Biomechanical Characteristics of Jerk Technique

Abstract

Researches in Olympic weightlifting have been conducted by many investigators. Baumann et d.(1986) analyzed the snatch technique by means of three-dimensional film analysis for data acquisition under competitive conditions. Grabe et a1.(1988) studied the jerk performance of Merent level weightlifters, but the two-dimensional filming technique was used for data collection. The purpose of this study was to identify the biomechanical characteristics of jerk technique using three-dimensional film analysis. 13 jerk attempts, executed by 7 world levelweightlifters, were filmed at World Cup Weightlifting Competition held in Beijing 1992 using two phase-locked synchronized cameras at the speed of 50 fps. The raw data were smoothed with digital filter at cut-off frequency 4Hz. The spatial coordinates were calculated from the smoothed data using DLT procedure. The results indicated that the weightlifters begin the braking phase at the average knee angle 121.1 degree (SD=9.1 ) and end it at the average knee angle 106.0 degree (SD=7.1). , The average braking time is 0.16 second (SD=0.03). The braking time is not only correlated with the maximal descending velocity of the bar during the half squat phase (r=0.72, p<0.01), but also correlated with the maximal force per barbell weight between the athlete and bar during the braking phase(r = - 0.79. pc0.01). This force can be as much as six times of body weight. The maximal ascending velocity f the barbell during the trust phase is correlated with the maximal power output per barbell weight generated by athlete (r =0.98. pi0.01). From these results-it can be concluded that the braking phase is the most important in jerk because it indicates the switch of the muscle work from eccentric to concentric. The shorter the duration of the braking phase is the more effective& stored elastic energy is transmitted in to the thrust phase of the jerk.