Phd Subject: Biomechanic global index of force generation

A motor task involve the application of functionals efforts on the environment. In the biomechanical point of view, the ability of a person to efficiency generate in amplitude as well as direction is linked to the position or the movement adopted and the musculo-squeletal characteritics. For a given posture, the assessing of force generation ability in any direction of the cartesian space presente a great interest. In fact, a better comprehension of the human motor is enable and it might contribute to the quantification of physical or "technical" aptitudes in as part of the ergonomics and the readaptation. The biomechanical index of the forces or articular torques production are limited to a particular direction or axis. Therefore, the abilities of force generation for a person can not be globaly characterised. For that purpose, with a biomechanical modelisation of the upper limb, those works aim to contribute in the development of global index of ability of force generation based on the force ellipsoid and polytope formalisms from the robotic field. Those seem interesting because, for a given posture, the abilities of force generation can be given for any direction of the cartesian space from hypothesis or datas about the articular torques. Those index would be adapted in order to take into account the specifities of the human musculo-squeletal system, especially the differences of maximal isometric articular torques between the articular axes and the direction of the movement, the present of bi-articular muscles and the synergic functionnement of muscles.

The maximal isometric torques consisting of an input data of the model have to be evaluated. Because of the bi-articular muscles, the maximal isometric torques for an articulation depend of the posture of other articulations. In this way, the objectif of a part of this work includes the development of a methodology which enables the definition of maximal isometric troques in function of the entire posture of the upper limb inside the whole work space of the arm.

At first, this methode will rely on the maximal isometric torques of the upper limb articulations measured with a dynamometer (Biodex 3) associated with a motion optoelectronic system (Qualisys). This type of instrumentation is appropriate to get precisely measures in a medical environment. However, this type of measure is desired in a less restrictive environment (home, doctor's surgery) which impose the use of cheaper and simplier sensors (accelerometer,pression sensor).

The next part include the development and the validation of global index of force porduction based on force ellipsoid and polytope formalisms from robotics. With a polyarticulated modelisation of the upper limb and by making use of the positions and maximal isometric torques measurements on a Biodex apparatus, the global index of force production would be evaluated and validated through the comparaison with the predicted maximal forces by the model and direct measurements by a multidirectional load sensor.

At last, the use of lighter devices, in fact less performant in terms of measure quality, to detect tends of variations on the index would be discuted, for a preventive medicine purpose.

The developed index would find interesting applications in the case of human motor assessment in ergonomics and handicap. But those would also contribute in the optimations of tools and positions regarding a particular task.

Last Update 28/01/2013
by Karim BAKAL
Biomechanic Phd Student