Lead Limb Used During Drop Jumps Affects Initial Vertical Ground Reaction Force Symmetry

Document Type

Article

Publication Date

5-28-2014

Publication Title

Medicine & Science in Sports & Exercise Supplemental

DOI

10.1249/01.mss.0000493177.43078.ea

Abstract

Drop jumps (DJ) are a commonly used training method that utilizes the stretch shortening cycle to produce explosive power from the lower body. Earlier research examining vertical ground reaction force (vGRF) symmetry during DJ performed with the dominant (DOM) limb leading saw a favoring of the DOM limb. The effects of leading with nondominant (NDOM) on vGRF symmetry are unknown.

PURPOSE: To determine the effect of lead limb on bilateral asymmetries on initial vGRF readings while performing a DJ from 30 cm, 45 cm, 60 cm, and 75 cm heights.

METHODS: 24 active males (24.2± 2.1 yrs, 1.78±.06 m, 79.4±9.4 kg) with six or more months resistance training experience completed a familiarization where they were taught proper DJ technique. Upon landing with each foot on adjacent forceplates, subjects immediately performed a maximal effort vertical jump. Subjects alternated between using DOM and NDOM as the lead limb for the drop phase. The familiarization session ended when both the instructor and subject determined that proper technique could be performed from each height. After a 72 hour rest period and being asked to avoid lower body exercise, subjects completed eight drop jumps from each height during which the recorded vGRF, normalized to body weight (BW), under the DOM and NDOM feet were used to compute ground contact time, loading rate (.1to.5BW), and impulse (100ms following ground contact) DOM-NDOM differences. Lead limb and height were randomly assigned for each subject. Height by lead limb repeated measures analysis of variance were conducted for each measure.

RESULTS: For initial ground contact time, when leading with NDOM, the DOM limb made ground contact significantly (P<.05) earlier (range:.002s to.020s) than the NDOM at each drop height. Additionally, when leading with NDOM, the loading rate (95% CIdiff=3.05 to 6.48BW·s-1, P<.001) and impulse (95% CIdiff=.012 to .025BW·s, P<.001) were significantly greater for DOM compared to the NDOM.

CONCLUSION: When leading with the NDOM, significantly greater asymmetry favoring the DOM limb was revealed for all three vGRF traits. These data suggest that subjects should perform DJs leading with DOM leg for greater symmetry during landing. Future research should consider vGRF characteristics occurring later during the ground contact phase as well as the initial contact kinematics.

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© 2014 American College of Sports Medicine

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