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19.14 Effect of lower body muscle fatigue on a whole body pointing task
Chapter 19. Pain and fatigue
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During passive shoulder movements patients move their head to the right during elevation and to the left during depression, while healthy subjects move their head in the opposite direction (p < 0.5). Active movements and vibration showed the same head movements in patients (p < 0.5) but did not reveal differences between groups. D i s c u s s i o n a n d c o n c l u s i o n : Patients seem to overestimate their shoulder position. An altered internal representation, probably due to inaccurate proprioception of shoulder and neck, might explain these observations. In addition, the opposite movements of the head are possibly caused by modified perception of self tilt and may reflect an offset in the egocentric reference frame. Better insight in the underlying mechanisms might lead to improved evaluation and treatment of patients with RNR
[•3]
Fatigue influence on postural coordination: comparison of observed and predicted pattern
A. Ponce 1, F. Fouque 1, A. Martin 1, L. Martin 2, V Cahou~t2.
M e t h o d s : We addressed the issue of the potential degradation of aiming precision connected with a possible derangement of the movement-posture coordination by selective perturbation of the postural component of the task. The protocol involved continuous repetition of ballistic whole-body pointing (WBP) tasks (implying pointing with the index fingers at a target, while lowering the body mass and returning to the initial position). This was repeated at a frequency of 0.1 Hz until exhaustion. Results: Such sequence led to EMG signs of fatigue in the quadriceps (active for body lowering and rising, therefore in eccentric and concentric conditions) while the deltoid (prime mover for the arm reaching component) showed no signs of fatigue. The precision of the aiming movement was unaffected by the quadriceps fatigue. However, the trajectory of the finger during the WBP task was drastically changed between the first and the last trials of the sequence. D i s c u s s i o n : The central nervous system takes into account the state of postural muscles and the concurrently ensuing equilibrium constraints to appropriately modify the trajectory of the aiming limb and obtain a constant precision at the target.
1Laboratoire Motricit&Plasticit~ INSERM/ERIT-M 207, UFRSTAPS, Universitd de Bourgogne BP 27877, 21078 Dijon, France," :Laboratoire Sport et Performance Motrice EA 597, Universitd Joseph Fourie~ 38041 Grenoble cedex 9, France
[1~
I n t r o d u c t i o n : Recent dynamic optimization model [1] (minimum
M. S c h m i d 1 , M. Schieppati 1,2. 1Human Movement Laboratory
torque change model) was use to predict behaviors during a fore~ft target tracking task. Predictions were very similar with experimental observations described in existing literature [2]. Results suggest that hang of different coordination modes (relative phase between ankle and hip movements) is define by mechanical and/or metabolic constraints. M e t h o d s : In order to test this, seven subjects were asked to track with the head (at different frequencies) the fore aft movements of a virtual target before and after solear muscles were fatigued using electromyostimulation. We added a constraint in the dynamic optimization model. This constraint checks that ankle torque always stay lower to a given proportion of maximal voluntary torque value. We provide simulations with two different maximal torques corresponding to those obtained in the two different conditions of fatigue and compared them with experimental results. Results: We observed a sudden switch from in-phase to anti-phase pattern with increasing frequency. Bifurcation appeared earlier in fatiguing condition and seemed to be linked to the system variability. D i s c u s s i o n : According to our results, predictions showed a decrease of switch frequency when maximal torque is decreased. This study confirms the model efficiency and the important role of metabolic and mechanical constraints in hanging pattern.
(CSAM), Fondazione Salvatore Maugeri (IRCCS), Scientific Institute of Pavia, eDepartment of Experimental Medicine, Section of Human Physiology, University of Pavia, Italy
References [1] Martin L., Cahouet V., Ferry M. & Fouque F. Optimization model prediction for postural coordination modes. J Biomech (in press). [2] Bardy B.G., Oullier O., Bootsma R.J. & Stoffregen T.A. Dynamics of human Postural transitions. Journal of Exp Psychol Human 2002; 38:499 514.
[•4]
Effect of lower body muscle fatigue on a whole body pointing task
M. S c h m i d 1 , T. P o z z o 2, M. Schieppati 1,3. 1C~AM,Salvatore Maugeri Foundation (IRCCS), Scientific Institute of Pavia, via Ferrata 8, 27100 Pavia, Italy," 2 ERM 207, Universitd de Bourgogne, Campus universitaire, Dijon 21004, France," 3Department of Experimental Medicine, Section of Human Physiology, University of Pavia, Italy I n t r o d u c t i o n : Appropriate coordination between movement and posture is the necessary condition for correct execution of voluntary motor acts. This is true under conditions in which aiming movements require displacement of several body segments including those normally engaged in balance. An example is represented by reaching from a standing position toward a target located low down and beyond arm length.
Neck muscle fatigue and spatial orientation during stepping-in-place in humans
I n t r o d u c t i o n : Neck proprioceptive input plays an important role in perception of body segment position and orientation in space. Neck muscle fatigue also produces destabilizing effects on stance. Our aim was to assess whether neck muscle fatigue can also perturb the orientation in space during a walking task. M e t h o d s : Direction and amplitude of the path covered during a stepping-in-place task were measured in ten blindfolded subjects, performing five 30 s-stepping trials before and after a 5 min-period of isometric dorsal neck muscle contraction against a load. Neck muscle EMG amplitude and median frequency during the head extensor effort were used to compute a fatigue index. Head and body kinematics was recorded by an optoelectronic system and stepping cadence was measured by sensorized insoles. Results: Prior to the contraction period, subjects normally stepped on the spot or drifted forwards. After contraction, some subjects reproduced the same behavior, whereas others reduced their forward progression or even stepped backwards. The former subjects showed minimal signs of neck muscle fatigue, the latter ones marked signs of fatigue. Head position and cadence were unaffected in either group of subjects. D i s c u s s i o n : We argue that the abnormal fatigue-induced afferent input can modulate the egocentric spatial reference frame and modify the orientation of the body in space in a walking task. The effects of neck muscle fatigue on orientation are opposite to those produced by neck proprioception.
•
Experimentally induced low back pain leads to reduced spinal motion but does not interfere with the compensation for postural sway with breathing
M. Smith, M.W. Coppieters, RW. Hodges. Division of Physiotherapy,
The University of Queensland, Brisbane, Australia Breathing perturbs balance. However, in healthy individuals minimal sway is detected at the ground because small movements of the spine and legs compensate for the postural disturbance. When people have chronic low back pain (LBP), displacement of centre of pressure (COP) with breathing is increased, possibly due to reduced compensatory trunk motion. This study investigated whether postural compensation for breathing is reduced during experimentally-induced LBR M e t h o d s : Subjects stood on a force plate with eyes open or closed, and while breathing quietly and with hypercapnoea, before and after Introduction:
S124
During passive shoulder movements patients move their head to the right during elevation and to the left during depression, while healthy subjects move their head in the opposite direction (p < 0.5). Active movements and vibration showed the same head movements in patients (p < 0.5) but did not reveal differences between groups. D i s c u s s i o n a n d c o n c l u s i o n : Patients seem to overestimate their shoulder position. An altered internal representation, probably due to inaccurate proprioception of shoulder and neck, might explain these observations. In addition, the opposite movements of the head are possibly caused by modified perception of self tilt and may reflect an offset in the egocentric reference frame. Better insight in the underlying mechanisms might lead to improved evaluation and treatment of patients with RNR
[•3]
Fatigue influence on postural coordination: comparison of observed and predicted pattern
A. Ponce 1, F. Fouque 1, A. Martin 1, L. Martin 2, V Cahou~t2.
M e t h o d s : We addressed the issue of the potential degradation of aiming precision connected with a possible derangement of the movement-posture coordination by selective perturbation of the postural component of the task. The protocol involved continuous repetition of ballistic whole-body pointing (WBP) tasks (implying pointing with the index fingers at a target, while lowering the body mass and returning to the initial position). This was repeated at a frequency of 0.1 Hz until exhaustion. Results: Such sequence led to EMG signs of fatigue in the quadriceps (active for body lowering and rising, therefore in eccentric and concentric conditions) while the deltoid (prime mover for the arm reaching component) showed no signs of fatigue. The precision of the aiming movement was unaffected by the quadriceps fatigue. However, the trajectory of the finger during the WBP task was drastically changed between the first and the last trials of the sequence. D i s c u s s i o n : The central nervous system takes into account the state of postural muscles and the concurrently ensuing equilibrium constraints to appropriately modify the trajectory of the aiming limb and obtain a constant precision at the target.
1Laboratoire Motricit&Plasticit~ INSERM/ERIT-M 207, UFRSTAPS, Universitd de Bourgogne BP 27877, 21078 Dijon, France," :Laboratoire Sport et Performance Motrice EA 597, Universitd Joseph Fourie~ 38041 Grenoble cedex 9, France
[1~
I n t r o d u c t i o n : Recent dynamic optimization model [1] (minimum
M. S c h m i d 1 , M. Schieppati 1,2. 1Human Movement Laboratory
torque change model) was use to predict behaviors during a fore~ft target tracking task. Predictions were very similar with experimental observations described in existing literature [2]. Results suggest that hang of different coordination modes (relative phase between ankle and hip movements) is define by mechanical and/or metabolic constraints. M e t h o d s : In order to test this, seven subjects were asked to track with the head (at different frequencies) the fore aft movements of a virtual target before and after solear muscles were fatigued using electromyostimulation. We added a constraint in the dynamic optimization model. This constraint checks that ankle torque always stay lower to a given proportion of maximal voluntary torque value. We provide simulations with two different maximal torques corresponding to those obtained in the two different conditions of fatigue and compared them with experimental results. Results: We observed a sudden switch from in-phase to anti-phase pattern with increasing frequency. Bifurcation appeared earlier in fatiguing condition and seemed to be linked to the system variability. D i s c u s s i o n : According to our results, predictions showed a decrease of switch frequency when maximal torque is decreased. This study confirms the model efficiency and the important role of metabolic and mechanical constraints in hanging pattern.
(CSAM), Fondazione Salvatore Maugeri (IRCCS), Scientific Institute of Pavia, eDepartment of Experimental Medicine, Section of Human Physiology, University of Pavia, Italy
References [1] Martin L., Cahouet V., Ferry M. & Fouque F. Optimization model prediction for postural coordination modes. J Biomech (in press). [2] Bardy B.G., Oullier O., Bootsma R.J. & Stoffregen T.A. Dynamics of human Postural transitions. Journal of Exp Psychol Human 2002; 38:499 514.
[•4]
Effect of lower body muscle fatigue on a whole body pointing task
M. S c h m i d 1 , T. P o z z o 2, M. Schieppati 1,3. 1C~AM,Salvatore Maugeri Foundation (IRCCS), Scientific Institute of Pavia, via Ferrata 8, 27100 Pavia, Italy," 2 ERM 207, Universitd de Bourgogne, Campus universitaire, Dijon 21004, France," 3Department of Experimental Medicine, Section of Human Physiology, University of Pavia, Italy I n t r o d u c t i o n : Appropriate coordination between movement and posture is the necessary condition for correct execution of voluntary motor acts. This is true under conditions in which aiming movements require displacement of several body segments including those normally engaged in balance. An example is represented by reaching from a standing position toward a target located low down and beyond arm length.
Neck muscle fatigue and spatial orientation during stepping-in-place in humans
I n t r o d u c t i o n : Neck proprioceptive input plays an important role in perception of body segment position and orientation in space. Neck muscle fatigue also produces destabilizing effects on stance. Our aim was to assess whether neck muscle fatigue can also perturb the orientation in space during a walking task. M e t h o d s : Direction and amplitude of the path covered during a stepping-in-place task were measured in ten blindfolded subjects, performing five 30 s-stepping trials before and after a 5 min-period of isometric dorsal neck muscle contraction against a load. Neck muscle EMG amplitude and median frequency during the head extensor effort were used to compute a fatigue index. Head and body kinematics was recorded by an optoelectronic system and stepping cadence was measured by sensorized insoles. Results: Prior to the contraction period, subjects normally stepped on the spot or drifted forwards. After contraction, some subjects reproduced the same behavior, whereas others reduced their forward progression or even stepped backwards. The former subjects showed minimal signs of neck muscle fatigue, the latter ones marked signs of fatigue. Head position and cadence were unaffected in either group of subjects. D i s c u s s i o n : We argue that the abnormal fatigue-induced afferent input can modulate the egocentric spatial reference frame and modify the orientation of the body in space in a walking task. The effects of neck muscle fatigue on orientation are opposite to those produced by neck proprioception.
•
Experimentally induced low back pain leads to reduced spinal motion but does not interfere with the compensation for postural sway with breathing
M. Smith, M.W. Coppieters, RW. Hodges. Division of Physiotherapy,
The University of Queensland, Brisbane, Australia Breathing perturbs balance. However, in healthy individuals minimal sway is detected at the ground because small movements of the spine and legs compensate for the postural disturbance. When people have chronic low back pain (LBP), displacement of centre of pressure (COP) with breathing is increased, possibly due to reduced compensatory trunk motion. This study investigated whether postural compensation for breathing is reduced during experimentally-induced LBR M e t h o d s : Subjects stood on a force plate with eyes open or closed, and while breathing quietly and with hypercapnoea, before and after Introduction: