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The effect of short-term resistance training on hip and knee kinematics during vertical drop jumps.

Abstract
The purpose of this study was to determine the effect of a weight-bearing free weight resistance training program alone on knee flexion, hip flexion, and knee valgus during unilateral and bilateral drop jump tasks. Twenty-nine young adult females with previous athletic experience were randomly divided into a control (n = 16) and a resistance training (n = 13) groups. The resistance training group completed 8 weeks of lower extremity, weight-bearing exercises using free weights, whereas the control group did not train. A pre- and posttest was conducted to measure knee valgus, knee flexion, and hip flexion during unilateral (30 cm) and bilateral (60 cm) vertical drop jumps for maximum height. Joint angles were determined using 3-dimensional electromagnetic tracking sensors (MotionMonitor; Innovative Sports Training, Inc., Chicago, IL, USA). Initial training intensity for the bilateral squat was 50% of the subject's 1 repetition maximum (RM), which increased 5% each week to 85% during the final week. Sets and repetitions ranged from 2 to 4 and from 4 to 12, respectively. The training loads for all other exercises (lunge, step-up, unilateral squat, and Romanian deadlift) increased from 15RM to 6RM from the initial to the final week. A repeated measures analysis of variance was used to determine differences in the hip and knee joint angles. No significant differences for knee valgus and hip flexion measures were found between the groups after training; however, knee flexion angle significantly increased in the training group from the pretest (77.2 ± 4.1°) to posttest (83.2 ± 3.7°) during the bilateral drop jump. No significant changes occurred during the unilateral drop jump. Bilateral measures for knee flexion, hip flexion, and knee valgus were significantly (p < 0.05) greater than the unilateral measures during the drop jump task, which indicate an increased risk for anterior cruciate ligament (ACL) injury during unilateral drop jumps. The data support that the strength and conditioning specialist can implement resistance training alone during a short-term training period to reduce the risk of ACL injury by increasing knee flexion during a bilateral drop jump task. Increased knee flexion angles after resistance training may indicate a reduced risk for knee injury from improved neuromuscular control, resulting in a softer landing.
AuthorsKevin McCurdy, John Walker, Joseph Saxe, Jonathan Woods
JournalJournal of strength and conditioning research (J Strength Cond Res) Vol. 26 Issue 5 Pg. 1257-64 (May 2012) ISSN: 1533-4287 [Electronic] United States
PMID22344064 (Publication Type: Journal Article, Randomized Controlled Trial, Research Support, Non-U.S. Gov't)
Topics
  • Adult
  • Analysis of Variance
  • Anterior Cruciate Ligament Injuries
  • Biomechanical Phenomena
  • Female
  • Hip Joint (physiology)
  • Humans
  • Knee Injuries (prevention & control)
  • Knee Joint (physiology)
  • Resistance Training
  • Time Factors
  • Young Adult

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