MINIMAXX PLAYER LOAD AS AN INDEX OF THE CENTER OF MASS DISPLACEMENT? A VALIDATION STUDY

The purpose of this study was to assess the concurrent validity of the player load computed by the MinimaxX accelerometers by comparing it to the player load computed by a gold standard method based on in series force platforms. Fourteen participants were instrumented with two accelerometers (MinimaxX S4, Catapult, Australia) during specific team sport displacements performed on the force plates. Pearson correlation coefficients were ranged from 0.74 to 0.93 while the coefficients of variation varied from 6.9 to 16.4%. The standard error of the estimate was small

FORCE-SHARING BETWEEN TRICEPS SURAE MUSCLES DURING REHABILITATION EXERCISES FOR ACHILLES TENDINOPATHY

The purpose of this study was to determine individual muscle forces of the Triceps Surae during a range of rehabilitation exercises for Achilles tendinopathy. We used experimental data (N=4) and musculoskeletal modelling to estimate muscle force (dynamic optimization). We observed clear peak muscle force differences between exercises. In addition, the force-sharing strategies used by the participants (i.e., individual muscle contribution to the total force produced within the Triceps Surae) were different between exercises. These preliminary results could be helpful to objectively determine the progression in exercise loading throughout rehabilitation programs. Additionally, new information regarding the influence of the type of exercise on load distribution within the Triceps Surae may better orientate practitioners in the choice of exercise

Muscle volume quantification: guiding transformers with anatomical priors

Muscle volume is a useful quantitative biomarker in sports, but also for the follow-up of degenerative musculo-skelletal diseases. In addition to volume, other shape biomarkers can be extracted by segmenting the muscles of interest from medical images. Manual segmentation is still today the gold standard for such measurements despite being very time-consuming. We propose a method for automatic segmentation of 18 muscles of the lower limb on 3D Magnetic Resonance Images to assist such morphometric analysis. By their nature, the tissue of different muscles is undistinguishable when observed in MR Images. Thus, muscle segmentation algorithms cannot rely on appearance but only on contour cues. However, such contours are hard to detect and their thickness varies across subjects. To cope with the above challenges, we propose a segmentation approach based on a hybrid architecture, combining convolutional and visual transformer blocks. We investigate for the first time the behaviour of such hybrid architectures in the context of muscle segmentation for shape analysis. Considering the consistent anatomical muscle configuration, we rely on transformer blocks to capture the longrange relations between the muscles. To further exploit the anatomical priors, a second contribution of this work consists in adding a regularisation loss based on an adjacency matrix of plausible muscle neighbourhoods estimated from the training data. Our experimental results on a unique database of elite athletes show it is possible to train complex hybrid models from a relatively small database of large volumes, while the anatomical prior regularisation favours better predictions

Impact of the type of surface on the response to exercise : from muscle to movement

Les propriétés des surfaces sportives peuvent impacter directement la performance et le risque de blessure en modulant la part d’énergie transmise à l'athlète lors de l'impact du pied sur la surface. Les pelouses naturelle et synthétique sont couramment utilisées sur les terrains de football et de rugby. Depuis quelques années, une nouvelle génération de pelouse dite naturelle renforcée a fait son apparition dans les clubs professionnels mais son influence sur la biomécanique du geste sportif est encore mal connue. Cette thèse vise à évaluer l'influence de trois types de surfaces (gazon naturel renforcée, gazon synthétique et tartan) sur les interactions muscle-tendon et les coordinations neuromusculaires des muscles gastrocnemius medialis (GM) et vastus lateralis (VL) lors de mouvements de réception uni et bilatérale ainsi que de saut. L’analyse des données échographiques dynamiques, de cinématique 2D et d’activité musculaire nous a permis de montrer que : i) les propriétés mécaniques des surfaces peuvent altérer les interactions entre les faisceaux musculaires et les tissus tendineux ainsi que l’amplitude d’activation musculaire ; ii) la pelouse naturelle renforcée semble avoir des propriétés plus optimales que la pelouse synthétique lors de sauts et réceptions ; iii) il existe des différences de comportement marquées entre le GM et VL qui dépendent du type de surface, du type de mouvement et de son intensité. Cela souligne l’importance de ne pas se limiter à l’étude des propriétés mécaniques des surface pour comprendre leur influence sur le mouvement sportif. Par ailleurs, l’étude des comportements musculo-tendineux in vivo en condition écologique permet de mieux comprendre les interactions complexes entre l’homme et la surface.Sports surface properties can substantially alter the overall performance and risk of injury. Surface mechanical properties influence the loading of the human musculoskeletal system by modulating the amount of foot-impact energy transmitted to the athlete. Natural grass and synthetic turf are commonly used pitches in football and rugby. More recently, reinforced natural grass technology has been used at the elite-level facilities, but its influence on player is not well defined. This thesis aimed at evaluating the influence of three different surfaces (reinforced natural grass, synthetic turf and athletic track) on the muscle-tendon interactions and neuromuscular coordination of gastrocnemius medialis (GM) and vastus lateralis (VL) muscles during landings and jumping tasks. Analysis of dynamic ultrasound imaging, 2D kinematics and electromyographic data showed that: i) surface mechanical properties influenced muscle-tendon interactions as well as the level of muscle activity; ii) the reinforced natural grass surface seems to optimize the muscular response during the movement and iii) GM and VL muscles displayed specific behaviors relative to the type of movement, its intensity and the type of surface. This emphasizes that the human response cannot be predicted by only analyzing the mechanical surface properties and highlights the important role of in vivo ecological testing to better understand player-surface interaction

Impact du type de surface sur la réponse à l’exercice : du muscle au mouvement

Sports surface properties can substantially alter the overall performance and risk of injury. Surface mechanical properties influence the loading of the human musculoskeletal system by modulating the amount of foot-impact energy transmitted to the athlete. Natural grass and synthetic turf are commonly used pitches in football and rugby. More recently, reinforced natural grass technology has been used at the elite-level facilities, but its influence on player is not well defined. This thesis aimed at evaluating the influence of three different surfaces (reinforced natural grass, synthetic turf and athletic track) on the muscle-tendon interactions and neuromuscular coordination of gastrocnemius medialis (GM) and vastus lateralis (VL) muscles during landings and jumping tasks. Analysis of dynamic ultrasound imaging, 2D kinematics and electromyographic data showed that: i) surface mechanical properties influenced muscle-tendon interactions as well as the level of muscle activity; ii) the reinforced natural grass surface seems to optimize the muscular response during the movement and iii) GM and VL muscles displayed specific behaviors relative to the type of movement, its intensity and the type of surface. This emphasizes that the human response cannot be predicted by only analyzing the mechanical surface properties and highlights the important role of in vivo ecological testing to better understand player-surface interaction.Les propriétés des surfaces sportives peuvent impacter directement la performance et le risque de blessure en modulant la part d’énergie transmise à l'athlète lors de l'impact du pied sur la surface. Les pelouses naturelle et synthétique sont couramment utilisées sur les terrains de football et de rugby. Depuis quelques années, une nouvelle génération de pelouse dite naturelle renforcée a fait son apparition dans les clubs professionnels mais son influence sur la biomécanique du geste sportif est encore mal connue. Cette thèse vise à évaluer l'influence de trois types de surfaces (gazon naturel renforcée, gazon synthétique et tartan) sur les interactions muscle-tendon et les coordinations neuromusculaires des muscles gastrocnemius medialis (GM) et vastus lateralis (VL) lors de mouvements de réception uni et bilatérale ainsi que de saut. L’analyse des données échographiques dynamiques, de cinématique 2D et d’activité musculaire nous a permis de montrer que : i) les propriétés mécaniques des surfaces peuvent altérer les interactions entre les faisceaux musculaires et les tissus tendineux ainsi que l’amplitude d’activation musculaire ; ii) la pelouse naturelle renforcée semble avoir des propriétés plus optimales que la pelouse synthétique lors de sauts et réceptions ; iii) il existe des différences de comportement marquées entre le GM et VL qui dépendent du type de surface, du type de mouvement et de son intensité. Cela souligne l’importance de ne pas se limiter à l’étude des propriétés mécaniques des surface pour comprendre leur influence sur le mouvement sportif. Par ailleurs, l’étude des comportements musculo-tendineux in vivo en condition écologique permet de mieux comprendre les interactions complexes entre l’homme et la surface

Made to order : American minimal art in the Netherlands, late 1960s to early 1970s

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Novel Accelerometry-Based Metric to Improve Estimation of Whole-Body Mechanical Load

International audienceWhile the Player Load is a widely-used parameter for physical demand quantification using wearable accelerometers, its calculation is subjected to potential errors related to rotational changes of the reference frame. The aims of this study were (i) to assess the concurrent validity of accelerometry-based Player Load against force plates; (ii) to validate a novel metric, the Accel’Rate overcoming this theoretical issue. Twenty-one recreational athlete males instrumented with two triaxial accelerometers positioned at the upper and lower back performed running-based locomotor movements at low and high intensity over six in-series force plates. We examined the validity of the Player Load and the Accel’Rate by using force plates. Standard error of the estimate was small to moderate for all tested conditions (Player Load: 0.45 to 0.87; Accel’Rate: 0.25 to 0.95). Accel’Rate displayed trivial to small mean biases (−1.0 to 6.1 a.u.) while the Player Load displayed systematic very large to extremely large mean biases (17.1 to 226.0 a.u.). These findings demonstrate a better concurrent validity of the Accel’Rate compared to the Player Load. This metric could be used to improve the estimation of whole-body mechanical load, easily accessible in sport training and competition settings

The Use of a Single Trunk-Mounted Accelerometer to Detect Changes in Center of Mass Motion Linked to Lower-Leg Overuse Injuries: A Prospective Study

Movement dynamics during running was previously characterized using a trunk-mounted accelerometer, and were associated with a history of overuse injuries. However, it remains unknown if these measures are also linked to the development of overuse injuries. The aim of this study was therefore to determine how movement dynamics alter in response to fatigue, and the possible link with developing lower-leg overuse injuries during a six-month follow-up period. Two hundred and eight movement science university students completed a 12-min all-out run while wearing a trunk-mounted accelerometer. Dynamic stability, dynamic loading and spatiotemporal measures were extracted from the accelerometer. Participants sustaining an injury within the 6-month period demonstrated significantly higher RMS ratio values in the vertical direction and lower RMS ratio values in the anteroposterior direction, and lower impact acceleration values in the anteroposterior direction in an unfatigued state compared to the uninjured group. They also demonstrated an increase in dynamic loading in the horizontal plane during the run. In addition, with running fatigue both groups exhibited changes in dynamic stability and loading measures. These results show the potential of using a single trunk-mounted accelerometer to detect changes in movement dynamics that are linked to lower-leg overuse injuries

Effects of Surface Properties on Gastrocnemius Medialis and Vastus Lateralis Fascicle Mechanics During Maximal Countermovement Jumping

Interactions between human movement and surfaces have previously been studied to understand the influence of surface properties on the mechanics and energetics of jumping. However, little is known about the muscle-tendon unit (MTU) mechanics associated with muscle activity and leg adjustments induced by different surfaces during this movement. This study aimed to examine the effects of three surfaces with different properties (artificial turf, hybrid turf, and athletic track) on the muscle mechanics and muscle excitation of the gastrocnemius medialis (GM) and vastus lateralis (VL) during maximal countermovement jumping (CMJ). Twelve participants performed maximal CMJs on the three sport surfaces. GM and VL muscle fascicles were simultaneously imaged using two ultrafast ultrasound systems (500 Hz). MTUs lengths were determined based on anthropometric models and two-dimensional joint kinematics. Surface electromyography (EMG) was used to record GM and VL muscle activity. Surface mechanical testing revealed systematic differences in surface mechanical properties (P = 0.006, η2: 0.26-0.32, large). Specifically, the highest force reduction and vertical deformation values have been observed on artificial turf (65 ± 2% and 9.0 ± 0.3 mm, respectively), while athletic track exhibited the lowest force reduction and vertical deformation values (28 ± 1% and 2.1 ± 0.1 mm, respectively) and the highest energy restitution (65 ± 1%). We observed no significant difference in CMJ performance between the three surfaces (∼35-36 cm, P = 0.66). GM and VL fascicle shortening (P = 0.90 and P = 0.94, respectively) and shortening velocity (P = 0.13 and P = 0.65, respectively) were also unaffected by the type of surface. However, when jumping from greater deformable surface, both GM muscle activity (P = 0.022, η2 = 0.18, large) and peak shortening velocity of GM MTU (P = 0.042, η2 = 0.10, medium) increased during the push-off phase. This resulted in a greater peak plantar flexion velocity late in the jump (P = 0.027, η2 = 0.13, medium). Our findings suggest that maximal vertical jumping tasks in humans is not affected by common sport surfaces with different mechanical properties. However, internal regulatory mechanisms exist to compensate for differences in surface properties.status: publishe

Surface properties affect the interplay between fascicles and tendinous tissues during landing

International audiencePurpose: Muscle–tendon units are forcefully stretched during rapid deceleration events such as landing. Consequently, tendons act as shock absorbers by buffering the negative work produced by muscle fascicles likely to prevent muscle damage. Landing surface properties can also modulate the amount of energy dissipated by the body, potentially effecting injury risk. This study aimed to evaluate the influence of three different surfaces on the muscle–tendon interactions of gastrocnemius medialis (GM), and vastus lateralis (VL) during single- and double-leg landings from 50 cm.Methods: Ultrasound images, muscle activity and joint kinematics were collected for 12 participants. Surface testing was also performed, revealing large differences in mechanical behavior.Results: During single-leg landing, stiffer surfaces increased VL fascicle lengthening and velocity, and muscle activity independent of joint kinematics while GM length changes showed no difference between surfaces. Double-leg landing resulted in similar fascicle and tendon behavior despite greater knee flexion angles on stiffer surfaces.Conclusion: This demonstrates that VL fascicle lengthening is greater when the surface stiffness increases, when performing single-leg landing. This is due to the combination of limited knee joint flexion and lower surface absorption ability which resulted in greater mechanical demand mainly withstood by fascicles. GM muscle–tendon interactions remain similar between landing surfaces and types. Together, this suggests that surface damping properties primarily affect the VL muscle–tendon unit with a potentially higher risk of injury as a result of increased surface stiffness when performing single-leg landing tasks