The present research aimed at the specific actions of the third phase of ski jumping after the takeoff, respectively the flight distance covered by the subjects until they reached the V-style ...posture, as well as the ski-opening angle. The subjects of the study were four athletes, members of the national junior ski jumping team. The research was carried out on the HS 100 m hill in Râșnov. The initial testing consisted of three complete jumps. Subsequently, for a period of 30 days, specific training methods consisting of imitative exercises were implemented, focusing on the third phase of the ski jump. In the final testing, the themes were the wide spread of the lower limbs above R2, as well as the maintenance of the skis spread in the plane that includes the body in order to benefit from the maximum lift. The results of the research highlighted the close connection between ballistics and aerodynamics, the achievement of the flight speed, as well as the increase of the lifting surface due to the identification of the optimum angle of ski spread. An increase in length performance was observed for all four subjects.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Large eddy simulations (LESs) are performed to study the flow characteristics around two flight posture models of ski jumping. These models are constructed by three-dimensionally scanning two ...national-team ski jumpers taking flight postures. The drag and lift forces on each component of a ski jumper and skis (head with helmet and goggle, body, arms, legs and skis) and their lift-to-drag ratios are obtained. For the two posture models, the drag forces on the body, legs and skis are larger than those on the arms and head with helmet and goggle, but the lift forces on the body and skis are larger than their drag forces, resulting in high lift-to-drag ratios on the body and skis and low lift-to-drag ratio on the legs. We construct simple geometric models, such as the circular cylinder, sphere and thin rectangular plate, predicting the drag and lift forces on each component of a ski jumper and skis, and validate them with those obtained from LES. Using these geometric models, we perform a parametric study on the position angles of flight posture for higher total lift-to-drag ratio. The flight postures obtained increase the total lift-to-drag ratios by 35% and 21% from those of two base postures, respectively. Finally, LESs are performed for the postures obtained and show the increases in the total lift-to-drag ratios by 21% and 16%, respectively, indicating the adequacy of using the simple geometric models for finding a flight posture of ski jumping having a higher lift-to-drag ratio at low cost.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To describe the incidence, type, aetiology and severity of injuries sustained by the International Ski Federation World Cup level female ski jumpers during the 2017-18 season.
Prospective cohort ...study.
Sixty-seven female ski jump athletes from 16 countries were followed throughout the 17-week winter season. Preseason baseline demographic data and injury history were recorded via questionnaire. Prospective biweekly reports and retrospective end-of-season interviews provided data on all injuries requiring medical attention.
Seventeen injuries were recorded, corresponding to an incidence of 25.4 injuries/100 athletes/season. The incidence of time-loss and severe injuries were found to be 17.9 and 4.5, respectively. The knee was the most common site of injury (4/17; 23.5%). Fourteen injuries occurred on the ski jump hill and crash-landing was the most common mechanism of injury (10/14; 71%). Eighty-five per cent of all moderate and severe injuries occurred in snow or windy conditions. Length of jumps resulting in injury averaged 83.7% (95% CI 72.9% to 94.4%) of hill size. Moderate injuries causing 8-28 days absence from training activities were most common (7/17; 41%) and there were three severe injuries necessitating >4 weeks absence.
Injuries among elite female ski jumpers are common and the majority are acute, resulting in time loss from training and competition. The knee was the most common site of injury and poor weather conditions may be a risk factor. Future studies are needed to identify risk factors for injury and to guide injury prevention initiatives.
The aim of this study was to perform a kinematic analysis of the in-run, take-off and early flight phases in water ski jumping and to analyse the differences in linear/angular parameters between ...males and females. Forty-two elite skiers participated in this study (27 males; 15 females); their jumps were video recorded during competitions: the time course of absolute (trunk, thigh, ski) and relative (hip, knee, ankle) angles was calculated, as well as the (trochanter) resultant speed. Males were able to reach faster in-run speeds than females (25.4 ± 1.9 and 21.8 ± 1.2 m/s, respectively) and jumped further (56.2 ± 8.6 and 40.4 ± 6.3 m). Longer jumps were correlated with faster speeds in all phases (r range: 0.87-0.91, p < 0.001, n = 42). From take-off to early flight skiers extend their hip (86-109°) and knee (136-171°) angles, lean their trunk forward (49-41°) and raise their skis (20-51°); no major sex differences were observed in the body position (or ski incline) in these phases and none of the angular parameters was correlated with jump distance. Our results suggest that skiers should focus on achieving a larger in-run speed to maximise performance in this discipline.
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BFBNIB, FSPLJ, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Abstract Three-dimensional analysis of the entire sequence in ski jumping is recommended when studying the kinematics or evaluating performance. Camera-based systems which allow three-dimensional ...kinematics measurement are complex to set-up and require extensive post-processing, usually limiting ski jumping analyses to small numbers of jumps. In this study, a simple method using a wearable inertial sensors-based system is described to measure the orientation of the lower-body segments (sacrum, thighs, shanks) and skis during the entire jump sequence. This new method combines the fusion of inertial signals and biomechanical constraints of ski jumping. Its performance was evaluated in terms of validity and sensitivity to different performances based on 22 athletes monitored during daily training. The validity of the method was assessed by comparing the inclination of the ski and the slope at landing point and reported an error of −0.2±4.8°. The validity was also assessed by comparison of characteristic angles obtained with the proposed system and reference values in the literature; the differences were smaller than 6° for 75% of the angles and smaller than 15° for 90% of the angles. The sensitivity to different performances was evaluated by comparing the angles between two groups of athletes with different jump lengths and by assessing the association between angles and jump lengths. The differences of technique observed between athletes and the associations with jumps length agreed with the literature. In conclusion, these results suggest that this system is a promising tool for a generalization of three-dimensional kinematics analysis in ski jumping.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The aerodynamic characteristics of sports suits play a crucial role in helping professional athletes gain a competitive edge in their chosen sport. The fluid forces acting on the body of the sports ...competitor are influenced by the surface topology of the fabric, position and size of the seams, use of fasteners, and air permeability of the fabric. Wind tunnel experiments and numerical simulations provide deep insight on the aerodynamic characteristics of sports suit designs. Ski jumping is a sport in which the competitor is judged based on the flight form and flight distance; therefore, ski jumpers attempt to fly as far as possible upon take-off. The fabric used for ski jumping suits plays a crucial role in achieving favorable aerodynamic characteristics. According to the rules and regulations for ski jumping competitions, the outstretched fabric should have a minimum air permeability of 40 L/m2/s at a water pressure of 98 Pa (10 mmAq). To date, little is known regarding the effects of air permeability on the aerodynamic characteristics of ski jumping suits, which forms the motivation of this study. The purpose of this study is to investigate the effect of air permeability on the aerodynamic characteristics of ski jumping suits. Wind tunnel experiments were carried out on an elliptic cylinder clothed with ski jumping suit fabrics of different air permeability. The aerodynamic forces acting on the fabric-clothed elliptic cylinder were measured using a three-component force balance. The velocity profiles were also measured to examine the effect of air permeability on the flow around the fabric-clothed elliptic cylinder. The experimental results show that the drag forces decrease with an increase in air permeability and the stall characteristics are greatly affected by the air permeability. The maximum lift coefficients are lower for fabrics with higher air permeability. However, this is compensated by the occurrence of stall delay for these fabrics and an increase in the lift-to-drag ratio at higher angles of attack. The velocity profiles around the fabric-clothed elliptic cylinder also vary, depending on the air permeability of the fabric.
Introduction:
Musculoskeletal simulation has been widely used to analyze athletes’ movements in various competitive sports, but never in ski jumping. Aerodynamic forces during ski jumping take-off ...have been difficult to account for in dynamic simulation. The purpose of this study was to establish an efficient approach of musculoskeletal simulation of ski jumping take-off considering aerodynamic forces and to analyze the muscle function and activity.
Methods:
Camera-based marker-less motion capture was implemented to measure the take-off kinematics of eight professional jumpers. A suitable full-body musculoskeletal model was constructed for the simulation. A method based on inverse dynamics iteration was developed and validated to estimate the take-off ground reaction force. The aerodynamic forces, which were calculated based on body kinematics and computational fluid dynamics simulations, were exerted on the musculoskeletal model as external forces. The activation and joint torque contributions of lower extremity muscles were calculated through static optimization.
Results:
The estimated take-off ground reaction forces show similar trend with the results from past studies. Although overall inconsistencies between simulated muscle activation and EMG from previous studies were observed, it is worth noting that the activation of the tibialis anterior, gluteus maximus, and long head of the biceps femoris was similar to specific EMG results. Among lower extremity extensors, soleus, vastus lateralis, biceps femoris long head, gluteus maximus, and semimembranosus showed high levels of activation and joint extension torque contribution.
Discussion:
Results of this study advanced the understanding of muscle action during ski jumping take-off. The simulation approach we developed may help guide the physical training of jumpers for improved take-off performance and can also be extended to other phases of ski jumping.
The purpose of this study was to investigate the effect of the air permeability of ski jumping suit fabric on aerodynamic characteristics. In the study, four types of fabric with different air ...permeabilities were installed onto a fabric-clothed elliptic cylinder, and the flow behavior around its surface was investigated through wind tunnel experiments. The stall was delayed by using the fabric with higher air permeability. The air flow permeated the surface of the elliptic cylinder through the fabric for the fabric with high air permeability. This air flowed out into the separation region through the fabric again, which suppress stall. The stall characteristics for the fabric-clothed elliptic cylinder were influenced by the air permeability of the fabric. The boundary layer thickness on the outer surface and the turbulence levels of the boundary layer affected the air permeability of the fabric. The higher air permeability fabrics improved the stall characteristics.
Purposeof the study isto develop and experimentally justify the design of the training process of ski jumpers, whichis based on the control of body composition and control of physical ...fitness.Materials & methods: the study involved qualified athletes (n=47, 20 young women and 27 young men aged 18± 1.56 years). The experiment took place during 2019 on the basis of the Federal training center for winter sports "snowflake" named after A. A. Danilova (Tchaikovsky city, Russia). Bioelectrical impedance analysis was performed on the basis of a hardware analyzer of body composition "InBody 720". Functional diagnostics was carried out with the use of medical diagnostic software and hardware complex "Esteck system complex". Pedagogical testing was carried out based on 8 tests. To assess the static balance the following tests were used: the balance of the frontal and sagittal position of the body on the board for the duration. Flexibility was assessed by exercises: tilt forward, determination of the angle of flexion of the ankle. Assessment of motor coordination abilities was carried out to assess coordination abilities in rectilinear motion ("barriers") and in curvilinear motion ("eight"). In order to monitor the speed and strength endurance, jumping over the bench and exercise "plank"were used. Determining the speed and power indicators: long andtriplelong jumpwere evaluated. The results were recorded in a specially designed individual athlete card.Results: experimental means of control of body composition within the season allowed to reach the reference values of the component composition of the body and increase the level of special physical training and improveathletic performance. Athletes showed a remarkable increase in the results of motor coordination and speed-power abilities, static balance, speed and strength endurance. Among young men significant differences were revealed in control exercises such as: balance sagittal body position on the board, exercise "eight", long jump, exercise "plank". Amongyoung women, significant changes were obtained in control exercises: balance of the frontal position of the body on the board, jumping over the bench, exercise "plank" with emphasis on the forearm. Conclusion: the training of qualified ski jumpers should be carried out taking into account the body composition and physical fitness of the athlete. The main means of optimizing the training process of ski jumpers should be an individual athlete's card. On the basis of data of the individual card of the athlete the strategy of training process is developed.
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FSPLJ, NUK, ODKLJ, UL, UM, UPUK
(1) Background: Previous studies have compared research into ski jumping in different motor processes, but there is a lack of comparative analysis of the biomechanical research methods used to ...investigate different ski jumping sports. (2) Content: Our study compared the advantages and disadvantages of six research methods and proposes future research directions. Motion video collection and analysis show that controlling angular momentum and achieving stable flight attitude in the take-off process are the most critical factors in ski jumping performance. Most research on force platforms focuses on dynamic performance at the time of take-off, but there are few training sites with an embedded force platform, and so, more empirical research is required. Wearable inertial measurement units, including gyroscopes and accelerometers, can be used to determine a series of forces, calculate the joint angle, and speculate the position of the centroid during motion. Surface EMG studies are primarily used to compare the activity characteristics of the lower limb muscles in the actual field of the jump, the exercise simulation, and the lack of complete training process data. Wind tunnel measurement can satisfy fluid mechanics simulation experiments and provide theoretical support for optimizing special ski jumping technology. Based on the theory of computational fluid dynamics, the optimal drag reduction posture data of ski jumpers can be derived using computer simulations. (3) Conclusions: Due to the wide range of ski jumping sports, the present research focused on the kinematics and dynamics of different movement stages, lacking the study of the complete exercise training process. The range of wearable inertial measurement and sensor equipment can cover the whole process of ski jumping, including kinematics and dynamics data, and is a feasible and reliable test method for monitoring ski jump training in natural environments. The simultaneous testing of surface electromyography, kinematics, and dynamics requires further exploration. (4) Future direction of development: Under computational fluid dynamics, wearable inertial measurement units and global navigation satellite systems (GNSSs), intelligent wind tunnel experimental training areas will become essential tools for ski jumping research.
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