Repetitive Impact Research Articles

Numerical investigation of rain droplet impact on offshore wind turbine blades under different rainfall conditions: A parametric study

The leading edge of a fiber composite wind turbine blade (WTB) is prone to erosion damages due to repeated rain droplet impact during its service life. Such damages are critical to the blade’s aerodynamic as well as structural performance, ultimately resulting in substantial repair costs. An effective design of a coating material for WTB is necessary and its analysis must include variables associated with erosive rain droplets such as (1) droplet diameter, (2) impact velocity, and (3) droplet impact angle. The present paper develops and validates a coupled fluid structure interaction (FSI) computational model for simulating rain droplet impact on WTBs, where the structure domain is modelled using conventional finite element method (FEM) and the fluid domain is modelled using smooth particle hydrodynamics (SPH). The 3D numerical model, developed in LS-DYNA, is validated with published experimental results. Further, a parametric study is considered to understand the effects of varying droplet size, impact angles and impact velocities on the impact responses of the leading edge coating system subjected to different rainfall conditions. The rainfall conditions considered for the analysis correspond to four different rainfall intensities (I) – light rainfall (2mm/hr), moderate rainfall (10mm/hr), heavy rainfall (25mm/hr), and very heavy rainfall (50mm/hr). The results show that the impact responses on the coating system increase with increasing droplet size and increasing droplet impact angle with maximum impulses, stresses and damages developed for normal impingement (90°). Also, the effects of droplet impact angles in the range of 50° to 90° are found critical for rainfall intensities representing very heavy rainfall conditions (I>25mm/hr). The results of the peak contact forces and impulses for the above combination of variables used in the numerical study are found in satisfactory agreement with analytical formulations developed through published experiments. Finally, repetitive rain droplet impact analyses are considered and number of impacts required for onset of erosion damages are found to increase by more than seven times upon reducing impact velocities from 140 m/s to 80 m/s for very heavy rainfall conditions (I>25mm/hr). The present study is expected to deliver a validated numerical model that can contribute towards enhancing the erosive capacity of a WTB.

Arc erosion dynamic of island- and skeleton-restricted microstructure evolution modes in Ag–CuO contact materials

Tuning the microstructure to optimize the arc erosion properties of contact materials via the dynamic model is quite important for their application in switches. In this work, we prepared Ag–CuOS (with skeleton CuO) and Ag–CuOI (with island CuO) materials to investigate the effects of microstructure on arc erosion resistance. In parallel, the three-dimensional models of Ag–CuO contacts are reconstructed by phase identification and microstructure analysis, then the arc erosion dynamic of microstructure evolution modes are tracked and studied using computational fluid dynamics (CFD) simulations. Simulation and experiment results both show that the repetitive thermal impact can cause the formation of crater surface and smooth surface in Ag–CuOI and Ag–CuOS, respectively. The local gap of Ag–CuOS contact can work as the driving force to reconstruct CuO skeleton, the newly formed CuO with anisotropic microstructure that can restrict the segregation and evaporation of Ag in molten pool. For the Ag–CuOI contact, the arc erosion merely restructures the initial island of CuO, and the continuous erosion is hardly restricted by this microstructure. Subsequently, we further quantify and evaluate the microstructural continuity of CuO. The results indicate that the CuO microstructure of Ag–CuOS shows a lower continuity coefficient (αnc) and a better continuity than that of Ag–CuOI during the arc erosion process.

Repetitive Subconcussive Head Impact and Neuro-ophthalmology

Repetitive Subconcussive Head Impact and Neuro-ophthalmology

Neuro-Ophthalmologic Response to Repetitive Subconcussive Head Impacts

Subconcussive head impacts have emerged as a complex public health concern. The oculomotor system is sensitive to brain trauma; however, neuro-ophthalmologic response to subconcussive head impacts remains unclear. To examine whether subconcussive head impacts cause impairments in neuro-ophthalmologic function as measured by the King-Devick test (KDT) and oculomotor function as measured by the near point of convergence. In this randomized clinical trial, adult soccer players were randomized into either a heading group or kicking (control) group. The heading group executed 10 headers with soccer balls projected at a speed of 25 mph. The kicking-control group followed the same protocol but with 10 kicks. Peak linear and rotational head accelerations were assessed with a triaxial accelerometer. The KDT speed and error and near point of convergence were assessed at baseline (preheading or prekicking) and at 0, 2, and 24 hours after heading or kicking. Ten soccer-ball headings or kicks. The primary outcome was the group-by-time interaction of KDT speed at 0 hours after heading or kicking. The secondary outcomes included KDT speed at 2 hours and 24 hours after heading or kicking, KDT error, and near point of convergence. A total of 78 individuals enrolled (heading group, n = 40; kicking-control group, n = 38). Eleven individuals (heading group: 4 women; mean [SD] age, 22.5 [1.0] years; kicking-control group, 3 women and 4 men; mean [SD] age, 20.9 [1.1] years) voluntarily withdrew from the study. Data from 67 participants with a mean (SD) age of 20.6 (1.7) years were eligible for analysis (heading, n = 36; kicking-control, n = 31). Mean (SD) peak linear accelerations and peak rotational accelerations per impact for the heading group were 33.2 (6.8) g and 3.6 (1.4) krad/s2, respectively. Conversely, soccer kicking did not induce a detectable level of head acceleration. Both groups showed improvements in KDT speed (heading group: 0 hours, -1.2 [95% CI, -2.2 to -0.1] seconds; P = .03; 2 hours, -1.3 [95% CI, -2.6 to 0] seconds; P = .05; 24 hours, -3.2 [95% CI, -4.3 to -2.2] seconds; P < .001; kicking-control group: 0 hours, -3.3 [95% CI, -4.1 to -2.5] seconds; P < .001; 2 hours, -4.1 [95% CI, -5.1 to -3.1] seconds; P < .001; 24 hours, -5.2 [95% CI, -6.2 to -4.2] seconds; P < .001). Group differences occurred at all postintervention points; the kicking-control group performed KDT faster at 0 hours (-2.2 [95% CI, -0.8 to -3.5] seconds; P = .001), 2 hours (-2.8 [95% CI, -1.2 to -4.4] seconds; P < .001), and 24 hours after the intervention (-2.0 [95% CI, -0.5 to -3.4] seconds; P = .007) compared with those of the heading group. These data support the hypothesis that neuro-ophthalmologic function is affected, at least in the short term, by subconcussive head impacts that may affect some individuals in some contact sports. Further studies may help determine if these measures can be a useful clinical tool in detecting acute subconcussive injury. ClinicalTrials.gov Identifier: NCT03488381.

A novel repetitive head impact exposure measurement tool differentiates player position in National Football League

American-style football participation poses a high risk of repetitive head impact (RHI) exposure leading to acute and chronic brain injury. The complex nature of symptom expression, human predisposition, and neurological consequences of RHI limits our understanding of what constitutes as an injurious impact affecting the integrity of brain tissue. Video footage of professional football games was reviewed and documentation made of all head contact. Frequency of impact, tissue strain magnitude, and time interval between impacts was used to quantify RHI exposure, specific to player field position. Differences in exposure characteristics were found between eight different positions; where three unique profiles can be observed. Exposure profiles provide interpretation of the relationship between the traumatic event(s) and how tissue injury is manifested and expressed. This study illustrates and captures an objective measurement of RHI on the field, a critical component in guiding public policy and guidelines for managing exposure.

Repetitive Impact Wear Behaviors of the Tempered 25Cr3Mo2NiWV Fe-Based Steel

This study aimed to reveal the impact wear behaviors of tempered 25Cr3Mo2NiWV steel. The specimens were subject to various heat treatment processes for generating different mechanical and wear properties. The impact wear tests were performed with an MLD-10 dynamic abrasive wear tester. Worn surface morphologies and micro-cracks of the cross-sections were analyzed by optical microscope and scanning electron microscope. The Vickers hardness of the sample and the impact wear mechanism were also analyzed. The steel with the best combination of hardness and toughness had the lowest wear. With the increase of wear time, the dominant wear mechanism varied from slight plastic deformation to micro-cutting and adhesive wear. Finally, micro fatigue peeling occurred. After impact wear, the cracks could initiate from the surface or the sub-surface. Micrographs of the crack in the cross-section demonstrated two different propagation modes of fatigue fractures. The results showed that the strength and toughness of steel affected the crack propagation, surface spalling, and wear failure mechanism during impact wear.

Erosive Wear Testing of Laser Clad and HVOF Coatings for Drilling in Mining

Drilling is a major cost factor to mining operations (exploration, drill and blast operations), and wear of components is a significant driver of drilling costs. For drilling, the so-called Down-the-Hole (DTH) hammers or Reverse Circulation (RC) hammers are used. These drills break the rock through repetitive impact. Cuttings are removed via a high-velocity air stream. The main wear mechanism for these hammers was found to be erosion. To combat erosive wear, laser clad coatings with a Nimatrix and different-sized fused tungsten carbides FTC (WC/W2C) (angular and spherical) and monocrystalline WC were developed. In addition, hard Fe-based HVOF coatings were investigated. Wear-resistant steel, WCCoCr HVOF, electroplated chrome and a high-chrome cast iron as bulk served as references. An erosion-testing apparatus which follows ASTM G76 was developed. Testing was carried out at incident angles from 15-90°. Coating performance was assessed via volume loss, obtained using 3D profilometry. At low angles, the WCCoCr coating lost the least volume, and at high angles a Ni/WC laser clad coating with spherical FTC provided the best erosion resistance. Imperfections like cracks, pores and voids serve as weak points where material loss out of the surface commences.

True variable-depth milling

When tool wears during machining, cost of the process increases. Rapid tool wear leads to even further contributions to process cost and hence must be taken well care of. Among the many forms of tool wear, notch wear is one that has a big effect on the tool change decision. When the tool contacts the workpiece, a high amount of impact is created where depth of cut is. With continuous machining operations such as turning, the impact may not be as important; however, with interrupted machining operations such as milling, repetitive impact between tool and workpiece occurs at every rotation. Therefore, notch wear can propagate rapidly when milling at a constant depth. When that happens, machine operator would be required to discard the tool and replace it with a fresh one. However, this may not have to be the case, if the depth of cut is varied throughout the milling process (variable-depth milling). Although different patterns of varying the depth of cut can be determined, the easiest route of continuously varying the depth of cut in increasing or decreasing direction should be as effective as any other. While varying the depth of cut, the direction of the variation is also found to have an effect on the end results. In this work, first the theoretical difference between end milling and variable-depth milling is discussed. Afterwards, benefit of using “true variable-depth milling” is explained. Then, machining experiments to quantify such benefits is detailed and the results are presented. It was found that when the same machining conditions were used to end-mill, variable-depth mill, and true variable-depth mill a workpiece, impact of notch wear can be minimized by continuously varying depth of cut in the right direction.

Effects of in vivo fatigue-induced subchondral bone microdamage on the mechanical response of cartilage-bone under a single impact compression

Subchondral bone (SCB) microdamage is prevalent in the joints of human athletes and animals subjected to high rate and magnitude cyclic loading of the articular surface. Quantifying the effect of such focal in vivo fatigue-induced microdamage on the mechanical response of the tissue is critical for the understanding of joint surface injury and the development of osteoarthritis. Thus, we aimed to quantify the mechanical properties of cartilage-bone from equine third metacarpal (MC3) condyles, which is a common area of accumulated microdamage due to repetitive impact loading. We chose a non-destructive technique, i.e. high-resolution microcomputed tomography (µCT) imaging, to identify various degrees of in vivo microdamage in SCB prior to mechanical testing; because µCT imaging can only identify a proportion of accumulated microdamage, we aimed to identify racing and training history variables that provide additional information on the prior loading history of the samples. We then performed unconfined high-rate compression of approximately 2% strain at 45%/s strain rate to simulate a cycle of gallop and used real-time strain measurements using digital image correlation (DIC) techniques to find the stiffness and shock absorbing ability (relative energy loss) of the cartilage-bone unit, and those associated with cartilage and SCB. Results indicated that stiffness of cartilage-bone and those associated with the SCB decreased with increasing grade of damage. Whole specimen stiffness also increased, and relative energy loss decreased with higher TMD, whereas bone volume fraction of the SCB was only associated negatively with the stiffness of the bone. Overall, the degree of subchondral bone damage observed with µCT was the main predictor of stiffness and relative energy loss of the articular surface of the third metacarpal bone of Thoroughbred racehorses under impact loading.

Dynamic fracture of CrN coating by highly-resolved nano-impact

Nano-impact testing has provided localized high strain rate deformation information in either (i) repetitive impact for fatigue of brittle materials or (ii) high-resolution data acquisition of single impacts for energy dissipation and dynamic hardness in ductile materials. The current study focusses on whether high-resolution data acquisition can be used to determine fracture occurring during a single impact event. A PVD CrN coating on 42CrMo4 high speed steel (HSS) was impacted with a cube corner indenter over a range of different acceleration forces. By analyzing the high precision depth-time curves during the first contact phase of the impact, an abrupt depth change was observed at and above 30 mN acceleration force. Focused ion beam technology confirmed through-thickness coating fracture without delamination on tests where the step was observed. The step was absent at lower force or on the more ductile HSS throughout the load range. The fracture dissipated energy and fracture toughness of the coating was estimated under 50 mN acceleration force based on the analysis of impact energy. The calculated dynamic fracture toughness of CrN coating is in the range of 2.75–7.74 MPa·m1/2, depended on the indenter geometry constant, which is comparable with the reported value of about 3.13 MPa·m1/2.

Interactive Effects of Racial Identity and Repetitive Head Impacts on Cognitive Function, Structural MRI-Derived Volumetric Measures, and Cerebrospinal Fluid Tau and Aβ.

BackgroundFactors of increased prevalence among individuals with Black racial identity (e.g., cardiovascular disease, CVD) may influence the association between exposure to repetitive head impacts (RHI) from American football and later-life neurological outcomes. Here, we tested the interaction between racial identity and RHI on neurobehavioral outcomes, brain volumetric measures, and cerebrospinal fluid (CSF) total tau (t-tau), phosphorylated tau (p-tau181), and Aβ1–42 in symptomatic former National Football League (NFL) players.Methods68 symptomatic male former NFL players (ages 40–69; n = 27 Black, n = 41 White) underwent neuropsychological testing, structural MRI, and lumbar puncture. FreeSurfer derived estimated intracranial volume (eICV), gray matter volume (GMV), white matter volume (WMV), subcortical GMV, hippocampal volume, and white matter (WM) hypointensities. Multivariate generalized linear models examined the main effects of racial identity and its interaction with a cumulative head impact index (CHII) on all outcomes. Age, years of education, Wide Range Achievement Test, Fourth Edition (WRAT-4) scores, CVD risk factors, and APOEε4 were included as covariates; eICV was included for MRI models. P-values were false discovery rate adjusted.ResultsCompared to White former NFL players, Black participants were 4 years younger (p = 0.04), had lower WRAT-4 scores (mean difference = 8.03, p = 0.002), and a higher BMI (mean difference = 3.09, p = 0.01) and systolic blood pressure (mean difference = 8.15, p = 0.03). With regards to group differences on the basis of racial identity, compared to White former NFL players, Black participants had lower GMV (mean adjusted difference = 45649.00, p = 0.001), lower right hippocampal volume (mean adjusted difference = 271.96, p = 0.02), and higher p-tau181/t-tau ratio (mean adjusted difference = −0.25, p = 0.01). There was not a statistically significant association between the CHII with GMV, right hippocampal volume, or p-tau181/t-tau ratio. However, there was a statistically significant Race x CHII interaction for GMV (b = 2206.29, p = 0.001), right hippocampal volume (b = 12.07, p = 0.04), and p-tau181/t-tau ratio concentrations (b = −0.01, p = 0.004).ConclusionContinued research on racial neurological disparities could provide insight into risk factors for long-term neurological disorders associated with American football play.

Word-reading ability as a “hold test” in cognitively normal young adults with history of concussion and repetitive head impact exposure: A CARE Consortium Study

Objective: Neuropsychological evaluations include hold tests like word-reading ability as estimates of premorbid intellect thought to be resilient to the effects of neurologic insult. We tested the alternative hypothesis that exposure to concussion or repetitive subclinical head impacts throughout early life may stunt acquisition of word-reading skills.Method: Data were obtained from student–athletes within the CARE Consortium that completed the Wechsler Test of Adult Reading (WTAR). Measures of head trauma burden included self-reported concussion history and cumulative years of exposure to collision sports. We evaluated the effects of head trauma, sociodemographic (race, SES), and academic (SAT/ACT scores, learning disorder) variables on WTAR standard score using linear regression. Analyses were repeated in a football-only subsample estimating age of first exposure to football as a predictor.Results: We analyzed data from 6,598 participants (72.2% white, 39.6% female, mean ± SD age = 18.8 ± 1.2 years). Head trauma variables collectively explained 0.1% of the variance in WTAR standard scores, with years of collision sport exposure weakly predicting lower WTAR standard scores (β = .026–.035, very small effect). In contrast, sociodemographic and academic variables collectively explained 20.9–22.5% of WTAR standard score variance, with strongest effects noted for SAT/ACT scores (β = .313–.337, medium effect), LD diagnosis (β = –.115 to –.131, small effect), and SES (β = .101–.108, small effect). Age of first exposure to football did not affect WTAR scores in a football-only sample.Conclusion: Wechsler Test of Adult Reading performance appears unrelated to history of self-reported concussion(s) and/or repetitive subclinical head trauma exposure in current collegiate athletes. Sociodemographic and academic variables should be incorporated in test score interpretations for diverse populations like athletes.

The Effect of Repetitive Head Impact in Sensory Reweighting in Collision College Athletes

ObjectiveTo compare sensory reweighting for upright stance between collegiate collision and non-contact sport athletes.BackgroundThe potentially adverse effects of repetitive head impact (RHI) exposure through routine collision sport participation have become a major public health concerns.Design/MethodsThirty male collegiate athletes were grouped by sport type, including collision (n = 15, 21.2 ± 2 years, 85.9 ± 13.8 kg, 179.7 ± 8.2 cm) and non-contact (n = 15, 20.8 ± 2.1 years, 72.9 ± 4.8 kg, 178.3 ± 4.3 cm) sport athletes. Participants underwent a standing balance assessment; they experienced simultaneous perturbations to visual, vestibular, and somatosensory systems. The visual stimulus consisted of 500 pyramids displayed on a virtual reality cave and translated in the anterior-posterior direction at 0.2 Hz in a sinusoidal waveform. The vestibular stimulus consisted of binaural-monopolar galvanic vestibular stimulation (GVS) at 0.36 Hz in a sinusoidal waveform. The somatosensory stimulus consisted of bilateral Achilles’ tendon vibration at 0.28 Hz in a square waveform with equal on/off times. Different frequencies were chosen for each modality so that we could calculate the gain to each stimulus independently. There were four conditions: two conditions of each high amplitude (0.2 m) and low amplitude (0.8 m) visual scene translation and two conditions of each vibration on and vibration off. The leg segment gain to each modality was compared between groups and across conditions using a repeated-measures ANOVA.ResultsThere were no changes in leg segment gain to vision (i.e. group effect; F = 2.624, p = 0.094, η2 = 0.086), gain to GVS (F = 1.341, p = 0.266, η2 = 0.46), or gain to vibration (F = 3.124, p = 0.088, η2 = 0.100). In addition, there were no changes in sensory reweighting for any modality (i.e. condition X group effect; vision, F = 0.074, p = 0.788, η2 = 0.003; GVS, F = 0.547, p = 0.46, η2 = 0.019; vibration, F = 0.734, p = 0.399, η2 = 0.026).ConclusionsOur findings suggest that there are no differences in sensory reweighting between collegiate collision and non-contact sport athletes. Despite concerns that RHI exposure through routine collision sport participation may result in balance disturbances, our results do not support this association.

Repetitive head impact exposure and sensory reweighting for upright stance

ObjectiveTo compare sensory reweighting between soccer players who report higher exposure to soccer heading and those who report lower exposure to soccer heading.BackgroundExposure to repetitive head impacts (RHI), such as through routine soccer heading, may have potentially detrimental effects.Design/MethodsThirty participants completed a self-reported questionnaire to estimate the number of RHI sustained weekly, and were divided into low-, medium-, and high-RHI groups based on their responses. Sensory reweighting was compared between low-RHI (N = 10, 4 males, 22.9 ± 3.0 years, 170.5 ± 7.7 cm, 70.0 ± 12.14 kg, 2 ± 2 RHI) and high-RHI groups (N = 10, 5 males, 20.0 ± 1.1 years, 170.4 ± 7.4 cm, 69.6 ± 13.4 kg, 60 ± 37 RHI). Participants experienced a visual stimulus at 0.2 Hz, a ±1 mA binaural monopolar galvanic vestibular stimulus (GVS) at 0.36 Hz, and a vibratory stimulus to their bilateral Achilles tendons at 0.28 Hz during standing. The visual stimulus was presented at different amplitudes (0.2, 0.8 m translation in the anterior-posterior direction) to measure the change in leg gain to vision, gain to vibration, and gain to GVS. A repeated-measures ANOVA was used to compare sensory reweighting between groups.ResultsThere were group differences in sensory reweighting for leg gain to GVS (i.e. condition X group effect; F3,54 = 5.068, p = 0.004, η2 = 0.220), whereby the high-RHI group did not reweight gain to GVS across conditions, and gain to vision (F3,54 = 3.397, p = 0.024, η2 = 0.159), whereby the high-RHI group had higher gains than the low-RHI group in the 0.2 m visual stimulus condition. There were no group differences in sensory reweighting for gain to vibration (F1,18 = 0.045, p = 0.834, η2 = 0.003).ConclusionsRoutine soccer heading is associated with relatively high head accelerations. These results suggest that exposure to frequent RHI may induce adaptation that diminishes reliance on vestibular function. Consequently, visual feedback is upweighted to maintain balance during upright stance.

A Comparison of Football and Rugby Tackling During Spring Ball

ObjectiveThe study examined the effects tackling style has on forces translated to the brain in football and rugby.BackgroundTackling is linked to concussion due to high or repetitive impact forces. A small number of NFL teams are incorporating the rugby tackle mechanics due to keeping the head out of the way. Rugby style tackle use is increasing in football.Design/MethodsA convenient sample of 30 male football and rugby participants from two universities participated in this observational study. 20 football participants (20 ± 1.61 YO, 71.63 ± 2.71 in, 210.84 ± 45.52 lbs.) had impact sensors placed in the helmet (CUE™ Sports Sensor, Athlete Intelligence, Kirkland, WA) and 10 rugby participants (20.22 ± 3.31 YO, 70.78 ± 2.11 in, 211.78 ± 40.62 lbs.) were fitted with an instrumented mouthguard (VECTOR™ Sports Sensor, Athlete Intelligence, Kirkland, WA) during their respective spring seasons. Participants practiced without intervention. Devices were returned to researchers after activity, and the data was uploaded. Welch’s ANOVA with a Games-Howell post-hoc analyzed the data with significance set at 0.05.ResultsFootball participants tallied 3921 impacts over the course of 12 practices, compared to 1868 impacts over 9 practices received by rugby participants. Welch’s ANOVA determined that there is a difference in the frequency of impacts between football and rugby participants (Welch’s F (1, 4119.84) = 29.41, p &lt; 0.001). Football participants encountered linear impacts at 62.95 ± 36.57g. Rugby participants sustained impacts 20.59 ± 15.79g. The Welch’s ANOVA determined a difference in impact force between the football and rugby participants exists (Welch’s F (1, 5741.884) = 3780.385, p &lt; 0.001).ConclusionsImpact frequency appears to be lower in rugby athletes than football athletes during spring ball. Also, the average impact force appears to be less in rugby athletes. The use of a rugby-style tackle generated lower impact forces in athletes when contact occurs.

Academic aptitude mediates the relationship between socioeconomic status and race in predicting ImPACT scores in college athletes

Objective: To evaluate the influences of sociodemographic factors, estimated head impact exposure, and academic aptitude on ImPACT scores in college athletes.Methods: Data were reported on 18,886 participants (58% male) from the NCAA/DoD CARE Consortium. Race, SES, concussion history, estimated repetitive head impact exposure (eRHIE), and academic aptitude (SAT or ACT score) were our predictors of interest. Cognition was measured using ImPACT composite scores. We evaluated the mediating effects of academic aptitude on sociodemographic predictors and eRHIE on ImPACT scores. We then evaluated a football-only subsample and added age of first exposure to football (AFE) to the model. Males, females, and football players were analyzed separately using structural equation modeling.Results: Academic aptitude was associated with Black/African American race, SES, and each of the ImPACT composite scores. There were significant indirect effects of Black/African American race and SES on all ImPACT composite scores. Academic aptitude fully mediated SES effects and either fully or partially mediated race effects. Contrary to expectation, greater concussion history and eRHIE predicted better ImPACT scores.Conclusions: Academic aptitude, a stable indicator of premorbid cognitive function, consistently and most strongly predicted baseline ImPACT scores in collegiate student-athletes. Concussion and eRHIE history demonstrated a small positive, but non-significant, relationship with cognitive scores at the time of college athletic participation. This study suggests that attempts to characterize cognitive ability across the lifespan must consider premorbid functioning and sociodemographic variables.

Understanding the Consequences of Repetitive Subconcussive Head Impacts in Sport: Brain Changes and Dampened Motor Control Are Seen After Boxing Practice.

ObjectivesThe potential effects of exposure to repetitive subconcussive head impacts through routine participation in sport are not understood. To investigate the effects of repetitive subconcussive head impacts we studied boxers following customary training (sparring) using transcranial magnetic stimulation (TMS), decomposition electromyographic (EMG) and tests of memory.MethodsTwenty amateur boxers performed three 3-min sparring bouts. Parameters of brain function and motor control were assessed prior to sparring and again immediately, 1 h and 24 h post-sparring. Twenty control participants were assessed following mock-sparring.ResultsOne hour after sparring boxers showed increased corticomotor inhibition, altered motor unit recruitment strategies, and decreased memory performance relative to controls, with values returning to baseline by the 24 h follow up.ConclusionRepetitive subconcussive head impacts associated with sparring resulted in acute and transient brain changes similar to those previously reported in soccer heading, providing convergent evidence that sport-related head impacts produce a GABAergic response. These acute changes in brain health are reminiscent of effects seen following brain injury, and suggest a potential mechanism underlying the damaging long-term effects of routine repetitive head impacts in sport.

The Effect of Shoe Type and Load Carrying on Electromyographic Activity of Lower Extremity Muscles during Stair Ascent and Descent

Objective Stair ascent and descent is an essential movement task in daily life in which individuals are subjected to repetitive impact forces. The purpose of this study was to evaluate the intensity of Electromyographic (EMG) activity in lower extremity muscles of healthy young men during stair ascent and descent task wearing different type of shoes and carrying loads. Methods Nine men with a mean age of 25.94±3.26 years, mean height of 174±7.4 cm, and mean weight of 70.95±8.25 kg were selected. Four stairs were fabricated and the electromyographic activity of their lower extremity muscles (two muscles in the posterior leg and three quadriceps muscles) in the right side of the body was measured using the 16-channel EMG system MA300 during the task. These tests were conducted in two conditions of with and without load carrying. The load was a cube-shaped box weighing 15% of the body weight. Three cases of footwear were set: barefoot, athletic shoes, and formal shoes. Repeated measure ANOVA was used for data analysis at the significant level of P&lt;0.05. Results The load factor had a significant effect on the intensity of muscle activity. The intensity of muscle activity during ascending stairs was higher than that during descending. In stair descent task, the EMG activity of the vastus medialis muscle was greater than that of the vastus lateralis and rectus femoris muscles, which causes the patella to be pulled inward more leading to patellofemoral articular cartilage wear in the long term. Conclusion Stair ascent puts more pressure on the ankle and knee joints. When carrying the load up stairs, the use of proper shoes can greatly reduce the intensity of muscle activity and delay fatigue. It is, therefore, recommended that people with patellofemoral articular cartilage wear should not use the stairs, if possible.

Enhancing fatigue wear resistance of a bulk metallic glass via introducing phase separation: A micro-impact test analysis

Bulk metallic glasses (BMGs) are potential candidate materials for numerous structural applications. However, this class of materials has a major limitation for engineering applications due to their inferior resistance to fatigue wear. In present work, a novel micro-scale repetitive impact test was utilized for fatigue testing of ZrCu-based BMGs (Zr63.6-xCu18Ni10.4Al8Fex, x = 0, 3, 5 at.%), and specific attention was paid to the micro-alloying effect on wear resistance. Transmission electron microscopy of as-cast Zr58.6Cu18Ni10.4Al8Fe5 revealed amorphous structure with the formation of a second glassy phase of few nanometers in diameter. Although these structural changes have minor effects on hardness and modulus, they have a substantial influence on fatigue wear resistance. Phase separation was found to promote numerous shear bands, which induced strain hardening, and improved the crack resistance. Consequently, all these features are considered to contribute the improved wear resistance. On the contrary, a monolithic glass without Fe addition lacks any microstructural features that can provide means for the local arrest of shear bands and incipient fatigue cracks. These findings improve the understanding of the impact fatigue mechanisms and provide suggestions for the future design of BMGs with excellent wear performance.

Repetitive Head Impacts in Youth Football: Description and Relationship to White Matter Structure.

Few studies have examined white matter with diffusion tensor imaging in 8- to 12-year-old collision sport (CS) athletes. Youth CS athletes will demonstrate change in brain fractional anisotropy (FA) after a season of CS compared with an age-matched noncollision sport (NCS) cohort, and the number, magnitude, and location of hits will correlate with changes in the brain determined via FA for CS athletes. Prospective cohort study. Level 3. Thirty-five 8- to 12-year-old males in a youth tackle football league (CS) and 12 males from local swim teams (NCS) were recruited. Participants underwent brain magnetic resonance imaging with FA before and after the football season. Number, magnitude, and direction of head impacts were recorded for CS participants throughout the season. A total of 1905 hits were recorded in the CS group for the season, 341 (17.9%) collected during 7 games and 1564 (82.1%) observed during 31 practices. No significant interaction between group (CS and NCS) and time (pre- and postseason) was observed for FA (P > 0.05). Correlation analysis revealed a significantly positive and moderate relationship between increase of left cingulate cortex (CgC) FA from pre- to postseason and the total magnitude of lateral head impacts (r = 0.40; P = 0.03). There was no significant change in FA measurement of white matter integrity in a cohort of 8- to 12-year-old males after a season of youth football, nor was any difference detected in FA between youth football players and an age-matched cohort of swimmers. There was a significant correlation between total magnitude of hits sustained by youth football players and an increase in FA in the left CgC; whether this is adaptive or pathologic remains unknown. These data can be used within the body of knowledge to counsel patients regarding the known risks of youth tackle football regarding brain health.