SONIC DIGITIZING: a new method for Kinematic Analysis in sports and movements of high precision - Air rifle Shooting

Abstract

In Shooting sports, according to Coaches opinion, body segments stabilization is considered as the most important factor which influences the performance of the athletes. Many researchers have used different instrumentation (Accelerometers, Force plates, Selspot system etc), to relate the performance with concrete Biomechanical parameters. As far as we know, none of the up to now proposed methods describes the 3dimensional Kinematics of Shooting sports techniques during the aiming process. It seems to be very interesting to become acquainted with the oscillations of the links of the kinematic chain, provided that from a mechanical pint of view, the Shooter and the rifle form an oscillating system around a static position and according to an important principle of General Systems Theory the behavior of a system emerges from the dynamic interactions of its parts. In the Institute of Biomechanics of Valencia, we have developed a new method, based on the use of ultrasounds, suitable for the description of the shooter-gun system geometry before and during the shot. The Sonic Digitizing system consists of the GP8-3D Sonic Digitizer which includes 16 sound emitters fixed on the shooter's body segments and on the barrel of the rifle, 4 microphone\sensors, the Multiplexer unit and the Control unit which communicates with the personal computer via a Parallel Interface Card (PIO 12). The sampling rate is 37 Hz divided by the number of emitters in an active volume of 2 meter side cube. This sampling rate seems to be enough for our study according to Shannon's theorem. The nominal resolution of the system is 0.1 mm and the calculated standard deviation is 0.15 mm. The system works emitting impulses of ultrasounds generated at the tip of every emitter. Cognizant of the speed of the sound in still air (343.8 m I sec, 20°C) and the time required for the sound to reach the microphones, the I program calculates, in REAL-TIME, the coordinates X, Y, Z respect to our reference system. In addition to the possibility of a complete Kinematic analysis, we can establish a real-time feedback loop, providing the shooter with a continuous auditory signal as function of the desviation of the aiming line, that define two emitters fixed on the gun, from the center of target. At last, but not at least, we can record simultaneously the displacement of the center of pressure on the force plate which complete our measurement setup.