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Arthur Alves Dos Santos, James Sorce, Alexandra Schonning and Grant Bevill

This study evaluated the performance of 6 commercially available hard hat designs—differentiated by shell design, number of suspension points, and suspension tightening system—in regard to their ability to attenuate accelerations during vertical impacts to the head. Tests were conducted with impactor materials of steel, wood, and lead shot (resembling commonly seen materials in a construction site), weighing 1.8 and 3.6 kg and dropped from 1.83 m onto a Hybrid III head/neck assembly. All hard hats appreciably reduced head acceleration to the unprotected condition. However, neither the addition of extra suspension points nor variations in suspension tightening mechanism appreciably influenced performance. Therefore, these results indicate that additional features available in current hard hat designs do not improve protective capacity as related to head acceleration metrics.

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Daniella M. DiGuglielmo, Mireille E. Kelley, Mark A. Espeland, Zachary A. Gregory, Tanner D. Payne, Derek A. Jones, Tanner M. Filben, Alexander K. Powers, Joel D. Stitzel and Jillian E. Urban

To reduce head impact exposure (HIE) in youth football, further understanding of the context in which head impacts occur and the associated biomechanics is needed. The objective of this study was to evaluate the effect of contact characteristics on HIE during player versus player contact scenarios in youth football. Head impact data and time-synchronized video were collected from 4 youth football games over 2 seasons in which opposing teams were instrumented with the Head Impact Telemetry (HIT) System. Coded contact characteristics included the player’s role in the contact, player speed and body position, contact height, type, and direction, and head contact surface. Head accelerations were compared among the contact characteristics using mixed-effects models. Among 72 instrumented athletes, 446 contact scenarios (n = 557 impacts) with visible opposing instrumented players were identified. When at least one player had a recorded impact, players who were struck tended to have higher rotational acceleration than players in striking positions. When both players had a recorded impact, lighter players and taller players experienced higher mean head accelerations compared with heavier players and shorter players. Understanding the factors influencing HIE during contact events in football may help inform methods to reduce head injury risk.

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Meena Makhija, Jasobanta Sethi, Chitra Kataria, Harpreet Singh, Paula M. Ludewig and Vandana Phadke

Two-dimensional fluoroscopic imaging allows measurement of small magnitude humeral head translations that are prone to errors due to optical distortion, out-of-plane imaging, repeated manual identification of landmarks, and magnification. This article presents results from in vivo and in vitro fluoroscopy-based experiments that measure the errors and variability in estimating the humeral head translated position in true scapular plane and axillary views. The errors were expressed as bias and accuracy. The variability with repeated digitization was calculated using the intraclass correlation coefficient (ICC) and the standard error of measurement. Optical distortion caused underestimation of linear distances. The accuracy was 0.11 and 0.43 mm for in vitro and in vivo experiments, respectively, for optical distortion. The intrarater reliability was excellent for both views (ICC = .94 and .93), and interrater reliability was excellent (ICC = .95) for true scapular view but moderate (ICC = .74) for axillary views. The standard error of measurement ranged from 0.27 to 0.58 mm. The accuracy for the humeral head position in 10° out of true scapular plane images ranged from 0.80 to 0.87 mm. The current study quantifies the magnitude of error. The results suggest that suitable measures could be incorporated to minimize errors and variability for the measurement of glenohumeral parameters.

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Katherine A.J. Daniels, Eleanor Drake, Enda King and Siobhán Strike

Cutting maneuvers can be executed at a range of angles and speeds, and these whole-body task descriptors are closely associated with lower-limb mechanical loading. Asymmetries in angle and speed when changing direction off the operated and nonoperated limbs after anterior cruciate ligament reconstruction may therefore influence the interpretation of interlimb differences in joint-level biomechanical parameters. The authors hypothesized that athletes would reduce center-of-mass heading angle deflection and body rotation during the change-of-direction stance phase when cutting from the operated limb, and would compensate for this by orienting their center-of-mass trajectory more toward the new intended direction of travel prior to touchdown. A total of 144 male athletes 8 to 10 months after anterior cruciate ligament reconstruction performed a maximum-effort sidestep cutting maneuver while kinematic, kinetic, and ground reaction force data were recorded. Peak ground reaction force and knee joint moments were lower when cutting from the operated limb. Center-of-mass heading angle deflection during stance phase was reduced for cuts performed from the operated limb and was negatively correlated with heading angle at touchdown. Between-limb differences in body orientation and horizontal velocity at touchdown were also observed. These systematic asymmetries in cut execution may require consideration when interpreting joint-level interlimb asymmetries after anterior cruciate ligament reconstruction and are suggestive of the use of anticipatory control to co-optimize task achievement and mechanical loading.

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Courtney M. Butowicz, Julian C. Acasio and Brad D. Hendershot

Altered trunk movements during gait in persons with lower-limb amputation are often associated with an increased risk for secondary health conditions; however, the postural control strategies underlying such alterations remain unclear. In this secondary analysis, the authors employed nonlinear measures of triplanar trunk accelerations via short-term Lyapunov exponents to investigate trunk local stability as well as spatiotemporal gait parameters to describe gait mechanics. The authors also evaluated the influence of a concurrent task on trunk local stability and gait mechanics to explore if competition for neuromuscular processing resources can assist in identifying unique strategies to control kinematic variability. Sixteen males with amputation—8 transtibial and 8 transfemoral—and 8 uninjured males (controls) walked on a treadmill at their self-selected speed (mean = 1.2 m/s ±10%) in 5 experimental conditions (8 min each): 4 while performing a concurrent task (2 walking and 2 seated) and 1 with no concurrent task. Individuals with amputation demonstrated significantly smaller Lyapunov exponents than controls in all 3 planes of motion, regardless of concurrent task or level of amputation (P < .0001). Individuals with transfemoral amputation walked with wider strides compared with individuals with transtibial amputation and controls (P < .0001). Individuals with amputation demonstrated more trunk kinematic variability in the presence of wider strides compared with individuals without amputation, and it appears that performing a concurrent cognitive task while walking did not change trunk or gait mechanics.

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Yumeng Li, Jupil Ko, Marika A. Walker, Cathleen N. Brown and Kathy J. Simpson

The purpose of the present study was to examine the effect of chronic ankle instability (CAI) on lower-extremity joint coordination and stiffness during landing. A total of 21 female participants with CAI and 21 pair-matched healthy controls participated in the study. Lower-extremity joint kinematics were collected using a 7-camera motion capture system, and ground reaction forces were collected using 2 force plates during drop landings. Coupling angles were computed based on the vector coding method to assess joint coordination. Coupling angles were compared between the CAI and control groups using circular Watson–Williams tests. Joint stiffness was compared between the groups using independent t tests. Participants with CAI exhibited strategies involving altered joint coordination including a knee flexion dominant pattern during 30% and 70% of their landing phase and a more in-phase motion pattern between the knee and hip joints during 30% and 40% and 90% and 100% of the landing phase. In addition, increased ankle inversion and knee flexion stiffness were observed in the CAI group. These altered joint coordination and stiffness could be considered as a protective strategy utilized to effectively absorb energy, stabilize the body and ankle, and prevent excessive ankle inversion. However, this strategy could result in greater mechanical demands on the knee joint.

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Matthew S. Briggs, Claire Spech, Rachel King, Mike McNally, Matthew Paponetti, Sharon Bout-Tabaku and Laura Schmitt

Obese (OB) youth demonstrate altered knee mechanics and worse lower-extremity performance compared with healthy weight (HW) youth. Our objectives were to compare sagittal plane knee landing mechanics between OB and HW youth and to examine the associations of knee and hip extension peak torque with landing mechanics in OB youth. Twenty-four OB and 24 age- and sex-matched HW youth participated. Peak torque was measured and normalized to leg lean mass. Peak knee flexion angle and peak internal knee extension moment were measured during a single-leg hop landing. Paired t tests, Pearson correlation coefficients, and Bonferroni corrections were used. OB youth demonstrated worse performance and lower knee extension (OB: 12.76 [1.38], HW: 14.03 [2.08], P = .03) and hip extension (OB: 8.59 [3.13], HW: 11.10 [2.89], P = .005) peak torque. Furthermore, OB youth demonstrated lower peak knee flexion angles (OB: 48.89 [45.41 to 52.37], HW: 56.07 [52.59 to 59.55], P = .02) and knee extension moments (OB: −1.73 [−1.89 to −1.57], HW: −2.21 [−2.37 to −2.05], P = .0001) during landing compared with HW youth. Peak torque measures were not correlated with peak knee flexion angle nor internal knee extension moment during landing in either group (P > .01). OB youth demonstrated altered landing mechanics compared with HW youth. However, no associations among peak torque measurements and knee landing mechanics were present.

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Jereme B. Outerleys, Michael J. Dunbar, Glen Richardson, Cheryl L. Hubley-Kozey and Janie L. Astephen Wilson

Total knee arthroplasty (TKA) surgery improves knee joint kinematics and kinetics during gait for most patients, but a lack of evidence exists for the level and incidence of improvement that is achieved. The objective of this study was to quantify patient-specific improvements in knee biomechanics relative to osteoarthritis (OA) severity levels. Seventy-two patients underwent 3-dimensional (3D) gait analysis before and 1 year after TKA surgery, as well as 72 asymptomatic adults and 72 with moderate knee OA. A combination of principal component analysis and discriminant analyses were used to categorize knee joint biomechanics for patients before and after surgery relative to asymptomatic, moderate, and severe OA. Post-TKA, 63% were categorized with knee biomechanics consistent with moderate OA, 29% with severe OA, and 8% asymptomatic. The magnitude and pattern of the knee adduction moment and angle (frontal plane features) were the most significant contributors in discriminating between pre-TKA and post-TKA knee biomechanics. Standard of care TKA improves knee biomechanics during gait to levels most consistent with moderate knee OA and predominately targets frontal plane features. These results provide evidence for the level of improvement in knee biomechanics that can be expected following surgery and highlight the biomechanics most targeted by surgery.

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Samantha M. Ross, Ellen Smit, Joonkoo Yun, Kathleen R. Bogart, Bridget E. Hatfield and Samuel W. Logan

A secondary data analysis of 33,093 children and adolescents age 6–17 years (12% with disabilities) from a 2016–2017 National Survey of Children’s Health nonrepresentative sample aimed to identify (a) unique clusters of sociodemographic characteristics and (b) the relative importance of disability status in predicting participation in daily physical activity (PA) and sports. Exploratory classification tree analyses identified hierarchical predictors of daily PA and sport participation separately. Disability status was not a primary predictor of daily PA. Instead, it emerged in the fifth level after age, sex, body mass index, and income, highlighting the dynamic intersection of disability with sociodemographic factors influencing PA levels. In comparison, disability status was a second-level predictor for sport participation, suggesting that unique factors influencing PA level are likely experienced by disabled children and adolescents. The authors employ an intersectionality lens to critically discuss implications for research in adapted PA.