Field-Based Assessment of Jump Landing Mechanics following Participation in Traditional versus Plyometric Lower Extremity Injury Prevention Programs
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Context: Validated, field-based assessment tools for jump landing mechanics provide clinicians with portable, low cost methods of assessing an individual’s risk of anterior cruciate ligament (ACL) injury. The Landing Error Scoring System (LESS) is one example of a field test that can be used for mass screenings. Little research has been done to quantify the influence of hip abductor strength on jump landing mechanics, particularly after fatigue has been induced in this muscle group. Objective: To investigate the effects of two 4-week lower extremity injury prevention programs (traditional hip abductor exercises versus lower extremity plyometric exercises) on field-based measurements of ACL injury risk before and after inducing neuromuscular fatigue. Design: Randomized controlled trial. Setting: Controlled laboratory setting. Participants: 33 women (age 20.97 ± 1.40 yrs; height, 1.63 ± 0.06 m; mass, 61.31 ± 8.59 kg); were randomly allocated into two groups: Traditional and Plyometric exercises. Interventions: Participation in one of two 4-week lower extremity injury prevention programs; hip abductor muscular fatigue was induced bilaterally using a concentric exercise protocol on an isokinetic dynamometer. Main Outcome Measures: Right and left limb concentric and eccentric hip abduction peak torque at 120°/s, closed kinetic chain single leg press peak force at 60°/s, and LESS test results. These measures were assessed pre- and post-fatigue at baseline (Week 0), and pre- and post-fatigue at Week 4. Results: Of the 4 outcome measures that quantified hip abduction peak torque, statistically significant strength gains were observed in both groups for left hip abduction concentric peak torque (p<0.001). Left hip abduction peak torque increased 28% in the Plyometric group and 20% in the Traditional group between Week 0 and Week 4 (p< 0.001, 2 = 0.362), but no significant between group differences were observed (p = 0.844, 1- = 0.054). Closed kinetic chain, concentric right leg press peak force improved 21% in the Traditional group and 12% in the Plyometric group from Week 0 to Week 4 (p< 0.001, 2 = 0.465), but there were no significant group differences present (p = 0.370, 1- = 0.143). The 4-week Plyometric lower extremity injury prevention program created significantly greater improvements in the LESS test scores on both the pre-fatigue and post-fatigue trials (16.7% and 11.6% improvements, respectively, between Week 0 and Week 4), than the Traditional exercise program, which demonstrated a 9.0% improvement on pre-fatigue and a 7.9% improvement on post-fatigue LESS test scores between Week 0 and Week 4. Conclusions: The lower extremity injury prevention programs that we employed were both effective in creating significant gains in lower extremity muscular strength of the participants over a 4-week period. Both interventions produced significant improvements (decreases) in LESS test scores within their groups. However, the Plyometric exercise group demonstrated significantly greater improvements in LESS test scores, a finding that supports the premise that plyometric exercises should continue to be a required component in lower extremity injury prevention programs.