The Oly Encyclopedia 31
January 20, 2022•410 words
The Third Phase of the Jerk: The Braking Phase
The braking phase normally takes about .12 of a second and encompasses a little more than one-third of the overall depth of the first and second phases of the dip. At its conclusion the downward progress of the center of the bar has stopped. The knees are typically at an angle of between 99' and 111'. Overall, between the first and second portions of the dip, the bar has typically been lowered between 8% and 12% of the height of the lifter. At the lowest point of the dip, the athlete normally pauses for between .01 and .04 of a second (i.e., there is virtually no detectable pause, but, rather, an immediate rebound).
The Fourth Phase of the Jerk: The Thrust or Explosion
The recovery from the lowest point in the dip for the jerk to the starting position of the dip takes approximately .02 of the second, or about half time it took to get from the starting position to the lowest point in the dip. The lifter is actively influencing the bar for about 85% of the time that it takes to perform the upward thrust, and acceleration is only taking place for 75% of the thrust. Maximum velocity of the bar is achieved at a point a little less than 1% higher than the initial position of the bar before the dip. At this point the athlete has shifted his or her area of support to the toes (and has risen somewhat on the toes), and the knees are nearly straight (and they appear to be straight). The velocity of the bar is between 1.45 and 1.8 meters per second (the lower figure is more common for shorter athletes, the higher for taller athletes). This velocity only accounts for about half of the height the bar reaches at its highest point in the jerk. It is hypothesized that the balance of the force that causes the bar to reach its ultimate height is generated by the force of the lifter's feet being replaced on the platform in the split-force delivered to the bar by the lifter's arms pushing up on the bar as the feet make contact with the platform-and the force generated by the arms and shoulders once the feet have been replaced on the platform. The thrust ends when the legs of the lifter have reached their maximum point of extension in the drive.