A PROCEDURE FOR DETERMINING THE ANGULAR VELOCITY OF UPPER ARM ABOUT ITS LONGITUDINAL AXIS RELATIVE TO THORAX IN JAVELIN THROWING

  • Enrique Navarro
  • Oliver Cabrero
  • Fernando Vizcaíno
  • Pedro Vera
Keywords: javelin throwing, kinematics 3D-kinematography, angular velocities

Abstract

INTRODUCTION: One of the most characteristics movements in skill throwing is the internal rotation of upper arm in the last instants before release. However, a lack of information exists in javelin throwing about the relative movements of segments about their longitudinal axis. The objective of this work is to present a procedure for determine the angular velocity of the upper arm relative to the thorax about its longitudinal axis. METHODS AND PROCEDURE: The experimental technique was the 3Dphotogrammetry (DLT algorithm). A total of 36 throws of two national level throwers were analyzed. Two cine cameras were used at 200 Hz. The data were smoothed by quintic spline functions. The procedure for calculating the angular velocity of the upper about its longitudinal axis relative to thorax was as it follows: 1. Thorax was modeled like a solid rigid (with three no collinear points: right and left shoulder and substernal) Upper arm was defined like a solid rigid (two own points -right shoulder and elbow- and an external third point -wrist- through one freedom degree joint -elbow-). 2. A local reference system was defined both in the upper arm and thorax (x: antero- posterior, y: transversal, z:longitudinal). 3. The rotation matrix in relation to a Inertial Reference System were calculated in at each photogram from the 3D co-ordinates of three point which defined each segment (0At: Thorax, 0Aua: upper arm). 4. The rotation matrix of upper arm in relation to the local reference system of thorax was calculated in each photogram by the expression: 0At: = {0At}T·0Aua.. 5. Interpolated (no smoothing) quintic spline functions were obtaining for each component of three unit vectors (i, j, k). 6. The angular velocity was calculated through wz = (di/dt)·j·(·: scalar product). RESULTS AND DISCUSSION: In both subject the temporal functions of angular velocity (normalized time: 0%: left foot contact; 100%: release) showed a movement of external rotation first and an external rotation at last instants. For subject A the average velocity was 47.4 1/s (SD=29.6 n=15; in subject B was 49.8 1/s (SD=33.6, n=20). In both subjects (independent samples) has been found a high standard deviation, that is the variability between throws is big. The linear correlation between wz and javelin velocity was 0.57 for subject A. In subject B was 0.54 . CONCLUSIONS: A procedure for obtaining the angular velocity of upper arm about the longitudinal axis has been developed. The increase of internal rotation velocity of upper arm in final moments seemed to produce higher release speed of javelin.