Non-contact Situations Research Articles

Three distinct mechanisms predominate in non-contact anterior cruciate ligament injuries in male professional football players: a systematic video analysis of 39 cases

BackgroundCurrent knowledge on anterior cruciate ligament (ACL) injury mechanisms in male football players is limited.AimTo describe ACL injury mechanisms in male professional football players using systematic video analysis.MethodsWe assessed videos...

Sports injuries in physical education teacher education students

Sports injuries could be highly detrimental to the career of a physical education teacher education (PETE) student. To enable the development of future sports injury prevention programs, sports injuries in 128 first-year academic bachelor PETE students were registered prospectively during one academic year. Common risk factors for sports injuries, taken from the literature, were also evaluated by means of logistic regression analysis. We found an incidence rate of 1.91 and an injury risk of 0.85, which is higher than generally found in a sports-active population. Most injuries involved the lower extremities, were acute, newly occurring injuries, and took place in non-contact situations. More than half of all injuries lead to an inactivity period of 1 week or more and over 80% of all injuries required medical attention. A major part of these injuries happened during the intracurricular sports classes. Few differences were seen between women and men. A history of injury was a significant risk factor (P = 0.018) for the occurrence of injuries, and performance of cooling-down exercises was significantly related to a lower occurrence of ankle injuries (P = 0.031). These data can inform future programs for the prevention of sports injuries in PETE students.

Epidemiological indoor soccer's team injuries profile in 2010 National League

The indoor soccer has high physical demands of strength and power, therefore the incidence of injuries increases. The literature shows age, position, features of training and competition's level as risk factors. The aim of this study was to understand the profile of indoor soccer players injuries from a team during the 2010 indoor soccer league, the major national league in Brazil. The team with 17 professional athletes, with a mean age of 23.24 years, who participated in the first and second phases of the championship, totaling 30 games from April to September 2010 were included in this study. During the performance of this championship, concomitantly, more 15 games were played for regional championships. All injuries were registered by the team's physiotherapist and were also described: the position of the athletes, if the injuries were in a situation of non-contact or contact, and if they occurred during training sessions, games or other time off. A descriptive analysis were realized. The total of 30 injuries led to the physical therapy treatment. The mean number of lesions treated per athlete was 2.7. The average of absence in training sessions and games was 7 days. The muscular strains (36.7%) were more prevalent then sprains (16.7%) and muscle spasms (16.7%). Regarding of the type of injury, muscle damage (53.3%) occurred in greater numbers, followed by ligament injuries (23.3%). Most injuries happened in non-contact situations and during games (66.7%). The Side Midfielder players, especially on the right side, had the largest number of non-contact injuries. The injury profile is very similar with other studies with soccer players, more muscle and ligament injuries, during games. Despite the popularity of indoor soccer, there are few scientific articles that describe the epidemiologyof this modality Like most of the injuries was non-contact (atraumatic) injuries as muscle damage, greater emphasis should be given to eccentric and plyometrics exercises, besides the importance of muscle recovery after training and after games. The athletes participated in other tournaments simultaneously, which according to the literature, may lead to the appearance of injuries. The injuries epidemiology profile of the team in 2010 Futsal League provides important data for injury prevention.

The relationship between pre-season fitness testing and injury in elite junior Australian football players

Australian Football (AF) is a collision sport containing high injury rates in junior competition. Successful performance at the elite junior level not only requires superior specific football knowledge and skills, but also well developed fitness qualities. However, no studies have examined the link between physical fitness qualities and injury in AF. Prospective cohort. Injury data were collected through the use of a Player Movement Record (PMR) and a standardized Injury Report Form (IRF). Fitness test data was collected during the pre-season of the 2010 and 2011 seasons. 382 players consented to participate in the study. The cohort experienced an injury incidence rate of 24.29/standardized club (40 players/club). A faster 5-m sprint was associated with 'injury status' (p=0.016) and a 'knee' region (p≤0.001) injury. A faster planned agility score was associated with an increased risk of a 'hip/groin/thigh' region (p=0.010) injury, and specifically a 'quadriceps strain' (p=0.005). A lower 20-m shuttle run was associated with an increased risk of a 'shin/ankle/foot' (p=0.045) injury. Increased injury severity was associated with a higher left foot running vertical jump (VJ) (p=0.040), and faster 5-m sprint (p=0.043). Lower aerobic endurance, faster 5-m acceleration and greater planned agility were associated with an increased risk of various injury types in elite junior AF players. Furthermore, a higher left foot running VJ and faster 5-m acceleration were associated with injury severity. These results may largely relate to a greater work capacity placing a higher load upon the musculoskeletal system in contact and non-contact situations.

Estimating Anterior Tibial Translation From Model-Based Image-Matching of a Noncontact Anterior Cruciate Ligament Injury in Professional Football: A Case Report

INTRODUCTION Although video analysis is the only method available to extract kinematic data from real injury situations to clarify the mechanisms for noncontact anterior cruciate ligament (ACL) injury, most studies have been limited to simple visual inspection, the accuracy of which has been shown to be limited. As an alternative, a model-based image-matching (MBIM) technique has been developed to extract joint kinematics from uncalibrated video recordings. This technique has been validated in noninjury situations in a laboratory environment and has also been found to be feasible for use in actual ACL injury situations. This study presents a noncontact ACL injury situation in a male footballer recorded during a television broadcast using 4 high-definition cameras from different views, including 2 high-speed recordings. We have used the MBIM technique to describe the detailed joint kinematics, including tibial translations.

On the contact detection for contact-impact analysis in multibody systems

One of the most important and complex parts of the simulation of multibody systems with contact-impact involves the detection of the precise instant of impact. In general, the periods of contact are very small and, therefore, the selection of the time step for the integration of the time derivatives of the state variables plays a crucial role in the dynamics of multibody systems. The conservative approach is to use very small time steps throughout the analysis. However, this solution is not efficient from the computational view point. When variable time-step integration algorithms are used and the preimpact dynamics does not involve high-frequencies, the integration algorithms may use larger time steps and the contact between two surfaces may start with initial penetrations that are artificially high. This fact leads either to a stall of the integration algorithm or to contact forces that are physically impossible which, in turn, lead to post-impact dynamics that is unrelated to the physical problem. The main purpose of this work is to present a general and comprehensive approach to automatically adjust the time step, in variable time-step integration algorithms, in the vicinity of contact of multibody systems. The proposed methodology ensures that for any impact in a multibody system the time step of the integration is such that any initial penetration is below any prescribed threshold. In the case of the start of contact, and after a time step is complete, the numerical error control of the selected integration algorithm is forced to handle the physical criteria to accept/reject time steps in equal terms with the numerical error control that it normally uses. The main features of this approach are the simplicity of its computational implementation, its good computational efficiency, and its ability to deal with the transitions between non-contact and contact situations in multibody dynamics. A demonstration case provides the results that support the discussion and show the validity of the proposed methodology.

Transparent Bilateral Control Architecture by State Convergence for Telerobotics

This paper presents a bilateral control scheme designed to achieve the two main goals of a teleoperation system: stability and transparency. The control scheme allows that the slave follows the master, ant that the force displayed to the operator was exactly the reaction force from the environment. In addition, the interaction force of the slave with the environment is adapted to the master/slave ratio when it is reflected to the operator, improving the transparency of the system. The bilateral control scheme can be used in contact situations or non-contact situations (free motion) of the slave with the environment. Together with the control scheme, the paper describes an analytical design method that allows to obtain the control gains.

Gender differences in knee kinematics and muscle activity during single limb drop landing

The likelihood of sustaining an ACL injury in a noncontact situation is two to eight times greater for females than for males. However, the mechanism and risk factors of ACL injury are still unknown. We compared knee kinematics as well as electromyographic activity during landing between male and female athletes. Eighteen male athletes and nineteen female athletes participated in the experiment. The angular displacements of flexion/extension, valgus/varus, and internal/external tibial rotation, as well as the translational displacements of anterior/posterior tibial translation during single limb drop landing were calculated. Simultaneous electromyographical activity of the rectus femoris (RF) and hamstrings (Ham) was taken. During landing, internal tibial rotation of the females was significantly larger than that of the males, while differences were not observed in flexion, varus, valgus, and anterior tibial translation. Hamstrings/quadriceps ratio (HQR) for the 50 ms time period before foot contact was greater in males than in females. The mechanism of noncontact ACL injury during a single limb drop landing would be internal tibial rotation combined with valgus rotation of the knee. Increased internal tibial rotation combined with greater quadriceps activity and a low HQR could be one reason female athletes have a higher incidence of noncontact ACL injuries.

Characteristics of anterior cruciate ligament injuries in Australian football

Anterior cruciate ligament (ACL) injuries are the most costly injuries in football at both professional and amateur levels (Orchard J, Seward H, McGivern J, Hood S. Intrinsic and extrinsic risk factors for anterior cruciate ligament injury in Australian footballers. Am J Sports Med 2001;29:196-200.). In this study video analysis of 34 ACL injuries in Australian football was performed to investigate the causes of these injuries. Factors that may have contributed to the cause of the injury were analysed, rated and reported. The factors analysed were: type of manoeuvre, direction the knee 'gave way', running speed, knee angle, cutting angle and if the player was accelerating or decelerating. The majority of the injuries analysed occurred in non-contact situations (56%). Of these 37% occurred during sidestepping manoeuvres, 32% in landing, 16% land and step, 10% stopping/slowing and 5% crossover cut manoeuvres. Ninety-two percent of the non-contact injuries occurred at extended knee angles of 30 degrees or less, which is also commonly known to place stress on the ACL and reduce the protective role of hamstrings. Over half (54%) of non-contact injuries occurred whilst decelerating. It would be expected that greater speed and angle cut too would increase the frequency of ACL injury. The results could not confirm this with most injuries occurring at running speeds of slow jogging to running and equal number of injuries occurred at cutting to angles of the ranges 15-45 degrees and 45-75 degrees. These results give greater understanding into potential causes or contributors of ACL injury and information to assist in the development of knee injury prevention programs.

A haptic representation system for a virtual plain wall

The purpose of this study is to develop a virtual wall display system for a walk simulator to grope its way in an 'invisible' situation, such as in a building filled with dense smoke, etc. To reproduce the realistic haptic sense of a building wall, the implementation of the wideness and the rigidity of wall are essential. Wideness of a virtual wall was realized by a hand-tracking control combined with a small wall panel which is mounted on a three-axis Cartesian manipulator. A 6-d.o.f. magnetic tracking system was utilized for the hand position tracking in the non-contact situation of the hand and the panel. In the contact situation, high rigidity of the wall was attained as stiffness in the normal direction is provided to the wall panel to represent the haptic sense of a rigid wall. Force-based tracking provides the low stiffness in the tangential direction to make the wall panel move easily along the direction of hand movement to represent a wide plain wall. A three-axis force sensor is attached on the wall panel to detect the contact force. The realization of smooth switching between both tracking controls provides the user with the haptic feel of the presence and continuity of a virtual wall. In addition, the frictional sensation has the effect of giving the system more reality. Experimental results have shown the effectiveness of the hybrid tracking method for the virtual wall system.

Injuries in Female Soccer Players

Background In contrast to the high number of studies about soccer injuries in men, epidemiologic data in high-level female soccer players are scarce. Purpose Analysis of injury incidence in elite female soccer players. Study Design Descriptive epidemiology study. Methods There were 165 female soccer players (age, 22.4 ± 5.0 years) from 9 teams competing in the German national league, who were followed for one complete outdoor season. Their trainers documented the exposure to soccer on a weekly basis for each player, and the team physical therapists reported all injuries with regard to location, type, and circumstances of occurrence. An injury was defined as any physical complaint associated with soccer that limited sports participation for at least 1 day. Results There were 241 injuries sustained by 115 players (70%) reported; 39 injuries (16%) were owing to overuse, and 202 injuries (84%) were traumatic. Overall, 42% of the traumatic injuries occurred during training (2.8/1000 hours of training; 95% confidence interval, 2.2-3.4) and 58% during matches (23.3/1000 match hours; 95% confidence interval, 19.1-27.5); 102 of the traumatic injuries were caused by a contact situation, whereas 95 occurred without any contact. Most injuries (80%) were located at the lower extremities, concerning mainly the thigh (n = 44), knee (n = 45), and ankle (n = 43). Ankle sprain (n = 37) was the most often diagnosed injury. There were 51% minor injuries, 36% moderate injuries, and 13% major injuries. Eleven anterior cruciate ligament ruptures were observed during the season. Conclusion The results revealed a high injury incidence rate in games as well as a comparably low incidence rate during training. An important finding of this investigation was the frequent occurrence of anterior cruciate ligament ruptures. Preventive measures should thus focus on the high prevalence of anterior cruciate ligament tears, mostly occurring in noncontact situations.

Penetration depth of laser Doppler flowmetry beam in teeth

The aim of this study was to determine the penetration depth of laser light in teeth for contact and noncontact probe tip. Fifty-one freshly extracted human mature maxillary and mandibular single rooted teeth were selected for the study. A laser Doppler flowmeter was used as a laser source. A digital camera was used to take pictures (with "night shot" mode in total darkness). When probe tip was in contact and when it was 1 mm away from the tooth, the depths of the areas illuminated in high and low density were measured. In contact probe, root was illuminated to 4.28 +/- 0.14 mm depth with high density and 13.27 +/- 0.27 mm depth with low density. In noncontact probe, 4.36 +/- 0.16 mm with high density and 13.28 +/- 0.30 mm with low density of illumination were seen on the root. Between contact and noncontact probe situations the difference was not statistically significant in the depth of illumination. On the other hand, in both groups the difference between areas illuminated in high and low density was statistically significant (P < .05). Contact or noncontact of the probe on tooth surface did not show any significant difference in light penetration. Besides, we think that, for the present, it is impossible to eliminate the contamination from periodontal tissues completely even if the necessary precautions (periodontal paste etc.) are taken.

Free-space propagation of diffuse light: theory and experiments.

In this Letter we present a simple and novel theoretical approach for modeling the intensity distribution from an arbitrarily shaped turbid volume in a noncontact geometry by considering diffuse light propagation in free space. This theory is validated with experiments for a diffusive volume of known geometry in a noncontact situation, both with and without the presence of an embedded absorber. The implications of this new formulation in the context of optical tomography in turbid media are discussed.

WISSENSCHAFTLICHER BEITRAG: Prävention von Rupturen des vorderen Kreuzbandes im Ballsport: eine Literaturübersicht

A number of epidemiological studies has shown that the rate of ACL ruptures in female athletes is 2.4 to 9.5 times higher than in male athletes. Approximately 70% of these injuires occur without direct contact to another player (noncontact situations). Various studies have shown that the most frequent situations are landing a jump, stopping and plant and cut maneuvers. However, there is evidence that gender specific differences in coordination and neuromuscular control may be an explanation for the high incidence of ACL injuries in female athletes. Female athletes tend to be more upright with a slightly flexed valgus knee when cutting and landing. The muscle mechanics in this position favors the qua-driceps while denying a favourable position for the hamstrings to conteract the quadriceps. Additionally, women also have greater quadriceps activation. Therefore, when cutting, women place their knee in a position that favor a quadriceps-induced anterior drawer maneuver, placing the knee in a position of increased risk for ACL injury. Various studies have shown that specific training programs can reduce the incidence of ACL injuries significantly: 1. The Henning prevention strategies stressed: – changing the plant and cut to an accelerated round turn, – landing with a bent knee rather than a straight knee, – changing a one step stop on a straight knee to a stopping with a multiple-step with a knee bent. 2. The Caraffa Program showed that incorporation of proprioceptive drills such as balance board exercises into pre-season conditioning program is able to reduce the ACL injury rate significantly. 3. The Cincinnati Sportsmetric Program includes a temporal staggered jump training. 4. The Kiel Team Handball Injury Prevention Program includes elements of all three former programs.

Simulation of section curve by phase constant dynamic mode atomic force microscopy in non-contact situation

We investigate the behavior of an oscillating tip operating in tapping mode, e.g. with fixed drive frequency and drive excitation while scanning horizontally an ideal flat surface holding a small corrugation. The numerical simulations are performed to compare the relative vertical and lateral sensitivity of the oscillator when the feedback loop controlling the tip–sample distance keeps constant the oscillator phase instead of the amplitude. In these simulations, a sphere lies on a flat surface and a Van der Waals force is assumed between the tip, the sphere and the substrate. Once the tip has approached from the substrate far from the sphere, the tip is scanned towards the sphere. It is found that the phase constant mode makes smaller indentation and better response height probably without larger damage by using wider setpoint value (SPV) than the cases of amplitude constant mode.

Surface mechanical instabilities and dissipation under the action of an oscillating tip

We analyze the mechanical response of a surface under the action of an oscillating tip in non-contact situations. The surface behavior is modelled as a simple viscoelastic material. In particular, special attention is paid to the surface displacement due to the attractive interaction between the tip and the surface. Analytical expressions describing the oscillation behavior of the tip at the proximity of the surface are obtained by considering two asymptotic regimes. The two asymptotic regimes are controlled by the characteristic relaxation time of the surface. Fast relaxation times correspond to time shorter than that of the residence time, e.g. the time during which the oscillating tip is at the proximity of the surface. Slow surface relaxation processes correspond to time larger than that of the oscillation period. The results allow the calculation of the non-contact dissipation as a function of the surface mechanical properties. Also, two criterions are derived that give the threshold values of the surface mechanical instability. The threshold values are shown to be strongly dependent of the characteristic time scale of the surface relaxation, thus of its dissipative properties.

Dissipation induced by attractive interaction in dynamic force microscopy: contribution of adsorbed water layers

At room temperature and under ambient conditions, due to the adsorption, a water film is always present on silica surfaces. If the surface is investigated with a scanning probe method in contact mode, this causes the formation of a meniscus between the tip and the surface. This liquid neck generates additional capillary forces between the nano-tip and the surface. In dynamic mode, due to the action of the oscillating tip on the surface, the mechanical response of the adsorbed water layers can induce additional dissipation that is probed through the phase variations of the oscillator. In the present work, we analyze by dynamic force microscopy the growth of a water film on a silica surface as a function of time. The silica sample is first cleaned and heated at 420 °C, then is exposed to dry conditions. The influence of the water film is checked with the dynamic mode by using intermittent contact and noncontact situations. To describe the experimental observations, additional dissipation is taken into account when the tip approaches the surface. The results of the fits allow the evaluation of the dissipation induced by the attractive interaction between the tip and the silica surface related to the adsorption of water molecules on surface as a function of time. Results are compared to previous tribological studies performed in contact mode and infrared spectroscopy measurements on the silica for which the key parameter was the surface temperature instead of time. The two experimental results are in good agreement.

Influence of noncontact dissipation in the tapping mode: Attempt to extract quantitative information on the surface properties with the local force probe method

In the Tapping mode, a variation of the oscillation amplitude and phase as a function of the tip sample distance is the necessary measurement to access quantitatively to the properties of the surface. In the present work, we give a systematic comparison between experimental data recorded on two surfaces, phase and amplitude, and theoretical curves. With an interaction between the tip and the surface taking into account an attractive and a repulsive term, the analytical approach is unable to properly describe the relationship between the phase variation and the oscillation amplitude variation. When an additional dissipation term is involved, due to the attractive interaction between the tip and the surface, the model gives a good agreement with the recorded data. Particularly, the trends in the phase variations related to the noncontact situations have been found to be amenable to an analysis based upon a simple viscoelastic behavior of the surface.

Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies.

An estimated 80,000 anterior cruciate ligament (ACL) tears occur annually in the United States. The highest incidence is in individuals 15 to 25 years old who participate in pivoting sports. With an estimated cost for these injuries of almost a billion dollars per year, the ability to identify risk factors and develop prevention strategies has widespread health and fiscal importance. Seventy percent of ACL injuries occur in noncontact situations. The risk factors for non-contact ACL injuries fall into four distinct categories: environmental, anatomic, hormonal, and biomechanical. Early data on existing neuromuscular training programs suggest that enhancing body control may decrease ACL injuries in women. Further investigation is needed prior to instituting prevention programs related to the other risk factors.

Nonlinear dynamical properties of an oscillating tip–cantilever system in the tapping mode

The dynamical properties of an oscillating tip–cantilever system are now widely used in the field of scanning force microscopy. The aim of the present work is to get analytical expressions describing the nonlinear dynamical properties of the oscillator in noncontact and intermittent contact situations in the tapping mode. Three situations are investigated: the pure attractive interaction, the pure repulsive interaction, and a mixing of the two. The analytical solutions obtained allow general trends to be extracted: the noncontact and the intermittent contact show a very discriminate variation of the phase. Therefore the measurement of the phase becomes a simple way to identify whether or not the tip touches the surface during the oscillating period. It is also found that the key parameter governing the structure of the dynamical properties is the product of the quality factor by a reduced stiffness. In the attractive regime, the reduced stiffness is the ratio of an attractive effective stiffness and the cantilever one. In the repulsive regime, the reduced stiffness is the ratio between the contact stiffness and the cantilever one. The quality factor plays an important role. For large values of the quality factor; it is predicted that a pure topography can be obtained whatever the value of the contact stiffness. For a smaller quality factor, the oscillator becomes more sensitive to change of the local mechanical properties. As a direct consequence, varying the quality factor, for example with a vacuum chamber, would be a very interesting way to investigate soft materials either to access topographic information or nanomechanical properties.