Effect of Strength Training on Jump-Landing Biomechanics in Adolescent Females

Background: Sex-based differences in neuromuscular characteristics relevant to anterior cruciate ligament (ACL) injury risk may arise as compensation for divergent strength development during puberty. Strength training during this period may prevent the development of these undesirable neuromuscular characteristics. Hypothesis: Strength-trained middle school girls will have improved jump-landing biomechanics compared with control participants. Study Design: Cohort study. Level of Evidence: Level 3. Methods: Maximum voluntary isometric contraction in hip extension and abduction and knee extension and flexion as well as Landing Error Scoring System (LESS) scores were collected for healthy female middle school students of grades 6 to 8. Strength-training participants (STR: N = 30; height, 1.63 ± 0.07 m; mass, 48.1 ± 7.6 kg; age, 12.5 ± 1.0 y) were matched with control participants (CON: N = 30; height, 1.60 ± 0.09 m; mass, 47.2 ± 8.9 kg; age, 12.6 ± 0.9 y). The training consisted of a 6-month strength-training program administered through a gym class curriculum that targeted the lower extremity. A repeated-measures mixed-model analysis of variance was used for comparisons between groups and across time (α = 0.05). Stepwise linear regression was used to examine the relationship between strength change and LESS score change. Results: Strength values (N·m/kg) increased across time and to a greater degree in STR for hip extension (baseline 3.98 ± 1.15 vs follow-up 4.77 ± 1.80), hip abduction (4.22 ± 1.09 vs 5.13 ± 2.55), and knee flexion (3.27 ± 0.62 vs 3.64 ± 1.40) compared with CON. LESS grades significantly decreased across time in STR (5.58 ± 1.21 vs 4.86 ± 1.44) and were significantly lower than CON (5.98 ± 1.42) at follow-up ( P < 0.001). The change in hip extension and knee extension strength explained 67% of the variance ( P < 0.001) in the LESS change score in the STR group. Conclusion: A school-based strength-training program that focused on hip and knee musculature significantly improved jump-landing biomechanics (as determined by LESS) relevant to ACL injury risk. Further investigation using different strength-training approaches in this age group is warranted. Clinical Relevance: Strength training during adolescence holds promise as an injury prevention program. The use of a school-based approach is novel and may represent a robust opportunity for injury prevention programs, as physical education class is often mandatory in this age group.

Femoral and Tibial Bony Risk Factors for Anterior Cruciate Ligament Injuries Are Present in More Than 50% of Healthy Individuals

Background: Anterior cruciate ligament (ACL) injuries are multifactorial events that may be influenced by morphometric parameters. Associations between primary ACL injuries or graft ruptures and both femoral and tibial bony risk factors have been well described in the literature. Purpose: To determine values of femoral and tibial bony morphology that have been associated with ACL injuries in a reference population. Further, to define interindividual variations according to participant demographics and to identify the proportion of participants presenting at least 1 morphological ACL injury risk factor. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Computed tomography scans of 382 healthy participants were examined. The following bony ACL risk factors were analyzed: notch width index (NWI), lateral femoral condylar index (LFCI), medial posterior plateau tibial angle (MPPTA), and lateral posterior plateau tibial angle (LPPTA). The proportion of this healthy population presenting with at least 1 pathological ACL injury risk factor was determined. A multivariable logistic regression model was constructed to determine the influence of demographic characteristics. Results: According to published thresholds for ACL bony risk factors, 12% of the examined knees exhibited an intercondylar notch width <18.9 mm, 25% had NWI <0.292, 62% exhibited LFCI <0.67, 54% had MPPTA <83.6°, and 15% had LPPTA <81.6°. Only 14.4% of participants exhibited no ACL bony risk factors, whereas 84.5% had between 2 and 4 bony risk factors and 1.1% had all bony risk factors. The multivariate analysis demonstrated that only the intercondylar notch width ( P < .0001) was an independent predictor according to both sex and ethnicity; the LFCI ( P = .012) and MMPTA ( P = .02) were independent predictors according to ethnicity. Conclusion: The precise definition of bony anatomic risk factors for ACL injury remains unclear. Based on published thresholds, 15% to 62% of this reference population would have been considered as being at risk. Large cohort analyses are required to confirm the validity of previously described morphological risk factors and to define which participants may be at risk of primary ACL injury and reinjury after surgical reconstruction.

Effect of Rearfoot Strikes on the Hip and Knee Rotational Kinetic Chain During the Early Phase of Cutting in Female Athletes

Background Biomechanical factors affecting horizontal-plane hip and knee kinetic chain and anterior cruciate ligament (ACL) injury risk during cutting maneuvers remain unclear. This study aimed to examine whether different foot strike patterns alter horizontal-plane hip and knee kinetics and kinematics during a cutting maneuver in female athletes and clarify the individual force contribution for producing high-risk hip and knee loadings. Twenty-five healthy female athletes performed a 60° cutting task with forefoot and rearfoot first strike conditions. Horizontal-plane hip and knee moment components, angles, and angular velocities were calculated using synchronized data of the marker positions on the body landmarks and ground reaction forces (GRFs) during the task. The one-dimensional statistical parametric mapping paired t test was used to identify the significant difference in kinetic and kinematic time-series data between foot strike conditions. Results In the rearfoot strike condition, large hip and knee internal rotation loadings were produced during the first 5% of stance due to the application of GRFs, causing a significantly larger hip internal rotation excursion than that of the forefoot strike condition. Dissimilarly, neither initial hip internal rotation displacement nor knee internal rotation GRF loadings were observed in the forefoot strike condition. Conclusions Rearfoot strike during cutting appears to increase noncontact ACL injury risk as the GRF tends to produce combined hip and knee internal rotation moments and the high-risk lower limb configuration. Conversely, forefoot strike during cutting appears to be an ACL-protective strategy that does not tend to produce the ACL-harmful joint loadings and lower extremity configurations. Thus, improving foot strike patterns during cutting should be incorporated in ACL injury prevention programs.

Sex, Military Occupation, and Rank Are Associated with Risk of Anterior Cruciate Ligament Injury in Tactical-Athletes

ABSTRACTBackgrounACL injury is frequent within the U.S. military and represents a significant loss to readiness. Since recent changes to operational tempo, there has not been an analysis of ACL injury risk. There is sparse evidence on salient risk factors for ACL injury across all service members.Hypothesis/PurposeThe aim of this study is to evaluate military occupation, sex, rank, and branch of service on ACL injury risk in the U.S. military from 2006 to 2018.Study DesignDescriptive Epidemiology Study.MethodsThe Defense Medical Epidemiology Database was queried for the number of U.S. military members with ICD diagnosis codes 717.83 (Old disruption of ACL), 844.2 (Sprain of knee cruciate ligament), M23.61 (Other spontaneous disruption of ACL), and S83.51 (Sprain of ACL of knee) on their initial encounter from 2006 to 2018. Relative risk (RR) and chi-square statistics were calculated to assess sex and military occupation effects on ACL injury. A multivariable negative binomial regression model evaluated changes in ACL injury incidence with respect to sex, branch of service, and rank.ResultsThe study period displayed a significant decrease in the ACL injury rate at 0.18 cases per 1000 person-years or relative decrease of 4.08% each year (p < 0.001) after averaging over the main and interactive effects of sex, rank, and branch of service. The interaction effect of time with sex indicated a steeper decline in ACL injury incidence in males as compared to females. The risk of ACL injury by sex was modified by rank. Furthermore, the incidence of ACL injury among military personnel varied depending on occupation.ConclusionDespite the decline in incidence among military members over time, the rates of ACL injury remain much higher than the general U.S. population. Sex, rank, branch of service, and military occupation were found to be risk factors for ACL injury.Clinical RelevanceThese results are evidence to support inquiry into the specific hazards associated with these factors. It is critical for policy makers to understand the salient risk factors for ACL injury to guide appropriate proactive measures to prevent injury.What is known about this subjectACL injury is a known command readiness issue in the military, and there is recent evidence of this within subpopulations of the military.What this study adds to existing literatureThis study provides updated trends in ACL injury across the military in light of changes to operational tempo and identifies salient risk factors for ACL injury, which have been previously unknown on a population basis.

Do ACL Injury Risk Reduction Exercises Reflect Common Injury Mechanisms? A Scoping Review of Injury Prevention Programs

Context: Anterior cruciate ligament (ACL) injury risk reduction programs have become increasingly popular. As ACL injuries continue to reflect high incidence rates, the continued optimization of current risk reduction programs, and the exercises contained within them, is warranted. The exercises must evolve to align with new etiology data, but there is concern that the exercises do not fully reflect the complexity of ACL injury mechanisms. It was outside the scope of this review to address each possible inciting event, rather the effort was directed at the elements more closely associated with the end point of movement during the injury mechanism. Objective: To examine if exercises designed to reduce the risk of ACL injury reflect key injury mechanisms: multiplanar movement, single limb stance, trunk and hip dissociative control, and a flight phase. Data Sources: A systematic search was performed using PubMed, Medline, EBSCO (CINAHL), SPORTSDiscus, and PEDro databases. Study Selection: Eligibility criteria were as follows: (1) randomized controlled trials or prospective cohort studies, (2) male and/or female participants of any age, (3) exercises were targeted interventions to prevent ACL/knee injuries, and (4) individual exercises were listed and adequately detailed and excluded if program was unable to be replicated clinically. Study Design: Scoping review. Level of Evidence: Level 4. Data Extraction: A total of 35 studies were included, and 1019 exercises were extracted for analysis. Results: The average Consensus on Exercise Reporting Template score was 11 (range, 0-14). The majority of exercises involved bilateral weightbearing (n = 418 of 1019; 41.0%), followed by single limb (n = 345 of 1019; 33.9%) and nonweightbearing (n = 256 of 1019; 25.1%). Only 20% of exercises incorporated more than 1 plane of movement, and the majority of exercises had sagittal plane dominance. Although 50% of exercises incorporated a flight phase, only half of these also involved single-leg weightbearing. Just 16% of exercises incorporated trunk and hip dissociation, and these were rarely combined with other key exercise elements. Only 13% of exercises challenged more than 2 key elements, and only 1% incorporated all 4 elements (multiplanar movements, single limb stance, trunk and hip dissociation, flight phase) simultaneously. Conclusion: Many risk reduction exercises do not reflect the task-specific elements identified within ACL injury mechanisms. Addressing the underrepresentation of key elements (eg, trunk and hip dissociation, multiplanar movements) may optimize risk reduction in future trials.

Clinical-Grade MRI-Based Methods to Identify Combined Anatomic Factors That Predict ACL Injury Risk in Male and Female Athletes

Background: Recently developed multivariate sex-specific statistical models can predict anterior cruciate ligament (ACL) injury risk using various knee anatomic factors. However, screening tools able to identify individuals at an increased injury risk are unlikely to be developed based on these models, given that sophisticated and time-consuming methods were used to measure those factors on research-grade resolution magnetic resonance images (MRIs). Purpose: To determine whether simpler methods, amenable to using clinical-grade resolution MRIs, can identify the same knee anatomic factors previously found to contribute to ACL injury risk using sophisticated methods and research-grade resolution images. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: High-resolution 3-dimensional MRIs previously acquired from 87 patients with primary, noncontact, grade III ACL injury and 87 uninjured matched control participants for a series of published studies were downgraded to clinical-grade resolution images. The 4 knee anatomic factors found to contribute to ACL injury risk in women and in men in these published studies—femoral intercondylar notch width at the anterior outlet of the ACL (NW_O), posterior-inferior directed slope of the middle region articular cartilage surface of the tibial plateau’s lateral compartment (LatTibMCS), ACL volume, and tibial plateau’s lateral compartment posterior meniscus to subchondral bone wedge angle (LatTibMBA)—were measured using clinical-grade resolution MRI-based methods. Stepwise multivariate conditional logistic regressions were used to identify the combinations of factors most highly associated with an ACL injury risk in women and men separately. Results: The multivariate model that best predicted ACL injury risk in the female participants included the LatTibMCS and the NW_O. For the male participants, this model included the ACL volume and the LatTibMBA. These results corroborate the previously published results that reported models with the same knee anatomic factors to best predict injury risk in this group of young women and men. Conclusion: Simpler methods using MRIs downgraded to a clinical-grade resolution can identify the same knee anatomic factors previously found to significantly contribute to ACL injury risk using sophisticated methods and research-grade resolution MRIs.

NEURAL ACTIVITY PROFILES ASSOCIATED WITH ACL INJURY-RISK MECHANICS IN ECOLOGICAL SPORT SPECIFIC VIRTUAL REALITY

Background: Anterior cruciate ligament (ACL) injury is secondary to a multifactorial etiology encompassing anatomical, biological, mechanical, and neurological factors. The nature of the injury being primarily due to non-contact mechanics further implicates neural control as a key injury-risk factor, though it has received considerably less study. Purpose: To determine the contribution of neural activity to injury-risk mechanics in ecological sport-specific VR landing scenarios. Methods: Ten female high-school soccer players (15.5±0.85 years; 165.0±6.09 cm; 59.1±11.84 kg) completed a neuroimaging session to capture neural activity during a bilateral leg press and a 3D biomechanics session performing a header within a VR soccer scenario. The bilateral leg press involved four 30 s blocks of repeated bilateral leg presses paced to a metronome beat of 1.2 Hz with 30 s rest between blocks. The VR soccer scenario simulated a corner-kick, requiring the participant to jump and head a virtual soccer ball into a virtual goal (Figure 1A-E). Initial contact and peak knee flexion and abduction angles were extracted during the landing from the header as injury-risk variables of interest and were correlated with neural activity. Results: Evidenced in Table 1 and Figure 1 (bottom row), increased initial contact abduction, increased peak abduction, and decreased peak flexion were associated with increased sensory, visual-spatial, and cerebellar activity (r2= 0.42-0.57, p corrected < .05, z max > 3.1, table & figure 1). Decreased initial contact flexion was associated with increased frontal cortex activity (r2= 0.68, p corrected < .05, z max > 3.1). Conclusion: Reduced neural efficiency (increased activation) of key regions that integrate proprioceptive, visual-spatial, and neurocognitive activity for motor control may influence injury-risk mechanics in sport. The regions found to increase in activity in relation to higher injury-risk mechanics are typically activated to assist with spatial navigation, environmental interaction, and precise motor control. The requirement for athletes to increase their activity for more basic knee motor control may result in fewer neural resources available to maintain knee joint alignment, allocate environmental attention, and handle increased motor coordination demands. These data indicate that strategies to enhance efficiency of visual-spatial and cognitive-motor control during high demand sporting activities is warranted to improve ACL injury-risk reduction. [Figure: see text][Table: see text]

Electromyographic Assessment of Anterior Cruciate Ligament Injury Risk in Male Tennis Players: Which Role for Visual Input? A Proof-of-Concept Study

Anterior cruciate ligament (ACL) injury incidence is often underestimated in tennis players, who are considered as subjects conventionally less prone to knee injuries. However, evaluation of the preactivation of knee stabilizer muscles by surface electromyography (sEMG) showed to be a predictive value in the assessment of the risk of ACL injury. Therefore, this proof-of-concept study aimed at evaluating the role of visual input on the thigh muscle preactivation through sEMG to reduce ACL injury risk in tennis players. We recruited male, adult, semiprofessional tennis players from July to August 2020. They were asked to drop with the dominant lower limb from a step, to evaluate—based on dynamic valgus stress—the preactivation time of the rectus femoris (RF), vastus medialis, biceps femoris, and medial hamstrings (MH), through sEMG. To highlight the influence of visual inputs, the athletes performed the test blindfolded and not blindfolded on both clay and grass surfaces. We included 20 semiprofessional male players, with a mean age 20.3 ± 4.8 years; results showed significant early muscle activation when the subject lacked visual input, but also when faced with a less-safe surface such as clay over grass. Considering the posteromedial–anterolateral relationship (MH/RF ratio), tennis players showed a significant higher MH/RF ratio if blindfolded (22.0 vs. 17.0% not blindfolded; p < 0.01) and percentage of falling on clay (17.0% vs. 14.0% in grass; p < 0.01). This proof-of-principle study suggests that in case of absence of visual input or falling on a surface considered unsafe (clay), neuro-activation would tend to protect the anterior stress of the knee. Thus, the sEMG might play a crucial role in planning adequate athletic preparation for semiprofessional male athletes in terms of reduction of ACL injury risk.