A CASE STUDY OF THE GENERATION OF ANGULAR MOMENTUM AND ANGULAR VELOCITY IN SOMERSAULT BACKWARD STRETCHED WITH 2/1 AND 3/1 TWISTS PERFORMED BY A SINGLE VARSITY MALE GYMNAST

The purpose of this study was to compare the angular momentum and angular velocity in somersault backward stretched with different number of twists performed by a single varsity male gymnast. The 3D motion captured system (Qualisys, 250Hz) was used to collect kinematic data of a single varsity male gymnast A who performed the somersault backward stretched with a double (2/1) and a triple (3/1) twist. The angular momenta and angular velocities of the body segments and whole body were calculated by the Tang’s method. More than a half of the twist angular momentum of the whole body in both 2/1 and 3/1 twists was generated during the take-off phase, which indicated that the gymnast A was classified as a contact twist type. In case of the gymnast A there seemed no difference in angular momenta of 2/1 and 3/1 twists, although he generated the angular momentum of the twist earlier in 3/1 than 2/1. He controlled the number of twists by his body maneuver before landing. Since these findings were obtained from a single gymnast, we need to investigate twist techniques and angular momentum date of various gymnasts

Anterior Limbus Vertebra and Intervertebral Disk Degeneration in Japanese Collegiate Gymnasts

Background: Magnetic resonance imaging (MRI) studies have shown that gymnasts have a high prevalence of radiologicalabnormalities, such as intervertebral disk degeneration (IDD) and anterior limbus vertebra (ALV). These 2 abnormalities may coexistat the same spinal level. However, the relationship between IDD and ALV remains unclear.Hypothesis: A significant relationship exists between IDD and ALV in Japanese collegiate gymnasts.Study Design: Case-control study.Methods: A total of 104 Japanese collegiate gymnasts (70 men and 34 women; age, 19.7 + 1.0 years) with 11.8 + 3.6 years ofsporting experience participated. T1- and T2-weighted MRIs were used to evaluate ALV and IDD.Results: The prevalence among the gymnasts of IDD and ALV was 40.4% (42/104) and 20.2% (21/104), respectively. Theprevalence of IDD was significantly higher in gymnasts with ALV than those without ALV, as determined using the chi-square test.Logistic regression analysis demonstrated a significant association between IDD and ALV (adjusted odds ratio [OR], 6.60; 95%confidence interval [CI], 2.14-20.35). IDD was further grouped by whether it was present in the upper lumbar region (L1-2, L2-3,and L3-4 disks) or in the lower lumbar region (L4-5 and L5-S1 disks). Upper IDD had a greater association with ALV (adjustedOR, 33.17; 95% CI, 7.09-155.25) than did lower IDD (adjusted OR, 6.71; 95% CI, 1.57-28.73).Conclusion: In Japanese collegiate gymnasts, ALV is a predictor of IDD, especially in the upper lumbar region.Clinical Relevance: Information regarding ALV is important to prevent IDD in Japanese collegiate gymnasts.Keywords: endplate lesion; gymnastics; intervertebral disk degeneration; magnetic resonance imagin

On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective

Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, Δ17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10’s of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation

A pristine record of outer Solar System materials from asteroid Ryugu’s returned sample

Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition

A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss

HOW FEMALE COLLAGIATE GYMNASTS GENERATE A DOUBLE TWIST IN THE BACKWARD STRETCHED SOMERSAULT

The purposes of this study were to describe how female gymnasts generate a double twist in the backward stretched somersault and to draw suggestions to improve twist techniques of female gymnasts by analysing female gymnasts twist motion three-dimensionally. Three varsity female gymnasts performed thebackward stretched somersault with a double twist several times and were motion-captured with a Vicon system (250 Hz). The angular velocities and angular momenta of the body segments and whole bodywere calculated, based on the Tang’s method. The female gymnasts of the contact-type twisted the trunk, especially the upper torso largely before the aerial-type onelaterallyflexed her trunk after the toe-off with her right arm swinging down.For female gymnasts who intend to gain larger twist angular momentum or increase it, it is recommended to quickly move the opposite arm and twist the upper torso toward the twist direction during the take-off phase

Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu

International audienceC-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2-7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca-Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics