A PROCEDURE FOR DETERMINING THE ACCELERATION PHASE IN JAVELIN THROWING

Abstract

Introduction. The throwing phase is the period from the moment both feet make contact with the ground to the delivery of the javelin. The majority of the authors - are in according with this phase can be divided en two parts. The second is the acceleration phase. Miller (1981) measured that the javelin gains the 50% of the his speed during the last 50 ms before the release. Ikegami (1981) considered the beginning of the acceleration phase in the named archedposition. It seems that arched position is one of the most important factor in the javelin throwing (Koltai, 1985). However, the definition of the beginning of the throwing phase -arched position- is no clear in the literature reviewed about javelin throwing. The aim of this work is to develop a quantitative way for determining the arched position Methodology. An upper arm model is used which considered the elbow joint with one degree of freedom. A Local Reference System fixed with the segment is determined for calculating the angular velocity of the upper arm. The arched position -beginning of acceleratiun phase- is defined like the instant of beginning of internal rotation of the upper arm. The experimental technique was the 3D-Cinematography with high speed cameras. The sampling frequency was 200 Hz. The DLT algoritm was used for determining the 3D coordinates of the markers. The coordinates was smoothed with Quintic Splines functions. The two best spanish thowers were the subjects of the study. 36 throwings were analyzed. Conclusions. The existence of one starting instant for the internal rotation upper arm has been confirmed. This instant determines the beginning of throwing phasearch position-. Subject A had an acceleration phase duration of 41.2 % (SD = 2. 8 %, n= 20) in relation to the throwing phase. Subject B had 45% (SD= 3.7%, n=16).