Understanding the first injury in athletics and its effect on dropout from sport:An online survey on 544 high-level youth and junior athletics (track and field) athletes

Objective To describe the first injury and to investigate whether it plays a role in altering athletics’ sustainable practice.Methods We conducted a cross-sectional study using an exploratory survey on the first injury and its consequences on athletics practice. In 2021, we asked all high-level athletes licensed with the French Federation of Athletics (FFA) under 18 years, under 20 years and under 23 years categories between 2007 and 2021.Results Out of 6560 emails sent by FFA, 544 athletes responded, and 93.6% (n=510) reported experiencing at least one injury during their career. The first injury occurred at a mean age of 17.5±3.3 years after 6.1±4.1 years of athletics practice. The main locations of the first injury were the posterior thigh (28.9%), the ankle (16.5%) and the knee (12.6%), and the principal reported injury types were muscle (37.7%), tendon (17.5%) and ligament (15.5%). More than a third of injured athletes (36.7%) reported experiencing ongoing symptoms or sequelae after their first injury, and about half (48.5%) experienced recurrences. About 20% had stopped athletics at the time of the survey, with injury problems the primary cause of athletes dropping out (46.2%), including the first injury (9.4%).Conclusions Injuries played an important role in altering sustainable athletics practice, with injury accounting for about 50% of all reported dropouts and the first injury accounting for about 10% of all reported causes. Our results provide evidence to target the prevention of the first injury, which could be considered the origin of the ‘vicious circle’ of injuries

Efficiency of knee braces: A biomechanical approach based on computational modeling.

International audienceThe knee is the largest joint in the body and is vulnerable to injury during athletic activities or to musculoskeletal conditions such as arthrosis. Knee orthotic devices are widely used by physicians as preventive and therapeutic adjuncts for both musculoskeletal conditions and sport injuries. Their goal is to stabilize or restrict non-physiological knee ranges of motion. The efficiency of these devices has been studied both from clinical and biomechanical perspectives, leading to controversial results from questionable methods. As for now, the mechanisms of force transfer from the device to the joint bones have never been characterized and both device manufacturers and clinicians still expect a standard procedure to compare and grade the efficiency of different knee braces. The objectives of this work are: 1. to quantify the mechanical reactions of knee braces against non-physiological movements; 2. to relate these mechanical reactions to the pressure applied by the braces onto the skin. The latter is particularly important because it refers to comfort issues, which play a key role in a patient's compliance to the orthopedic treatment. A Finite Element Model of a braced human leg is developed. The model is first applied for characterizing the behavior of different kinds of knee braces, focusing on the mechanical reactions against non-physiological movements. In the model, a special attention is paid to the interfaces between knee-braces and the skin and between the skin and the muscles. The interface properties of the model are calibrated against experimental data measured by full-field measurements of 3D displacement over the surface of a patient's leg. The results show that the mechanical action of knee braces is essentially limited by skin/fabric and skin/muscles sliding. Finally, the model leads to a better understanding of the knee/brace interaction, and of the role of the brace components on the stability of the injured knee. Thanks to this computational tool, novel brace designs can be tested and evaluated for an optimal mechanical efficiency of the devices. Future work consists in considering the patient's comfort in the approach

Toward CFD-DEM simulations of the blast furnace raceway

Gas injections at the bottom of the blast furnace create void regions in the coke matrix called the raceways which play a role in the gas distribution in the furnace and is directly linked to the iron production. In this region, complex physical phenomena occur, including particle-fluid with combustion, and, to our knowledge, there is no consensus on its shape and dynamics as well as its creation and stability. A better understanding of the raceway region could lead to a more efficient and stable blast furnace process. An unresolved CFD-DEM approach is used to study the gas-solid flows where coke particles are modelled as a discrete phase and the gas as continuous solving the RANS modelling of the turbulence. In order to clarify the main phenomena occurring in the raceway dynamics, we develop a CFD-DEM model of a 1/5 scale 2d slot pilot of the blast furnace for which alternative raceway collapses are monitored. First, DEM simulations are realized without the fluid contribution and shows that the pilot geometry influences the mechanical load applied on the raceway with a saturation of the granular stress inside the pilot. Also, dry raceway collapse shows a modification of this stress in a short characteristic time. Then, CFD-DEM model of the pilot permits to investigate the gas and granular flows when the raceway is imposed as in the experiment. The dynamics of the collapse with the coupling is solved and displays a complex particle-gas 3d flow. Further implementation in the model will allow coke particle combustion

Mechanical determinants of 100-m sprint running performance

International audienceSprint mechanics and field 100-m performances were tested in 13 subjects including 9 non-specialists, 3 French national-level sprinters and a world-class sprinter, to further study the mechanical factors associated with sprint performance. 6-s sprints performed on an instrumented treadmill allowed continuous recording of step kinematics, ground reaction forces (GRF), and belt velocity and computation of mechanical power output and linear force–velocity relationships. An index of the force application technique was computed as the slope of the linear relationship between the decrease in the ratio of horizontal-to-resultant GRF and the increase in velocity. Mechanical power output was positively correlated to mean 100-m speed (P0.683; P0.21). Last, anthropometric data of body mass index and lowerlimb- to-height ratio showed no significant correlation with 100-m performance. We concluded that the main mechanical determinants of 100-m performance were (1) a ‘‘velocity-oriented’’ force–velocity profile, likely explained by (2) a higher ability to apply the resultant GRF vector with a forward orientation over the acceleration, and (3) a higher step frequency resulting from a shorter contact time

Infographic:Useful steps in the prevention of illnesses during international athletics championships

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Regional Trade and Competitiveness of Rwandan Agriculture: Empirical Analysis of Selected Priority Foodstuffs

This study aims at investigating the impact of regional integration on the agricultural trade development by focusing on wheat flour, maize grain, maize flour, potato, rice and soybean, fresh bean and dried beans sectors selected among priority foodstuffs in Rwanda. This is motivated by the lack of the studies comparing the competitive performance of all priority staple foods sub-sectors in Rwanda in the context of regional trade. The analysis used secondary data obtained through documentary reviews and those collected from the National Bank of Rwanda and FAOSTAT on imports and exports of Rwanda from 2007 to 2017. Apart from the literature review, the analysis was conducted using the Net Export Index (NEI) and the Grubel-Lloyd (GL) measure. The literature review and empirical results reveal that Rwanda benefited from its accession to regional and global trade blocks, especially in terms of the ease of access to external markets through the establishment of the Common Market, the Customs Union and the alleviation of some of trade barriers for basic foodstuffs and consumer goods. The analysis of the Net Export Index and the Grubel-Lloyd measures revealed that Rwanda can have a comparative advantage for wheat flour, fresh beans and dried beans at regional and global markets if measures aiming at developing a dynamic commercial network and improving agricultural value chains productivity are put forward

Sprint Acceleration Mechanics in Fatigue Conditions: Compensatory Role of Gluteal Muscles in Horizontal Force Production and Potential Protection of Hamstring Muscles

Aim: Hamstring muscle injury is the main injury related to sports requiring sprint acceleration. In addition, hamstring muscles have been reported to play a role in horizontal force production during sprint acceleration performance. The aim of the present study was to analyze (i) the determinants of horizontal force production and (ii) the role of hip extensors, and hamstring muscles in particular, for horizontal force production during repeated sprint-induced fatigue conditions.Method: In this experimental laboratory setting study including 14 sprint-trained male athletes, we analyzed (i) the changes in sprint mechanics, peak torque of the knee and hip extensors and flexors, muscle activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus, and sagittal plane lower limb motion, before and after twelve 6-s sprints separated by 44 s rest on an instrumented motorized treadmill, and (ii) the determinants of horizontal force production (FH) during the sprint acceleration in a fatigue state (after 12 sprints).Results: The repeated-sprint protocol induced a decrease in maximal power output (Pmax) [-17.5 ± 8.9%; effect size (ES): 1.57, large] and in the contact-averaged horizontal force component (FH) (-8.6 ± 8.4%; ES: 0.86, moderate) but not meaningful changes in the contact-averaged resultant (total) force (FTot) (-3.4 ± 2.9%; ES: 0.55, small) and vertical force component (FV) (-3.1 ± 3.2%; ES: 0.49, small). A decrease was found in concentric peak torque of the knee flexors and extensors and in gluteus and vastus lateralis muscle activity during entire swing and end-of-swing phase. An increase was found in contact time and swing time, while step frequency and knee speed before ground contact decreased. Muscular determinants associated with FH and its decrease after the repeated-sprint protocol were concentric peak torque of the hip extensors (p = 0.033) and a decrease in gluteus maximus activity at the end-of-swing (p = 0.007), respectively.Conclusion: Sprint-induced fatigue lead to changes in horizontal force production muscular determinants: hamstring muscle seems not to have the same role than in non-fatigue condition. Horizontal force production seems to be more dependent on the hip extensors and gluteus maximus function. Given the fatigue-induced decrease in hamstring muscle strength, we can hypothesize that muscle compensatory and kinematic strategies reported in a fatigued state could be an adaptation to allow/maintain performance and a protective adaptation to limit hamstring muscles constraints

Evolution monitoring of a solution-mining cavern in salt : identifying and analysing early-warning signals prior to collapse

International audienceRisk management of underground cavities requires a good working knowledge of accidental phenomena like subsidence or large-scale collapse. This was the context when the opportunity was taken to instrument a large size in use saline cavern, so as to test various auscultation techniques available under controlled conditions. A microseismic monitoring network coupled to a surface measurement system was installed to improve our knowledge of the mechanisms that initiate and govern the evolution of the cavern up to its collapse. After a stationary period combined with partial depressurization tests conducted in 2005 and 2007, the cavern appears to have entered into its final evolution phase, and this probably since early 2008. This results in continuous and highly sustained microseismic activity as well as the occurrence of a number of microseismic episodes localized around the cavern roof. The localization of the microseismic events, for some of these episodes, is closely correlated to the quasi-dynamic brine pressure variations and to the evolutions of the roof depth measured at observation boreholes. The microseismic activity turns out to be more precise when it comes to the evolution affecting the mine cavern than the movement measurements taken on the surface or sub-surface

Effects of the Methanol Extract of Basella alba L (Basellaceae) on Steroid Production in Leydig Cells

In this study, Leydig cells were purified from 70 day-old Sprague Dawley male rats and incubated with 10 and 100 μg/mL of methanol extract of Basella alba (MEBa) for 4 hours followed by the evaluation of cell viability, steroid (testosterone and estradiol) production, and the level of aromatase mRNA. Results showed that MEBa did not affect Leydig cell viability. At the concentration of 10 μg/mL, MEBa significantly stimulated testosterone and estradiol production (p < 0.01 and p < 0.03, respectively), and enhanced aromatase mRNA level (p < 0.04). These observations suggest that MEBa directly stimulated testosterone, estradiol and aromatase mRNA levels in isolated Leydig cells