Alterations of mechanical characteristics of human skeletal muscle during strength training

Summary To investigate the influence of strength training on the mechanical characteristics of human skeletal muscle, 14 male subjects went through training of combined heavy concentric and eccentric contractions three times a week for 16 weeks. The strength training program consisted mainly of dynamic exercises for leg extensors with loads of 80 to 120% of one maximum repetition. The force-time curves produced during various vertical jumps were the basis for calculation of various mechanical parameters. In addition to a great increase (p<0.001) in maximal isometric force, heavy resistance strength training also caused significant (p<0.05–0.01) increases in heights and in various mechanical parameters in positive work phases of vertical and drop jumps. The increase in positive force during a fast dynamic contraction was correlated (p<0.01) with the reduced time to produce a certain submaximal force level in isometric condition. No changes in the elastic properties of the muscle were observed as judged from the difference between the counter-movement and squat jumps. When the training was followed by the 8-week detraining period a great decrease (p<0.001) in maximal force took place, but only minor changes (ns) were observed in fast force production.Supported in part by the grants from The Finnish Olympic Committee and Central Sport Federation     

Dynamic simulation of the natural and replaced human ankle joint

Disappointing results for total ankle replacement have been explained by poor knowledge of the mechanics of the intact and replaced joints. Dynamic simulation tools have the capacity to simulate dynamic conditions that occur in human joints. The Working Model 2D tool was used to simulate the mechanics of the intact and replaced ankle joints, based on previously validated mathematical models. Elementary objects were used to model ligaments, articular surfaces, retinacula and muscle-tendon units. The performance of several pairs of prosthetic articular surfaces was also analysed. According to the results of these simulations, rolling as well as sliding motion occurs in the natural ankle, governed by a ligamentous linkage. Elongation of the tibiocalcaneal and calcaneofibular ligaments was found to be 1.5% and 4.8%, respectively. A 13% change in lever arm length occurred for both the tibialis anterior and gastrocnemius muscles during ankle flexion. Unlike the currently available three-component designs, the newly proposed convex-tibial ligament-compatible prosthesis was found to be able to restore the original mobility and physiological function of the ligaments. This prosthesis combines freedom from restraint with congruity of the components throughout the range of flexion.     

Trabecular architecture of the ankle joint

Summary The trabecular architecture of the human ankle joint was studied three dimensionally by microradiography. The trabecular arrangement of the tibia and fibula was divided into four groups. The most characteristic orientation was observed in the bases of both malleoli where pressure-tension was caused by inversion and eversion of the talus. The talus showed two main trabecular arrangements: Trabeculae running between the trochlea and the posterior subtalar joint which supported body weight, and other trabeculae which belonged to part of the longitudinal foot-arch. The calcaneus showed four main trabecular arrangements. The first one was from the posterior subtalar joint to the tuber calcanei for supporting body weight, the second one was a part of the longitudinal foot-arch, the third one was the counterbrace of the second trabeculae, and the fourth one was the response to tension of the Achilles tendon.

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Etude architecturale des travées osseuses an niveau de l'articulation de la cheville

Résumé L'architecturale des travées osseuses au niveau de l'articulation de la cheville a été étudiée en trois dimensions par microradiographie. La disposition des travées au niveau du tibia et du péroné a été schématisée en quatre groupes. L'orientation la plus caractéristique s'observe à la base des deux malléoles où des phénomènes de pression et de traction sont dûs au varus ou au valgus de l'astragale. Au niveau de l'astragale on observe essentiellement deux types de travée osseuse: les unes s'étendent entre la poulie astragalienne et la surface articulaire postérieure et inférieure qui supporte le poids du corps alors que les autres font partie d'un ensemble s'intégrant dans la voûte plantaire. Au niveau du calcanéum on observe quatre types principaux de travées. La première va de la surface articulaire postérieure ou facette thalamique à la tubérosité postérieure qui supporte le poids du corps, la deuxième s'intègre dans l'ensemble de la voûte plantaire, la troisième forme une contrearche à la précédente et la quatrième est induite par la tension du tendon d'Achille.

     

Model-based ankle joint angle tracing by cuff electrode recordings of peroneal and tibial nerves

The main goal of the present study was to estimate the ankle joint angle from the peroneal and tibial electroneurography (ENG) recordings. Two single-channel cuff electrodes for recording ENG were placed on the proximal part of rabbit peroneal and tibial nerves respectively and static positioning and ramp-and-hold stretches were performed to characterize the static and dynamic ENG responses. An ENG model, consisting of static and dynamic parts, was constructed to relate ENG to ankle angle trajectory and an inverse ENG model was derived to predict ankle angle. The results showed that the new model could accurately estimate large-range ankle angles during and after ramp-and-hold movements. Our study provides a basis for implementing joint angle tracing without using artificial angle sensors.     

Influence of aging on the mechanical behavior of leg extensor muscles

Summary Age dependence of the mechanical behavior of leg extensor muscle was investigated using vertical jumps with and without a stretch-shortening cycle on the force-platform. A total 226 subjects (113 females and 113 males) ranging in age from 4–73 years were examined. The results indicated in general that performance in males was better than that in females. This difference was reduced when body weight was taken into consideration. The peak performance of the various parameters, such as average force, height of rise of center of gravity, net impulse, and also the average power output, was reached in both sexes between the ages of 20 and 30 years. For example, the average vertical force in squatting had the following mean values in the various age groups of the male subjects: 114 N (4–6 years), 402 N (13–17), 618 N (18–28), 508 N (29–40), 435 N (41–49), 320 N (54–65), 315 N (71–73 years). When the jumps were performed using the stretch-shortening cycle, the potential of the mechanical performance after prestretching was also sensitive to aging in a similar manner. The results suggest that it is not only the performance of pure concentric contraction that is influenced by the maturation and aging processes but, the that elastic behavior of muscle and reflex potentiation are also affected by the same processes.Supported in part by a grant No. 8318/78/78 from the Ministry of Education, Finland     

Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle

Whereas the acuity of the position sense at the ankle can be disturbed by muscle fatigue, it recently also has been shown to be improved, under normal ankle neuromuscular state, through the use of an artificial tongue-placed tactile biofeedback. The underlying principle of this biofeedback consisted of supplying individuals with supplementary information about the position of their matching ankle position relative to their reference ankle position through electrotactile stimulation of the tongue. Within this context, the purpose of the present experiment was to investigate whether this biofeedback could mitigate the deleterious effect of muscle fatigue on joint position sense at the ankle. To address this objective, sixteen young healthy university students were asked to perform an active ankle-matching task in two conditions of No-fatigue and Fatigue of the ankle muscles and two conditions of No-biofeedback and Biofeedback. Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed that the availability of the biofeedback allowed the subjects to suppress the deleterious effects of muscle fatigue on joint position sense at the ankle. In the context of sensory re-weighting process, these findings suggested that the central nervous system was able to integrate and increase the relative contribution of the artificial tongue-placed tactile biofeedback to compensate for a proprioceptive degradation at the ankle.     

The effects of acceleration on the mechanical impedance response of a primate model exposed to sinusoidal vibration

Criteria for developing active and passive isolation mechanisms for reducing the effects of whole-body vibration exposure rely on a thorough understanding of the stiffness, damping, and resonance behaviors of the human or human surrogate body. Three Rhesus monkeys were exposed to seated whole-body sinusoidal vibration between 3 and 20 Hz at 0.69 and 3.47 msec⁻² rms (0.1 and 0.5 g peak) accelerations. The mechanical impedance magnitude and phase were calculated as the ratio and phase relation between the transmitted force and input velocity, respectively, at the seat. The resultant profiles showed a significant decrease in the primary resonance frequency with increasing acceleration. At the lower acceleration level, a second lower impedance peak was observed at approximately 5 Hz. A three-mass, two degree-of-freedom model, which included upper torso and leg representation, was used to determine the mechanical parameters that best described the measured responses. The mean stiffness coefficients and the mean undamped natural frequencies associated with the upper torso and leg subsystems showed a significant decrease with increases in the acceleration level. The results of this study strongly suggested that nonlinear stiffness properties were responsible for the observed differences in the biodynamic response of the Rhesus monkey with acceleration level.     

On the mechanical power of joint extensions as affected by the change in muscle force (or cross-sectional area), ceteris paribus

This paper offers a reference prediction for the changes of mechanical power generated during a maximal (vertical, horizontal or inclined) joint extension, as a consequence of just the changes of muscle force or cross-sectional area (CSA). Ceteris paribus (all other things being equal), for a given joint, the exponents at which the force changes have to be raised to predict the duration, final speed and power of the maximal extension are –0.5, 0.5, and 1.5, respectively, for horizontal movements. For example, a force decrease of 30% leads to an increase of 19.5% of the duration of the extension and to a decrease of 16.3% and of 41.4% of its final speed and power. The equations for vertical or inclined extension performances are subject to the same exponents. However, the actual prediction is dependent upon the ratio between muscle strength and body weight, reflecting the fraction of the muscle strength (or CSA) acting against gravity during the manoeuvre. For instance, during a vertical extension, a force decrease of 30% leads to an increase of 30.9% of the duration of the extension and to a decrease of 29.3% and of 50.5% of its final speed and power. Based on the proposed model, a methodology is also described to detect the effects on the extension power of other determinants, in addition to CSA, of the useful force change (e.g. neuromuscular factors, motor control). Electronic Publication     

距骨滑车关节面的形态对踝关节稳定性的影响

目的：探讨距骨滑车关节面的形态对踝关节稳定性的影响。方法：用电子数显游标卡尺测量了９３副（男５１，女４２）距骨滑车上关节面前、后宽和内、外侧面长４项指标，数据用ＳＰＳＳ软件处理。结果：距骨滑车面上面前宽男２９．４±２．８ｍｍ、女２７．４±２．６ｍｍ；后宽男２２．６±２．４ｍｍ、女２０．６±２．７ｍｍ；内踝面长男３２．９±３．０ｍｍ、女３０．９±２．５ｍｍ；外踝面长男２９．２±２．５ｍｍ、女２７．２±２．４ｍｍ。距骨滑车上面的前宽与后宽、内踝面长与外踝面长均具有显著性差异。结论：当踝关节跖屈时，处于一种相对不稳定性状态，易损伤。     

A method to evaluate reflex excitability of the human ankle plantarflexors despite changes in maximal activation capacities

Stretch reflexes were evoked in the submaximally activated ankle extensors during sinusoidal length perturbations. A mean stretch reflex (SR) amplitude ((-)SRA), i.e., SR area/SR duration was quantified for the soleus muscle and for the gastrocnemii muscles. (-)SRA was also expressed in relative values ((-)SRA(rel)), i.e., SRA was related to the corresponding background electromyogram (EMG). Sinusoidal length perturbations were applied in two ways: (1) at a fixed frequency (16 Hz) and at different levels of voluntary contraction [10% to 70% maximal voluntary contraction (MVC)] and (2) at a constant activation level (50% MVC) and at frequencies ranging from 6 to 16 Hz. Then, new parameters are proposed to characterize muscle reflex excitability. The first parameter, SR(index), consisting in the slope of the (-)SRA-EMG relationship, was considered to be more representative of central influences on the reflex pathway. Secondly, the frequency distribution of the stretch reflex was analyzed and the area under the (-)SRA(rel)-frequency curve gave the second parameter (FD-(-)SRA(rel)). This parameter should account for both central and peripheral mechanisms on the reflex pathway. These parameters were found to be higher for the highly excitable soleus than for the less excitable gastrocnemii muscles. SR(index) and FD-(-)SRA(rel) can be proposed as a tool to analyze changes in reflex excitability, which can accompany a process of neuromuscular plasticity. In order to validate the procedure, the proposed parameters were quantified in a case study before and after a period of plyometric training.     

以踝关节解剖结构及生物力学特征分析慢性踝关节不稳

背景：长期慢性踝关节不稳可引起创伤性关节病及继发粘连关节囊炎,甚至成为永久性功能障碍。 目的：分析踝关节的生物力学,明确慢性踝关节不稳的形成原因,探讨慢性踝关节不稳的诊断方法及治疗方案。 方法：检索1990年1月至2014年12月PubMed数据库和万方医学网,选取与慢性踝关节不稳有关解剖、生物力学、诊治等相关方面的综述及基础实验研究的文章。检索词：“慢性踝关节不稳,踝关节解剖,生物力学,治疗方法,研究进展”和“Chronic ankle instability,Anatomy of ankle joint,Biomechanics,Therapy, Research”。经过筛选后纳入40篇文献,对踝关节解剖学结构、慢性踝关节外侧不稳机制及分级、诊断方法、治疗方法等内容的总结。 结果与结论：慢性踝关节不稳的诊断方法包括踝关节内翻应力试验、踝关节前抽屉试验、超声检测、现代影像学检测;慢性踝关节不稳的治疗方法分为保守治疗和手术治疗,手术可分为非解剖学重建和受损韧带解剖修复。慢性踝关节不稳患者应进行早期的诊断和有效的治疗,应综合踝关节解剖结构、生物力学特征、发病原因、诊断结果等因素决定治疗方案。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Potentiation of the mechanical behavior of the human skeletal muscle through prestretching

Force–velocity and power–velocity curves in a vertical jump involving movements around several joints were derived from vertical ground reaction forces and knee angular velocities. The jumps were performed with weights from 10 to 160 kg added on the shoulders. The obtained curves from a semi–squatting static starting position resembled those reported for isolated muscles or single muscle groups. Vertical jumps were also performed in the conditions where the shortening of the leg extensors was preceded by prestretching of the active muscles either through a preparatory counter–movement or dropping down on the force–platform from the various heights ranging from 20 to 100 cm. Prestretching modified through a range of velocities the force–velocity and power–velocity curves by increasing both the ground reaction forces and the calculated mechanical power. Thus the results are similar to those reported in isolated muscles. In studies with isolated muscle preparation the nervous connections have not been intact and therefore it is suggested that increase in the performance of the skeletal muscles through prestretching, in the conditions of the present study, was attributed to the combined effects of the utilization of stored elastic energy and the reflex potentiation of muscle activation.     

In vivo determination of mechnical properties of the human ulna by means of mechanical impedance tests: Experimental results and improved mathematical model

An experimental technique and associated apparatus for measuringin vivo the mechanical impedance of the human ulna are described in detail. An electromagnetic shaker is used to apply a steady-state harmonic excitation to the ulna near its mid-span and measurements of the complex driving-point impedance are made. Both stiffness and resonant frequency information, useful in assessing the mechanical integrity of bone, are inferred from the impedance measurements by means of a third-generation mathematical model of the system. Results for three male and two female test subjects are reported.     

Influence of mechanical and metabolic strain on the oxygen consumption slow component during forward pulled running

The possible influence of increased eccentric mechanical work on the increase in oxygen uptake (O₂) after 3 min of running (O₂) was investigated through forward pulled running. Ten subjects ran at individually predetermined constant velocity on a treadmill, while being pulled forward. Ground reaction forces, expired gas and EMGs from leg muscles were collected after 3 min and at the end of the run. O₂ and mechanical work were then calculated. The amplitude of O₂ was 138 (139) ml·min^–1 [mean (SD)]. Increased ventilation explained only 8% of O₂. Stride frequency slightly decreased, inducing a similar decrease in internal work and total mechanical work (all P<0.01), while integrated EMG showed no modifications. It was concluded that O₂ does not come from either an increase in mechanical work production or an increase in muscular activity. O₂ could come from a lower muscle efficiency that could be due to a modification of fibre type recruitment.     

踝关节外骨骼助行模式对下肢肌肉激活与协调模式的影响EI北大核心CSCD

踝关节外骨骼可用来提高人的行走效率,辅助老年人、运动功能障碍患者等进行日常活动或康复训练,但外骨骼的助行模式会对穿戴者的下肢肌肉激活与协调模式产生影响。本文利用一款绳驱动踝关节外骨骼,设计了不同助力时机与助力大小组合的助行模式,采集了7名穿戴者在跑步机上以1.25 m/s速度水平行走时的下肢表面肌电信号,研究不同助行模式对穿戴者下肢肌肉激活与协调模式的影响。实验结果表明,比目鱼肌激活程度在踝关节外骨骼助力时有明显降低,在助力时机为步态周期49%、助力大小为0.7 N·m/kg时,最高可降低(38.5±10.8)%。并且,相对于助力时机,助力大小对比目鱼肌激活程度影响更为显著。踝关节外骨骼不同模式助行时,所测量下肢肌肉可分解为5个基本协同模式,且合适的助力时机与助力大小条件下,下肢肌肉协调模式和正常行走相比改变较小。此外,比目鱼肌-胫骨前肌、股直肌-半腱肌的协同收缩度在外骨骼助力时比正常行走均有升高。本研究有助于理解健康穿戴者如何调整自身的神经肌肉控制机制来适应不同外骨骼助力,并为选择合适的助行模式以及合理利用外骨骼提高行走效率提供依据。     

Angle dependency in strength measurements of the ankle plantar flexors

Summary Muscle strength (or muscular moment) generated during dynamic contractions varies with joint angle. This raises the question about the choice of a representative angle in the evaluation of strength capacity. To assess this angle dependency in strength measurements, dynamic moment-angle curves for plantar flexor muscles were obtained in 43 healthy subjects (28 men and 15 women) with a controlled acceleration dynamometer at 0.52 rad s^–1 (30° s^–1) and using maximal static preloading before the beginning of movement to attenuate the force development phase. Differences between gender and correlations between strength and anthropometric measures were calculated at each 0.087 rad (5°). The plantar flexion moment was larger in men, in general, but this difference was largest when the ankle was most dorsiflexed. The correlations between moment and anthropometric measures were also higher in the first half of the plantar flexion movement. These results stress the importance of reporting joint angles at which moment of force measures were made. Furthermore, they show that the maximal strength capacity of the plantar flexors is best represented by the moment measured in dorsiflexion angles when the muscles are lengthened.     

Electrical impedance tomography as a tool for monitoring mechanical ventilation. An introduction to the technique

Electrical impedance tomography (EIT) is a non-invasive, radiation-free method of diagnostics imaging, allowing for a bedside, real-time dynamic assessment of lung function. It stands as an alternative for other imagining methods, such as computed tomography (CT) or ultrasound. Even though the technique is rather novel, it has a wide variety of possible applications. In the era of modern mechanical ventilation, a dynamic assessment of patient's respiratory condition appears to fulfil the idea of personalized treatment. Additionally, an increasing frequency of respiratory failure among intensive care populations raises demand for improved monitoring tools. This review aims to raise awareness and presents possible implications for the use of EIT in the intensive care setting.     

Effects of stretch-shortening cycle training on mechanical properties and fibre type transition in the rat soleus muscle

The effects of exercise training on mechanical properties and fibre type transitions have been investigated in rat soleus muscle. The exercise was a repetition of stretch-shortening cycles. A method of dual controlled releases was applied to obtain tension/extension curves, which characterize the elastic behaviour of the series elastic component (SEC), and the force/velocity relationship characterizing the contractile elements. Other contractile measurements included: contraction time (t _c), half-relaxation time (t _1/2) and twitch/tetanus ratio (P _t/P _o). Additionally, the muscle fibre type composition was determined by a classical histochemical method. A 12-week period of training induced a significantly higher percentage of fast-twitch fibres and a lower percentage of slow-twitch fibres (P<0.01). This fibre adaptation led to a significant (P<0.01) decrease in t _c and an increase in maximum shortening velocity (V _max). An increase in compliance of the SEC was also observed. This elastic adaptation is interpreted in terms of modification of the active components of the SEC. All the histochemical and mechanical data presented in this study show that rat soleus muscles trained by stretch-shortening cycles acquired faster characteristics. Thus the results confirm that a slow-twitch to a fast-twitch fibre transition is obtainable in mature rats.     

The estimated mechanical advantage of the prosimian ankle joint musculature,and implications for locomotor adaptation

In this study we compared the power arm lengths and mechanical advantages attributed to 12 lower leg muscles across three prosimian species. The origins and insertions of the lower leg muscles in Garnett's galago, the ring‐tailed lemur, and the slow loris were quantified and correlated with positional behaviour. The ankle joint of the galago has a speed‐oriented mechanical system, in contrast to that of the slow loris, which exhibits more power‐oriented mechanics. The lemur ankle joint exhibited intermediate power arm lengths and an intermediate mechanical advantage relative to the other primates. This result suggests that the mechanical differences in the ankle between the galago and the lemur, taxa that exhibit similar locomotory repertoires, reflect a difference in the kinematics and kinetics of leaping (i.e. generalised vs. specialised leapers). In contrast to leaping primates, lorises have developed a more power‐oriented mechanical system as a foot adaptation for positional behaviours such as bridging or cantilevering in their arboreal habitat.