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Effects of reducing plantar support on anticipatory postural and intentional activities associated with flexion of the lower limb
Abstracts-International Society of Biomechanics XIV Congress 1993 POSTURO-KINETIC EFFECTS ON KICKING M O V E M E N T SOF A LACK OF INITIAL GROUND SUPPORT UNDER THE MOVING LEG Y. Gah6ry and P. BBraud CNRS, URA Cognition et Mouvement, Marseille, France force exerted under the Kicking movements are preceded by an increase in the vertical moving foot and a simultaneous decrease under the other foot. In order to throw light on the role of these early force variations, we studied the movements performed from an unipedal standing position, thus eliminating the force exerted against the ground by the moving foot. Under these conditions, strong differences were observed in the posturo-kinetic organization of the kicking movement. Under the postural foot we still observed an initial decrease in a shorter duration and a smaller the vertical force but with a conspicuously longer latency, amplitude then in the bipedal situation. The amplitude of the backward movement of the trunk also increased and an initial displacement of the moving foot occurred in the direction opposite that of the voluntary movement. These associated movements seem to have compensate for the lack of the force exerted against the ground. However this compensation was not fully achieved, as the efficiency of the resulting movement decreased significantly : the velocity and the acceleration of the moving foot decreased by 10 to 20% in the unipedal as compared to the bipedal situation. These results therefore confirm the dependence of postural adjustments on the initial position and they help to specify the functional role of postural adjustments in the efficiency of voluntary movements.
THE USE OF QUANTITATIVE EMG AS A MEANS OF ESTIMATING FUNCTIONAL BITE FORCES Thomas Gay,’ Jill RendelI,’ Aurelie Majoureau,’ and F. Tim Maloney’ University of Connecticut Health Center, Farmington, CT 06030 USA,’ The Procter & Gamble Company, Cincinnati, OH 45241’ This study used the EMGlForce function curve as a means for estimating functional bite forces. Ten normally dentate adults were used as subjects. Surface EMG recordings were made for the masseter and anterior temporalis muscles. Incisal bite forces for each subject were obtained using a force transducer system that includes a miniature quartz transducer imbedded in custom made hydroplastic bite blocks. Each subject was first instructed to develop a maximum level of bite force, and then to develop bite force levels that corresponded to decreasing percentages of his maximum bite force, from 90 to 10 per cent levels, in 10 per cent decrements. After the force measurements were made, each subject was required to incise various food substances. The power density spectrum and rms power level were calculated for each sample. Maximum bite force levels varied considerably among the 10 subjects, ranging from a minimum of 4.5 kg to a maximum of 40 kg. For all the subjects as a whole, estimated bite forces for the different types of food ranged from 1.5 kg - 8.5 kg. This range was independent of the subjects’maximum bite force levels. Thus, bite forces exerted to incise different foods probably depends more on the food than on the individual’s bite force capabilities. There was variability within this range, although as expected, bite forces were greatest for the apple and carrot.
EFFECTS OF REDUCING PLANTAR SUPPORT ON ANTICIPATORY POSTURAL AND INTENTIONAL ACTIVITIES ASSOCIATED WITH FLEXION OF THE LOWER LIMB. M. Gilles and M.C. Do Laboratoire de Physiologie du Mouvement. U.R.A. CNRS 631, UniversitC Paris-Sud, 91405 Orsay (France). The study reported here was designedto examinethe influence of plantar afferentsduring the voluntary lower limb flexion. Subjectsmade flexion of the right lower limb, i.e. elevation of the thigh to the horizontal position, executed as fast as possible following an auditory signal. Three configurations of plantar support surfacewere examined: subjectswere standingi) on a plane surfaceii) on an unilateral reducesurfaceby two narrow rods under the moving iii) under the stance foot. Two set of variables were recorded: mechanical variables (acceleration of the center of gravity and displacementof the center of foot pressure) and EMG activity of ipsi and contralateral(to the moving leg) soleus(SOL) and tibialis anterior (TA). In comparison with the plane surface situation, the reduction of the plantar surface under the moving limb induced a decreasein the EMG anticipatory activity of both TA and in the intentionnal ipsilateral SOL EMG activity. However the anticipatory activity of SOL did not change.The lateral and vertical accelerationsof the centerof gravity was lower. When the reduction was under the stancelimb, the biomechanicaltracesdid not changemarkedly and the EMG activity was similar to that of the plane surfacesituation. The differential effects in mechanicalbehaviourand EMG activity, dependingon whether the reducedplantar surfacewas under the moving or stancefoot, suggestthat tonic plantar stimulation induces complex actions on musclesinvolved in the preparation and execution of voluntary movement.The functional demandcould explain the gating from one motor organizationto another.
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THE USE OF QUANTITATIVE EMG AS A MEANS OF ESTIMATING FUNCTIONAL BITE FORCES Thomas Gay,’ Jill RendelI,’ Aurelie Majoureau,’ and F. Tim Maloney’ University of Connecticut Health Center, Farmington, CT 06030 USA,’ The Procter & Gamble Company, Cincinnati, OH 45241’ This study used the EMGlForce function curve as a means for estimating functional bite forces. Ten normally dentate adults were used as subjects. Surface EMG recordings were made for the masseter and anterior temporalis muscles. Incisal bite forces for each subject were obtained using a force transducer system that includes a miniature quartz transducer imbedded in custom made hydroplastic bite blocks. Each subject was first instructed to develop a maximum level of bite force, and then to develop bite force levels that corresponded to decreasing percentages of his maximum bite force, from 90 to 10 per cent levels, in 10 per cent decrements. After the force measurements were made, each subject was required to incise various food substances. The power density spectrum and rms power level were calculated for each sample. Maximum bite force levels varied considerably among the 10 subjects, ranging from a minimum of 4.5 kg to a maximum of 40 kg. For all the subjects as a whole, estimated bite forces for the different types of food ranged from 1.5 kg - 8.5 kg. This range was independent of the subjects’maximum bite force levels. Thus, bite forces exerted to incise different foods probably depends more on the food than on the individual’s bite force capabilities. There was variability within this range, although as expected, bite forces were greatest for the apple and carrot.
EFFECTS OF REDUCING PLANTAR SUPPORT ON ANTICIPATORY POSTURAL AND INTENTIONAL ACTIVITIES ASSOCIATED WITH FLEXION OF THE LOWER LIMB. M. Gilles and M.C. Do Laboratoire de Physiologie du Mouvement. U.R.A. CNRS 631, UniversitC Paris-Sud, 91405 Orsay (France). The study reported here was designedto examinethe influence of plantar afferentsduring the voluntary lower limb flexion. Subjectsmade flexion of the right lower limb, i.e. elevation of the thigh to the horizontal position, executed as fast as possible following an auditory signal. Three configurations of plantar support surfacewere examined: subjectswere standingi) on a plane surfaceii) on an unilateral reducesurfaceby two narrow rods under the moving iii) under the stance foot. Two set of variables were recorded: mechanical variables (acceleration of the center of gravity and displacementof the center of foot pressure) and EMG activity of ipsi and contralateral(to the moving leg) soleus(SOL) and tibialis anterior (TA). In comparison with the plane surface situation, the reduction of the plantar surface under the moving limb induced a decreasein the EMG anticipatory activity of both TA and in the intentionnal ipsilateral SOL EMG activity. However the anticipatory activity of SOL did not change.The lateral and vertical accelerationsof the centerof gravity was lower. When the reduction was under the stancelimb, the biomechanicaltracesdid not changemarkedly and the EMG activity was similar to that of the plane surfacesituation. The differential effects in mechanicalbehaviourand EMG activity, dependingon whether the reducedplantar surfacewas under the moving or stancefoot, suggestthat tonic plantar stimulation induces complex actions on musclesinvolved in the preparation and execution of voluntary movement.The functional demandcould explain the gating from one motor organizationto another.
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