SPORTS RELATED INJURIES AND PREVENTION

The purpose of this applied session is to illustrate the importance of the collaboration between physicians (both sports doctors and/or orthopaedic surgeons) and biomecanichal researchers to improve the performance of our athletes while reducing sports related injuries

Estimation of temporal parameters during sprint running using a trunk-mounted inertial measurement unit

This research was supported by a grant of the Universit a Italo-Francese (Call Vinci) awarded to E. Bergamini.The purpose of this study was to identify consistent features in the signals supplied by a single inertial measurement unit (IMU), or thereof derived, for the identification of foot-strike and foot-off instants of time and for the estimation of stance and stride duration during the maintenance phase of sprint running. Maximal sprint runs were performed on tartan tracks by five amateur and six elite athletes, and durations derived from the IMU data were validated using force platforms and a high-speed video camera, respectively, for the two groups. The IMU was positioned on the lower back trunk (L1 level) of each athlete. The magnitudes of the acceleration and angular velocity vectors measured by the IMU, as well as their wavelet-mediated first and second derivatives were computed, and features related to foot-strike and foot-off events sought. No consistent features were found on the acceleration signal or on its first and second derivatives. Conversely, the foot-strike and foot-off events could be identified from features exhibited by the second derivative of the angular velocity magnitude. An average absolute difference of 0.005 s was found between IMU and reference estimates, for both stance and stride duration and for both amateur and elite athletes. The 95% limits of agreement of this difference were less than 0.025 s. The results proved that a single, trunk-mounted IMU is suitable to estimate stance and stride duration during sprint running, providing the opportunity to collect information in the field, without constraining or limiting athletes’ and coaches’ activities

A method for the field assessment of rolling resistance properties of manual wheelchairs, Computer Methods in Biomechanics and Biomedical Engineering

This article presents an examination and validation of a method to measure the field deceleration of a manual wheelchair (MWC) and to calculate the rolling resistances properties of the front and rear wheels. This method was based on the measurements of the MWC deceleration for various load settings from a 3D accelerometer. A mechanical model of MWC deceleration was developed which allowed computing the rolling resistance factors of front and rear wheels on a tested surface. Four deceleration sets were conducted on two paths on the same ground to test the repeatability. Two other deceleration sets were conducted using different load settings to compute the rolling resistance parameters (RPs). The theoretical decelerations of three load settings were computed and compared with the measured decelerations. The results showed good repeatability (variations of measures represented 6–11% of the nominal values) and no statistical difference between the path results. The rolling RPs were computed and their confidence intervals were assessed. For the last three sets, no significant difference was found between the theoretical and measured decelerations. This method can determine the specific rolling resistance properties of the wheels of a MWC, and be employed to establish a catalogue of the rolling resistance properties of wheels on various surfaces.The authors would like to thank the French National Research Agency (ANR) for its financial support to the SACR-FRM project (ANR-06-TecSan-020) and to the CERAH for the loan of all the manual wheelchairs evaluated in this work

INFLUENCE OF PLAYING SURFACE ON KNEE LOADS DURING RUNNING, SIDESTEP CUTTING AND DROP JUMPING

The purpose of this study was to analyse the influence of 3 different playing surfaces on knee load during sport tasks. 15 young skilled rugby players (17-19 year old) performed running, sidestep cutting and drop jumping tasks on 3 different tracks; i.e. a natural turf, an artificial turf and an hybrid turf (natural grass rooted in artificial rootzone). Kinematic analysis and inverse dynamic methods were applied to assess the knee loads during these exercises. A special attention was paid to knee valgus and internal rotation moments related to ACL injury risk. Results showed that moment of knee valgus during running and sidestep cutting were significantly higher on artificial turf compared with natural ones (3.73 ± 1.13 vs. 1.98 ±. 0.83 N.m.kg-1). In the same way, internal rotation moments in sidestep cutting displayed higher values on artificial track than natural grass (2.97 ± 1.21 vs. 2.51 ±. 1.15 N.m.kg-1). Furthermore, hybrid turf exhibited the lowest knee moments except for the running task. In conclusion, the type of the playing surface play an important role in knee loads related to ACL injury risk

Spring jumpers vs power jumpers: ankle joint behavior in elite wushu athletes and implications for performance and injury risk

Wushu, better known as kungfu, is the modern athletic form of Chinese martial arts, and consists of performing a routine of martial arts movements as well as acrobatic jumps. Since those acrobatic jumps are performed on a hard floor, vertical jump height plays a major role in elite performance. Wushu coaches often mention two differ- ent types of athletes: spring jumpers and power jumpers. From this empirical point of view, spring jumpers seem to jump more easily. As in many sports, wushu jumps are performed with a run up followed by a stance phase with eccentric and concentric phases, often referred to as a ‘stretch-short- ening cycle’ (SSC). Vertical jump height, in this case, is the result of three main components acting during the concentric phase: muscle fiber shortening, coordination between joints and recoil of elastic energy stored during the eccentric phase. Whereas the squat jump exercise (SJ) is used to evaluate the first component, the drop jump (DJ) can be used as a standard exercise to analyze the whole SSC. The overall ability of an athlete to benefit from a previous eccentric phase can be evaluated by pre-stretch augmentation (PSA), defined as the ratio of DJ and SJ performances (Kubo et al. 2007). Ankle behavior can be characterized by the evolution of joint torque, obtained with inverse dynamics, with respect to joint angle during the different phases of the support phase, with the slope being considered as overall joint stiffness. The aim of this study was to characterize spring and power jumpers in elite wushu athletes in terms of PSA, ankle laxity, and overall ankle stiffness during the concen- tric phase. The influence of the chosen jumping strategies on performance and injury risk will be also discussed

SPRING JUMPERS VS POWER JUMPERS: ROLE OF THE ANKLE JOINT IN ELITE WUSHU PERFORMANCE AND INJURY RISK

The purpose of this study was to characterize two jumping strategies observed in elite wushu athletes: power and spring jumping. Inverse dynamics analysis was conducted on 12 male wushu athletes performing squat jumps, drop jumps and wushu-specific acrobatic jumps. Ankle laxity and Achilles tendon elasticity were also measured. Spring jumpers showed lower ankle laxity and a bilinear evolution of overall ankle stiffness during the concentric phase of the stance, compared to power jumpers. They also showed higher peak valgus reaction moments at the knee joint. Tendon elasticity was similar between groups. As spring jumping strategy is more efficient in terms of energy expenditure and fatigue dependence, lower limb injury risk can be higher. Attention must be paid to athlete-specific jumping strategies for personalized conditioning and injury prevention

COMPARISON OF PEAK LUMBAR LORDOSIS BETWEEN SOME BASIC MOVEMENTS OF RHYTHMIC GYMNASTICS

To assist coaches in managing gymnasts, a good knowledge of the movements most likely to cause back pain is required. In rhythmic gymnastics (RG), this can be considered as identifying movements involving very high lumbar curvatures. To quantify the lumbar lordosis during some basic RG movements (ring, penché, penché with rotation, split leap, turning split leap, and front and back walkovers), eight gymnasts were enrolled and a 3D motion analysis was performed based on motion capture data, a musculoskeletal model and low-dose biplanar radiographs for model personalisation purposes. The ring and both the front and back walkovers were the movements studied involving the lumbar spine in extension the most but also resulting in the highest dispersion between gymnasts. Hence, future works should investigate the causes of this greater dispersion

Fast Subject Specific Finite Element Mesh Generation of Knee Joint from Biplanar X-ray Images

Numerous finite element (FE) models of the knee joint have been developed to investigate knee pathology, post-surgery assessment and natural knee biomechanics. However, because of the extensive computational effort required for preparing subject specific model from CT-scan or MRI data, most of the models in literature are done only for one subject resulting in poor validation of the model and limits the predictive power of the conclusions. Biplanar X-ray is a promising alternative to perform 3D reconstruction of bony structures because of low radiation dose and very less reconstruction time [1]. Moreover, an accurate and fast computational mesh is a prerequisite for generating subject specific mesh in order to perform personalized FE analysis. Traditionally, both triangular/tetrahedral and quadrilateral/hexahedral FE elements are used for 3D mesh generation. But because of distinct numerical advantages quadrilateral/hexahedral elements are preferred to avoid numerical instability, specifically for problems involving high strains at soft tissues [2]. The aim of the current study is to develop fast and automatic subject specific mesh for knee joint from biplanar X-ray images. This approach was successfully tested for 6 cadaveric specimen, where from the biplanar radiographic images of each, 3D reconstruction models were built with a mean time of about 10 min for each specimen by adapting the strategy of [1]. From the reconstruction models, subject specific mesh (4 noded shell) for bony and cartilage structures were generated based on the mapping from the generic model to subject specific model with about 10 sec of time for each specimen (Fig. 1). Both the meniscus were meshed with 8 noded hex elements using the nodes of femoral and tibial cartilage in a dedicated Matlab code with numerical cost of almost 1 min. So, a total of about 12 min computational time was required to build each subject specific knee from 3D reconstruction to mesh generation which is promising for clinical applications. Quality of mesh for individual specimen was also checked using mesh quality indicators (Jacobian ratio, aspect ratio etc.) and surface representation accuracy, which showed less than 1% (warning only) and 0.8 mm (at soft tissue regions) respectively for individual specimen

Comparison of hip joint mechanical energetics in table tennis forehand and backhand drives: a preliminary study

Hip joints are highly involved in table tennis. Some authors found both pelvic angular velocity and hip joint torques are related to the racket velocity. Others have also demonstrated how some of the best players have higher ranges of motion of the lower-limb joints. Therefore, the mechanical work generated by the playing-side-hip can be seen as indicator of the playing intensity associated with different strokes. The aim of this study was to quantify the hip joint mechanical work and power during four classical strokes. Motion capture acquisitions were performed on two international players. A biplanar radiographic acquisition was also performed to personalize the biomechanical model. Hip joint velocity and torques were calculated on the dominant side, allowing mechanical power and work to be calculated between the end of backswing and the ball impact. The highest level of mechanical work from the hip joint was found for forehand drive against backspin and forehand topspin drive with pivot. A backhand drive required the lowest hip mechanical work, and the forehand drive against topspin was found to be intermediate. The lower work required from the backhand stroke makes it suitable as a waiting stroke

A method for the field assessment of rolling resistance properties of manual wheelchairs, Computer Methods in Biomechanics and Biomedical Engineering

This article presents an examination and validation of a method to measure the field deceleration of a manual wheelchair (MWC) and to calculate the rolling resistances properties of the front and rear wheels. This method was based on the measurements of the MWC deceleration for various load settings from a 3D accelerometer. A mechanical model of MWC deceleration was developed which allowed computing the rolling resistance factors of front and rear wheels on a tested surface. Four deceleration sets were conducted on two paths on the same ground to test the repeatability. Two other deceleration sets were conducted using different load settings to compute the rolling resistance parameters (RPs). The theoretical decelerations of three load settings were computed and compared with the measured decelerations. The results showed good repeatability (variations of measures represented 6–11% of the nominal values) and no statistical difference between the path results. The rolling RPs were computed and their confidence intervals were assessed. For the last three sets, no significant difference was found between the theoretical and measured decelerations. This method can determine the specific rolling resistance properties of the wheels of a MWC, and be employed to establish a catalogue of the rolling resistance properties of wheels on various surfaces.The authors would like to thank the French National Research Agency (ANR) for its financial support to the SACR-FRM project (ANR-06-TecSan-020) and to the CERAH for the loan of all the manual wheelchairs evaluated in this work