The Influence of Sport-Related Concussion on Lower Extremity Injury Risk: A Review of Current Return-to-Play Practices and Clinical Implications

International Journal of Exercise Science 13(3): 873-889, 2020. Sport-related concussions (SRCs) are now classified as a major health concern affecting athletes across all sporting levels, with recent evidence suggesting upwards of 3.8 million SRCs occur each year. Multiple injury surveillance datasets have recently determined that athletes post-SRC, compared to non-concussed counterparts, are at greater risk for lower extremity (LE) injury beyond the resolution of traditional SRC assessment batteries. However, it is presently uncertain if common clinical practices (symptom reporting, neuropsychological (NP) examination, and static postural control analysis) can determine athletes at risk for LE injury following an SRC. A comprehensive review of the literature determined that these tools may not reveal subtle cognitive and neuromuscular deficits that lead to subsequent LE injury during dynamic sporting tasks. Current return-to-play (RTP) protocols should consider clarifying the addition of specific objective locomotor analysis, such as gait tasks and sport-specific maneuvers, to determine the risk of LE injury after an athlete has sustained an SRC

The Relationship Between Concussion History and Sex on Lower Extremity Biomechanics During a Cutting Task

Athletes with a history of sports related concussion (SRC) have been shown to exhibit lower extremity (LE) mechanics during high impact landing tasks that are conducive to increased injury risk. The underlying cause, and extent of this phenomena is currently unknown. PURPOSE: The purpose of this study was to analyze the relationship between SRC history and sex on LE biomechanics during a land-and-cut task. METHODS: College athletes with a history of SRC and a control group of healthy athletes matched by sport, position, sex, and age were recruited for this study. Both groups were comprised of 9 males and 11 females. Athletes performed an unanticipated land-and-cut task. The task consisted of each athlete standing on a 60 cm box with a visual stimulus positioned three meters away from the athlete. Various colors (green, pink, blue, and red) were presented as the visual stimulus. Athletes were instructed to only respond to a green or red light. When a red or green light was shown, athletes were instructed to step off the box, land on both limbs and perform a 45-degree cutting movement to the left or right, respectively. Two separate point biserial correlations were conducted (one for each sex) correlating group (0 = control, 1 = SRC) with the following dependent variables: vertical ground reaction force (vGRF), peak knee extensor moment (pKEM), peak knee abduction moment (pKAM), peak ankle dorsiflexion angle (pDF), peak knee flexion angle (pKFA), and peak knee abduction angle (pKA). A linear regression equation was obtained for significant correlations. RESULTS: There was a significant negative moderate correlation between group and KF in males (r = -.69, p \u3c .01). There were no other significant correlations between group and LE biomechanical variables in either males or females (p \u3e .05). A linear regression analysis showed SRC history was a significant predictor of KF (KF = 63.71 – 12.43(group); R2 = .473, p = .002) CONCLUSION: Males in the SRC group were associated with lower KF. Specifically, the regression analysis indicated that males with an SRC history had a predicted 12.4 degree decrease in KF during the land-and-cut task. This suggests previously concussed males may be at increased risk for LE injury

The Influence of Sports-Related Concussion on Lower Extremity Injury Risk in Adolescent and Collegiate Athletes

Sports-related concussion (SRC) represents a major epidemiological concern in the adolescent and collegiate athlete populations, with conservative estimates of approximately four million SRCs occurring each year in the United States. While the majority of previous research has emphasized the management and recovery of the cognitive aspects of SRC, recent data indicates subtle motor behavior is altered following a concussive event. Injury surveillance literature indicates that adolescent and collegiate athletes are at an approximately 2–4 greater risk for lower extremity (LE) injury following an SRC when compared to matched controls and pre-SRC LE injury rates. Furthermore, athletes with a previous SRC history are sustaining high rates of LE injuries at time periods well-beyond clinical clearance to resume sport, in certain cases upwards of one year after SRC occurrence. However, the biomechanical and cognitive mechanisms that underpin the relationship between SRC and LE injury have yet to be fully elucidated by the present literature. Further study of sport-specific tasks, in conjunction with cognitive performance markers, is necessary to provide a mechanistic rationale as to why athletes with SRC histories are sustaining LE injuries at a greater rate than controls. Therefore, multiple literature reviews (Chapters 1–3) were warranted to orient the reader to the current knowledge base surrounding SRC and its associations with LE injury risk. The purposes of the literature reviews were as follows: 1) to provide a comprehensive overview of the current literature relating to SRC; 2) to examine current SRC management strategies and their utility in identifying concussed athletes at-risk for LE injury; and 3) to systematically investigate the influence of cognitive performance on LE injury risk. The overall purpose of these dissertation studies was to identify whether adolescent and collegiate athletes with and without an SRC history demonstrated differences in LE biomechanics and cognitive performance during sport-specific jump-landing maneuvers. Additionally, this dissertation sought to identify biomechanical and cognitive predictors of SRC injury history in collegiate athletes. This dissertation utilized common LE biomechanical and cognitive testing tools to assess whether previously concussed adolescent and collegiate athletes were at greater risk for LE injury compared to non-concussed controls. The first study (Chapter 4) examined group differences in drop-landing biomechanics in adolescent athletes with and without an SRC history. LE kinematic and kinetic patterns previously associated with LE injury risk during landing tasks were measured and it was determined that previously concussed adolescents performed drop-landings with significantly less sagittal plane landing motion versus controls. In the second quantitative study (Chapter 5), the associations between LE landing biomechanics during a land-and-cut task and cognitive performance on various assessments were measured in a collegiate athlete cohort with and without an SRC history. Pearson correlation coefficients indicated significant associations between functional visuomotor reaction time and peak knee flexion, as well as associations between knee abduction moment and computerized cognitive performance, only in collegiate athletes with an SRC history. In the final study (Chapter 6), LE landing biomechanics were measured in collegiate athletes with a previous SRC history and healthy matched controls during a reactionary jump-landing maneuver. Additionally, cognitive performance was measured with a battery of clinical and functional tasks in both cohorts. Group-based (ANOVA) and predictive modeling (binary logistic regression and a C5.0 decision algorithm tree) were implored to identify the most relevant LE landing biomechanics and cognitive performance variables associated with SRC history. Compared to the control cohort, previously concussed collegiate athletes demonstrated significantly less knee flexion on both dominant (DOM) and non-dominant (NDOM) limbs during the land-and-cut tasks. Additionally, Multiple Object Tracking score and knee flexion (binary logistic regression) as well as Verbal Memory, knee flexion, and Go / No Go total score (C5.0 decision tree algorithm) were identified as the strongest indicators of previous SRC injury history. In summary, this dissertation utilized a multifaceted approach to identify subtle biomechanical and cognitive mechanisms in previously concussed athletes that may provide an objective rationale for the relationship between SRC and future LE injury risk. Specifically, adolescent and collegiate athletes performed landing tasks with significantly less sagittal plane motion versus control athlete, suggesting a potential biomechanical mechanism for LE injury after an SRC. Additionally, worsening performance on cognitive measures of working memory and attentional capacity were indicative of a previous SRC history. The present findings suggest clinical management of an SRC should incorporate specific assessments to monitor both motor and cognitive performance in concussed athletes. Future research should examine both pre- and post-SRC biomechanical performance during sport-specific tasks with an imposed cognitive load to further our understanding of LE injury risk in athletes who sustain an SRC

The Relationship Between Concussion History And Lower Extremity Biomechanics During A Land And Cut Task

In high impact landing tasks, athletes with a history of sports related concussion (SRC) have been found to demonstrate lower extremity (LE) biomechanics that are associated with elevated injury risk. However, the exact relationships between SRC history and LE biomechanics are inconclusive. PURPOSE: The purpose of this study was to investigate the relationship between SRC history and LE biomechanics during a cutting task. METHODS: A cohort of athletes with a history of SRC (n=20) and a control group of healthy athletes (n=20) were recruited for this study. The control group were matched by age, sex, and sport. Athletes performed an unanticipated land and cut task. Athletes stood on a 60 cm box and focused on a visual light positioned three meters away from them. The light displayed green, pink, blue, or red. Athletes were instructed to step off the box, land on both limbs, and perform a 45-degree cutting maneuver to left or right when they saw red or green light respectively. A point biserial correlation was conducted correlating group (0 = control, 1 = SRC) with the following dependent variables: dominant limb ground reaction force (D_GRF), dominant limb ankle dorsiflexion angle (D_DF), dominant limb knee flexion angle (D_KFA), dominant limb knee flexion moment (D_KFM), dominant limb knee abduction angle (D_KAA), and dominant limb knee abduction moment (D_KAM). A linear regression equation was obtained for any significant correlations. RESULTS: There was a small significant negative correlation between group and KFA (r = -.342, p \u3c .01). There were no other significant correlations between group and LE biomechanical variables (p \u3e .05). A linear regression analysis showed SRC history as a significant predictor of KFA (KFA = 60.24 - 6.16(group); R2 = 0.117, p = .03). CONCLUSION: The SRC group was associated with lower KFA. According to our regression analysis, athletes with an SRC history had predicted a 6.2 degree decrease in KFA compared to the control group during the land and cut task. Furthermore, approximately 12% of the variance in KFA can be explained by SRC. This suggests that previously concussed athletes may be at a higher risk for LE injury. Further research in this area is needed to confirm this relationship

Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt

The official published version of the article can be accessed at the link below.It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites.Financial support under Grant EP/H026177/1 from the EPSRC

Skilled Throwing Performance: A Test of the OPTIMAL Theory

The OPTIMAL theory of motor learning postulates that autonomy support (AS), enhanced expectancies (EE), and an external focus of attention (EF) facilitate improved motor learning and performance. However, its applicability to elite-level throwing athletes has not been investigated by previous literature. The primary purpose of this study was to investigate the successive implementation of AS, EE, and EF factors on overhand throwing performance in elite collegiate softball athletes (14.44 ± 2.75 years of softball experience). The secondary purpose was to determine whether self-efficacy beliefs would be augmented by factor manipulation. Twenty-four participants threw softballs at a bullseye target during five blocks. The Baseline test (Block 1) was used to subsequently assign participants to either the OPTIMAL or control group. Three middle blocks (Block 2 to 4) followed with successive factor implementation for the OPTIMAL group and without instruction for the control group. The final block (Block 5) served as the Transfer test, at which time throwing distance was increased. During Blocks 2 to 4, the OPTIMAL group was given the choice between softballs (AS), a liberal definition of successful throwing performance (EE), and instructed to focus on the bullseye (EF). Self-efficacy beliefs were assessed after applying the factors and before all blocks. There were no significant differences between the groups in throwing accuracy or self-efficacy scores across all blocks. The results suggest that the OPTIMAL theory does not augment skilled throwing performance or alter self-efficacy in elite softball throwing, potentially attributed to a natural adoption of EF and previously high self-efficacy

Influence of Cognitive Performance on Musculoskeletal Injury Risk: A Systematic Review

Background: While a large number of studies have investigated the anatomic, hormonal, and biomechanical risk factors related to musculoskeletal (MSK) injury risk, there is growing evidence to suggest that cognition is an important injury contributor in the athletic population. A systematic review of the available evidence regarding the influence of cognitive performance on MSK injury risk has yet to be published in the sports medicine literature. Purpose/Hypothesis: The purpose was to determine the effects of cognition on (1) MSK biomechanics during sports-specific tasks and (2) MSK injury occurrence in the athletic population. It was hypothesized that athletes with lower cognitive performance would demonstrate biomechanical patterns suggestive of MSK injury risk and that injured athletes would perform worse on baseline measures of cognition as compared with their noninjured counterparts. Study Design: Systematic review. Methods: PubMed and SPORTDiscus were searched from January 2000 to January 2020. Manual searches were performed on the reference lists of the included studies. A search of the literature was performed for studies published in English that reported MSK biomechanics as a function of cognitive performance and MSK injury occurrence after baseline measures of cognition. Two independent reviewers extracted pertinent study data in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2009 guidelines and assessed study quality using the Quality Assessment Tool for Observational Cohort and Cross-sectional Studies from the National Institutes of Health. A meta-analysis was not performed, owing to the heterogeneous nature of the study designs. Results: Ten studies met inclusion criteria: 4 cognition–MSK biomechanics studies and 6 cognition–MSK injury studies. All 4 cognition–MSK biomechanics studies demonstrated that worse performance on measures of cognition was associated with lower extremity MSK biomechanical patterns suggestive of greater risk for MSK injury. The majority of the cognition–MSK injury studies demonstrated that injured athletes significantly differed on baseline cognition measures versus matched controls or that cognitive performance was a significant predictor for subsequent MSK injury. Conclusion: Although the literature exploring cognitive contributions to MSK injury risk is still in its infancy, it is suggested that sports medicine personnel conduct baseline assessments of cognition—in particular, reaction time and working memory—to identify which athletes may be at elevated risk for future MSK injury

Investigation of Compression Behavior of Mg-4Zn-2(Nd,Gd)-0.5Zr at 350°C by In Situ

As-cast Mg-4Zn-0.5Zr, Mg-4Zn-2Gd-0.5Zr and Mg-4Zn-2Nd-0.5Zr alloys were investigated by in situ synchrotron radiation diffraction during hot compression at 350 °C using the facilities of P07 beamline of Petra III at Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany. The specimens were heated at a rate of 100 K/min and compressed with an initial strain rate of 1.1 x 10$^{3}$ s$^{1}$ up to 30 % strain. The addition of rare earth elements improved the yield strength from 23 MPa in the Mg-4Zn-0.5Zr alloy up to 40 MPa in the alloy with Nd and Gd. Continuous dynamic recrystallization played an important role in the Mg-4Zn-0.5Zr alloy during deformation and twinning was not dominant. Discontinuous dynamic recrystallization was observed in the inthe Mg-4Zn-2Gd-0.5Zr along the grain boundary regions while the grains remained largely without any recrystallization. In the Mg-4Zn-2Gd-0.5Zr and Mg-4Zn-2Nd-0.5Zr alloys the contribution of twinning to deformation was observed at 350 °C. Reasons for these differences will be discussed with respect to microstructures of the alloys

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al-Mg alloys

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 ElsevierThe mechanisms involved in the grain refinement of Al–Mg alloys through varying the Mg content and applying intensive melt shearing were investigated. It was found that the oxide formed in Al–Mg alloys under normal melting conditions is MgAl2O4, which displays an equiaxed and faceted morphology with {1 1 1} planes exposed as its natural surfaces. Depending on the Mg content, MgAl2O4 particles exist either as oxide films in dilute Al–Mg alloys (Mg 1 wt.%). Such MgAl2O4 particles can act as potent sites for nucleation of α-Al grains, which is evidenced by the well-defined cube-on-cube orientation relationship between MgAl2O4 and α-Al. Enhanced heterogeneous nucleation in Al–Mg alloys can be attributed to the high potency of MgAl2O4 particles with a lattice misfit of 1.4% and the increased number density of MgAl2O4 particles due to either natural dispersion by the increased Mg content or forced dispersion through intensive melt shearing. It was also found that intensive melt shearing leads to significant grain refinement of dilute Al–Mg alloys by effective dispersion of the MgAl2O4 particles entrapped in oxide films, but it has marginal effect on the grain refinement of concentrated Al–Mg alloys, where MgAl2O4 particles have been naturally dispersed into individual particles by the increased Mg content.This study is funded from the EPSRC Grant EP/H026177/1