european college of sport science

Saturday, June 27th, 2009
Department of Biology of Physical Activity
University of Jyväskylä, Finland
Introduction: Modeling the force-velocity dependence of a muscle-tendon unit has been one of the most interesting objectives in the field
of muscle mechanics. The so-called Hill’s equation (Hill 1938 and 1970) is widely used to describe the force-velocity relationship of muscle
fibers. Hill’s equation was based on the laboratory measurements of muscle fibers and its application to the practical measurements in
muscle mechanics has been problematic. Therefore, the purpose of this study was to develop a new explicit calculation method to determine
the force – velocity relationship, and test its function in experimental measurements. This study continues the development of
earlier study (Rahikainen 2004).
Methods: Herein the force-velocity relationship has been given as an equation of motion. The model was based on the motion analysis
of arm movements. Experiments on forearm rotations and whole arm rotations were performed downwards and upwards at maximum
velocity. According to the present theory the movement proceeds as follows: start of motion, movement proceeds at constant maximum
force, movement proceeds at constant maximum power, stopping of motion. The measurements of arm movements were performed by
a special motion camera system which represents the movement as a series of object images. Between these images the paths of the
mark light attached to the moving object can be seen as a broken light-line.
Results: Theoretically derived equation, in which the motion proceeds at a constant maximum power (hypothesis), fitted well the experimentally
measured results. The values of friction coefficient C and power and friction coefficient ratio P/C were obtained within the curve
fitting, whole arm rotation downwards C = 2.83 kg m / s^2, P/C =360 1/s^2, whole arm rotation upwards C = 2.83 kg m / s^2, P/C =250
1/s^2 and forearm rotation downwards C = 2.38 kg m / s^2 and P/C =285 1/s^2. The constant maximum force hypothesis did not seem
to fit the measured results.
Conclusions: A further development of Hill’s force–velocity relationship was derived, in which Hill’s model was transformed into a certain
kind of a constant maximum power model. The results of the present study were compared with the mechanics of Hill’s model. For the
constant maximum force hypothesis a different kind of equation was suggested which would better fit the measured results.
References
Hill A, (1938). Proc. Royal Soc. London. 126 (B), pp. 136-195.
Hill A, (1970). Cambridge University Press, Cambridge.
Rahikainen A, Luhtanen P, (2004). Russian Journal of Biomechanics, Vol. 8, No 2: 78-93.
DEVELOPMENT OF BIOMECHANICAL MODELS WITH ADAMS LIFEMODELER SOFTWARE
AGUIAR, L., VELOSO, A., SANTOS-ROCHA, R., BRANCO, M., JOÃO, F., MONIZ-PEREIRA, V.
FACULTY OF HUMAN KINETICS, TECHNICAL UNIVERSITY OF LISBON, AND THE SPORT SCIENCES SCHOOL OF RIO MAIOR, POLYTECHNIC
INSTITUTE OF SANTARÉM
Mechanical loading is related with the magnitude of the external and internal forces; with the frequency of forces applied on the body;
with the repetition of load application; and with the way musculoskeletal structures deal with the internal forces. Computer models using
ADAMS Lifemodeler software (Mechanical Dynamics, In.) are being developed in order to study the complex movements of the joints and
the mechanical loads in specific anatomical structures. These models simulate the dynamic behaviour of a rigid multibody system and
allow recreate various conditions of movement performance, allowing the analysis of daily physical activities, several sports and individual
motor performance. This software derivates a series of movement equations for the model, applying the methods of Lagrangian
dynamics. The resulting motion equations are integrated, resulting in a model simulation. Mathematically, the inverse dynamics solves
the movement equations that define the model to obtain the joints reaction forces and joints moments. The main goal of this study is the
development of biomechanical models that simulate physical locomotion activities of high and low intensity with a moderate speed
which allow characterize the biomechanical effect, caused by applied external loads. For the construction of models, the transfer of data
between software is a key to facilitate the process of modelling. This is the main focus of the present study. Three-dimensional multibodies
mechanical dynamic models will be created, allowing simulating the motor tasks in real conditions. The internal forces can be
calculated after the ground reaction forces and kinematics data are obtained, using an inverse dynamics solution and anthropometric
information. Muscle forces can be determined using electromyography and anthropometric information. Inverse dynamics is the specialised
branch of mechanics that bridges the areas of kinematics and kinetics. It is the process by which forces and moments are indirectly
determined from the kinematics and inertial properties of moving bodies. In this work, the main tool in the modeling process and dynamic
simulation is the inverse dynamics. Two areas of research are of major interest: the quantification of mechanical load acting on the
biological structures of the young and the elder woman; and the simulation of conditions of practice.
3D ANALYSIS OF SWITCH LEAP TO RING POSITION ACCORDING TO THE INTERNATIONAL CODE OF POINTS
GRANDE RODRIGUEZ, I.
PHYSICAL EDUCATION AND SPORT SCIENCES FACULTY, POLITECNICA UNIVERSITY
Introduction: Gymnastics disciplines are characterized by its high technical demands. To check the results of technical training it’s necessary
to measure if the skill achieve the requirements exposed in the International Code of Points (FIG, 2009). For this purpose it´s useful to
applied biomechanics tools to carry out a completed 3D video analysis of each skill. But kinematics variables must be translated to these
requirements to make these results more interesting to coaches. The aim of our study was to define a comprehensible card including
kinematics results that can help coaches to know if the skill achieves the requirements exposed in the International Code of Points.
Methods: A 3D video analysis of switch leap to ring position was performed. 10 gymnasts from Junior and Senior Spanish national team
were filmed. Two synchronized DV video cameras at 50 Hz and 1/1000 exposure time were used. The area was calibrated with a prism
(4x2x2 m) that defined 12 control points. A 17 segment body model was used to calculate temporal, angular and spatial variables. 20
body points were manual digitized in all frames. The raw position data were smoothed by the fifth order splines (Woltring, 1986).
Results: The mean results of this leap were: The impulsion phase duration was 0.13±0.01 s. The take off velocity was 3.21±0.13 m•s-1 and
the angle of release was 59.31±4.15º.The amplitude of the swing leg was 61.2±12.4º. During this phase gymnasts perform a
34.44±11.56º knee extension.
The mean flight phase duration was 0.53±0.02 s flight. During the flight gymnasts reached a maximum split angle of 179.3±18.90º. The
foot tip achieved a height of 8.7±12.6 cm above shoulder. The angle between the front leg and the horizontal was 12.4±8.9º.
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