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High-Risk Lower-Extremity Biomechanics Evaluated in Simulated Soccer-Specific Virtual Environments

Christopher A. DiCesare, Adam W. Kiefer, Scott Bonnette, and Gregory D. Myer

Context: Laboratory-based biomechanical analyses of sport-relevant movements such as landing and cutting have classically been used to quantify kinematic and kinetic factors in the context of injury risk, which are then used to inform targeted interventions designed to improve risky movement patterns during sport. However, the noncontextual nature of standard assessments presents challenges for assessing sport-relevant skill transfer. Objective: To examine injury-risk biomechanical differences exhibited by athletes during a jump-landing task performed as part of both a standard biomechanical assessment and a simulated, sport-specific virtual reality (VR)-based assessment. Design: Observational study. Setting: Medical center laboratory. Participants: Twenty-two female adolescent soccer athletes (age = 16.0 [1.4] y, height = 165.6 [4.9] cm, and weight = 60.2 [11.4] kg). Interventions: The landing performance was analyzed for a drop vertical jump task and a VR-based, soccer-specific corner-kick scenario in which the athletes were required to jump to head a virtual soccer ball and land. Main Outcome Measures: Hip, knee, and ankle joint kinematic differences in the frontal and sagittal planes. Results: Athletes exhibited reduced hip and ankle flexion, hip abduction, and frontal plane ankle excursion during landing in realistic sport scenario compared with the standard drop vertical jump task. Conclusion: VR-based assessments can provide a sport-specific context in which to assess biomechanical deficits that predispose athletes for lower-extremity injury and offer a promising approach to better evaluate skill transfer to sport that can guide future injury prevention efforts.

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Differentiating Successful and Unsuccessful Single-Leg Drop Landing Performance Using Uncontrolled Manifold Analysis

Christopher A. DiCesare, Scott Bonnette, Gregory D. Myer, and Adam W. Kiefer

Biomechanical analysis can effectively identify factors associated with task performance and injury risk, but often does not account for the interaction among the components that underlie task execution. Uncontrolled manifold (UCM) analyses were applied to data from 38 female, adolescent athletes performing single-leg drop landings and were used to differentiate successful and unsuccessful task performance by examining the frontal plane joint variance within the UCM (V UCM) that stabilized the horizontal center of mass position (V UCM) and within the orthogonal subspace (V ORT). The UCM revealed stronger coordination, indicated by the V UCM/V ORT ratio, in the successful condition. This may inform future research examining reduced motor coordination in failed movement tasks and its relation to injury risk and allow for targeted interventions that consider coordination processes rather than joint-specific outcomes.

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The Amount and Pattern of Reciprocal Compensations Predict Performance Stability in a Visually Guided Finger Force Production Task

Valéria Andrade, Nicole S. Carver, Francis M. Grover, Scott Bonnette, and Paula L. Silva

Previous work suggests that synergistic activity among motor elements implicated in force production tasks underlies enhanced performance stability associated with visual feedback. A hallmark of synergistic activity is reciprocal compensation, that is, covariation in the states of motor elements that stabilizes critical performance variables. The present study examined if characteristics of reciprocal compensation are indicators of individuals’ capacity to respond adaptively to variations in the resolution of visual feedback about criterion performance. Twenty healthy adults (19.25 ± 1.25 years; 15 females and five males) pressed two sensors with their index fingers to produce a total target force equivalent to 20% of their maximal voluntary contraction under nine conditions that differed in the spatial resolution of real-time feedback about their performance. By combining within-trial uncontrolled manifold and sample entropy analyses, we quantified the amount and degree of irregularity (i.e., non-repetitiveness) of reciprocal compensations over time. We found a U-shaped relationship between performance stability and gain. Importantly, this relationship was moderated by the degree of irregularity of reciprocal compensation. Lower irregularity in reciprocal compensation patterns was related to individuals’ capacity to maintain (or minimize losses in) performance under changes in feedback resolution. Results invite future investigation into how interindividual variations in reciprocal compensation patterns relate to differences in control strategies supporting adaptive responses in complex, visually guided motor tasks.

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A Dynamical Approach to the Uncontrolled Manifold: Predicting Performance Error During Steady-State Isometric Force Production

Francis M. Grover, Valéria Andrade, Nicole S. Carver, Scott Bonnette, Michael A. Riley, and Paula L. Silva

The uncontrolled manifold (UCM) approach quantifies the presence of compensatory variability between musculoskeletal elements involved in a motor task. This approach has proved useful for identifying synergistic control strategies for a variety of everyday motor tasks and for investigating how control strategies are affected by motor pathology. However, the UCM approach is limited in its ability to relate compensatory motor variance directly to task performance because variability along the UCM is mathematically agnostic to performance. We present a new approach to UCM analysis that quantifies patterns of irregularity in the compensatory variability between motor elements over time. In a bimanual isometric force stabilization task, irregular patterns of compensation between index fingers predicted greater performance error associated with difficult task conditions, in particular for individuals who exploited a larger set of compensatory strategies (i.e., a larger subspace of the UCM). This relationship between the amount and structure of compensatory motor variance might be an expression of underlying processes supporting performance resilience.

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Myoelectric Responses of Lower-Body Muscles Performing Squat and Lunge Exercise Variations Adopting Visual Feedback With a Laser Sensor

Gabriel Andrade Paz, Lohanne Almeida, Larissa Ruiz, Sabrina Casseres, Giovanna Xavier, João Lucas, Haroldo Gualter Santana, Humberto Miranda, Scott Bonnette, and Jeffrey Willardson

Study design: Cross-over study. Context: The squat, single-leg squat, forward lunge, and reverse lunge are fundamental movements often performed in activities of daily living, sports competitions, and sport-specific training. Objective: The purpose of this study was to investigate the effect of visual feedback with a laser sensor (VFLS) versus a control condition on the myoelectric activity (surface electromyography [sEMG]) of the vastus medialis oblique (VMO), vastus lateralis, gluteus medius (Gmed), and erector spinae muscles during the performance of several squat variations with bodyweight. Methods: Nineteen female college students (20 [2.5] y, 165.3 [10.2] cm, 66.4 [4.1] kg, 2 [1.2] y of resistance training experience) with a background in strength or sports training volunteered to participate in this study. Over 4 separate visits, subjects performed 2 sets of 10 repetitions of a squat variation exercise in random order (ie, squat, single-leg squat, forward lunge, and reverse lunge). The first set of a given squat variation condition was considered a control set, and then after 3-minute rest, a second set was performed with VFLS. Results: Significant decreases in VMO and Gmed myoelectric activity were observed during the VFLS set versus the control set for the forward lunge exercise (P = .03). No differences were observed between the control set and VFLS set in the sEMG normalized signal for all muscles analyzed for the squat and single-leg squat, respectively. However, the sample entropy of the sEMG signal for the erector spinae became more irregular during the VFLS set versus the control set for the squat exercise (P = .01), whereas the Gmed presented a more irregular sEMG signal during the VFLS set versus the control set for the single-leg squat (P = .08). Conclusion: Laser sensor biofeedback may induce significant decreases in VMO and Gmed activation performing forward lunge exercise. Therefore, laser sensor biofeedback may induce a reduction in muscle activity of neutralizers muscles during a few squat bodyweight variations (bilateral, single-leg, forward, and reverse lunge).

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Injury Risk Factors Integrated Into Self-Guided Real-Time Biofeedback Improves High-Risk Biomechanics

Scott Bonnette, Christopher A. DiCesare, Adam W. Kiefer, Michael A. Riley, Kim D. Barber Foss, Staci Thomas, Katie Kitchen, Jed A. Diekfuss, and Gregory D. Myer

Context: Existing anterior cruciate ligament (ACL) injury prevention programs have failed to reverse the high rate of ACL injuries in adolescent female athletes. Objective: This investigation attempts to overcome factors that limit efficacy with existing injury prevention programs through the use of a novel, objective, and real-time interactive visual feedback system designed to reduce the biomechanical risk factors associated with ACL injuries. Design: Cross-over study. Setting: Medical center laboratory. Participants: A total of 20 females (age = 19.7 [1.34] y; height = 1.74 [0.09] m; weight = 72.16 [12.45] kg) participated in this study. Methods: Participants performed sets of 10 bodyweight squats in each of 8 training blocks (ie, 4 real-time and 4 control blocks) and 3 testing blocks for a total of 110 squats. Feedback conditions were blocked and counterbalanced with half of participants randomly assigned to receive the real-time feedback block first and half receiving the control (sham) feedback first. Results: Heat map analysis revealed that during interaction with the real-time feedback, squat performance measured in terms of key biomechanical parameters was improved compared with performance when participants squatted with the sham stimulus. Conclusions: This study demonstrates that the interactive feedback system guided participants to significantly improve movement biomechanics during performance of a body weight squat, which is a fundamental exercise for a longer term ACL injury risk reduction intervention. A longer training and testing period is necessary to investigate the efficacy of this feedback approach to effect long-term adaptations in the biomechanical risk profile of athletes.

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Movement Regularity Differentiates Specialized and Nonspecialized Athletes in a Virtual Reality Soccer Header Task

Christopher D. Riehm, Scott Bonnette, Michael A. Riley, Jed A. Diekfuss, Christopher A. DiCesare, Andrew Schille, Adam W. Kiefer, Neeru A. Jayanthi, Stephanie Kliethermes, Rhodri S. Lloyd, Mathew W. Pombo, and Gregory D. Myer

Background: Young athletes who specialize early in a single sport may subsequently be at increased risk of injury. While heightened injury risk has been theorized to be related to volume or length of exposure to a single sport, the development of unhealthy, homogenous movement patterns, and rigid neuromuscular control strategies may also be indicted. Unfortunately, traditional laboratory assessments have limited capability to expose such deficits due to the simplistic and constrained nature of laboratory measurement techniques and analyses. Methods: To overcome limitations of prior studies, the authors proposed a soccer-specific virtual reality header assessment to characterize the generalized movement regularity of 44 young female athletes relative to their degree of sport specialization (high vs low). Participants also completed a traditional drop vertical jump assessment. Results: During the virtual reality header assessment, significant differences in center of gravity sample entropy (a measure of movement regularity) were present between specialized (center of gravity sample entropy: mean = 0.08, SD = 0.02) and nonspecialized center of gravity sample entropy: mean = 0.10, SD = 0.03) groups. Specifically, specialized athletes exhibited more regular movement patterns during the soccer header than the nonspecialized athletes. However, no significant between-group differences were observed when comparing participants’ center of gravity time series data from the drop vertical jump assessment. Conclusions: This pattern of altered movement strategy indicates that realistic, sport-specific virtual reality assessments may be uniquely beneficial in exposing overly rigid movement patterns of individuals who engage in repeated sport specialized practice.

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Brain-Behavior Mechanisms for the Transfer of Neuromuscular Training Adaptions to Simulated Sport: Initial Findings From the Train the Brain Project

Dustin R. Grooms, Adam W. Kiefer, Michael A. Riley, Jonathan D. Ellis, Staci Thomas, Katie Kitchen, Christopher A. DiCesare, Scott Bonnette, Brooke Gadd, Kim D. Barber Foss, Weihong Yuan, Paula Silva, Ryan Galloway, Jed A. Diekfuss, James Leach, Kate Berz, and Gregory D. Myer

Context: A limiting factor for reducing anterior cruciate ligament injury risk is ensuring that the movement adaptions made during the prevention program transfer to sport-specific activity. Virtual reality provides a mechanism to assess transferability, and neuroimaging provides a means to assay the neural processes allowing for such skill transfer. Objective: To determine the neural mechanisms for injury risk–reducing biomechanics transfer to sport after anterior cruciate ligament injury prevention training. Design: Cohort study. Setting: Research laboratory. Participants: Four healthy high school soccer athletes. Interventions: Participants completed augmented neuromuscular training utilizing real-time visual feedback. An unloaded knee extension task and a loaded leg press task were completed with neuroimaging before and after training. A virtual reality soccer-specific landing task was also competed following training to assess transfer of movement mechanics. Main Outcome Measures: Landing mechanics during the virtual reality soccer task and blood oxygen level–dependent signal change during neuroimaging. Results: Increased motor planning, sensory and visual region activity during unloaded knee extension and decreased motor cortex activity during loaded leg press were highly correlated with improvements in landing mechanics (decreased hip adduction and knee rotation). Conclusion: Changes in brain activity may underlie adaptation and transfer of injury risk–reducing movement mechanics to sport activity. Clinicians may be able to target these specific brain processes with adjunctive therapy to facilitate intervention improvements transferring to sport.