Ground Reaction Force Characteristics In Power Cleans With And Without The Double Knee Bend Technique

Abstract

INTRODUCTION: Muscular power (i.e. muscular force x shortening velocity) is arguably the most important physical quality an athlete can possess. Many athletes use power cleans to improve muscular power but are not taught to use a double knee bend (DKB). The DKB is used by competitive weightlifters to increase muscular power produced in the second pull of the power clean exercise. Thus, athletes using power cleans to improve muscular power without using the DKB may not experience optimal benefit from the exercise. PURPOSE: To determine differences in ground reaction force characteristics between a power clean from the floor both with, and without, the use of a DKB in athletes with weightlifting experience. METHODS: Six participants with weightlifting experience each performed three power cleans with and without a DKB at 80% of their self-reported one-repetition maximum. Ground reaction forces (GRFs) were captured using two force platforms (1200Hz). Commercially available biomechanical analysis software was used to calculate concentric impulse (IMPCON), peak vertical ground reaction force (VGRFPEAK), and rate of force development (RFD) in the second pull for each trial. Paired samples t-tests were used to compare dependent variables in each condition: DKB and NO DKB. Cohen’s d estimates of effects size were used to determine meaningful differences. RESULTS: RFD was greater in the second pull of the power clean when a DKB was used (p <.001, d = 2.25; DKB: 6922±1664; NO DKB: 4710±277 N/s). IMPCON was lower in the DKB condition (p <.001, d = 1.09; DKB: 146±28.8 N•s; NO DKB: 174±36.6 N•s), and no differences were observed in VGRFPEAK (p = 0.375, d = 0.15; DKB: 1607±221 N; NO DKB: 1582±169 N). CONCLUSIONS: Although no differences were observed in VGRFPEAK and IMPCON was reduced, RFD was significantly greater in the second pull with the DKB. These data suggest that DKB may enhance the training stimulus by enabling the athlete to produce comparable peak forces in shorter time periods by increasing muscular shortening velocity. This may be due to a positional optimization of muscular length-tension properties in the hip, knee, and ankle extensor musculature uniquely offered by utilizing a DKB technique.