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Purpose: The capacity to explosively contract quadriceps within the critical timeframe associated with anterior cruciate ligament (ACL) injury, quantified by the rate of torque development, is potentially essential for safe landing mechanics. This study aimed to investigate the influence of explosive quadriceps strength on ACL-related sagittal-plane landing mechanics in females with and without ACL reconstruction (ACLR)., Methods: Quadriceps explosive strength and landing mechanics were assessed in 19 ACLR and 19 control females during isometric contractions and double- and single-leg jump landings. A stepwise multiple linear regression model determined the variance in each of the landing biomechanics variables for the ACLR limb and nondominant limb of controls that could be explained by the group, rate of torque development and/or their interaction. If peak kinetic variables could be predicted by the rate of torque development or interaction, additional analyses were conducted, accounting for knee flexion as a covariate in the regression model., Results: During single-leg landings, ACLR females exhibited greater knee flexion at initial contact than controls (p = 0.04). Greater quadriceps rate of torque development predicted higher peak posterior ground reaction force and anterior tibial shear force in both groups (p = 0.04). However, after controlling for knee flexion angle at those peak forces, quadriceps rate of torque development was not predictive. In double-leg landings, greater explosive quadriceps strength was associated with quicker attainment of peak knee extension moment and posterior ground reaction force in the ACLR limb (p = 0.03)., Conclusion: Regardless of ACL injury status, females with greater explosive quadriceps strength adopted safer single-leg landings through increased knee flexion, potentially mitigating ACL loading despite encountering higher peak forces. During double-leg landings, a greater explosive quadriceps strength of the ACLR limb is associated with faster achievement of peak force upon landing. Incorporating explosive quadriceps strengthening into post-ACLR rehabilitation and injury prevention programmes may enhance landing mechanics for reducing primary and subsequent ACL injury risks., Level of Evidence: Level II., (© 2024 European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

This study investigated the influences of explosive quadriceps strength and landing task on sagittal plane knee biomechanics. Forty female participants performed isometric knee extensions on a dynamometer and had lower extremity biomechanics assessed during double-leg jump-landings (DLJL) and single-leg jump-cuts (SLJC). Explosive quadriceps strength was quantified by calculating rate of torque development (RTD) between torque onset and 100 ms after onset on a dynamometer. Participants were stratified into high and low RTD groups. Landing biomechanics were compared using 2 (Group) × 2 (Task) mixed-model ANOVAs. The relationships between quadriceps RTD and landing biomechanics were also assessed using simple, bivariate correlations. Across RTD groups, greater knee flexion at initial contact (KFIC), peak vertical ground reaction force, peak anterior tibial shear force, and peak internal knee extension moment, and lesser peak knee flexion was observed during SLJC compared to DLJL. The high RTD group exhibited significantly greater KFIC than the low RTD group across landing tasks. Greater quadriceps RTD was significantly associated with greater KFIC during SLJC, but not during DLJL. As landing with lesser KFIC is a risk factor for ACL injury, greater explosive quadriceps strength capacity might be beneficial for facilitating the use of safer landing mechanics during athletic tasks.

Context: Noncontact anterior cruciate ligament injury often occurs during rapid deceleration and change-of-direction maneuvers. These activities require an athlete to generate braking forces to slow down the center of mass and change direction in a dynamic environment. During preplanned cutting, athletes can use the penultimate step for braking before changing direction, resulting in less braking demand during the final step. During reactive cutting, athletes use different preparatory movement strategies during the penultimate step when planning time is limited. However, possible differences in the deceleration profile between the penultimate and final steps of preplanned and reactive side-step cuts remain unknown., Objective: To comprehensively evaluate deceleration during the penultimate and final steps of preplanned and reactive cutting., Design: Cross-sectional study., Setting: Laboratory., Patients or Other Participants: Thirty-six women (age = 20.9 ± 1.7 years, height = 1.66 ± 0.07 m, mass = 62.4 ± 8.7 kg)., Intervention: Participants completed 90° side-step cutting maneuvers under preplanned and reactive conditions., Main Outcome Measure(s): Approach velocity, velocity at initial contact, and cutting angle were compared between conditions. Stance time, deceleration time, and biomechanical indicators of deceleration were assessed during the penultimate and final steps of preplanned and reactive 90° cuts. Separate repeated-measures analysis-of-variance models were used to assess the influence of step, condition, and their interaction on the biomechanical indicators of deceleration., Results: Approach velocity (P = .69) and velocity at initial contact of the penultimate step (P = .33) did not differ between conditions. During reactive cutting, participants achieved a smaller cutting angle (P < .001). We identified a significant step-by-condition interaction for all biomechanical indicators of deceleration (P values < .05)., Conclusions: A lack of planning time resulted in less penultimate step braking and greater final step braking during reactive cutting. As a result, participants exhibited a decreased cutting angle and longer stance time during the final step of reactive cutting. Improving an athlete's ability to respond to an external stimulus may facilitate a more effective penultimate step braking strategy that decreases the braking demand during the final step of reactive cutting., (© by the National Athletic Trainers’ Association, Inc.)

Objective: To determine whether individuals with a prior concussion exhibit biomechanical alterations in balance, gait and jump-landing tasks with and without cognitive demands that are associated with risk of lateral ankle sprain (LAS) and anterior cruciate ligament (ACL) injury., Design: Systematic review and meta-analysis., Data Sources: Five electronic databases (Web of Science, Scopus, PubMed, SPORTDiscus and CiNAHL) were searched in April 2023., Eligibility Criteria: Included studies involved (1) concussed participants, (2) outcome measures of spatiotemporal, kinematic or kinetic data and (3) a comparison or the data necessary to compare biomechanical variables between individuals with and without concussion history or before and after a concussion., Results: Twenty-seven studies were included involving 1544 participants (concussion group (n=757); non-concussion group (n=787)). Individuals with a recent concussion history (within 2 months) had decreased postural stability (g=0.34, 95% CI 0.20 to 0.49, p<0.001) and slower locomotion-related performance (g=0.26, 95% CI 0.11 to 0.41, p<0.001), both of which are associated with LAS injury risk. Furthermore, alterations in frontal plane kinetics (g=0.41, 95% CI 0.03 to 0.79, p=0.033) and sagittal plane kinematics (g=0.30, 95% CI 0.11 to 0.50, p=0.002) were observed in individuals approximately 2 years following concussion, both of which are associated with ACL injury risk. The moderator analyses indicated cognitive demands (ie, working memory, inhibitory control tasks) affected frontal plane kinematics (p=0.009), but not sagittal plane kinematics and locomotion-related performance, between the concussion and non-concussion groups., Conclusion: Following a recent concussion, individuals display decreased postural stability and slower locomotion-related performance, both of which are associated with LAS injury risk. Moreover, individuals within 2 years following a concussion also adopt a more erect landing posture with greater knee internal adduction moment, both of which are associated with ACL injury risk. While adding cognitive demands to jump-landing tasks affected frontal plane kinematics during landing, the altered movement patterns in locomotion and sagittal plane kinematics postconcussion persisted regardless of additional cognitive demands., Prospero Registration Number: CRD42021248916., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2023. No commercial re-use. See rights and permissions. Published by BMJ.)

The objective of this study was to describe the purpose, methods, and effects of the Pac-12 Health Analytics Program (HAP) approach on sports medicine informatics, research, analytics, and health care operations. Sports injury-surveillance initiatives have been supporting the clinical research community in sports medicine for nearly 4 decades. Whereas the initial systems tracked only a few sports, current surveillance programs have expanded to include entire professional and elite athlete organizations, providing important statistics on sports injury risk management. The HAP is a conference-wide data-sharing and-analytics program. It collects authorized, deidentified clinical data, encompassing multiple domains of sports medicine injury management, including sports injuries and illnesses, concussions, risk exposure, and COVID-19 testing elements. The HAP provides clinicians with access to curated data to inform evidence-based practice and support local health care operations with respect to emerging sports injury trends. The HAP supplies approved research groups with access to a data repository that describes a homogeneous, elite intercollegiate athlete sample, thereby supporting nonresearch clinical initiatives as well as contributions to peer-reviewed research that can improve the health and well-being of Pac-12 student-athletes. The HAP is a novel approach to sports injury epidemiology and surveillance that has allowed the Pac-12 Conference to meet larger objectives regarding improving the student-athlete experience and clinical research among its member schools. Data quality control has improved the accuracy of the data and value to clinical athletic trainers within the conference. Curated dashboards displaying aggregated project data offer clinicians data-driven decision-making tools that help inform sports injury risk management. As of 2021, the HAP had supported more than 3 dozen data requests. These investigations have resulted in numerous peer-reviewed research contributions to the sports medicine community with findings that have great potential to improve the health and well-being of Pac-12 student-athletes., (© by the National Athletic Trainers’ Association, Inc.)

Context: The single-legged triple hop is a commonly used functional task after anterior cruciate ligament reconstruction (ACLR). Recently, researchers have suggested that individuals may use a compensatory propulsion strategy to mask underlying quadriceps dysfunction and achieve symmetric hop performance., Objective: To evaluate the performance and propulsion strategies used by females with and those without ACLR during a single-legged triple hop., Design: Cross-sectional study., Setting: Laboratory., Patients or Other Participants: A total of 38 females, 19 with ACLR (age = 19.21 ± 1.81 years, height = 1.64 ± 0.70 m, mass = 63.79 ± 7.59 kg) and 19 without ACLR (control group; age = 21.11 ± 3.28 years, height = 1.67 ± 0.73 m, mass = 67.28 ± 9.25 kg)., Main Outcome Measure(s): Hop distance and limb symmetry index (LSI) were assessed during a single-legged triple hop for distance. Propulsion strategies were evaluated during the first and second hops of the single-legged triple hop. Separate 2-way analysis-of-variance models were used to examine the influence of ACLR, joint, and their interaction on mechanical joint work, moment impulse, and the relative joint contributions to total work and moment impulse in females with and those without a history of ACLR., Results: Despite achieving a mean LSI of approximately 96%, the ACLR group produced less total work in the reconstructed than the uninvolved limb during single-legged triple-hop propulsion (first hop: t18 = -3.73, P = .002; second hop: t18 = -2.55, P = .02). During the first and second hops, the reconstructed knee generated 19.3% (t18 = -2.33, P = .03) and 27.3% (t18 = -4.47, P < .001) less work than the uninvolved knee. No differences were identified between the involved and uninvolved limbs of the ACLR group in moment impulse (first hop: t18 = -0.44, P = .67; second hop: t18 = -0.32; P = .76). Irrespective of limb or group, the ankle was the largest contributor to both work and moment during both the first and second hops (P < .001)., Conclusions: Clinicians should exercise caution when using a single-legged triple hop as a surrogate for restored lower extremity function in females post-ACLR. This recommendation is driven by the compelling findings that knee-joint deficits persisted in the reconstructed limb despite an LSI of approximately 96% and, regardless of previous injury status, single-legged triple-hop propulsion was predominantly driven by the ankle., (© by the National Athletic Trainers' Association, Inc.)

Context: The single-legged triple hop is a commonly used functional task after anterior cruciate ligament reconstruction (ACLR). Recently, researchers have suggested that individuals may use a compensatory propulsion strategy to mask underlying quadriceps dysfunction and achieve symmetric hop performance., Objective: To evaluate the performance and propulsion strategies used by females with and those without ACLR during a single-legged triple hop., Design: Cross-sectional study., Setting: Laboratory., Patients or Other Participants: A total of 38 females, 19 with ACLR (age = 19.21 ± 1.81 years, height = 1.64 ± 0.70 m, mass = 63.79 ± 7.59 kg) and 19 without ACLR (control group; age = 21.11 ± 3.28 years, height = 1.67 ± 0.73 m, mass = 67.28 ± 9.25 kg)., Main Outcome Measure(s): Hop distance and limb symmetry index (LSI) were assessed during a single-legged triple hop for distance. Propulsion strategies were evaluated during the first and second hops of the single-legged triple hop. Separate 2-way analysis-of-variance models were used to examine the influence of ACLR, joint, and their interaction on mechanical joint work, moment impulse, and the relative joint contributions to total work and moment impulse in females with and those without a history of ACLR., Results: Despite achieving a mean LSI of approximately 96%, the ACLR group produced less total work in the reconstructed than the uninvolved limb during single-legged triple-hop propulsion (first hop: t18 = -3.73, P = .002; second hop: t18 = -2.55, P = .02). During the first and second hops, the reconstructed knee generated 19.3% (t18 = -2.33, P = .03) and 27.3% (t18 = -4.47, P < .001) less work than the uninvolved knee. No differences were identified between the involved and uninvolved limbs of the ACLR group in moment impulse (first hop: t18 = -0.44, P = .67; second hop: t18 = -0.32; P = .76). Irrespective of limb or group, the ankle was the largest contributor to both work and moment during both the first and second hops (P < .001)., Conclusions: Clinicians should exercise caution when using a single-legged triple hop as a surrogate for restored lower extremity function in females post-ACLR. This recommendation is driven by the compelling findings that knee-joint deficits persisted in the reconstructed limb despite an LSI of approximately 96% and, regardless of previous injury status, single-legged triple-hop propulsion was predominantly driven by the ankle., (© by the National Athletic Trainers' Association, Inc.)

Background: Tailored, challenging and progressed exercise programs addressing risk factors are recommended for preventing falls in community-dwelling older adults. Knowing the biomechanical demands of exercises commonly performed in efficacious falls prevention programs provides evidence for exercise prescription., Methods: Twenty-one non-sedentary older adults (10 men, 11 women, mean age 69 [SD 5] years) performed five standing exercises (hip abduction, side-step, squat, forward lunge, and side lunge). A biomechanical analysis of the dominant limb was performed to calculate peak joint angles and net joint moments at the ankle, knee and hip in multiple planes. Repeated-measures one-way analyses of variance followed by post-hoc comparisons were performed to identify differences in the calculated variables between exercises., Findings: Peak hip abduction moments during hip abduction were greater than during the forward lunge and squat (P < 0.001). During the side-step, peak plantar flexion moments were greater than the squat and peak hip abduction moments were greater than the squat and forward lunge (P < 0.001). During the squat, peak hip flexion was greatest (P < 0.001) while peak plantar flexion (P < 0.001) and hip abduction moments (P ≤ 0.002) were less than all other exercises. During the forward lunge, peak hip extension moments (P < 0.001) were greatest. During the side lunge, peak knee extension moments were greater than all other exercises (P < 0.001)., Interpretation: These biomechanical data will allow clinicians to tailor exercises for falls prevention to efficiently challenge but not overload muscle groups and minimize exercise prescription redundancies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Institutions sponsoring athletics must be prepared for emergencies. Due to this, more governing bodies are requiring a sports-related emergency action plan (EAP). Yet, the effects of these policies are unknown. We compared adoption of EAPs and associated best practices in Oregon high schools before and after a policy requiring an EAP. Athletic directors were invited to complete a survey during the year before the policy went into effect and again the following year. We assessed whether the school had a written EAP and if they did, was the EAP venue specific, available at the venue, distributed to personnel, and annually reviewed and rehearsed. Pre/post-policy proportions were analyzed using Fisher exact tests for all schools and then schools that completed both surveys. There was a significant increase of schools that reported having an EAP after the policy went into effect (all schools: 55% to 99% [p < 0.001] and schools responding both years: 60% to 98% [p < 0.001]). Venue specific EAPs also significantly increased but only when analyzing all responses (59% to 71% [p = 0.03]). No best practice recommendations related to EAP availability, distribution, review, or rehearsal changed after the policy. Schools met the minimum requirements of the policy, but other related best practices did not significantly improve.

Context: Emerging evidence suggests that a lower quadriceps rate of torque development (RTD) after anterior cruciate ligament (ACL) reconstruction (ACLR) may be associated with altered landing mechanics. However, the influence of quadriceps RTD magnitude and limb symmetry on landing mechanics limb symmetry remains unknown., Objective: To assess the influence of quadriceps RTD magnitude and limb symmetry on limb symmetry in sagittal-plane landing mechanics during functional landing tasks in females with or without ACLR., Design: Cross-sectional study., Setting: Laboratory., Patients or Other Participants: A total of 19 females with ACLR (age = 19.21 ± 1.81 years, height = 164.12 ± 6.97 cm, mass = 63.79 ± 7.59 kg, time after surgery = 20.05 ± 9.50 months) and 19 females serving as controls (age = 21.11 ± 3.28 years, height = 167.26 ± 7.26 cm, mass = 67.28 ± 9.25 kg)., Main Outcome Measure(s): Landing mechanics were assessed during a double-legged (DL) jump-landing task, a single-legged jump-landing task, and a side-cutting task. Quadriceps RTD was collected during isometric muscle contractions. Separate stepwise multiple linear regression models were used to determine the variance in limb symmetry in the sagittal-plane knee moment at initial contact, peak vertical ground reaction force, and loading rate that could be explained by quadriceps RTD magnitude or limb symmetry, group (ACLR or control), and their interaction., Results: In the ACLR group, greater limb symmetry in quadriceps RTD was associated with greater symmetry in sagittal-plane knee moment at initial contact during the DL task (P = .004). Peak vertical ground reaction force and loading rate could not be predicted by quadriceps RTD magnitude or limb symmetry, group, or their interaction during any task., Conclusions: Developing greater symmetry but not magnitude in quadriceps RTD likely enabled more symmetric sagittal-plane knee landing mechanics during the DL task in the ACLR group and thus may reduce the risk of a second ACL injury. Such a protective effect was not found during the single-legged or side-cutting tasks, which may indicate that these tasks do not allow for the compensatory landing mechanism of shifting load to the uninvolved limb that was possible during the DL task., (© by the National Athletic Trainers' Association, Inc.)

Lower explosive quadriceps strength, quantified as rate of torque development (RTD), may contribute to landing mechanics associated with anterior cruciate ligament (ACL) injury risk. However, the association between quadriceps RTD and landing mechanics during high demand tasks remains unclear. Therefore, this study investigated the influence of quadriceps RTD on sagittal plane landing mechanics during double-leg jump landings (DLJL) and single-leg jump cuts (SLJC) in females with and without ACL reconstruction (ACLR). Quadriceps RTD was measured during isometric muscle contractions. Landing mechanics were collected during DLJL and SLJC tasks. Separate stepwise multiple linear regression models determined the amount of variance in sagittal plane landing mechanics that could be explained by quadriceps RTD, group (ACLR or Control), and their interaction. The results indicate that greater quadriceps RTD is associated with lower loading rate ( p = 0.02) and longer time to peak vertical ground reaction force ( p = 0.001) during SLJC, regardless of ACLR status. As greater loading rate may lead to higher risk of ACL injuries and post-traumatic knee osteoarthritis post-ACLR, explosive muscle strength interventions might be useful for individuals with and without ACLR to facilitate the use of safer landing mechanics.

Purpose: A functional test battery (FTB) has been proposed to evaluate the readiness of return to activity after ACLR. However, there is limited evidence documenting the usefulness of an FTB. Therefore, the purpose of the current investigation was to compare knee joint landing biomechanics asymmetry during double-leg jump landing (DLJL) and single-leg jump cutting (SLJC) between healthy females and ACLR females who pass (ACLR-pass) or fail (ACLR-fail) an FTB before and after the completion of a sustained exercise protocol., Method: Eighteen ACLR females (ten ACLR-pass and eight ACLR-fail) and twelve healthy females performed an FTB including The 2000 International Knee Documentation Committee Subjective Knee Evaluation Form, the Knee Outcome Survey Activities of Daily Living Scale, quadriceps strength, and single-leg hop tests. DLJL and SLJC knee joint biomechanics asymmetry were measured before and after exercise., Results: During DLJL, there were significant main effects of group on peak anterior tibial shear force (ATSF) asymmetry [F (2,27)  = 3.86, p < 0.05, [Formula: see text] = 0.214] and peak vertical ground reaction force (vGRF) asymmetry [F (2,27)  = 3.34, p = 0.05, [Formula: see text] = 0.198]. During SLJC, there was a significant group main effect for peak ATSF asymmetry [F (2,27)  = 3.494, p = 0.04, [Formula: see text] = 0.206]., Conclusion: ACLR-fail exhibited greater asymmetry in peak ATSF during DLJL and SLJC compared to healthy females. In addition, ACLR-pass exhibited greater asymmetry in peak ATSF and peak vGRF during DLJL and SLJC, respectively, compared to healthy females. However, ACLR-fail did not exhibit any significant differences in landing biomechanics asymmetry during either task compared with ACLR-pass. Furthermore, the completion of a sustained exercise protocol did not affect knee joint landing biomechanics asymmetry across groups., Level of Evidence: II.

Background: Anterior cruciate ligament (ACL) injury prevention programs (IPPs) are generally accepted as being valuable for reducing injury risk. However, significant methodological limitations of previous meta-analyses raise questions about the efficacy of these programs and the extent to which meeting current best-practice ACL IPP recommendations influences the protective effect of these programs., Purpose: To (1) estimate the protective effect of ACL IPPs while controlling for common methodological limitations of previous meta-analyses and (2) systematically categorize IPP components and factors related to IPP delivery to assess the validity of current best-practice IPP recommendations., Study Design: Systematic review with meta-analysis., Methods: A systematic search of 5 electronic scientific databases was conducted to identify studies testing the efficacy of ACL IPPs. Studies were included if (1) the intervention aimed to prevent ACL injury, (2) the incidence rate (IR) or other outcome data that made it possible to calculate the IR for both the intervention and control groups were reported, and (3) the study design was a prospective randomized controlled trial (RCT) or cluster-RCT., Results: Of the 2219 studies screened, 8 studies were included in the quantitative synthesis, and their analysis revealed a significant reduction in ACL IR when athletes received IPPs (IR ratio = 0.47; 95% CI, 0.30-0.73; P < .001). The majority of included IPPs tended to meet minimum best-practice recommendations and incorporated plyometric, strengthening, and agility exercises along with feedback on proper landing technique. However, the specific exercises included in each IPP and key factors related to IPP delivery were highly variable., Conclusion: Despite limiting the analysis to only high-quality studies and controlling for time at risk and potential clustering effects, the study showed that ACL IPPs had a significant protective effect and reduced injury rates by 53%. However, significant variability in the specific exercises and the manner of program delivery suggests that ACL IPPs may be able to be designed within an overarching best-practice framework. This may allow practitioners the flexibility to develop IPPs that meet the specific characteristics of the target population and potentially increase the likelihood that these programs will be widely adopted and implemented.

Numerous studies have investigated anterior cruciate ligament (ACL) injury risk by examining gender differences in knee and hip biomechanics during a side-step cutting manoeuvre since it is known that ACL injury often occurs during such a task. Recent investigations have also examined lower extremity (LE) biomechanics during side-step cutting in individuals following ACL reconstruction (ACLR). Common research practice is to compare knee and hip biomechanics of the dominant limb between groups but this can add considerable complexity for clinicians and researchers. At this time, it is not known if there is a difference in LE biomechanics between the dominant and non-dominant limb during side-step cutting. Three-dimensional kinematics and kinetics were collected while 31 healthy participants performed five, side-step cutting manoeuvres with the dominant and non-dominant limbs. Knee and hip variables examined are those commonly investigated in ACL injury literature. There were no differences between limbs in all but one variable (knee internal rotation). These results demonstrate that healthy individuals exhibit little side-to-side differences in certain LE biomechanics when performing a side-step cutting manoeuvre. These findings can be utilised by clinicians when conducting dynamic evaluations of their ACLR patients and when developing injury prevention and rehabilitation programmes.

Background: Increasing athletic trainer (AT) services in high schools has attracted widespread interest across the nation as an effective instrument to manage injuries and improve children's health, but there is a lack of evidence on potential medical savings. Our study aimed to address this knowledge gap and provide evidence of AT impacts on medical payments and utilizations to inform public policy decision., Methods: We obtained medical claims of patients aged 14 to 18 years from the 2011-2014 Oregon All Payer All Claims limited dataset. We calculated payer payments and utilizations for medical claims under AT's scope of practice. We used zip codes to link patients with the enrollment boundaries of Oregon public high schools, which were classified as either "AT group" or "non-AT group". We implemented an innovative microsimulation analysis to address the uncertainty of linkage between children and schools., Results: Our analysis included 64,115 and 84,968 eligible children with Medicaid and commercial insurance, respectively. Associated with high school AT services, Medicaid saved an average of $64 per patient during the study period, while commercial insurance payment rarely changed. AT services may reduce emergency visits for both insurance types but increase total visits for commercially insured patients., Conclusions: Our study provides evidence for the differential impacts of AT services on medical payments and utilizations. The legislators should consider to allocate funds for high schools to directly employ ATs. This will encourage ATs to work to their highest ability to improve children's wellbeing while containing avoidable medical cost., Competing Interests: Competing interestsMichael C.Koester (co-author) is a partner in Slocum Center for Orthopedics and Sports Medicine. The other authors have indicated that they have no potential conflict of interest to disclose.

Context: Hiring athletic trainers (ATs) in high schools may lower medical payments by third-party payers such as Medicaid or commercial insurers by reducing injury risks or may increase medical payments due to more referrals to other health care providers. To date, evidence is lacking on the actual financial effect of high school ATs based on an analysis of medical claims., Objective: To assess the overall cost-benefit of hiring ATs in Oregon high schools based on medical claims data across years., Design: Cost-benefit study., Setting: Oregon public high schools., Patients or Other Participants: Patients aged 14 to 18 years old., Main Outcome Measure(s): We analyzed the 2011-2014 limited dataset from the Oregon Health Authority's All Payer All Claims database. Paired t tests were used to compare claims payments at the zip code level between periods of having and not having ATs in Oregon high schools. We also used the percentage of AT effort to adjust for AT investment. The main outcome measure was the return on investment associated with hiring ATs in high schools., Results: The presence of ATs in Oregon high schools may have had different effects on medical payments for Medicaid and commercial insurance. With every dollar invested in hiring ATs in Oregon public high schools from 2011 to 2014, Medicaid payments increased by 24 cents per month at the zip code level, while commercial insurance payments decreased by 24 cents, although the changes were not statistically significant., Conclusions: Hiring ATs in an outreach model for high schools may not necessarily generate medical savings for Medicaid or commercial insurers. Further research is needed to determine if the lack of cost savings in our study was a factor of the employment model, resulted from increased health care utilization, or reflected the need for ATs to deliver more on-site AT services.

The objective was to determine estrogen's influence on control of a skeletal muscle through measurements of motorneuron excitability (H:M ratio) and presynaptic inhibition (PI). Estrogen serum concentrations were measured at menses and ovulation of female subjects and compared to male controls. Data were analyzed from 12 women and 13 men reporting no history of knee ligament injury. Women reported regular menstrual cycles and no hormone-based contraceptive use for the previous year. Women were tested at menses (Time1) and ovulation (Time2). Men were tested twice, approximately 14 days apart. Analysis indicated no difference in the H:M ratio between the sexes at either time point. A significant difference for the sexes was detected in the magnitude of estrogen change (∆EST) between observations. At Time1, the male and female estrogen concentrations were not different; however, they were different at Time2, primarily due to the large rise observed in the women. A significant difference between the sexes was also seen in the magnitude of change for PI (∆PI) between observations. As with EST, the levels of PI between the sexes at Time1 were not different; however, a difference existed at Time 2. Estrogen interacts with GABA at several nervous system locations affecting inhibition of synaptic transmission. This is the first study to investigate changes in PI of a skeletal muscle between times of low and high estrogen. Improving the understanding of estrogen's influence on skeletal muscles may provide answers to why noncontact anterior cruciate ligament injuries of the knee occur more frequently in women., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

In the original publication the name of the fourth reviewer was incorrectly published.

Background: Lower extremity injuries are common among runners. Recent trends in footwear have included minimal and maximal running shoe types. Maximal running shoes are unique because they provide the runner with a highly cushioned midsole in both the rearfoot and forefoot. However, little is known about how maximal shoes influence running biomechanics., Purpose: To examine the influence of maximal running shoes on biomechanics before and after a 5-km (5K) run as compared with neutral running shoes., Study Design: Controlled laboratory study., Methods: Fifteen female runners participated in 2 testing sessions (neutral shoe session and maximal shoe session), with 7 to 10 days between sessions. Three-dimensional kinematic and kinetic data were collected while participants ran along a 10-m runway. After 5 running trials, participants completed a 5K treadmill run, followed by 5 additional running trials. Variables of interest included impact peak of the vertical ground-reaction force, loading rate, and peak eversion. Differences were determined by use of a series of 2-way repeated-measures analysis of variance models (shoe × time)., Results: A significant main effect was found for shoe type for impact peak and loading rate. When the maximal shoe was compared with the neutral shoe before and after the 5K run, participants exhibited an increased loading rate (mean ± SE: pre-maximal shoe, 81.15 body weights/second [BW/s] and pre-neutral shoe, 60.83 BW/s [ P < .001]; post-maximal shoe, 79.10 BW/s and post-neutral shoe, 61.22 BW/s [ P = .008]) and increased impact peak (pre-maximal shoe, 1.76 BW and pre-neutral shoe, 1.58 BW [ P = .004]; post-maximal shoe, 1.79 BW and post-neutral shoe, 1.55 BW [ P = .003]). There were no shoe × time interactions and no significant findings for peak eversion., Conclusion: Runners exhibited increased impact forces and loading rate when running in a maximal versus neutral shoe. Because increases in these variables have been associated with an increased risk of running-related injuries, runners who are new to running in a maximal shoe may be at an increased risk of injury., Clinical Relevance: Understanding the influence of running footwear as an intervention that affects running biomechanics is important for clinicians so as to reduce patient injury., Competing Interests: The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.

Lower extremity injuries have immediate and long-term consequences. Lower extremity movement assessments can assist with identifying individuals at greater injury risk and guide injury prevention interventions. Movement assessments identify similar movement characteristics and evidence suggests large magnitude kinematic relationships exist between movement patterns observed across assessments; however, the magnitude of the relationships for electromyographic (EMG) measures across movement assessments remains largely unknown. This study examined relationships between lower extremity kinematic and EMG measures during jump landings and single leg squats. Lower extremity three-dimensional kinematic and EMG data were sampled from healthy adults (males = 20, females = 20) during the movement assessments. Pearson correlations examined the relationships of the kinematic and EMG measures and paired samples t-tests compared mean kinematic and EMG measures between the assessments. Overall, significant moderate correlations were observed for lower extremity kinematic (r avg  = 0.41, r range  = 0.10-0.61) and EMG (r avg  = 0.47, r range  = 0.32-0.80) measures across assessments. Kinematic and EMG measures were greater during the jump landings. Jump landings and single leg squats place different demands on the body and necessitate different kinematic and EMG patterns, such that these measures are not highly correlated between assessments. Clinicians should, therefore, use multiple assessments to identify aberrant movement and neuromuscular control patterns so that comprehensive interventions can be implemented.

Competing Interests: One or more of the authors have declared the following potential conflicts of interest or source of funding: M.C.K. serves as chair of the National Federation of State High School Associations (NFHS) and Oregon School Activities Association (OSAA) Sports Medicine Advisory Committees. S.T.J. and M.F.N. are members of the OSAA Sports Medicine Advisory Committee. The views expressed in this letter have not been approved or endorsed by the NFHS, OSAA, or their respective Sports Medicine Advisory Committees.

Objectives: Normalization of joint moments to reduce anthropometric influences prior to making group comparisons is a widely-accepted practice. However, a seminal prospective study reported greater non-normalized knee abduction moment (KAM) in nine females who subsequently sustained an ACL injury. It is not clear if this finding may have been influenced by the fact that the ACL-injured females were on average 3.6cm taller and 2.4kg heavier than uninjured females., Design: Cross-sectional., Methods: Peak KAM was identified in thirty-six females completing jump landings. A custom software program randomly divided participants into two groups that were compared on: (1) non-normalized KAM, (2) KAM normalized to body mass, and (3) KAM normalized to body height times weight a total of 500,000 times and the results categorically coded for statistical significance (α≤0.05). For the 10,591 iterations in which one group was 3-4cm taller and 2-3kg heavier, the agreement between results obtained using non-normalized versus normalized data were assessed using non-parametric analyses., Results: Despite moderate-strong agreement between the results obtained using non-normalized and normalized data (Κ=0.614-0.744), a significant effect of normalization on the interpretation of group differences in peak KAM was identified (p<0.001). In 30.4-41.9% of the cases in which non-normalized KAM was deemed significantly different between groups, no group differences were identified when using normalized KAM., Conclusions: While it is unlikely the magnitude of the difference in non-normalized KAM identified prospectively in ACL-injured females was attributable solely to anthropometric differences, caution should be exercised when evaluating research findings reporting non-normalized KAM., (Copyright © 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

Background: Best practice recommendations for sports-related emergency preparation include implementation of venue-specific emergency action plans (EAPs), access to early defibrillation, and first responders-specifically coaches-trained in cardiopulmonary resuscitation and automated external defibrillator (AED) use. The objective was to determine whether high schools had implemented these 3 recommendations and whether schools with a certified athletic trainer (AT) were more likely to have done so., Hypothesis: Schools with an AT were more likely to have implemented the recommendations., Study Design: Cross-sectional study., Level of Evidence: Level 4., Methods: All Oregon School Activities Association member school athletic directors were invited to complete a survey on sports-related emergency preparedness and AT availability at their school. Chi-square and Fisher exact tests were used to analyze the associations between emergency preparedness and AT availability., Results: In total, 108 respondents (37% response rate) completed the survey. Exactly half reported having an AT available. Only 11% (95% CI, 6%-19%) of the schools had implemented all 3 recommendations, 29% (95% CI, 21%-39%) had implemented 2, 32% (95% CI, 24%-42%) had implemented 1, and 27% (95% CI, 19%-36%) had not implemented any of the recommendations. AT availability was associated with implementation of the recommendations (χ 2 = 10.3, P = 0.02), and the proportion of schools with ATs increased with the number of recommendations implemented (χ 2 = 9.3, P < 0.01). Schools with an AT were more likely to implement venue-specific EAPs (52% vs 24%, P < 0.01) and have an AED available for early defibrillation (69% vs 44%, P = 0.02) but not more likely to require coach training (33% vs 28%, P = 0.68)., Conclusions: Despite best practice recommendations, most schools were inadequately prepared for sports-related emergencies. Schools with an AT were more likely to implement some, but not all, of the recommendations. Policy changes may be needed to improve implementation., Clinical Relevance: Most Oregon high schools need to do more to prepare for sports-related emergencies. The results provide evidence for sports medicine professionals and administrators to inform policy changes that ensure the safety of athletes.

Objective: To introduce athletic trainers to the benefits of using a population-based approach to injury and illness prevention and to explore opportunities for partnering with public health professionals on these initiatives., Background: Athletic trainers play leading roles in individual injury and illness prevention but are less familiar with policy development, evaluation, and implementation from a population-level standpoint. The Athletic Training and Public Health Summit was convened to understand, explore, and develop the intersection of athletic training and public health., Conclusions: To further the integration of athletic training within the public health arena, athletic trainers must expand their professional focus beyond the individual to the population level.

Background: The relationships between hip abductor and extensor strength and frontal plane hip and knee motions that are associated with anterior cruciate ligament injury risk are equivocal. However, previous research on these relationships has evaluated relatively low-level movement tasks and peak torque rather than a time-critical strength measure such as the rate of torque development (RTD)., Hypothesis: Females with greater hip abduction and extension RTD would exhibit lesser frontal plane hip and knee motion during a single-leg jump-cutting task., Study Design: Descriptive laboratory study., Methods: Forty recreationally active females performed maximal isometric contractions and single-leg jump-cuts. From recorded torque data, hip extension and abduction RTD was calculated from torque onset to 200 ms after onset. Three-dimensional motion analysis was used to quantify frontal plane hip and knee kinematics during the movement task. For each RTD measure, jump-cut biomechanics were compared between participants in the highest (high) and lowest (low) RTD tertiles., Results: No differences in frontal plane hip and knee kinematics were identified between high and low hip abduction RTD groups. However, those in the high hip extension RTD group exhibited lower hip adduction (high, 3.8° ± 3.0°; low, 6.5° ± 3.0°; P = .019) and knee valgus (high, -2.5° ± 2.3°; low, -4.4° ± 3.2°; P = .046) displacements during the jump-cut., Conclusion: In movements such as cutting that are performed with the hip in a relatively abducted and flexed position, the ability of the gluteus medius to control hip adduction may be compromised. However, the gluteus maximus, functioning as a hip abductor, may take on a pivotal role in controlling hip adduction and knee valgus motion during these types of tasks., Clinical Relevance: Training with a specific emphasis on increasing explosive strength of the hip extensors may be a means through which to improve frontal plane hip and knee control during high-risk maneuvers such as cutting.

Objectives: Despite documented efficacy of injury prevention programs (IPPs) to reduce sport-related lower extremity injury risk, there is evidence of a lack of widespread IPP adoption by high school coaches. This study identified factors related to non-adoption of IPPs by assessing coaches' knowledge, attitudes, and behaviors related to prevention programs and comparing attitudes between adopter and non-adopter coaches., Design: Cross-sectional., Methods: Head soccer and basketball coaches (n=141) from 15 Oregon high schools were invited to complete a web-based survey assessing their IPP-related knowledge, attitudes, and behaviors., Results: Of the 66 coach respondents, 52% reported being aware of IPPs; 21% reported using an IPP with their team; and 9% reported having their student-athletes perform the IPP exactly as designed. No apparent differences in the attitudes toward the importance of injury prevention or the effectiveness of IPPs were identified between coaches that did and did not adopt an IPP. Perceptions that efficacious IPPs do not offer a relative advantage over coaches' existing practices, do not align with coaches' needs (compatibility), and are difficult to implement in their setting (complexity) emerged as key factors underlying coaches' decisions not to adopt a program. Of those that did report adopting an IPP, just 43% (6/14) reported implementing the program as designed., Conclusions: Improving preventative practices of high school coaches requires more than improved dissemination to increase coach awareness. To improve the rate of IPP adoption and implementation fidelity, coach education should directly address issues related to relative advantage, compatibility, and complexity., (Copyright © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

During explosive movements and potentially injurious situations, the ability to rapidly generate torque is critical. Previous research has suggested that different phases of rate of torque development (RTD) are differentiately controlled. However, the extent to which supraspinal and spinal mechanisms predict RTD at different time intervals is unknown. RTD of the plantarflexors across various phases of contraction (i.e., 0-25, 0-50, 0-100, 0-150, 0-200, and 0-250 ms) was measured in 37 participants. The following predictor variables were also measured: (a) gain of the resting soleus H-reflex recruitment curve; (b) gain of the resting homonymous post-activation depression recruitment curve; (c) gain of the GABAergic presynaptic inhibition recruitment curve; (d) the level of postsynaptic recurrent inhibition at rest; (e) level of supraspinal drive assessed by measuring V waves; and (f) the gain of the resting soleus M wave. Stepwise regression analyses were used to determine which variables significantly predicted allometrically scaled RTD. The analyses indicated that supraspinal drive was the dominant predictor of RTD across all phases. Additionally, recurrent inhibition predicted RTD in all of the time intervals except 0-150 ms. These results demonstrate the importance of supraspinal drive and recurrent inhibition to RTD., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Previous observations suggest that females utilize a more erect initial landing posture than males with sex differences in landing posture possibly related to sex-specific energy absorption (EA) strategies. However, sex-specific EA strategies have only been observed when accompanied by sex differences in initial landing posture. This study (a) investigated the potential existence of sex-specific EA strategies; and (b) determined the influences of sex and initial landing posture on the biomechanical determinants of EA. The landing biomechanics of 80 subjects were recorded during drop landings in Preferred, Flexed, and Erect conditions. No sex differences in joint EA were identified after controlling for initial landing posture. Males and females exhibited greater ankle EA during Erect vs Flexed landings with this increase driven by 12% greater ankle velocity, but no change in ankle extensor moment. No differences in hip and knee EA were observed between conditions. However, to achieve similar knee EA, subjects used 7% greater mean knee extensor moment but 9% less knee angular velocity during Flexed landings. The results suggest that sex-specific EA strategies do not exist, and that the magnitude of knee joint EA can be maintained by modulating the relative contributions of joint moment and angular velocity to EA., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The purpose of this study was to examine the relationships between maximum vertical jump height and (a) rate of torque development (RTD) calculated during 2 time intervals, 0-50 milliseconds (RTD50) and 0-200 milliseconds (RTD200) after torque onset and (b) peak torque (PT) for each of the triple extensor muscle groups. Thirty recreationally active individuals performed maximal isometric voluntary contractions (MVIC) of the hip, knee and ankle extensors, and a countermovement vertical jump. Rate of torque development was calculated from 0 to 50 (RTD50) and 0 to 200 (RTD200) milliseconds after the onset of joint torque. Peak torque was identified and defined as the maximum torque value during each MVIC trial. Greater vertical jump height was associated with greater knee and ankle extension RTD50, RTD200, and PT (p ≤ 0.05). However, hip extension RTD50, RTD200, and PT were not significantly related to maximal vertical jump height (p > 0.05). The results indicate that 47.6 and 32.5% of the variability in vertical jump height was explained by knee and ankle extensor RTD50, respectively. Knee and ankle extensor RTD50 also seemed to be more closely related to vertical jump performance than RTD200 (knee extensor: 28.1% and ankle extensor: 28.1%) and PT (knee extensor: 31.4% and ankle extensor: 13.7%). Overall, these results suggest that training specifically targeted to improve knee and ankle extension RTD, especially during the early phases of muscle contraction, may be effective for increasing maximal vertical jump performance.

Greater hamstring musculotendinous stiffness is associated with lesser ACL loading mechanisms. Stiffness is enhanced via training, but previous investigations evaluated tendon rather than musculotendinous stiffness, and none involved the hamstrings. We evaluated the effects of isometric and isotonic training on hamstring stiffness and ACL loading mechanisms. Thirty-six healthy volunteers were randomly assigned to isometric, isotonic, and control groups. Isometric and isotonic groups completed 6 weeks of training designed to enhance hamstring stiffness. Stiffness, anterior tibial translation, and landing biomechanics were measured prior to and following the interventions. Hamstring stiffness increased significantly with isometric training (15.7%; p=0.006), but not in the isotonic (13.5%; p=0.089) or control (0.4%; p=0.942) groups. ACL loading mechanisms changed in manners consistent with lesser loading, but these changes were not statistically significant. These findings suggest that isometric training may be an important addition to ACL injury prevention programs. The lack of significant changes in ACL loading mechanisms and effects of isotonic training were likely due to the small sample sizes per group and limited intervention duration. Future research using larger sample sizes and longer interventions is necessary to determine the effects of enhancing hamstring stiffness on ACL loading and injury risk., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Context: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks., Objective: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury., Design: Cross-sectional study., Setting: Research laboratory., Patients or Other Participants: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg)., Intervention(s): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests., Main Outcome Measure(s): Hamstrings stiffness was normalized to body mass (N/m·kg(-1)). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height., Results: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05)., Conclusions: Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

Context: Eccentric muscle actions of the lower extremity absorb kinetic energy during landing. Greater total sagittal-plane energy absorption (EA) during the initial impact phase (INI) of landing has been associated with landing biomechanics considered high risk for anterior cruciate ligament (ACL) injury. We do not know whether groups with different INI EA magnitudes exhibit meaningful differences in ACL-related landing biomechanics and whether INI EA might be useful to identify ACL injury-risk potential., Objective: To compare biomechanical factors associated with noncontact ACL injury among sagittal-plane INI EA groups and to determine whether an association exists between sex and sagittal-plane INI EA group assignment to evaluate the face validity of using sagittal-plane INI EA to identify ACL injury risk., Design: Descriptive laboratory study., Setting: Research laboratory., Patients or Other Participants: A total of 82 (41 men, 41 women; age = 21.0 ± 2.4 years, height = 1.74 ± 0.10 m, mass = 70.3 ± 16.1 kg) healthy, physically active individuals volunteered., Intervention(s): We assessed landing biomechanics using an electromagnetic motion-capture system and force plate during a double-legged jump-landing task., Main Outcome Measure(s): Total INI EA was used to group participants into high, moderate, and low tertiles. Sagittal- and frontal-plane knee kinematics; peak vertical and posterior ground reaction forces (GRFs); anterior tibial shear force; and internal hip extension, knee extension, and knee varus moments were identified and compared across groups using 1-way analyses of variance. We used a χ (2) analysis to compare male and female representation in the high and low groups., Results: The high group exhibited greater knee-extension moment and posterior GRFs than both the moderate (P < .05) and low (P < .05) groups and greater anterior tibial shear force than the low group (P < .05). No other group differences were noted. Women were not represented more than men in the high group (χ(2) = 1.20, P = .27)., Conclusions: Greater sagittal-plane INI EA likely indicates greater ACL loading, but it does not appear to influence frontal-plane biomechanics related to ACL injury. Women were not more likely than men to demonstrate greater INI EA, suggesting that quantification of sagittal-plane INI EA alone is not sufficient to infer ACL injury-risk potential.

Background: Excessive trunk motion and deficits in neuromuscular control (NMC) of the lumbopelvic hip complex are risk factors for anterior cruciate ligament (ACL) injury. However, the relationship between trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads during a sidestep cutting task has not been examined., Purpose: To determine if there is an association between multiplanar trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads with ACL injury during a sidestep cutting task., Study Design: Descriptive laboratory study., Methods: The hip and knee biomechanics and trunk motion of 30 participants (15 male, 15 female) were analyzed during a sidestep cutting task using an optoelectric camera system interfaced to a force plate. Trunk and lower extremity biomechanics were calculated from the kinematic and ground-reaction force data during the first 50% of the stance time during the cutting task. Pearson product moment correlation coefficients were calculated between trunk and lower extremity biomechanics. Multiple linear regression analyses were carried out to determine the amount of variance in triplanar knee loading explained by trunk motion and hip moments., Results: A greater internal knee varus moment (mean, 0.11 ± 0.12 N·m/kg*m) was associated with less transverse-plane trunk rotation away from the stance limb (mean, 20.25° ± 4.42°; r = -0.46, P = .011) and a greater internal hip adduction moment (mean, 0.33 ± 0.25 N·m/kg*m; r = 0.83, P < .05). A greater internal knee external rotation moment (mean, 0.11 ± 0.08 N·m/kg*m) was associated with a greater forward trunk flexion (mean, 7.62° ± 5.28°; r = 0.42, P = .020) and a greater hip internal rotation moment (mean, 0.15 ± 0.16 N·m/kg*m; r = 0.59, P = .001). Trunk rotation and hip adduction moment explained 81% (P < .05) of the variance in knee varus moment. Trunk flexion and hip internal rotation moment explained 48% (P < .05) of the variance in knee external rotation moment., Conclusion: Limited trunk rotation displacement toward the new direction of travel and hip adduction moment are associated with an increased internal knee varus moment, while a combined increase in trunk flexion displacement and hip internal rotation moment is associated with a higher internal knee external rotation moment., Clinical Relevance: Prevention interventions for ACL injury should encourage trunk rotation toward the new direction of travel and limit excessive trunk flexion while adjusting frontal- and transverse-plane hip NMC.

Context: Greater sagittal-plane energy absorption (EA) during the initial impact phase (INI) of landing is consistent with sagittal-plane biomechanics that likely increase anterior cruciate ligament (ACL) loading, but it does not appear to influence frontal-plane biomechanics. We do not know whether frontal-plane INI EA is related to high-risk frontal-plane biomechanics., Objective: To compare biomechanics among INI EA groups, determine if women are represented more in the high group, and evaluate interplanar INI EA relationships., Design: Descriptive laboratory study., Setting: Research laboratory., Patients or Other Participants: Participants included 82 (41 men, 41 women; age = 21.0 ± 2.4 years, height = 1.74 ± 0.10 m, mass = 70.3 ± 16.1 kg) healthy, physically active volunteers., Intervention(s): We assessed landing biomechanics with an electromagnetic motion-capture system and force plate., Main Outcome Measure(s): We calculated frontal- and sagittal-plane total, hip, knee, and ankle INI EA. Total frontal-plane INI EA was used to create high, moderate, and low tertiles. Frontal-plane knee and hip kinematics, peak vertical and posterior ground reaction forces, and peak internal knee-varus moment (pKVM) were identified and compared across groups using 1-way analyses of variance. We used a χ (2) analysis to evaluate male and female allocation to INI EA groups. We used simple, bivariate Pearson product moment correlations to assess interplanar INI EA relationships., Results: The high-INI EA group exhibited greater knee valgus at ground contact, hip adduction at pKVM, and peak hip adduction than the low-INI EA group (P < .05) and greater peak knee valgus, pKVM, and knee valgus at pKVM than the moderate- (P < .05) and low- (P < .05) INI EA groups. Women were more likely than men to be in the high-INI EA group (χ(2) = 4.909, P = .03). Sagittal-plane knee and frontal-plane hip INI EA (r = 0.301, P = .006) and sagittal-plane and frontal-plane ankle INI EA were associated (r = 0.224, P = .04). No other interplanar INI EA relationships were found (P > .05)., Conclusions: Greater frontal-plane INI EA was associated with less favorable frontal-plane biomechanics that likely result in greater ACL loading. Women were more likely than men to use greater frontal-plane INI EA. The magnitudes of sagittal- and frontal-plane INI EA were largely independent.

Context: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks., Objective: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury., Design: Cross-sectional study., Setting: Research laboratory., Patients or Other Participants: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg)., Intervention(s): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests., Main Outcome Measure(s): Hamstrings stiffness was normalized to body mass (N/m·kg -1 ). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height., Results: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t 22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t 22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t 22 range = 1.729-2.224, P < .05)., Conclusions: Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Purpose: Hormonal fluctuations are one potential reason why females might have a greater rate of noncontact ACL injury. The hamstrings are capable of limiting anterior cruciate ligament (ACL) loading. This study examined whether relationships existed between reproductive hormones (estradiol-β-17, free testosterone, and progesterone) and hamstring neuromechanical variables (hamstring musculotendinous stiffness (MTS), rate of force production (RFP), time to 50% peak torque (T50%), and electromechanical delay (EMD)) in genders combined and independently., Methods: Muscle properties of the hamstrings and reproductive hormones were evaluated in 30 subjects (15 males and 15 females) that were free from lower extremity injury and had no history of ACL injury. Females were tested 3-5 days after the onset of menses and were not using oral contraceptive. Pearson correlation coefficients were calculated for each hormone and muscle property., Results: For genders combined, estrogen (mean = 46.0 ± 28.2 pg/mL) was negatively correlated with RFP (mean = 758.8 ± 507.6 N/kg s(-1), r = -0.43, P = 0.02) and MTS (mean = 12.8 ± 2.6 N/cm, r = -0.43, P = 0.02). Free testosterone (mean = 13.2 ± 13.0 pg/mL) was positively correlated with RFP (r = 0.56, P < 0.01) and MTS (r = 0.46, P = 0.01) but negatively correlated with T50% (mean = 114.7 ± 38.9 ms, r = -0.43, P = 0.02). When gender was considered separately, females demonstrated negative correlation between estrogen (mean = 68.0 ± 23.2 pg/mL) and MTS (mean = 11.7 ± 1.5 N/cm, r = -0.53, P = 0.05) and free testosterone (mean = 1.5 ± 0.6 pg/mL) and MTS (r = -0.52, P = 0.05). Males alone displayed no significant correlations between the selected hormones and muscle properties., Conclusions: Correlations exist between muscle properties and reproductive hormones. Females, however, may be more sensitive to reproductive hormones and their fluctuations.

Objective: To determine the effect of oral contraceptives (OC) on hamstring neuromechanics and lower extremity stiffness across the menstrual cycle (MC)., Design: Causal comparative., Setting: Research laboratory., Participants: Thirty, healthy, normally menstruating female volunteers who were using OC (OC group, n = 15) or not (non-OC group, n = 15)., Assessment of Risk Factors: Stiffness and hamstring neuromechanics were assessed at 2 points of the MC corresponding to low (menses) and high (ovulation) hormone concentrations. Menses testing took place 3 to 5 days after the onset of menses (or pills 3-5 for the OC group). Ovulation test session occurred 2 to 4 days after ovulation identified using a commercial ovulation kit (or pills 15-17 in the OC group)., Main Outcome Measures: Lower extremity stiffness and hamstring neuromechanics [stiffness, electromechanical delay, rate of force production (RFP), time to 50% peak force (T50%)] and blood plasma concentrations of estradiol-β-17, free testosterone, and progesterone., Results: Estradiol-β-17, free testosterone, and progesterone increased at ovulation in the non-OC group and remained constant in the OC group. No changes were observed across the MC or between the groups in other variables (P > 0.05)., Conclusions: Although previous literature suggests a prophylactic effect of OC use with respect to musculoskeletal injury risk, our results indicate that OC use does not affect muscle properties in manners thought to reduce ACL injury risk.

Background: Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively., Methods: Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests., Findings: Anterior tibial translation was correlated with hamstring stiffness (r=-0.538; P=0.002), but not with hamstring strength (r=-0.088; P=0.644). Hamstring stiffness and strength were not correlated (r=0.054; P=0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t(28)=2.186; P<0.037; ES=0.36), but hamstring strength did not differ between these groups (t(28)=1.057; P<0.300; ES=0.17)., Interpretation: Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings' ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Context: A smaller amount of ankle-dorsiflexion displacement during landing is associated with less knee-flexion displacement and greater ground reaction forces, and greater ground reaction forces are associated with greater knee-valgus displacement. Additionally, restricted dorsiflexion range of motion (ROM) is associated with greater knee-valgus displacement during landing and squatting tasks. Because large ground reaction forces and valgus displacement and limited knee-flexion displacement during landing are anterior cruciate ligament (ACL) injury risk factors, dorsiflexion ROM restrictions may be associated with a greater risk of ACL injury. However, it is unclear whether clinical measures of dorsiflexion ROM are associated with landing biomechanics., Objective: To evaluate relationships between dorsiflexion ROM and landing biomechanics., Design: Descriptive laboratory study., Setting: Research laboratory., Patients or Other Participants: Thirty-five healthy, physically active volunteers., Intervention(s): Passive dorsiflexion ROM was assessed under extended-knee and flexed-knee conditions. Landing biomechanics were assessed via an optical motion-capture system interfaced with a force plate., Main Outcome Measure(s): Dorsiflexion ROM was measured in degrees using goniometry. Knee-flexion and knee-valgus displacements and vertical and posterior ground reaction forces were calculated during the landing task. Simple correlations were used to evaluate relationships between dorsiflexion ROM and each biomechanical variable., Results: Significant correlations were noted between extended-knee dorsiflexion ROM and knee-flexion displacement (r  =  0.464, P  =  .029) and vertical (r  =  -0.411, P  =  .014) and posterior (r  =  -0.412, P  =  .014) ground reaction forces. All correlations for flexed-knee dorsiflexion ROM and knee-valgus displacement were nonsignificant., Conclusions: Greater dorsiflexion ROM was associated with greater knee-flexion displacement and smaller ground reaction forces during landing, thus inducing a landing posture consistent with reduced ACL injury risk and limiting the forces the lower extremity must absorb. These findings suggest that clinical techniques to increase plantar-flexor extensibility and dorsiflexion ROM may be important additions to ACL injury-prevention programs.

Background: Greater total energy absorption by the lower extremity musculature during landing may reduce stresses placed on capsuloligamentous tissues with differences in joint contributions to energy absorption potentially affecting anterior cruciate ligament injury risk. However, the relationships between energy absorption and prospectively identified biomechanical factors associated with non-contact anterior cruciate ligament injury have yet to be demonstrated., Methods: Sagittal plane total, hip, knee and ankle energy absorption, and peak vertical ground reaction force, anterior tibial shear force, knee flexion and knee valgus angles, and internal hip extension and knee varus moments were measured in 27 individuals (14 females, 13 males) performing double leg jump landings. Correlation coefficients assessed the relationships between energy absorption during three time intervals (initial impact phase, terminal phase, and total landing) and biomechanical factors related to anterior cruciate ligament injury., Findings: More favorable values of biomechanical factors related to non-contact anterior cruciate ligament injury were associated with: 1) Lesser total (R(2)=0.178-0.558), hip (R(2)=0.229-0.651) and ankle (R(2)=0.280), but greater knee (R(2)=0.147) energy absorption during the initial impact phase; 2) Greater total (R(2)=0.170-0.845), hip (R(2)=0.599), knee (R(2)=0.236-0.834), and ankle (R(2)=0.276) energy absorption during the terminal phase of landing; and 3) Greater knee (R(2)=0.158-0.709), but lesser hip (R(2)=0.309) and ankle (R(2)=0.210-0.319) energy absorption during the total landing period., Interpretation: These results suggest that biomechanical factors related to anterior cruciate ligament injury are influenced by both the magnitude and timing of lower extremity energy absorption during landing., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Normalization of electromyographic (EMG) amplitudes is necessary in the study of human motion. However, there is a lack of agreement on the most reliable and appropriate normalization method. This study evaluated the reliability of single leg stance (SLS) and maximal voluntary isometric contraction (MVIC) normalization methods and the relationship between these measures for the gluteus maximus (GMax), gluteus medius (GMed), rectus femoris (RF), vastus lateralis (VL), hip adductor group (ADD), and biceps femoris (BF). Surface EMG was recorded in 20 subjects during three 5s trials of SLS and MVIC. SLS and MVIC methods both demonstrated good-to-excellent reliability in all muscles (ICCs>0.80). Intrasubject coefficients of variation were lower for the MVIC method (9-36%) than for the SLS method (20-59%). EMG amplitudes during MVIC and SLS were significantly correlated for all muscles (Pearson r's=0.604-0.905, p<0.005) except GMax (r=0.250, p=0.288). Use of SLS normalization for the RF, VL, and BF is not recommended due to a lack of measurement precision. However, this method is justified in the GMax, GMed, and ADD and may provide a better representation of coordinated muscle function during a functional task., ((c) 2009 Elsevier Ltd. All rights reserved.)

The hamstrings limit anterior cruciate ligament (ACL) loading, and neuromuscular control of these muscles is crucial for dynamic knee joint stability. Sex differences in electromechanical delay (EMD) and rate of force production (RFP) have been reported previously, and attributed to differences in musculotendinous stiffness (MTS). These characteristics define the neuromechanical response to joint perturbation, and sex differences in these characteristics may contribute to the greater female ACL injury risk. However, it is unclear if these differences exist in the hamstrings, and the relationship between MTS and neuromechanical function has not been assessed directly. Hamstring MTS, EMD, the time required to produce 50% peak force (Time50%), and RFP were assessed in 20 males and 20 females with no history of ACL injury. EMD did not differ significantly across sex (p=0.788). However, MTS (p<0.001) and RFP (p=0.003) were greater in males, Time50% (p=0.013) was shorter in males, and Time50% was negatively correlated with MTS (r=-0.332, p=0.039). These results suggest that neuromechanical hamstring function in females may limit dynamic knee joint stability, potentially contributing to the greater female ACL injury risk. However, future research is necessary to determine the direct influences of MTS and neuromechanical function on dynamic knee joint stability and ACL injury risk.

Background: Musculotendinous stiffness provides an estimate of resistance to joint perturbation, thus contributing to joint stability. Females demonstrate lesser hamstring stiffness than males, potentially contributing to the sex discrepancy in anterior cruciate ligament injury risk. However, it is unclear if the sex difference in hamstring stiffness is due to differences in muscle size or to inherent/material properties of the musculotendinous unit. It was hypothesized that hamstring stiffness, stress, strain, and elastic modulus would be greater in males than in females, and that hamstring stiffness would be positively correlated with muscle size., Methods: Stiffness was assessed in 20 males and 20 females from the damping effect imposed by the hamstrings on oscillatory knee flexion/extension following joint perturbation. Hamstring length and change in length were estimated via motion capture, and hamstring cross-sectional area was estimated using ultrasound imaging. These characteristics were used to calculate hamstring material properties (i.e., stress, strain, and elastic modulus)., Findings: Stiffness was significantly greater in males than in females (P<0.001). However, stress, strain, and elastic modulus did not differ across sex (P>0.05). Stiffness was significantly correlated with cross-sectional area (r=0.395, P=0.039) and the linear combination of cross-sectional area and resting length (R(2)=0.156, P=0.043)., Interpretation: Male's hamstrings possess a greater capacity for resisting changes in length imposed via joint perturbation from a structural perspective, but this property is similar across sex from a material perspective. Females demonstrate lesser hamstring stiffness compared to males in response to standardized loading conditions, indicating a compromised ability to resist changes in length associated with joint perturbation, and potentially contributing to the higher female ACL injury risk. However, the difference in hamstring stiffness is attributable in large part to differences in muscle size.