Biomechanics of a Motor Pattern and its Sports Application

Abstract

Man is capable of acquiring an ever increasing number of motor responses and in this way to improve his relationship with the environment. Obviously, if it was necessary to create a new motor organization for each new situation, the human motor behaviour would be chaotic for the sheer number of motor responses which would have to be available for ready utilization. Indeed, it is easier for the central nervous system to adjust to new environmental conditions and to different goals by compounding new motor programs from previously learnt subroutines. These subroutines -the motor patterns -evolve during the performer's life through general learning and specific training processes. The pattern approach to the motor organization is not new. Broer (1966) relates the shape of the movement with the skill goal and gives a set of examples with different goals but for which the shape is conserved. Wickstrom (1977) calls these shapes «Movement patterns». Obviously, similar limb kinematic relationships correspond to similar kinetic relationships, a fact already pointed out by Higgins (1972) when he states that each motor skill consists of three -motor, muscular and movement components. According to Wickstrom the development of each skill is an extensive process focused successively upon three major steps: the minimal form, the mature form and the sport skill form. The core of the mature form is the fundamental motor pattern. The sport skill is adapted to special requirements by the rules or by the strategy of each sport. From a mechanical point of view the human body «is» an articulated link system which simultaneously behaves as a rigid one when it resorts to external support to achieve the mechanical energy flows envolved in a desired performance. The efficiency of such a performance is determined by the mechanical work of the limbs but its final effect can be deduced from the knowledge of the center of mass kinematics and of the force exerted on the support. The motor organization may thus be conceived as integrating two simultaneous mechanical behaviours: an articulated link system relatively to the limb movements and a rigid system relatively to the external environment. Indeed if the human body behaved strictly as a «rigid system» it would have the tendency to rotate about the center of the support by an amount which would be proportional to the energy it possessed. In reality this does not occur and, instead, the system performs a set of intersegmental movements in accordance with the goal proposed for the desired skill and the result of this «articulated» behaviour is transferred to that of the «rigid» mode. Two complementary approaches to the biomechanical study of human motor patterns are thus available: the evaluation of the internal work performed by the limbs and the dynamical analysis of the center of mass of the «rigid body» system.