Context: Identifying neuromuscular screening factors for anterior cruciate ligament (ACL) injury is a critical step toward large-scale deployment of effective ACL injury-prevention programs. The Landing Error Scoring System (LESS) is a valid and reliable clinical assessment of jump-landing biomechanics.Objective: To investigate the ability of the LESS to identify individuals at risk for ACL injury in an elite-youth soccer population.Design: Cohort study. Setting: Field-based functional movement screening performed at soccer practice facilities.Patients or Other Participants: A total of 829 elite-youth soccer athletes (348 boys, 481 girls; age ¼ 13.9 6 1.8 years, age range ¼ 11 to 18 years), of whom 25% (n ¼ 207) were less than 13 years of age.Intervention(s): Baseline preseason testing for all participants consisted of a jump-landing task (3 trials). Participants were followed prospectively throughout their soccer seasons for diagnosis of ACL injuries (1217 athlete-seasons of follow-up).Main Outcome Measure(s): Landings were scored for ''errors'' in technique using the LESS. We used receiver operator characteristic curves to determine a cutpoint on the LESS. Sensitivity and specificity of the LESS in predicting ACL injury were assessed.Results: Seven participants sustained ACL injuries during the follow-up period; the mechanism of injury was noncontact or indirect contact for all injuries. Uninjured participants had lower LESS scores (4.43 6 1.71) than injured participants (6.24 6 1.75; t 1215 ¼ À2.784, P ¼ .005). The receiver operator characteristic curve analyses suggested that 5 was the optimal cutpoint for the LESS, generating a sensitivity of 86% and a specificity of 64%.Conclusions: Despite sample-size limitations, the LESS showed potential as a screening tool to determine ACL injury risk in elite-youth soccer athletes.Key Words: children, knee, biomechanics, movement patterns Key PointsThe Landing Error Scoring System (LESS) score may effectively identify elite-youth soccer athletes at higher risk of sustaining anterior cruciate ligament (ACL) injuries. Elite-youth soccer athletes with LESS scores of 5 or more were at higher risk of sustaining ACL injuries than athletes with LESS scores less than 5. Individuals with LESS scores of 5 or more may be targeted for ACL injury-prevention exercise programs.

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Multicomponent injury-prevention training programs are recommended for reducing noncontact and indirect-contact ACL injuries and strongly recommended for reducing noncontact and indirect-contact knee injuries during physical activity. These programs are advocated for improving balance, lower extremity biomechanics, muscle activation, functional performance, strength, and power, as well as decreasing landing impact forces. A multicomponent injury-prevention training program should, at minimum, provide feedback on movement technique in at least 3 of the following exercise categories: strength, plyometrics, agility, balance, and flexibility. Further guidance on training dosage, intensity, and implementation recommendations is offered in this statement.

Implementing an injury prevention program to athletes under age 12 years may reduce injury rates. There is limited knowledge regarding whether these young athletes will be able to modify balance and performance measures after completing a traditional program that has been effective with older athletes or whether they require a specialized program for their age. The purpose of this study was to compare the effects of a pediatric program, which was designed specifically for young athletes, and a traditional program with no program in the ability to change balance and performance measures in youth athletes. We used a cluster-randomized controlled trial to evaluate the effects of the programs before and after a 9-week intervention period. Sixty-five youth soccer athletes (males: n = 37 mass = 34.16 +/- 5.36 kg, height = 143.07 +/- 6.27 cm, age = 10 +/- 1 yr; females: n = 28 mass = 33.82 +/- 5.37 kg, height = 141.02 +/- 6.59 cm) volunteered to participate and attended 2 testing sessions in a research laboratory. Teams were cluster-randomized to either a pediatric or traditional injury prevention program or a control group. Change scores for anterior-posterior and medial-lateral time-to-stabilization measures and maximum vertical jump height and power were calculated from pretest and post-test sessions. Contrary with our original hypotheses, the traditional program resulted in positive changes, whereas the pediatric program did not result in any improvements. Anterior-posterior time-to-stabilization decreased after the traditional program (mean change +/- SD = -0.92 +/- 0.49 s) compared with the control group (-0.49 +/- 0.59 s) (p = 0.003). The traditional program also increased vertical jump height (1.70 +/- 2.80 cm) compared with the control group (0.20 +/- 0.20 cm) (p = 0.04). There were no significant differences between control and pediatric programs. Youth athletes can improve balance ability and vertical jump height after completing an injury prevention program. Training specificity appears to affect improvements and should be considered with future program design.

Context: Long-term effects of ankle bracing on lower extremity kinematics and kinetics are unknown. Ankle motion restriction may negatively affect the body's ability to attenuate ground reaction forces (GRFs).Objective: To evaluate the immediate and long-term effects of ankle bracing on lower extremity kinematics and GRFs during a jump landing.Design Setting: Sports medicine research laboratory. Patients or Other Participants: A total of 37 healthy subjects were assigned randomly to either the intervention (n 5 11 men, 8 women; age 5 19.63 6 0.72 years, height 5 176.05 6 10.58 cm, mass 5 71.50 6 13.15 kg) or control group (n 5 11 men, 7 women; age 5 19.94 6 1.44 years, height 5 179.15 6 8.81 cm, mass 5 74.10 6 10.33 kg).Intervention(s): The intervention group wore braces on both ankles and the control group did not wear braces during all recreational activities for an 8-week period.Main Outcome Measure(s): Initial ground contact angles, maximum joint angles, time to reach maximum joint angles, and joint range of motion for sagittal-plane knee and ankle motion were measured during a jump-landing task. Peak vertical GRF and the time to reach peak vertical GRF were assessed also.Results: While participants were wearing the brace, ankle plantar flexion at initial ground contact (brace 5 356 6 136, no brace 5 386 6 156, P 5 .024), maximum dorsiflexion (brace 5 216 6 76, no brace 5 226 6 66, P 5 .04), dorsiflexion range of motion (brace 5 566 6 146, no brace 5 596 6 166, P 5 .001), and knee flexion range of motion (brace 5 796 6 166, no brace 5 826 6 166, P 5 .036) decreased, whereas knee flexion at initial ground contact increased (brace 5 126 6 96, no brace 5 96 6 96, P 5 .0001). Wearing the brace for 8 weeks did not affect any of the outcome measures, and the brace caused no changes in vertical GRFs (P . .05).Conclusions: Although ankle sagittal-plane motion was restricted with the brace, knee flexion upon landing increased and peak vertical GRF did not change. The type of lace-up brace used in this study appeared to restrict ankle motion without increasing knee extension or vertical GRFs and without changing kinematics or kinetics over time.

Players with the greatest amount of movement errors experienced the most improvement. A program's effectiveness may be enhanced if this population is targeted.

Context:There is a need for reliable clinical assessment tools that can be used to identify individuals who may be at risk for injury. The Landing Error Scoring System (LESS) is a reliable and valid clinical assessment tool that was developed to identify individuals at risk for lower extremity injuries. One limitation of this tool is that it cannot be assessed in real time and requires the use of video cameras.Objective:To determine the interrater reliability of a real-time version of the LESS, the LESS-RT.Design:Reliability study.Setting:Controlled research laboratory.Participants:43 healthy volunteers (24 women, 19 men) between the ages of 18 and 23.Intervention:The LESS-RT evaluates 10 jump-landing characteristics that may predispose an individual to lower extremity injuries. Two sets of raters used the LESS-RT to evaluate participants as they performed 4 trials of a jump-landing task.Main Outcome Measures:Intraclass correlation coefficient (ICC2,1) values for the final composite score of the LESS-RT were calculated to assess interrater reliability of the LESS-RT.Results:Interrater reliability (ICC2,1) for the LESS-RT ranged from .72 to .81 with standard error of measurements ranging from .69 to .79.Conclusions:The LESS-RT is a quick, easy, and reliable clinical assessment tool that may be used by clinicians to identify individuals who may be at risk for lower extremity injuries.

Context: Anterior tibial shear force and knee valgus moment increase anterior cruciate ligament (ACL) loading. Muscle coactivation of the quadriceps and hamstrings influences anterior tibial shear force and knee valgus moment, thus potentially influencing ACL loading and injury risk. Therefore, identifying exercises that facilitate balanced activation of the quadriceps and hamstrings might be beneficial in ACL injury rehabilitation and prevention.Objective: To quantify and compare quadriceps with hamstrings coactivation electromyographic (EMG) ratios during commonly used closed kinetic chain exercises.Design: Cross-sectional study. Setting: Research laboratory.Patients or Other Participants: Twenty-seven healthy, physically active volunteers (12 men, 15 women; age ¼ 22.1 6 3.1 years, height ¼ 171.4 6 10 cm, mass ¼ 72.4 6 16.7 kg).Intervention(s): Participants completed 9 separate closed chain therapeutic exercises in a randomized order.Main Outcome Measure(s): Surface electromyography quantified the activity level of the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH), and biceps femoris (BF) muscles. The quadriceps-to-hamstrings (Q:H) coactivation ratio was computed as the sum of average quadriceps (VM, VL) EMG amplitude divided by the sum of average hamstrings (MH, BF) EMG amplitude for each trial. We used repeated-measures analyses of variance to compare Q:H ratios and individual muscle contributions across exercises (a ¼ .05), then used post hoc Tukey analyses.Results: We observed a main effect for exercise (F 3,79 ¼ 22.6, P , .001). The post hoc Tukey analyses revealed smaller Q:H ratios during the single-limb dead lift (2.87 6 1.77) than the single-limb squat (5.52 6 2.89) exercise. The largest Q:H ratios were observed during the transverse-lunge (7.78 6 5.51, P , .001), lateral-lunge (9.30 6 5.53, P , .001), and forward-lunge (9.70 6 5.90, P , .001) exercises.Conclusions: The most balanced (smallest) coactivation ratios were observed during the single-limb dead-lift, lateral-hop, transverse-hop, and lateral band-walk exercises. These exercises potentially could facilitate balanced activation in ACL rehabilitation and injury-prevention programs. They also could be used in postinjury rehabilitation programs in a safe and progressive manner.Key Words: anterior cruciate ligament, closed kinetic chain exercises Key PointsExercises that use a quadriceps-dominant activation might negatively affect the knee by increasing strain on the anterior cruciate ligament. The hamstrings muscles can counteract the deleterious effect of the quadriceps except when activation is minimal. The most balanced quadriceps-to-hamstrings coactivation ratios were produced during the single-limb dead-lift, lateral-hop, transverse-hop, and lateral band-walk exercises. Exercises with a more balanced quadriceps-to-hamstrings coactivation ratio may benefit anterior cruciate ligament rehabilitation and injury-prevention programs.