Changes in the mechanical properties of the thigh and lower leg muscle-tendon units during the early follicular and early luteal phases.

Background: This study aimed to determine changes in the muscle and tendon stiffness of the thigh and lower leg muscle-tendon units during the early follicular and early luteal phases, and check for possible relations between muscle and tendon stiffness in each phase. Methods: The sample consisted of 15 female university students with regular menstrual cycles. The basal body temperature method, ovulation kit, and salivary estradiol concentration measurement were used to estimate the early follicular and early luteal phases. A portable digital palpation device measured muscle-tendon stiffness in the early follicular and early luteal phases. The measurement sites were the rectus femoris (RF), vastus medialis (VM), patellar tendon (PT), medial head of gastrocnemius muscle, soleus muscle, and Achilles tendon. Results: No statistically significant differences in the thigh and lower leg muscle-tendon unit stiffness were seen between the early follicular and early luteal phases. Significant positive correlations were found between the stiffness of the RF and PT (r = 0.608, p = 0.016) and between the VM and PT (r = 0.737, p = 0.002) during the early luteal phase. Conclusion: The present results suggest that the stiffness of leg muscle-tendon units of the anterior thigh and posterior lower leg do not change between the early follicular and early luteal phases and that tendons may be stiffer in those women who have stiffer anterior thigh muscles during the early luteal phase.

Determining a musculoskeletal system's pre-stretched state using continuum-mechanical forward modelling and joint range optimization.

The subject-specific range of motion (RoM) of a musculoskeletal joint system is balanced by pre-tension levels of individual muscles, which affects their contraction capability. Such an inherent pre-tension or pre-stretch of muscles is not measureable with in vivo experiments. Using a 3D continuum mechanical forward simulation approach for motion analysis of the musculoskeletal system of the forearm with 3 flexor and 2 extensor muscles, we developed an optimization process to determine the muscle fibre pre-stretches for an initial arm position, which is given human dataset. We used RoM values of a healthy person to balance the motion in extension and flexion. The performed sensitivity study shows that the fibre pre-stretches of the m. brachialis, m. biceps brachii and m. triceps brachii with 91 % dominate the objective flexion ratio, while m. brachiradialis and m. anconeus amount 7.8 % and 1.2 % . Within the multi-dimensional space of the surrogate model, 3D sub-spaces of primary variables, namely the dominant muscles and the global objective, flexion ratio, exhibit a path of optimal solutions. Within this optimal path, the muscle fibre pre-stretch of two flexors demonstrate a negative correlation, while, in contrast, the primary extensor, m. triceps brachii correlates positively to each of the flexors. Comparing the global optimum with four other designs along the optimal path, we saw large deviations, e.g., up to 15 ∘ in motion and up to 40% in muscle force. This underlines the importance of accurate determination of fibre pre-stretch in muscles, especially, their role in pathological muscular disorders and surgical applications such as free muscle or tendon transfer.

Association between the phase angle and muscle-tendon complex function in Japanese athletes: a comparative study.

[Purpose] In this study, we investigated the association between the phase angle and the muscle-tendon complex in Japanese athletes and the effects of aging on this association. [Participants and Methods] The study included 61 adult male high school soccer players. Body composition was evaluated using an analyzer, and grip strength and rebound jump index were measured to evaluate muscle-tendon complex function. Study participants were categorized into two groups, and statistical analyses were performed for intergroup comparison of outcomes and to determine the correlation between the phase angle and muscle-tendon complex function. [Results] We observed significant intergroup differences in the phase angle, total body muscle mass, grip strength, and rebound jump index. Additionally, we observed a significant positive correlation between the phase angle and grip strength in adult soccer players. [Conclusion] Our results showed a correlation between the phase angle and muscle-tendon complex function in mature adult athletes but not in high school athletes. These findings suggest that the phase angle may serve as an indicator of muscle quality and overall physical condition in adult athletes. Further research is warranted to investigate the association between the phase angle and other performance measures to gain a better understanding of soccer players' athletic abilities.

Model of calf muscle tear during a simulated eccentric contraction, comparison between ex-vivo experiments and discrete element model.

The tearing of the muscle-tendon complex (MTC) is one of the common sports-related injuries. A better understanding of the mechanisms of rupture and its location could help clinicians improve the way they manage the rehabilitation period of patients. A new numerical approach using the discrete element method (DEM) may be an appropriate approach, as it considers the architecture and the complex behavior of the MTC. The aims of this study were therefore: first, to model and investigate the mechanical elongation response of the MTC until rupture with muscular activation. Secondly, to compare results with experimental data, ex vivo tensile tests until rupture were done on human cadavers {triceps surae muscle + Achilles tendon}. Force/displacement curves and patterns of rupture were analyzed. A numerical model of the MTC was completed in DEM. In both numerical and experimental data, rupture appeared at the myotendinous junction (MTJ). Moreover, force/displacement curves and global rupture strain were in agreement between both studies. The order of magnitude of rupture force was close between numerical (858 N for passive rupture and 996 N-1032 N for rupture with muscular activation) and experimental tests (622 N ± 273 N) as for the displacement of the beginning of rupture (numerical: 28-29 mm, experimental: 31.9 mm ± 3.6 mm). These differences could be explained by choices of DEM model and mechanical properties of MTC's components or their rupture strain values. Here we show that he MTC was broken by fibers' delamination at the distal MTJ and by tendon disinsertion at the proximal MTJ in agreement with experimental data and literature.

Stimuli for Adaptations in Muscle Length and the Length Range of Active Force Exertion-A Narrative Review.

Treatment strategies and training regimens, which induce longitudinal muscle growth and increase the muscles' length range of active force exertion, are important to improve muscle function and to reduce muscle strain injuries in clinical populations and in athletes with limited muscle extensibility. Animal studies have shown several specific loading strategies resulting in longitudinal muscle fiber growth by addition of sarcomeres in series. Currently, such strategies are also applied to humans in order to induce similar adaptations. However, there is no clear scientific evidence that specific strategies result in longitudinal growth of human muscles. Therefore, the question remains what triggers longitudinal muscle growth in humans. The aim of this review was to identify strategies that induce longitudinal human muscle growth. For this purpose, literature was reviewed and summarized with regard to the following topics: (1) Key determinants of typical muscle length and the length range of active force exertion; (2) Information on typical muscle growth and the effects of mechanical loading on growth and adaptation of muscle and tendinous tissues in healthy animals and humans; (3) The current knowledge and research gaps on the regulation of longitudinal muscle growth; and (4) Potential strategies to induce longitudinal muscle growth. The following potential strategies and important aspects that may positively affect longitudinal muscle growth were deduced: (1) Muscle length at which the loading is performed seems to be decisive, i.e., greater elongations after active or passive mechanical loading at long muscle length are expected; (2) Concentric, isometric and eccentric exercises may induce longitudinal muscle growth by stimulating different muscular adaptations (i.e., increases in fiber cross-sectional area and/or fiber length). Mechanical loading intensity also plays an important role. All three training strategies may increase tendon stiffness, but whether and how these changes may influence muscle growth remains to be elucidated. (3) The approach to combine stretching with activation seems promising (e.g., static stretching and electrical stimulation, loaded inter-set stretching) and warrants further research. Finally, our work shows the need for detailed investigation of the mechanisms of growth of pennate muscles, as those may longitudinally grow by both trophy and addition of sarcomeres in series.

Modeling of muscular activation of the muscle-tendon complex using discrete element method.

The tearing of a muscle-tendon complex (MTC) is caused by an eccentric contraction; however, the structures involved and the mechanisms of rupture are not clearly identified. The passive mechanical behavior the MTC has already been modeled and validated with the discrete element method. The muscular activation is the next needed step. The aim of this study is to model the muscle fiber activation and the muscular activation of the MTC to validate their active mechanical behaviors. Each point of the force/length relationship of the MTC (using a parabolic law for the force/length relationship of muscle fibers) is obtained with two steps: 1) a passive tensile (or contractile) test until the desired elongation is reached and 2) fiber activation during a position holding that can be managed thanks to the Discrete Element model. The muscular activation is controlled by the activation of muscle fiber. The global force/length relationship of a single fiber and of the complete MTC during muscular activation is in agreement with literature. The influence of the external shape of the structure and the pennation angle are also investigated. Results show that the different constituents of the MTC (extracellular matrix, tendon), and the geometry, play an important role during the muscular activation and enable to decrease the maximal isometric force of the MTC. Moreover, the maximal isometric force decreases when the pennation angle increases. Further studies will combine muscular activation with a stretching of the MTC, until rupture, in order to numerically reproduce the tearing of the MTC.

High-density electromyographic assessment of stretch reflex activity during drop jumps from varying drop heights.

This study investigated how drop heights and their associated drop jump performance relate to stretch reflex modulations. Eleven male subjects performed ten drop jumps from each of three individually predetermined drop heights. These were the drop height resulting in maximal performance (OPT), as well as 10 cm below (LOW) and above (HIGH) maximal performance. To quantify drop jump performance the reactive strength index, derived from force plate measures, was used. High-density surface EMG provided both stretch reflex response timing and size, as well as novel insight into the associated motor unit recruitment via muscle fiber conduction velocity estimations. These measures were examined in the vastus lateralis (VL), soleus (SOL) and gastrocnemius medialis (GM). Drop jump performance improved by 9% (p < 0.001) from LOW to OPT and decreased by 5% (p = 0.008) from OPT to HIGH. Despite decreasing performance, stretch reflex responses were largest at HIGH. Stretch reflex responses timing did not change; staying within the short (SOL, <60 ms) and medium (VL, GM; 60-85 ms) latency response time-frames. Motor unit recruitment appeared to change across drop heights only for VL, whereas activation intensity only changed for SOL. These results indicate that during drop jumps above OPT neuromuscular modifications result in VL no longer being maximally recruited.

Potential relationship between passive plantar flexor stiffness and sprint performance in sprinters.

OBJECTIVE: To investigate the relationship between passive planter flexor stiffness and sprint performance in sprinters. DESIGN: Cross-sectional study. PARTICIPANTS: Fifty well-trained male sprinters (age: 20.7 ±â€¯1.9 years, height: 175.6 ±â€¯4.9 cm, weight: 66.7 ±â€¯5.1 kg) were participated in this study. Their best personal times in a 100-m sprint ranged from 10.22 to 11.86 s (mean, 11.12 ±â€¯0.43 s). METHODS: Passive stiffness of the plantar flexors measured using a dynamometer system. Passive stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. RESULTS: Plantar flexor passive stiffness was significantly correlated with personal best 100-m sprint time (r = -0.334, P = 0.018). CONCLUSION: The present findings suggest that although the relationship between plantar flexor passive stiffness and personal best 100-m sprint time was relatively minimal, a higher plantar flexor passive stiffness may be a potential factor for achieving superior sprint performance in sprinters. Therefore, in the clinical setting, measurement of passive planter flexor stiffness may be useful for assessing sprint performance.

A mathematical model characterising Achilles tendon dynamics in flexion.

The purpose of this study is to acquire mechanistic knowledge of the gastrocnemius muscle-Achilles tendon complex behaviour during specific movements in humans through mathematical modelling. Analysis of this muscle-tendon complex was performed to see if already existing muscle-tendon models of other parts of the body could be applied to the leg muscles, especially the gastrocnemius muscle-Achilles tendon complex, and whether they could adequately characterise its behaviour. Five healthy volunteers were asked to take part in experiments where dorsiflexion and plantar flexion of the foot were studied. A model of the Achilles tendon-gastrocnemius muscle was developed, incorporating assumptions regarding the mechanical properties of the muscle fibres and the tendinous tissue in series. Ultrasound images of the volunteers, direct measurements and additional mathematical calculations were used to parameterise the model. Ground reaction forces, forces on specific joints and moments and angles for the ankle were obtained from a Vicon 3D motion capture system. Model validation was performed from the experimental data captured for each volunteer and from reconstruction of the movements of specific trajectories of the joints, muscles and tendons involved in those movements.

Influence of preactivation on fascicle behavior during eccentric contraction.

BACKGROUND: Because muscle fascicle behavior affects to the force-generating capability, understanding of muscle fascicle length changes during dynamic movements is important. Preactivation may affect the muscle fascicle length changes, especially in the case of eccentric contraction. However, its influence has not been clarified. To this end, muscle fascicle behavior during eccentric contraction was compared between preactivation and no-preactivation conditions. RESULTS: Seven healthy men (24.6 ± 2.2 years, 169 ± 2 cm, 68.0 ± 5.1 kg) participated in this study. An eccentric knee extension controlled by a Biodex system was adopted as the testing motion. Muscle fascicle behavior of vastus lateralis during eccentric knee extensions was compared following two conditions. In preactivation condition, isometric preactivation was conducted before initiating eccentric contraction. On the other hand, in no-preactivation condition, muscle contraction was initiated immediately after initiating the knee angle change induced by a dynamometer. The muscle fascicle length at the onset of eccentric contraction was significantly shorter in preactivation condition than in no-preactivation condition (Cohen's d = 0.98, p < 0.001) although that at the end of eccentric contraction was not different (Cohen's d = 0.08, p = 0.844). The muscle fascicle was elongated throughout the eccentric contraction phase in preactivation condition. On the other hand, muscle fascicle was shortened in the first part, and then elongated in the latter part of the eccentric contraction phase in no-preactivation condition. CONCLUSIONS: The muscle fascicle is shortened even during eccentric contraction phase. However, this shortening is disappeared when preactivation is conducted.

Resultados de la electrólisis percutánea intratisular en el dolor en el hombro: infraespinoso, un ensayo controlado aleatorio / Résultats de l'Électrolyse Percutanée Intra-tissulaire contre la douleur de l'épaule: Muscle sous-épineux. Une étude contrôlée et randomisée / Results of the Electrolysis Percutaneous Intratissue in the shoulder pain: infraspinatus, A Randomized Controlled Trial

Background: The Electrolysis Percutaneous Intratissue (EPI®) is a novel technique that provokes a local inflammatory process, allowing the phagocytises and affected tissue to repair. Objectives: The work is aimed to: a) verify the effectiveness of the EPI® when there is shoulder pain, b) locate where the EPI® should be applied, c) and find the possible interaction between the trigger points and the tendon pain. Design: Randomized controlled trial. Setting: Institute of Physiotherapy and Sports. Method: A double randomized experimental longitudinal study was conducted on four groups of 10 people aged 34-47 years with pain in the shoulder. In the first study there were three intervention groups and a control group. In the second study, the group with the best results in the first study served as a control group. Measurements: The variables measured were the perceived pain and the restriction for abduction, internal and external rotation. Results: Although the three intervention groups improved respect to the control group when the EPI® was applied, the results show that the EPI® is more effective when it is applied in all detected trigger points and to tendon pain. Conclusions: The EPI® is more effective if applied in the infraspinatus muscle and the tendon than applied only to one of the two structures, when both structures have pain. Limitations: The study could have tested the involvement of different structures and its related biomechanical implications. It could have also considered more variables(AU)

Introducción: la electrólisis percutánea intratisular (EPI®) es una novedosa técnica que provoca un proceso inflamatorio local, que permite la fagocitosis y la reparación del tejido afectado. Objetivos: verificar la efectividad de la EPI® cuando hay dolor del hombro, b) localizar dónde debería ser aplicada la EPI® y C) y determinar la interacción entre los posibles puntos de activación y el dolor del tendón. Diseño: estudio controlado aleatorio. Ubicación: Instituto de Fisioterapia y el Deporte. Método: se realizó un estudio longitudinal experimental aleatorizado doble en cuatro grupos de 10 personas con edades entre 34-47 años que sufrían dolor en el hombro. En el primer estudio hubo tres grupos de intervención y un grupo de control. En el segundo estudio, el grupo que tuvo mejores resultados en el primer estudio sirvió como grupo de control. Mediciones: las variables que se midieron fueron dolor percibido y la restricción de la abducción, rotación interna y rotación externa. Resultados: aunque los tres grupos de intervención mejoraron respecto al grupo de control cuando se aplicó la EPI®, los resultados muestran que la EPI® es más eficaz cuando se aplica en todos los puntos de activación detectados y donde hay dolor en los tendones. Conclusiones: la EPI® es más eficaz si se aplica en el músculo infraespinoso y el tendón que si se aplica solo a una de las dos estructuras, cuando ambas presentan dolor. Limitaciones: el estudio podría haber probado la participación de diferentes estructuras y sus implicaciones biomecánicas relacionadas. Podría también haber tenido en cuenta más variables(AU)

Introduction: L'Électrolyse Percutanée Intra-tissulaire (EPI®) est une nouvelle technique qui produit une réaction inflammatoire locale permettant la régénération tissulaire du tendon, ligament, muscle, etc. Objectifs: Le but de ce travail est de, a) confirmer l'effectivité de l'EPI® lorsqu'il y a une douleur au niveau de l'épaule, b) localiser la région sur laquelle l'EPI® doit être appliqué, et c) trouver la possible interaction entre les points de stimulation et la douleur tendineuse. Dessin: Une étude contrôlée et randomisée. Lieu: Institut de physiothérapie et de sports. Méthode: Une étude randomisée, expérimentale et longitudinale de quatre groupes de 10 personnes, âgées de 34 - 47 ans et atteintes d'une douleur au niveau de l'épaule, a été réalisée. Dans la première étude, il y a eu trois groupes expérimentaux et un groupe témoin. Dans la deuxième étude, le groupe ayant les meilleurs résultats dans la première étude a servi de groupe témoin. Évaluations: Parmi les variables analysées, on peut trouver la perception de la douleur et la limitation de l'adduction et de la rotation interne et externe. Résultats: Quoique les trois groupes expérimentaux ont éprouvé une amélioration vis-à-vis le groupe témoin après l'application de l'EPI®, les résultats ont montré que cette technique est plus effective si elle est appliquée sur tous les points de stimulation détectés et contre la douleur tendineuse. Conclusions: L'EPI® est plus effective si elle est appliquée sur le muscle sous-épineux et les tendons que sur une seule de ces deux structures, quand toutes les deux sont douloureuses. Limitations: L'étude pouvait avoir examiné les différentes structures compromises et leurs implications biomécaniques associées. Elle pouvait avoir aussi considéré beaucoup plus de variables(AU)

Influence of muscle-tendon complex geometrical parameters on modeling passive stretch behavior with the Discrete Element Method.

The muscle-tendon complex (MTC) is a multi-scale, anisotropic, non-homogeneous structure. It is composed of fascicles, gathered together in a conjunctive aponeurosis. Fibers are oriented into the MTC with a pennation angle. Many MTC models use the Finite Element Method (FEM) to simulate the behavior of the MTC as a hyper-viscoelastic material. The Discrete Element Method (DEM) could be adapted to model fibrous materials, such as the MTC. DEM could capture the complex behavior of a material with a simple discretization scheme and help in understanding the influence of the orientation of fibers on the MTC׳s behavior. The aims of this study were to model the MTC in DEM at the macroscopic scale and to obtain the force/displacement curve during a non-destructive passive tensile test. Another aim was to highlight the influence of the geometrical parameters of the MTC on the global mechanical behavior. A geometrical construction of the MTC was done using discrete element linked by springs. Young׳s modulus values of the MTC׳s components were retrieved from the literature to model the microscopic stiffness of each spring. Alignment and re-orientation of all of the muscle׳s fibers with the tensile axis were observed numerically. The hyper-elastic behavior of the MTC was pointed out. The structure׳s effects, added to the geometrical parameters, highlight the MTC׳s mechanical behavior. It is also highlighted by the heterogeneity of the strain of the MTC׳s components. DEM seems to be a promising method to model the hyper-elastic macroscopic behavior of the MTC with simple elastic microscopic elements.

The manipulation of strain, when stress is controlled, modulates in vivo tendon mechanical properties but not systemic TGF-ß1 levels.

Modulators of loading-induced in vivo adaptations in muscle-tendon complex (MTC) mechanical properties remain unclear. Similarly contentious, is whether changes in MTC characteristics are associated with growth factor levels. Four groups were subjected to varying magnitudes of stress/strain: Group 1 trained with the MTC at a shortened position (MTCS; n = 10); Group 2 at a lengthened position (MTCL; n = 11; stress levels matched to MTCS); Group 3 over a wide range of motion (MTCX; n = 11); and Group 4 (n = 10) was the control population (no training). Patella tendon Stiffness (P < 0.001), Young's modulus, and quadriceps torque (P < 0.05) increments (only seen in the training groups), showed MTCL and MTCX groups responses to be superior to those of MTCS (P < 0.05). In addition, MTCL and MTCX better maintained adaptations compared to MTCS (P < 0.05) following detraining, with a pattern of slower loss of improvements at the early phase of detraining in all training groups. There were no significant changes (P > 0.05) in antagonist cocontraction, patella tendon dimensions or circulating transforming growth factor beta (TGF-ß1) levels following training or detraining in any of the groups. We conclude that chronically loading the MTC in a relatively lengthened position (which involves greater strains) enhances its mechanical properties, more so than loading in a shortened position. This is true even after normalizing for internal stress. The underlying endocrine mechanisms do not appear to be mediated via TGF-ß1, at least not at the systemic level. Our findings have implications with regard to the effectiveness of eccentric loading on improved tendon structural and mechanical properties.

MUSCULOSKELETAL FACTORS INFLUENCING ANKLE JOINT RANGE OF MOTION IN THE MIDDLE-AGED AND ELDERLY INDIVIKUALS / 体力科学

The factors influencing ankle range of motion were investigated for 185 middle-aged and elderly subjects (116 women and 69 men, aged 48-86 years) . Each subject was seated with the right knee extended, and the ankle joint was passively dorsiflexed by a dynamometer with torque just tolerable for each subject, to measure the maximal dorsiflexion angle. During passive loading, elongation of muscle fibers in the gastrocnemius and Achilles tendon was determined in vivo by ultrasonography. There was a difference between women and men for the passive dorsiflexion angle (men smaller than women), which negatively correlated with muscle thickness of the posterior portion of the leg determined by ultrasonography. Both in women and men, the passive dorsiflexion angle negatively correlated with age, even after normalizing for maximal voluntary plantar flexion torque. Both elongation of muscle fibers and tendon was related to the passive dorsiflexion angle, and the ratio of tendon elongation to muscle fiber elongation positively correlated with the passive dorsiflexion angle. The active dorsiflexion angle, measured separately with the subject maximally dorsiflexing the ankle with no load, correlated with the passive dorsiflexion angle but not with age, and there was no gender difference. From the results it was suggested 1) that the mobility of the ankle joint is affected by elongation of both muscle fibers and tendon, but with the effect of the tendon being greater than that of muscle fibers, and 2) that muscle mass negatively affects passively-induced joint range of motion. Actively performed joint range of motion would be affected by elongation of the muscle-tendon corn plex and force-generating capability of the ankle. Gender difference in joint range of motion and the aging effect are related to these factors.