% of their estimatedmaxiurum.Ankie, knee,and hip angles(measuredvia a two-camera Watsmartm system)and pulling force were analyzedfor the first 10 trials on Day 1 and the last 10 trials on Day 3. On each day, the number of tightly linked joints was assessedas the number of joint pairs that showed linearly relatedmotions (sharedvariance2.9). Gain and phaserelationshipswere evaluatedfor tightly linked joint pairs. In contrastto the hypothesisthat subjects“freeze”all but onejoint motion early in practice,all joints showed significant motion on Day 1. The data also did not support for Bernstein’shypothesisthat subjectswould use more kinematic DFs (fewer tightly coupledjoints) after practice: Three subjectsdid not changeand one subject increasedthe number of tightly linked joint motions betweenDay 1 and Day 3; only one subjectdecreasedthe numberof tightly linked joints. Subjectsdiffered in whetherthe samejoint patternswere usedon Day 1 and Day 3. Subjectswho used the samejoint patternson both days showedmore consistentgain and phaserelationships after practice. These resultsargue againstBernstein’shypothesisabout how coordination changeswith practice, althoughthey must be regardedcautiouslydue to the small samplesize and the limited practice. The gain and phasedata suggestthat some practice-relatedchangesin coordinationmay be quantitative.
IS VELOCITY OF A POINTING MOVEMENT PERFORMED IN A SITTING POSTURE INCREASED BY UPPER BODY INSTABILITY ? F&h& Lino and Simon Bouisset Laboratoire de Physiologie du Mouvement, URA-CNRS 631, Universite Paris&d, 91405 ORSAY, FRANCE This study was carried out to detemline whether the configuration of support base influences the maximal velocity of a pointing task performed by a sitting subject. Different ischio-femoral surfacecontacts were considered,while keeping the overall perimeter of the support basethe same.The subject was askedto point, at maximal velocity, at a target located iii front of him at shoulder level and at his maxiiual reach.The contact with the seat included 100 %, 60 %, and 30 % of the ischio-femoral length according to the experimentalcondition. The main result of this study is that the maximal movementvelocity changedwith the ischio-femoral contact area. For a given global support perimeter, the seat contact area was found to be a parameter of motor organization, in so far as its changes induced corresponding changes in movement velocity. Faster movement velocities were associatedwith a smaller of ischio-femoral support, and greater changesin the ischio-femoral supportingforces.Therefore,smaller trunk stability appearsto favor the velocity of upper limb movements.The reaction forces at the feet and at ischio-femoral level varied in the opposite way, depending on the support conditions. While the former are negative and therefore decreased,the later increased.This result suggeststhat the lower limbs contribute to postural reaction, and that its dynamics are coordinatedwith the dynamics of the upper body.
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PRACTICE-RELATED CHANGES IN LOWER EXTREMITY JOINT COORDINATION DURING PULLS MADE WHILE STANDING Wynne A. Lee and Aileen M. Russo Programsin Physical Therapy and The NorthwesternInstitute for Neuroscience NorthwesternUniversity Medical School, Chicago,IL USA This study evaluatedBernstein’shypothesisthat novicesto a motor task restrict joint motion and minimize their kinematic degreesof freedom(DFs), but after practiceusefewer tightly coupledmotions (more DFs). We evaluatedhow five subjects’ankle, knee and hip joint angle coordinationchangedover three days’ practiceon a task where they attemptedto make accuratebilaterally symmetrical,impulse-like pulls to a force *aget qual to 55% of their estimatedmaxiurum.Ankie, knee,and hip angles(measuredvia a two-camera Watsmartm system)and pulling force were analyzedfor the first 10 trials on Day 1 and the last 10 trials on Day 3. On each day, the number of tightly linked joints was assessedas the number of joint pairs that showed linearly relatedmotions (sharedvariance2.9). Gain and phaserelationshipswere evaluatedfor tightly linked joint pairs. In contrastto the hypothesisthat subjects“freeze”all but onejoint motion early in practice,all joints showed significant motion on Day 1. The data also did not support for Bernstein’shypothesisthat subjectswould use more kinematic DFs (fewer tightly coupledjoints) after practice: Three subjectsdid not changeand one subject increasedthe number of tightly linked joint motions betweenDay 1 and Day 3; only one subjectdecreasedthe numberof tightly linked joints. Subjectsdiffered in whetherthe samejoint patternswere usedon Day 1 and Day 3. Subjectswho used the samejoint patternson both days showedmore consistentgain and phaserelationships after practice. These resultsargue againstBernstein’shypothesisabout how coordination changeswith practice, althoughthey must be regardedcautiouslydue to the small samplesize and the limited practice. The gain and phasedata suggestthat some practice-relatedchangesin coordinationmay be quantitative.
IS VELOCITY OF A POINTING MOVEMENT PERFORMED IN A SITTING POSTURE INCREASED BY UPPER BODY INSTABILITY ? F&h& Lino and Simon Bouisset Laboratoire de Physiologie du Mouvement, URA-CNRS 631, Universite Paris&d, 91405 ORSAY, FRANCE This study was carried out to detemline whether the configuration of support base influences the maximal velocity of a pointing task performed by a sitting subject. Different ischio-femoral surfacecontacts were considered,while keeping the overall perimeter of the support basethe same.The subject was askedto point, at maximal velocity, at a target located iii front of him at shoulder level and at his maxiiual reach.The contact with the seat included 100 %, 60 %, and 30 % of the ischio-femoral length according to the experimentalcondition. The main result of this study is that the maximal movementvelocity changedwith the ischio-femoral contact area. For a given global support perimeter, the seat contact area was found to be a parameter of motor organization, in so far as its changes induced corresponding changes in movement velocity. Faster movement velocities were associatedwith a smaller of ischio-femoral support, and greater changesin the ischio-femoral supportingforces.Therefore,smaller trunk stability appearsto favor the velocity of upper limb movements.The reaction forces at the feet and at ischio-femoral level varied in the opposite way, depending on the support conditions. While the former are negative and therefore decreased,the later increased.This result suggeststhat the lower limbs contribute to postural reaction, and that its dynamics are coordinatedwith the dynamics of the upper body.
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