Weightlifting Notes

The Pull in Olympic Weightlifting

Abstract

  • The study analyzes the vertical forces applied to the barbell and lifter during the pull in Olympic weightlifting.
  • The double knee bend consists of two extension stages interrupted by a realignment period.
  • The vertical component of the ground reaction force (Rz) has three phases: Weighting I, Unweighting, and Weighting II.
  • The most experienced lifter produced the larger phase of positive acceleration first.
  • Rebending the knees is associated with the Unweighting phase.

Purpose

  • Measure the vertical component of the ground reaction force.
  • Examine the influence of the externally applied force on barbell displacement to determine the significance of the second knee bend.

Methods

  • Five experienced weightlifters performed three trials at 70, 85, and 100% of their maximum lift.
  • A LOCAM camera recorded the lifting performance at 59.2 frames/s.
  • The vertical component of the ground reaction force (Rz) was measured using a Kistler force platform.
  • A Benson-Lehner digitizing system was used for cinematographic records, and a Butterworth filter smoothed the data.

Results and Discussion

  • The Rz-time record consists of three major phases: Weighting I, Unweighting, and Weighting II.
  • Equation: −W+Rz=maz-W + Rz = maz
    • Where -W is system weight, Rz is the vertical ground reaction force, m is system mass, and az is vertical acceleration.
  • Weighting phases indicate positive system acceleration.
  • Unweighting indicates negative system acceleration.
  • Subject 2, with more experience, showed significant differences in the RzI:SWI relationship.

Second Knee Bend

  • The second knee bend involves lifter realignment characterized by knee flexion.
  • There is a slight offset between Unweighting and the second knee bend.
  • Enhancement of force developed by knee extensors occurs due to re-employment of this muscle group over their optimum range of motion.

Conclusions

  • System and barbell accelerations consist of Weighting I, Unweighting, and Weighting II phases.
  • The Unweighting phase is produced by the second knee bend.
  • Realignment during the second knee bend enhances muscle re-employment and decreases the required back and trunk extensor force.