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6.2 The circle performed on a pommel horse ingymnastics: The critical role of double support phase
Chapter 6. Multi-segmental coordination
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2. the coordination of synergies provides the compensation of equilibrium disturbance caused both due to external or internal actions, 3. the observed compensation is limited but limitations might possibly be expanded by some special training. Supported by grants RFBR 04-01-00215a, 02-04-48410a, 01-0448989a, RFH 00-06-00248a, NIH-AG06457.
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circle performed on a pommel horse in gymnastics: the critical role of double support phase
and lower segments in balance control changes during visual tracking and depends on its parameters. The data obtained are in agreement with both electrophysiological data on eye, head and body movement coordination and clinical data on the role of upper segment in body stabilization during visual tasks.
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Squatting: a universal resting posture that minimises instability?
B. Bril, L. Ferrufino. Laboratoire Action, Mouvement, Adaptation,
Universitd Paris' 5
EHESS, 54 Bd Raspail, 75006 Paris', France
L. Baudry 1, D. Leroy 1'2, D. Chollet 1. 1C.E.T.A.P.S. Laboratory,
UPRES JE 2318, Faculty of Sports Sciences', Boulevard Siegfried, 76821 Mont-Saint Aignan, Rouen University, France," 2G.R.H.A.L. Laboratory, Rouen University Hospital Charles Nicole, France The circle is a gyrating movement with alternate support holds on onearm (laterals phases) and two-arms (front and back phases). Baudry [1 ] established an initial profile for the pommel horse techniques: it was appeared that the gymnasts require 0.97±0.05 s to perform a circle with a ratio between the double-arm support and the single-arm support close to 1:3. The aim of this study was to highlight the role of the double support phase during circle according to the level of expertise of the gymnasts. Eighteen gymnasts, distributed into two groups (expert vs. non-expert), performed ten consecutive circles on a pommel horse recorded by the Vicon system (Vicon 512 TM, Oxford, UK). The aim of the procedure was to record the time spent on each circle phase. The main results proved that the relative duration of the two-arm support phase decreased with the gymnast's expertise (front phase: 17.8±1.2% for the non-expert vs. 8.8±2.0% for the expert; back phase: 13.6±1.7% for non-expert vs. 8.2±1.4% for the expert). As proved in some studies concerning the walking, the reduced time spent on the double support phase could indicate an improvement in the subject's dynamic balance. It seems to us that non-experts cannot maintain their dynamic banlance on one arm, and thus, give preference to the safety phases on two-arm.
References [1] Baudry, L., Leroy, D., and Chollet, D. Spatio-temporal variables of the circle on a pommel horse according to the level of expertise of the gymnast. Journal of Human Movement Studies, 2003; 44 195 208.
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Segmental stabilization during upright standing under fixation and tracking of visual target
E.V Bobrova 1, Y.S. Levick 2, VY. Shlykov2. 1Parlor Institute of Physiology of Russian Academy of Science, 2Institute of Information Transmission of Russian Academy of Science, Russia
Introduction: Squatting is characterised by a hyperflexion of the joints of the lower limbs. Widely used among mankind as a resting and a working posture, squatting has not given rise to scientific investigation except in the domain of archaeology [1]. Meanwhile studying this posture may be relevant for postural control investigations. It is indeed reasonable to put forward the hypothesis that the choice of such a posture for resting and working is based on the minimisation of effort and thus energy expenditure. Methods: Healthy adults were recorded in 4 experimental conditions (unloaded or loaded with varying weight) while they were either squatting or standing on a force platform. Two parameters were computed: the surface of the body-sway and the total trajectory of the center of pressure (COP). Preliminary Results: For all the participants the total surface and length of CoP trajectory is significantly smaller in the squatting conditions when compared with the corresponding standing position; however we observed an important inter-individual variability. Discussion: These results support the hypothesis of a greater stability of the squatting posture when compared with the standing posture, due to the smaller distance between CoP and center of mass (CoM) [2]. If we consider the body as an inverted pendulum having the centre of pressure as rotation point and the weight concentrated at the CoM, a deviation of the CoM from the vertical by a given angle generate a disequilibrium much higher in the standing position compared with the squatting position. Thus stabilising the body in the squatting position appears less energy consuming.
References [1] Boulle, E-L. Etude anthropologique de la position accroupie. Th~se Anthropologie biologique. Universit~ M~diterran~e-AixMarseille II. 1998; 345pp. [2] Breni~re, Y. Why we walk the way we do? Journal of Motor Behavior, 1996; 28(4): 291 298.
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Motor aftereffects during a combined hand-trunk grasping task
K.L. Bunday, D.A. Green, A.M. Bronstein. Department of Movement Segmental stabilization during upright standing under fixation and tracking of visual target was compared. Stabilogram, electrooculogram and trajectory of upper and lower segments of body in frontal plane were recorded. All the joints besides ankle and hip were restrained. Subjects fixated target or tracked its horizontal movement with the frequency 0.1 and 0.01 Hz, amplitude±35deg of arc. Comparing fixation tracking decreases correlation between stabilogram and trajectory of both segments; correlation between frontal stabilogram and upper segment higher then one between frontal stabilogram and lower segment during tracking. Correlation between frontal and sagittal stabilogram is increased during tracking. These changes are more pronounced during tracking with frequency 0.01 Hz then 0.1 Hz. Significant correlation is revealed between eye movement and center of pressure trajectory in frontal plane, but not in sagittal one. Crosscorrelation analysis demonstrates significant correlation between eye movement and center of pressure trajectory in both planes, maximums of cross-correlation functions are shifted by phase. The value of phase shift is individual: from 360 up to 3380. Torsion movements of body are supposed to appear during tracking which provide more central eye position in the orbit. The role of upper
& Balance, Division of Neuroscience, Imperial College, London, UK Introduction: When subjects walk onto a platform previously experienced as moving, a gait aftereffect in the form of increased gait velocity and a trunk overshoot is observed. This aftereffect, as in the 'broken escalator' phenomenon [1], occurs despite full knowledge that the platform will not move (action-knowledge dissociation). We now investigate whether similar aftereffects occur during a task which combines manual grasping with postural control. Method: Initially, subjects stood in a fixed resting stance and were instructed to grasp a stationary horizontal bar placed at arms length in front of them (5 BEFORE trials). Subsequently, subjects grasped the bar that accelerated at 1.3 m/s/s away from them (15 MOVING trials), without moving their feet. The bar stopped when grasped so this had to be done quickly to prevent the bar moving away from reach. Lastly, the subjects completed a second set of 5 stationary trials (AFTER). Results: During the MOVING trials subjects grasped the bar faster than during the BEFORE trials. This was the result of higher peak and mean velocity of both arm and trunk movements. During the first and to a lesser extent the second AFTER trials both hand and trunk
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2. the coordination of synergies provides the compensation of equilibrium disturbance caused both due to external or internal actions, 3. the observed compensation is limited but limitations might possibly be expanded by some special training. Supported by grants RFBR 04-01-00215a, 02-04-48410a, 01-0448989a, RFH 00-06-00248a, NIH-AG06457.
[
•
T
h
e
circle performed on a pommel horse in gymnastics: the critical role of double support phase
and lower segments in balance control changes during visual tracking and depends on its parameters. The data obtained are in agreement with both electrophysiological data on eye, head and body movement coordination and clinical data on the role of upper segment in body stabilization during visual tasks.
[•
Squatting: a universal resting posture that minimises instability?
B. Bril, L. Ferrufino. Laboratoire Action, Mouvement, Adaptation,
Universitd Paris' 5
EHESS, 54 Bd Raspail, 75006 Paris', France
L. Baudry 1, D. Leroy 1'2, D. Chollet 1. 1C.E.T.A.P.S. Laboratory,
UPRES JE 2318, Faculty of Sports Sciences', Boulevard Siegfried, 76821 Mont-Saint Aignan, Rouen University, France," 2G.R.H.A.L. Laboratory, Rouen University Hospital Charles Nicole, France The circle is a gyrating movement with alternate support holds on onearm (laterals phases) and two-arms (front and back phases). Baudry [1 ] established an initial profile for the pommel horse techniques: it was appeared that the gymnasts require 0.97±0.05 s to perform a circle with a ratio between the double-arm support and the single-arm support close to 1:3. The aim of this study was to highlight the role of the double support phase during circle according to the level of expertise of the gymnasts. Eighteen gymnasts, distributed into two groups (expert vs. non-expert), performed ten consecutive circles on a pommel horse recorded by the Vicon system (Vicon 512 TM, Oxford, UK). The aim of the procedure was to record the time spent on each circle phase. The main results proved that the relative duration of the two-arm support phase decreased with the gymnast's expertise (front phase: 17.8±1.2% for the non-expert vs. 8.8±2.0% for the expert; back phase: 13.6±1.7% for non-expert vs. 8.2±1.4% for the expert). As proved in some studies concerning the walking, the reduced time spent on the double support phase could indicate an improvement in the subject's dynamic balance. It seems to us that non-experts cannot maintain their dynamic banlance on one arm, and thus, give preference to the safety phases on two-arm.
References [1] Baudry, L., Leroy, D., and Chollet, D. Spatio-temporal variables of the circle on a pommel horse according to the level of expertise of the gymnast. Journal of Human Movement Studies, 2003; 44 195 208.
[•
Segmental stabilization during upright standing under fixation and tracking of visual target
E.V Bobrova 1, Y.S. Levick 2, VY. Shlykov2. 1Parlor Institute of Physiology of Russian Academy of Science, 2Institute of Information Transmission of Russian Academy of Science, Russia
Introduction: Squatting is characterised by a hyperflexion of the joints of the lower limbs. Widely used among mankind as a resting and a working posture, squatting has not given rise to scientific investigation except in the domain of archaeology [1]. Meanwhile studying this posture may be relevant for postural control investigations. It is indeed reasonable to put forward the hypothesis that the choice of such a posture for resting and working is based on the minimisation of effort and thus energy expenditure. Methods: Healthy adults were recorded in 4 experimental conditions (unloaded or loaded with varying weight) while they were either squatting or standing on a force platform. Two parameters were computed: the surface of the body-sway and the total trajectory of the center of pressure (COP). Preliminary Results: For all the participants the total surface and length of CoP trajectory is significantly smaller in the squatting conditions when compared with the corresponding standing position; however we observed an important inter-individual variability. Discussion: These results support the hypothesis of a greater stability of the squatting posture when compared with the standing posture, due to the smaller distance between CoP and center of mass (CoM) [2]. If we consider the body as an inverted pendulum having the centre of pressure as rotation point and the weight concentrated at the CoM, a deviation of the CoM from the vertical by a given angle generate a disequilibrium much higher in the standing position compared with the squatting position. Thus stabilising the body in the squatting position appears less energy consuming.
References [1] Boulle, E-L. Etude anthropologique de la position accroupie. Th~se Anthropologie biologique. Universit~ M~diterran~e-AixMarseille II. 1998; 345pp. [2] Breni~re, Y. Why we walk the way we do? Journal of Motor Behavior, 1996; 28(4): 291 298.
[•
Motor aftereffects during a combined hand-trunk grasping task
K.L. Bunday, D.A. Green, A.M. Bronstein. Department of Movement Segmental stabilization during upright standing under fixation and tracking of visual target was compared. Stabilogram, electrooculogram and trajectory of upper and lower segments of body in frontal plane were recorded. All the joints besides ankle and hip were restrained. Subjects fixated target or tracked its horizontal movement with the frequency 0.1 and 0.01 Hz, amplitude±35deg of arc. Comparing fixation tracking decreases correlation between stabilogram and trajectory of both segments; correlation between frontal stabilogram and upper segment higher then one between frontal stabilogram and lower segment during tracking. Correlation between frontal and sagittal stabilogram is increased during tracking. These changes are more pronounced during tracking with frequency 0.01 Hz then 0.1 Hz. Significant correlation is revealed between eye movement and center of pressure trajectory in frontal plane, but not in sagittal one. Crosscorrelation analysis demonstrates significant correlation between eye movement and center of pressure trajectory in both planes, maximums of cross-correlation functions are shifted by phase. The value of phase shift is individual: from 360 up to 3380. Torsion movements of body are supposed to appear during tracking which provide more central eye position in the orbit. The role of upper
& Balance, Division of Neuroscience, Imperial College, London, UK Introduction: When subjects walk onto a platform previously experienced as moving, a gait aftereffect in the form of increased gait velocity and a trunk overshoot is observed. This aftereffect, as in the 'broken escalator' phenomenon [1], occurs despite full knowledge that the platform will not move (action-knowledge dissociation). We now investigate whether similar aftereffects occur during a task which combines manual grasping with postural control. Method: Initially, subjects stood in a fixed resting stance and were instructed to grasp a stationary horizontal bar placed at arms length in front of them (5 BEFORE trials). Subsequently, subjects grasped the bar that accelerated at 1.3 m/s/s away from them (15 MOVING trials), without moving their feet. The bar stopped when grasped so this had to be done quickly to prevent the bar moving away from reach. Lastly, the subjects completed a second set of 5 stationary trials (AFTER). Results: During the MOVING trials subjects grasped the bar faster than during the BEFORE trials. This was the result of higher peak and mean velocity of both arm and trunk movements. During the first and to a lesser extent the second AFTER trials both hand and trunk