The Behaviour of Stratified Fabrics of Aramid Fibres under Stabbing Conditions.

This paper presents research on several factors influencing the stabbing behaviour of stratified panels made of aramid fabric Twaron® SRM509 Teijin Aramid BV (Arnhem, The Netherlands). The inputs in the test campaign were the number of layers, the impact energy, and the sample size. Tests were performed on small samples (130 mm × 130 mm) on an Instron® CEAST 9350 drop-tower impact system (Norwood, MA, USA) and on larger samples (400 mm × 400 mm) using a test installation with the same values of the impact energy. Knife type S1 was used, with the geometry recommended in NIJ Standard 0115.00 Stab Resistance of Body Armor SEM, and macro photography investigations revealed the failure mechanisms of panel, layers and fibres. A very important conclusion of this study regarding the stabbing performance of fabric Twaron® SRM 509 in particular, but also in general for panels for body protection is that a research study could start on small size samples, with an accurately instrumented machine, in order to establish the influence of significant factors of stab resistance (energy level, number of layers in a panel, etc.), as these samples are less expensive and less time consuming, but the study should be continued to examine larger size samples. The obtained data are useful for the prototype.

Bilateral differences of isokinetic knee extensor strength are velocity- and task-dependent.

The purpose of this study was to investigate the concordance of isokinetic bilateral strength differences of the knee extensors in single- and multi-joint movement tasks. One hundred and nineteen male athletes performed isokinetic legpresses at 0.1 m/s and 0.7 m/s as well as isokinetic knee extensions at 60°/s and 180°/s. Bilateral differences and directed bilateral differences (sign indicating the direction of the difference) were calculated for all measurements. Bland-Altman-Plots were plotted to investigate if the different conditions detect bilateral differences of the same magnitude. Additionally, concordance correlations for the directed bilateral differences of the different tests were calculated to investigate magnitude and direction. The results indicate poor to fair concordance between the bilateral differences in the legpress conditions as well as between single- and multi-joint tasks. The single-joint knee extensions displayed a moderate level of agreement. Bilateral strength differences in isokinetic movement tasks are dependent on movement velocity and the nature of the task (single- or multi-joint movement) in the lower extremities. Both the value and the direction of the strength differences show no clear pattern across the investigated measurements and cannot be used interchangeably. Therefore, to assess interlimb strength balance, multiple different tests should be performed.

On the mechanical significance of vascular imprints of the human neurocranium when impacted at 11 m/s.

The course of the middle meningeal vessels can be traced through imprints on the inner table of the human neurocranium. It is as yet unexplored whether these notches lower the load-bearing capacity of the bone when compared to areas that are free of vascular imprints. Here, 310 temporo-parietal samples with and without vascular imprints, from 52 human Crosado-embalmed cadavers, were tested in a three-point bending setup with a half-cylindrical impactor (1 mm radius of curvature) contacting the sample at 11 m/s. The maximum forces before breaking, and the thicknesses of the samples, were statistically compared, including comparing the avascular group to several groups with vascular imprints of different orientations. Furthermore, the influence of sample length and impact location were investigated. To investigate structure and mechanical function of vascular imprints concomitantly, scanning electron microscopy was performed on selected samples in two different planes. The results showed that avascular samples were on average thicker (p < 0.001) and stronger (p ≤ 0.050) compared to samples with vascular imprints. When only thickness-matched samples were analysed, the observed maximum forces of vascular and avascular samples were statistically similar (p ≥ 0.531). Regarding the load-bearing capacity of samples with vascular imprints, it was irrelevant whether the imprint was placed parallel to and directly underneath the impactor, parallel to and offset from the impactor, or perpendicular to the impactor (p > 0.999). The overall results of this study were statistically unrelated to both sample length (p ≥ 0.720) and impact location (p > 0.999). Scanning electron microscopy revealed that vascular imprints are formed through a curve of the inner table. Perforating holes of the inner table are present in avascular areas, however, they are considerably larger in size and higher in number within vascular imprints. In conclusion, vascular imprints are formed through curving of the inner table. In numerical models of human head mechanics, vascular imprints can be accounted for through a simple thinning of the bone assuming the same load-bearing capacity as for the surrounding imprint-free areas.

The Effect of Supplemental Lighting during the Late Gestation Period on Post-Partum Mechanical Properties of Mare and Foal Guard Hair.

This study investigates Thoroughbred mares exposed or not to supplemental blue light at the end of the gestation. Sixty mares and their 60 foals were selected for the investigation. Guard hair samples were collected from the shoulder just after (within 12 h) the parturition or birth. The foals of the light-treated mares developed significantly (p < 0.05) shorter hair than those of the control mares. A general effect of light treatment on basal hair diameter thinning could be demonstrated (p < 0.005). The maximum force of hair samples of light-treated mares and foals (0.098 and 0.085 N, respectively) was significantly lower than that of the control (0.272 and 0.178 N, respectively). The tensile strength (82.2 N/mm2) of the foal hair samples of the light-treated mares was significantly lower than that of the control foals (121.6 N/mm2). Although no significant difference was found in the elongation (ΔL), the hair of the control animals (mares and foals together) was more elastic than that of the treated animals (335 vs. 262 µm). In conclusion, the supplemental blue light treatment of the pregnant mares has a decreasing effect on both mares and their foals on the mechanical properties of the hair, making it shorter, thinner, and weaker.

Enhancing/Improving Forming Limit Curve and Fracture Height Predictions in the Single-Point Incremental Forming of Al1050 Sheet Material.

Single-point incremental forming (SPIF) has emerged as a cost-effective and rapid manufacturing method, especially suitable for small-batch production due to its minimal reliance on molds, swift production, and affordability. Nonetheless, SPIF's effectiveness is closely tied to the specific characteristics of the employed sheet materials and the intricacies of the desired shapes. Immediate experimentation with SPIF often leads to numerous product defects. Therefore, the pre-emptive use of numerical simulations to predict these defects is of paramount importance. In this study, we focus on the critical role of the forming limit curve (FLC) in SPIF simulations, specifically in anticipating product fractures. To facilitate this, we first construct the forming limit curve for Al1050 sheet material, leveraging the modified maximum force criterion (MMFC). This criterion, well-established in the field, derives FLCs based on the theory of hardening laws in sheet metal yield curves. In conjunction with the MMFC, we introduce a graphical approach that simplifies the prediction of forming limit curves at fracture (FLCF). Within the context of the SPIF method, FLCF is established through both uniaxial tensile deformation (U.T) and simultaneous uniform tensile deformation in bi-axial tensile (B.T). Subsequently, the FLCF predictions are applied in simulations and experiments focused on forming truncated cone parts. Notably, a substantial deviation in fracture height, amounting to 15.97%, is observed between simulated and experimental samples. To enhance FLCF prediction accuracy in SPIF, we propose a novel method based on simulations of truncated cone parts with variable tool radii. A FLCF is then constructed by determining major/minor strains in simulated samples. To ascertain the validity of this enhanced FLCF model, our study includes simulations and tests of truncated cone samples with varying wall angles, revealing a substantial alignment in fracture height between corresponding samples. This research contributes to the advancement of SPIF by enhancing our ability to predict and mitigate product defects, ultimately expanding the applicability of SPIF in diverse industrial contexts.

Investigation and Prediction of Tensile, Flexural, and Compressive Properties of Tough PLA Material Using Definitive Screening Design.

The material extrusion fused deposition modeling (FDM) technique has become a widely used technique that enables the production of complex parts for various applications. To overcome limitations of PLA material such as low impact toughness, commercially available materials such as UltiMaker Tough PLA were produced to improve the parent PLA material that can be widely applied in many engineering applications. In this study, 3D-printed parts (test specimens) considering six different printing parameters (i.e., layer height, wall thickness, infill density, build plate temperature, printing speed, and printing temperature) are experimentally investigated to understand their impact on the mechanical properties of Tough PLA material. Three different standardized tests of tensile, flexural, and compressive properties were conducted to determine the maximum force and Young's modulus. These six properties were used as responses in a design of experiment, definitive screening design (DSD), to build six regression models. Analysis of variance (ANOVA) is performed to evaluate the effects of each of the six printing parameters on Tough PLA mechanical properties. It is shown that all regression models are statistically significant (p<0.05) with high values of adjusted and predicted R2. Conducted confirmation tests resulted in low relative errors between experimental and predicted data, indicating that the developed models are adequately accurate and reliable for the prediction of tensile, flexural, and compressive properties of Tough PLA material.

Age, Gender, Body Mass Index, and Foot Loading During Gait.

Background: The aim was to analyze changes in normal functional parameters of gait analysis by aging, sex, and body mass index (BMI). Methods: A cross-sectional study with a consecutive sample of asymptomatic subjects was performed between 2014 and 2020. Primary outcomes were time and force parameters (contact time and center of force [CoF] time), in the heel, midfoot, and metatarsal areas, measured using an in-office force platform. Results: A total of 156 subjects (312 feet) were included, including 67% of women with a mean age of 47 years. The mean of total contact time was similar in males and females (P = .695) and across BMI (P = .413). Contact time did not show differences by region (P = .648 heel, P = .286 midfoot, and P = .690 metatarsal). CoF time in the heel and metatarsal areas did not change between males and females (P = .288 and P = .879, respectively); meanwhile, it was different in midfoot (P = .002). Maximum force showed a reduction between sexes in the heel (P = .039) but did not in the midfoot and metatarsal areas. By age, differences were detected in the heel and metatarsal areas in females (P = .002 and P = .001) and the metatarsal area in males (P = .001). According to the age groups, total contact time increased in females (P = .001) but not in males (P = .018), and no differences were detected between foot areas. In females, CoF time did not change either foot areas or age groups. In males, CoF time values increased in the midfoot area in the older group (P = .001). Conclusion: Time variables did not change by foot region, independent of age, sex, and BMI. Heel maximum force decreased in females, probably linked to adaptive phenomena by aging. The midfoot remains stable, and acts as an undamaged "bridge." These parameters could be interpreted as normal in asymptomatic subjects. Level of Evidence: Level III, diagnostic and prognostic.

Identifying the role of the reticulospinal tract for strength and motor recovery: A scoping review of nonhuman and human studies.

In addition to the established postural control role of the reticulospinal tract (RST), there has been an increasing interest on its involvement in strength, motor recovery, and other gross motor functions. However, there are no reviews that have systematically assessed the overall motor function of the RST. Therefore, we aimed to determine the role of the RST underpinning motor function and recovery. We performed a literature search using Ovid Medline, Embase, CINAHL Plus, and Scopus to retrieve papers using key words for RST, strength, and motor recovery. Human and animal studies which assessed the role of RST were included. Studies were screened and 32 eligible studies were included for the final analysis. Of these, 21 of them were human studies while the remaining were on monkeys and rats. Seven experimental animal studies and four human studies provided evidence for the involvement of the RST in motor recovery, while two experimental animal studies and eight human studies provided evidence for strength gain. The RST influenced gross motor function in two experimental animal studies and five human studies. Overall, the RST has an important role for motor recovery, gross motor function and at least in part, underpins strength gain. The role of RST for strength gain in healthy people and its involvement in spasticity in a clinical population has been limitedly described. Further studies are required to ascertain the role of the RST's role in enhancing strength and its contribution to the development of spasticity.

Reliability of a Custom Device Used to Measure Isometric Knee Flexor and Extensor Strength in Standing Position.

Background: Assessing lower limb strength in the field is problematic, as the "gold standard assessment" with isokinetic strength is cumbersome, and the device is costly and not transportable and keeps the angle of the hip at around 90°. Methods: We evaluated isometric muscle strength in a standing position with the help of an exoskeleton that holds the subject and makes the test easily repeatable. Results: The optimal device angles for hip and knee were, respectively, 20° and 80° for flexor tests and 30° and 40° for extensor tests. Test-retest reliability was very high for the right knee extensor (ICC 0.96-0.98), left knee extensor (ICC 0.96-0.97), right knee flexor (ICC 0.91-0.96), and left knee flexor (ICC 0.96-0.97). Furthermore, the typical error in percent (T.E.%) ranged from 2.50 to 5.50%, and the change in the mean in percent ranged from 0.84 to 7.72%, making it possible to determine even a slight variation in force. Conclusions: this new method could represent a valid alternative for assessing strength, due to the high reliability and the favorable joint position, particularly in football.

Differences between Maximum Tongue Force in Women Suffering from Chronic and Asymptomatic Temporomandibular Disorders-An Observational Study.

Background: Temporomandibular disorders are craniofacial disorders characterized by the presence of chronic pain in masticatory muscles, with higher incidence in the women population. There is little research that has studied tongue force related to temporomandibular disorders, but there are a lot of studies that have demonstrated the impact of tongue force in vital functions, such as chewing, swallowing, phonation, or breathing. According to this, the aim of this study was to compare the maximum force of the tongue between females with chronic temporomandibular disorders and asymptomatic females. We also wanted to establish whether any relationship existed between the pain and fatigue versus the maximum force developed in females with chronic temporomandibular disorders. Material and methods: A cross-sectional study of 67 women between the ages of 18 and 65 years old was performed. The included women were assigned to one of two groups, according to whether they had chronic temporomandibular disorders or not. The procedure was the same for both groups. Outcome measures included the maximum tongue force, intensity of perceived orofacial pain, and intensity of perceived orofacial fatigue. Results: The results showed significant statistical differences for the maximum tongue force measurement between the chronic temporomandibular disorders group and the control group (p < 0.05) for all the movements, except the lip pressure measurement. Furthermore, the analysis revealed significant statistical differences between the intensity of perceived orofacial fatigue between the groups (p < 0.05). Moreover, the data showed no significant correlations between variables. Conclusion: The study found significant differences in maximum tongue force when comparing women with chronic temporomandibular disorders and asymptomatic women (being superior in these). Likewise, we found that the intensity of perceived orofacial fatigue after tongue exercises showed significant differences between groups. However, this study reveals no correlations between the intensity of perceived orofacial pain and fatigue and the maximum tongue force.

Experimental study of risk of medial hinge fracture during distal femoral varus osteotomy.

INTRODUCTION: Lateral opening wedge distal femoral osteotomy (LOWDFO) is indicated for isolated lateral osteoarthritis in the valgus morphotype. Medial hinge fracture is a factor for poor prognosis. The present study had two aims: (1) to assess the impact of a temporary K-wire on hinge fracture risk; and (2) to assess the impact of LOWDFO opening speed. HYPOTHESIS: The main study hypothesis was that a temporary hinge K-wire reduces hinge fracture risk. The second hypothesis was that faster opening speed increases fracture risk. MATERIAL AND METHOD: Twenty femurs were produced by 3D printing from a CT database, reproducing LOWDFO anatomy. The ABS® polymer showed the same breaking-point behavior as human bone. Ten specimens were included in the "K-wire" group (KW+) and 10 in the "No K-wire" group (KW-). To determine high and low speed, a motion-capture glove was used by 2 operators, providing 3D modeling of the surgeon's hand. High speed was defined as 152mm/min and low speed as 38mm/min. The KW+ and KW- groups were subdivided into high- and low-speed subgroups (HS, LS) of 5 each. Compression tests were conducted using an Instron® mechanical test machine up to hinge fracture. The main endpoint was maximum breaking-point force (N); the secondary endpoints were maximum displacement (mm) and maximum speed (min) at breaking point. RESULTS: The K-wire significantly increased maximum breaking-point force (LS, 143.08N vs. 93.71N, p<0.01; and HS, 186.98N vs. 95.22N, p<0.01), but not maximum displacement (LS, 26.17mm vs. 24.11mm, p=0.31; and HS 26.18mm vs. 23.66mm, p=0.14) or maximum time (LS, 27.07s vs. 24.94s, p=0.31; and HS, 5.24s vs. 4.73s, p=0.14). Speed did not affect maximum force (KW+, 143.08N vs. 186.98N, p=0.06; and KW-, 93.71N vs. 95.22N, p=0.42) or maximum displacement (KW+, 26.17mm vs. 26.18mm, p=1; and KW-, 24.11mm vs. 23.66mm, p=0.69). Only maximum time was greater at low speed (KW+, 27.07s vs. 5.24s, p>0.01; and KW-, 24.94s vs. 4.73s, p<0.01), which is obvious for constant distance. DISCUSSION: The first study hypothesis was confirmed, with significantly lower hinge fracture risk with the K-wire, independently of opening speed. The second hypothesis was not confirmed. The study was performed under strict experimental conditions, unprecedented to our knowledge in the literature. However, complementary clinical studies are needed to confirm the present findings. LEVEL OF EVIDENCE: IV, experimental study.

The Behavior of Glass Fiber Composites under Low Velocity Impacts.

This paper presents experimental results on the behavior of a class of glass fiber composites under low velocity impacts, in order to analyze their usage in designing low velocity impact-resistant components in car and marine industries. Also, a finite element model at the meso level (considering yarn as a compact, homogenous and isotropic material) was run with the help of Ansys Explicit Dynamics in order to point out the stages of the failure and the equivalent stress distribution on the main yarns in different layers of the composite. The composites were manufactured at laboratory scale via the laying-up and pressing method, using a quadriaxial glass fiber fabric (0°/+45°/90°/-45°) supplied by Castro Composites (Pontevedra, Spain) and an epoxy resin. The resin was a two-component resin (Biresin® CR82 and hardener CH80-2) supplied by Sika Group (Bludenz, Austria). The mass ratio for the fabric and panel was kept in the range of 0.70-0.77. The variables for this research were as follows: the number of layers of glass fiber fabric, the impact velocity (2-4 m/s, corresponding to an impact energy of 11-45 J, respectively) and the diameter of the hemispherical impactor (Φ10 mm and Φ20 mm) made of hardened steel. The tests were performed on an Instron CEAST 9340 test machine, and at least three tests with close results are presented. We investigated the influence of the test parameters on the maximum force (Fmax) measured during impact, the time to Fmax and the duration of impact, tf, all considered when the force is falling to zero again. Scanning electron microscopy and photography were used for discussing the failure processes at the fiber (micro) and panel (macro) level. At a velocity impact of 2 m/s (corresponding to an impact energy of 11 J), even the thinner panels (with two layers of quadriaxial glass fiber fabric, 1.64 mm thickness and a surface density of 3.51 kg/m2) had only partial penetration (damages on the panel face, without damage on panel back), but at a velocity impact of 4 m/s (corresponding to an impact energy of 45 J), only composite panels with six layers of quadriaxial fabric (5.25 mm thickness and a surface density of 9.89 kg/m2) presented back faces with only micro-exfoliated spots of the matrix for tests with both impactors. These results encourage the continuation of research on actual components for car and naval industries subjected to low velocity impacts.

A Review of the Analysis of Ground Reaction Force among Adults with Lower Limb Problems (Tinjauan Analisis Daya Tindak Balas Tanah di Kalangan Orang Dewasa dengan Masalah Anggota Bawah) / Jurnal Sains Kesihatan Malaysia

@#The ground reaction force (GRF) is the equal opposing load transfer from the body to the ground, also called vertical load transfer. The GRF would produce stress waves transmitted toward the lower extremities during the heel strike of a gait cycle. Too much force imposed on the lower extremities for an extended period will cause harmful effects such as injuries or alterations in gait. This article presents a review of the literature on GRF analysis among adults with lower limb problems where comparisons between healthy and unhealthy subjects were analyzed, focusing on the compensation in each lower limb. A literature search of published articles in Science Direct and PubMed databases from August 2015 to March 2021 was analyzed. The keywords used for the search were (plantar force OR vertical load transfer OR ground reaction force) AND (lower limb OR lower extremities OR leg OR foot) AND (impairment OR problem OR injury). The literature search identified 22 relevant studies which were screened independently by two reviewers. Lower limb problems such as unilateral transfemoral amputation, unilateral transtibial amputation, patellofemoral pain, anterior cruciate ligament injury, knee arthroplasty, knee osteoarthritis, diabetic foot, total hip replacement, pronated foot proved to alter the GRF significantly. Patients used to shift their weight on the opposite leg as compensation, which acts as a pain-free mechanism. This paper has provided sufficient understanding regarding GRF among adults with lower limb problems. The knowledge concerning compensation may help physical therapists implement the appropriate intervention for patients with lower limb problems.

The force-velocity relationship obtained during the squat jump exercise is meaningfully influenced by the initial knee angle.

This study aimed to compare the magnitude of the force-velocity (F-V) relationship parameters (maximum force [F0], maximum velocity [V0], F-V slope, and maximum power [Pmax]) between the squat jumps (SJ) performed from different knee angles. The F-V relationships of 12 men were assessed in 3 sessions during the SJ performed from a knee angle of 80° (SJ80), 90° (SJ90) and 100° (SJ100). The SJ100 provided likely to very likely higher values of F0 and Pmax compared to SJ80 (86% and 98%, respectively) and SJ90 (73% and 94%, respectively), while unclear and trivial differences were observed for the remaining comparisons. The magnitude of the correlations between the 3 SJ types was very large to nearly perfect for Pmax (r range = 0.864 to 0.940), moderate to very large for F0 (r range = 0.438 to 0.778), and small to large for V0 (r range = 0.361 to 0.642) and the F-V slope (r range = 0.178 to 0.645). These results suggest that the F-V relationship assessed during the SJ exercise is affected by the initial knee angle with the increase of the knee angle from 80° to 100° being associated with higher values of F0 and Pmax, while V0 remains unchanged.

A Comparative Evaluation of Third-Generation Advanced High-Strength Steels for Automotive Forming and Crash Applications.

While the third generation of advanced high-strength steels (3rd Gen AHSS) have increasingly gained attention for automotive lightweighting, it remains unclear to what extent the developed methodologies for the conventional dual-phase (DP) steels are applicable to this new class of steels. The present paper provides a comprehensive study on the constitutive, formability, tribology, and fracture behavior of three commercial 3rd Gen AHSS with an ultimate strength level ranging from 980 to 1180 MPa which are contrasted with two DP steels of the same strength levels and the 590R AHSS. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then evaluated in 3D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen 1180 AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels was similar but with a stark contrast in the local formability whereas the opposite trend was observed for the 3rd Gen 980 and the DP980 steel. The forming limit curves could be accurately predicted using the experimentally measured hardening behavior and the deterministic modified Bressan-Williams through-thickness shear model or the linearized Modified Maximum Force Criterion. The resistance to sliding of the three 3rd Gen AHSS in the Twist Compression Test revealed a comparable coefficient of friction to the 590R except for the electro-galvanized 3rd Gen 1180 V1. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion, biaxial punch tests, and the VDA 238-100 bend test were performed to construct stress-state dependent fracture loci for use in forming and crash simulations. It is demonstrated that, the 3rd Gen 1180 V2 can potentially replace the DP980 steel in terms of both the global and local formability.

Comparison of the strength of various disposable videolaryngoscope blades.

PURPOSE: Breaking of disposable blades during emergency endotracheal intubation has been reported. Breakage can cause serious injury and foreign body ingestion. We aimed to measure and analyze the strength characteristics of different disposable videolaryngoscope blades with the application of an upward-lifting force. METHODS: We measured the strength of four disposable videolaryngoscope blades (C-Mac® S Video laryngoscope MAC #3, Glidescope GVL® 3 stat, Pentax AWS® PBlade TL type, and King Vision® aBlade #3) using the fracture test. The strength of 12 samples of each type of disposable videolaryngoscope blade was measured using an Instron 5,966 tensile tester by applying an upward-lifting force. RESULTS: After the fracture test using C-Mac, Glidescope GVL, Pentax AWS, and King Vision, the number of deformed blades were 0, 12, 3, and 7, respectively, and the number of broken blades were 12, 0, 9, and 5, respectively. The mean (standard deviation) maximum force strengths of Pentax AWS, C-Mac, King Vision, and Glidescope GVL blades were 408.4 (27.4) N, 325.8 (26.5) N, 291.8 (39.3) N, and 262.7 (3.8) N, respectively (P < 0.001). CONCLUSION: Clinicians should be aware of the varied strength characteristics of the four types of disposable videolaryngoscope blades when they are used in endotracheal intubation.

RéSUMé: OBJECTIF: Des bris des lames jetables pendant l'intubation endotrachéale d'urgence ont été rapportés. Un bris peut causer des blessures graves et l'ingestion de corps étrangers. Nous avons cherché à mesurer et à analyser les caractéristiques de résistance de différentes lames de vidéolaryngoscope jetables en appliquant une force de traction vers le haut. MéTHODE: Nous avons mesuré la résistance de quatre lames de vidéolaryngoscope jetables (C-Mac® S Video laryngoscope MAC #3, Glidescope GVL® 3 stat, Pentax AWS® type PBlade TL, et King Vision® aBlade #3) en utilisant un test de rupture. La résistance de 12 échantillons de chaque type de lame de vidéolaryngoscope jetable a été mesurée à l'aide d'un dynamomètre Instron 5,966 en appliquant une force de traction vers le haut. RéSULTATS: Après le test de rupture sur les lames C-Mac, Glidescope GVL, Pentax AWS et King Vision, le nombre de lames déformées était de 0, 12, 3 et 7, respectivement, et le nombre de lames brisées était de 12, 0, 9 et 5, respectivement. Les forces de résistance maximales moyennes (écart type) des lames Pentax AWS, C-Mac, King Vision et Glidescope GVL étaient de 408,4 (27,4) N, 325,8 (26,5) N, 291,8 (39,3) N et 262,7 (3,8) N, respectivement (P < 0,001). CONCLUSION: Les cliniciens devraient être conscients des variations dans les caractéristiques de résistance de ces quatre types de lames de vidéolaryngoscope jetables lors de leur utilisation pour l'intubation endotrachéale.

Are peak ground reaction forces related to better sprint acceleration performance?

This study aimed to elucidate whether the peak (maximum) ground reaction force (GRF) can be used as an indicator of better sprint acceleration performance. Eighteen male sprinters performed 60-m maximal effort sprints, during which GRF for a 50-m distance was collected using a long force platform system. Then, step-to-step relationships of running acceleration with mean and peak GRFs were examined. In the anteroposterior direction, while the mean propulsive force was correlated with acceleration during the initial acceleration phase (to the 5th step) (r = 0.559-0.713), peak propulsive force was only correlated with acceleration at the 9th step (r = 0.481). Moreover, while the mean braking force was correlated with acceleration at the 20th and 22nd steps (r = 0.522 and 0.544, respectively), peak braking force was not correlated with acceleration at all steps. In the vertical direction, significant negative correlations of mean and peak vertical forces with acceleration were found at the same steps (16th, 20th and 22nd step). These results indicate that while the peak anteroposterior force cannot be an indicator of sprint acceleration performance, the peak vertical force is likely an indicator for achieving better acceleration during the later stage of maximal acceleration sprinting.

Magnitude and reliability of mechanical outputs obtained during loaded squat jumps performed from different knee angles.

This study aimed to explore the effect of the knee angle and loading condition on the magnitude and reliability of squat jump (SJ) performance variables. Thirteen male sport sciences students performed in a random order 4 SJ types (knee angle of 80º [SJ80], 90º [SJ90], 100º [SJ100], and self-preferred [SJpref]) against 3 external loads. The push-off distance (HpO), jump height (Hmax), maximum force (Fmax) and maximum power (Pmax) were obtained from force platform recordings. The HpO during the SJpref (43.4 ± 6.4 cm) was always between SJ90 (44.3 ± 4.8 cm) and SJ100 (40.5 ± 4.2 cm). The magnitudes of Hmax, Fmax and Pmax were comparable or higher during the SJpref. The increase of the knee angle was associated with larger values of Fmax and Pmax, but no significant differences were observed for Hmax. An acceptable reliability was observed for HpO (coefficient of variation [CV]≤5.09% and intraclass correlation coefficient [ICC]≥0.78), Hmax (CV≤6.06% and ICC≥0.84), Fmax (CV≤3.25% and ICC≥0.96) and Pmax (CV≤2.93% and ICC≥0.96). Reliability did not systematically differ between the 4 SJ types. In conclusion, the higher magnitudes and comparable reliability of the performance variables obtained during the SJpref support its use for testing lower-body ballistic performance against different loads.

Sensory-to-Motor Overflow: Cooling Foot Soles Impedes Squat Jump Performance.

Evidence from recent studies on animals and humans suggest that neural overflow from the primary sensory cortex (S1) to the primary motor cortex (M1) may play a critical role in motor control. However, it is unclear if whole-body maximal motor tasks are also governed by this mechanism. Maximum vertical squat jumps were performed by 15 young adults before cooling, then immediately following a 15-min cooling period using an ice-water bath for the foot soles, and finally immediately following a 15-min period of natural recovery from cooling. Jump heights were, on average, 3.1 cm lower immediately following cooling compared to before cooling (p = 3.39 × 10-8) and 1.9 cm lower following natural recovery from cooling (p = 0.00124). The average vertical ground reaction force (vGRF) was also lower by 78.2 N in the condition immediately following cooling compared to before cooling (p = 8.1 × 10-5) and 56.7N lower following natural recovery from cooling (p = 0.0043). The current study supports the S1-to-M1 overflow mechanism in a whole-body dynamic jump.