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Effects of pre-tension on isometric force production
Abstracts
of the third meeting
GAIT OF CHILDREN (Division
of the European
197
Society of Biomechanics
WITH HEARING
IMPAIRMENTS
U. P. WYSS, L. C. BREWSTER,V. A. P~LLAK and R. J. FLEC;~; of Biomedical Engineering, University of Saskatchewan, Saskatoon,
Canada)
Many children with hearing impairments exhibit problems with the normal development of gait due to disturbances of the balance function. The gait of some of the subjects seems to improve when they are fitted with hearing aids. Gait analysis is performed on one- to four-year-old children with special attention being given to those parameters which have been shown to change during maturation of gait. The choice of the room for performing gait analysis experiments with children is also very important. This makes necessary the use of instrumentation which is transportable and relatively easy to set up. A simple system for a three-dimensional recording of body markers that are attached over anatomical landmarks was chosen. The computer analysis which follows investigates the differences between normal and children with hearing impairments and some early results are shown.
EFFECTS
OF PRE-TENSION
ON ISOMETRIC
FORCE
PRODUCTION
Jt KKA T. VIITASALO(Department of Biology of Physical University of Jyvaskyla, Jyvaskyla. Finland)
Activity,
The study was designed to investigate the effect of muscle fibre distribution and pre-tension at various submaximal contraction levels on the isometric force-time curve during knee extension. Thirteen male physical education students volunteered as subjects. They were instructed to react to an auditory and light signal by extending their right knee as quickly and forcefully as possible. The contractions were performed from seven pretension levels ranging from 0 to 70:/, of maximal voluntary contraction value. The isometric force-time curves were analyzed for their maximal rate of isometric force production. Preliminary tension was found to have statistically significant. decreasing effects on isometric maximal strength and on the rate of isometric force production (RFD). Relatively the decrease was much greater for the RFD than for the maximal strength. The effects of the preliminary tensions on the RFD were greater for subjects rich in fast twitch muscle fibres in their m. vastus lateralis than for subjects rich in slow twitch fibres.
OPTIMAL
INITIAL
CONDITIONS
FOR EASTERN
ROLL HIGH JUMP
M. H~II~BARDand J. C. TRINKLE (Department of Mechanical Engineering, University of California, Davis, California, 95616, U.S.A.) Attaining maximum high jump height results from combining optimal airborne muscle torque time histories with optimal conditions at take-off is the subject of this paper. The question answered is: subject to constraints on jumper initial kinetic energy, how should it be apportioned into rotational and translational and what should the take-off angle be to clear the maximum height? The model for thejumper is a single rigid body (mass m, length 1, centroidal moment of inertia I, center of mass height ri) assumed to move in a vertical plane containing the crossbar. Parameter optimization techniques are used to calculate the optimal take-off angle, angular velocity and vertical velocity given jumper kineticenergy and geometry. The general conclusion is that it is advantageous for the jumper to lean back, sacrificing some initial potential energy so that less rotational kinetic energy will be required to become horizontal at the instant the bar is cleared.
FORCE,
POWER
AND WORK ANALYSIS OF THE TAKE-OFF JUMP IN THREE JOINTS
PHASE OF THE VERTICAL
1. VERGRO~SFN.R. W. DE BOER and G. J. VAN INGEN SCHESA~~(Interfaculty Free University, Amsterdam, The Netherlands)
of Physical
Education
Ten well-trained volleyball players (w.t. group) and ten untrained students (ut. group) performed three countermovement jumps (c.m.j.) starting from a standing position and three squatting jumps (s.j.) starting from a bend position in the knee of a hundred degrees. For each joint some mechanical parameters were calculated during the take-off phase with the help of force plate data, anthropometric data, film analysis data and a four-segment model. All parameters were normalized for body weight. The groups did not differ in total peak push-off forces nor in peak power in the knee. The w.t. group jumped higher, supplied higher peak power as well as more positive work in ankle and hip compared to the ut. group for both jumps. The jumping modes showed remarkable differences in total peak push-off force. peak power in the ankle and positive work as far as the knee and hip were concerned. To explain these results it is not necessary to make assumptions of storage of elastic energy in stretched muscles as other fundamental mechanical factors can satisfactorily explain the higher positive work output in c.m.j. The possible role of polyarticular muscles in transmitting power from proximal to distal joints will be discussed.
of the third meeting
GAIT OF CHILDREN (Division
of the European
197
Society of Biomechanics
WITH HEARING
IMPAIRMENTS
U. P. WYSS, L. C. BREWSTER,V. A. P~LLAK and R. J. FLEC;~; of Biomedical Engineering, University of Saskatchewan, Saskatoon,
Canada)
Many children with hearing impairments exhibit problems with the normal development of gait due to disturbances of the balance function. The gait of some of the subjects seems to improve when they are fitted with hearing aids. Gait analysis is performed on one- to four-year-old children with special attention being given to those parameters which have been shown to change during maturation of gait. The choice of the room for performing gait analysis experiments with children is also very important. This makes necessary the use of instrumentation which is transportable and relatively easy to set up. A simple system for a three-dimensional recording of body markers that are attached over anatomical landmarks was chosen. The computer analysis which follows investigates the differences between normal and children with hearing impairments and some early results are shown.
EFFECTS
OF PRE-TENSION
ON ISOMETRIC
FORCE
PRODUCTION
Jt KKA T. VIITASALO(Department of Biology of Physical University of Jyvaskyla, Jyvaskyla. Finland)
Activity,
The study was designed to investigate the effect of muscle fibre distribution and pre-tension at various submaximal contraction levels on the isometric force-time curve during knee extension. Thirteen male physical education students volunteered as subjects. They were instructed to react to an auditory and light signal by extending their right knee as quickly and forcefully as possible. The contractions were performed from seven pretension levels ranging from 0 to 70:/, of maximal voluntary contraction value. The isometric force-time curves were analyzed for their maximal rate of isometric force production. Preliminary tension was found to have statistically significant. decreasing effects on isometric maximal strength and on the rate of isometric force production (RFD). Relatively the decrease was much greater for the RFD than for the maximal strength. The effects of the preliminary tensions on the RFD were greater for subjects rich in fast twitch muscle fibres in their m. vastus lateralis than for subjects rich in slow twitch fibres.
OPTIMAL
INITIAL
CONDITIONS
FOR EASTERN
ROLL HIGH JUMP
M. H~II~BARDand J. C. TRINKLE (Department of Mechanical Engineering, University of California, Davis, California, 95616, U.S.A.) Attaining maximum high jump height results from combining optimal airborne muscle torque time histories with optimal conditions at take-off is the subject of this paper. The question answered is: subject to constraints on jumper initial kinetic energy, how should it be apportioned into rotational and translational and what should the take-off angle be to clear the maximum height? The model for thejumper is a single rigid body (mass m, length 1, centroidal moment of inertia I, center of mass height ri) assumed to move in a vertical plane containing the crossbar. Parameter optimization techniques are used to calculate the optimal take-off angle, angular velocity and vertical velocity given jumper kineticenergy and geometry. The general conclusion is that it is advantageous for the jumper to lean back, sacrificing some initial potential energy so that less rotational kinetic energy will be required to become horizontal at the instant the bar is cleared.
FORCE,
POWER
AND WORK ANALYSIS OF THE TAKE-OFF JUMP IN THREE JOINTS
PHASE OF THE VERTICAL
1. VERGRO~SFN.R. W. DE BOER and G. J. VAN INGEN SCHESA~~(Interfaculty Free University, Amsterdam, The Netherlands)
of Physical
Education
Ten well-trained volleyball players (w.t. group) and ten untrained students (ut. group) performed three countermovement jumps (c.m.j.) starting from a standing position and three squatting jumps (s.j.) starting from a bend position in the knee of a hundred degrees. For each joint some mechanical parameters were calculated during the take-off phase with the help of force plate data, anthropometric data, film analysis data and a four-segment model. All parameters were normalized for body weight. The groups did not differ in total peak push-off forces nor in peak power in the knee. The w.t. group jumped higher, supplied higher peak power as well as more positive work in ankle and hip compared to the ut. group for both jumps. The jumping modes showed remarkable differences in total peak push-off force. peak power in the ankle and positive work as far as the knee and hip were concerned. To explain these results it is not necessary to make assumptions of storage of elastic energy in stretched muscles as other fundamental mechanical factors can satisfactorily explain the higher positive work output in c.m.j. The possible role of polyarticular muscles in transmitting power from proximal to distal joints will be discussed.