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Nowadays, active human body models are becoming essential tools for the development of integrated occupant safety systems. However, their broad application in industry and research is limited due to the complexity of incorporated muscle controllers, the long simulation runtime, and the non-regular use of physiological motor control approaches. The purpose of this study is to address the challenges in all indicated directions by implementing a muscle controller with several physiologically inspired control strategies into an open-source extended Hill-type muscle model formulated as LS-DYNA user-defined umat41 subroutine written in the Fortran programming language. This results in increased usability, runtime performance and physiological accuracy compared to the standard muscle material existing in LS-DYNA. The proposed controller code is verified with extensive experimental data that include findings for arm muscles, the cervical spine region, and the whole body. Selected verification experiments cover three different muscle activation situations: (1) passive state, (2) open-loop and closed-loop muscle activation, and (3) reflexive behaviour. Two whole body finite element models, the 50th percentile female VIVA OpenHBM and the 50th percentile male THUMS v5, are used for simulations, complemented by the simplified arm model extracted from the 50th percentile male THUMS v3. The obtained results are evaluated additionally with the CORrelation and Analysis methodology and the mean squared error method, showing good to excellent biofidelity and sufficient agreement with the experimental data. It was shown additionally how the integrated controller allows simplified mimicking of the movements for similar musculoskeletal models using the parameters transfer method. Furthermore, the Hill-type muscle model presented in this paper shows better kinematic behaviour even in the passive case compared to the existing one in LS-DYNA due to its improved damping and elastic properties. These findings provide a solid evidence base motivating the application of the enhanced muscle material with the internal controller in future studies with Active Human Body Models under different loading conditions. [ABSTRACT FROM AUTHOR]

Delivering health care at home emerged as a key advancement to reduce healthcare costs and infection risks, as during the SARS-Cov2 pandemic. In particular, in motor training applications, wearable and portable devices can be employed for movement recognition and monitoring of the associated brain signals. This is one of the contexts where it is essential to minimize the monitoring setup and the amount of data to collect, process, and share. In this paper, we address this challenge for a monitoring system that includes high-dimensional EEG and EMG data for the classification of a specific type of hand movement. We fuse EEG and EMG into the magnitude squared coherence (MSC) signal, from which we extracted features using different algorithms (one from the authors) to solve binary classification problems. Finally, we propose a mapping-and-aggregation strategy to increase the interpretability of the machine learning results. The proposed approach provides very low mis-classification errors ( < 0.1 ), with very few and stable MSC features ( < 10 % of the initial set of available features). Furthermore, we identified a common pattern across algorithms and classification problems, i.e., the activation of the centro-parietal brain areas and arm's muscles in 8-80 Hz frequency band, in line with previous literature. Thus, this study represents a step forward to the minimization of a reliable EEG-EMG setup to enable gesture recognition. [ABSTRACT FROM AUTHOR]

The coracobrachialis muscle (CB) represents one of the anterior arm compartment muscles. It has been defined by classic anatomy textbooks and old papers, as a muscle of one belly arising from the coracoid process tip and partially from the tendon of the biceps brachii short head, and inserted into the humeral shaft, above the bone's midpoint. However, recent cadaveric studies have confirmed that in the majority of cases, the CB is a two-headed muscle consisting of a superficial and a deep head. This finding has caused confusion regarding the terminology of CB's morphology. Typical CB morphology, according to recent data should not be considered the muscle of one belly, but the two-headed muscle. In particular, the musculocutaneous nerve's (MCN) course plays an important role in defining the CB morphological characteristics. If the MCN courses medially to the CB, with no signs of penetration after dissection, it can be concluded, that the CB is composed of one head; otherwise, if the muscle is composed of two or more heads, the MCN will courses between the CB bellies. In conclusion, it is of paramount importance to adopt common-universal terminology. Hence, considering recent findings, if the CB origin and/or the insertion differs from the typical anatomy, an "atypical CB" is the proper definition of the muscle, while if this "atypical CB" coexists with a typical CB, the terminology "accessory CB" may be used. [ABSTRACT FROM AUTHOR]

The motor system relies on the recruitment of motor modules to perform various movements. Muscle synergies are the modules used by the central nervous system to simplify the control of complex motor tasks. In this paper, we aim to explore the primitive synergies to reflect different modes of coordination in upper limb motions. Muscle synergies and corresponding activation coefficients were extracted via non-negative matrix factorization from the electromyography signals of three basic and four complex upper limb motions in sagittal plane and coronal plane. Similarities of muscle synergies and activation coefficients between different tasks and different subjects were compared. Moreover, we used network theory to assess the coordination between multiple muscles and to elucidate the neural implementation of muscle synergies. The results showed that the combination of different sets of primitive muscle synergies can achieve complex motions in different planes. The muscle synergy network topology differed significantly between different tasks. We also demonstrated the potential of this study for the understanding of human motor control mechanism and implications for neurorehabilitation. [ABSTRACT FROM AUTHOR]

A key problem for biological motor control is to establish a link between an idea of a movement and the generation of a set of muscle-stimulating signals that lead to the movement execution. The number of signals to generate is thereby larger than the body's mechanical degrees of freedom in which the idea of the movement may be easily expressed, as the movement is actually executed in this space. A mathematical formulation that provides a solving link is presented in this paper in the form of a layered, hierarchical control architecture. It is meant to synthesise a wide range of complex three-dimensional muscle-driven movements. The control architecture consists of a 'conceptional layer', where the movement is planned, a 'structural layer', where the muscles are stimulated, and between both an additional 'transformational layer', where the muscle-joint redundancy is resolved. We demonstrate the operativeness by simulating human stance and squatting in a three-dimensional digital human model (DHM). The DHM considers 20 angular DoFs and 36 Hill-type muscle–tendon units (MTUs) and is exposed to gravity, while its feet contact the ground via reversible stick–slip interactions. The control architecture continuously stimulates all MTUs ('structural layer') based on a high-level, torque-based task formulation within its 'conceptional layer'. Desired states of joint angles (postural plan) are fed to two mid-level joint controllers in the 'transformational layer'. The 'transformational layer' communicates with the biophysical structures in the 'structural layer' by providing direct MTU stimulation contributions and further input signals for low-level MTU controllers. Thereby, the redundancy of the MTU stimulations with respect to the joint angles is resolved, i.e. a link between plan and execution is established, by exploiting some properties of the biophysical structures modelled. The resulting joint torques generated by the MTUs via their moment arms are fed back to the conceptional layer, closing the high-level control loop. Within our mathematical formulations of the Jacobian matrix-based layer transformations, we identify the crucial information for the redundancy solution to be the muscle moment arms, the stiffness relations of muscle and tendon tissue within the muscle model, and the length–stimulation relation of the muscle activation dynamics. The present control architecture allows the straightforward feeding of conceptional movement task formulations to MTUs. With this approach, the problem of movement planning is eased, as solely the mechanical system has to be considered in the conceptional plan. [ABSTRACT FROM AUTHOR]

Biomimetic robots yearn for compliant actuators that are comparable to biological muscle in both functions and structural properties. For that, electrostatic actuators have been developed to imitate bio-muscle in features of fast response, high power, energy-efficiency, etc. However, those actuators typically lack impact damping performance, making them vulnerable and unstable in real applications. Here, we present auxetic electrostatic actuators that address this issue and demonstrate muscle-like performance by using elastomer-enhanced auxetics and electrostatic zipping mechanism. The proposed actuators contract linearly on applied voltage, producing large actuation strength (15 N) and contraction ratio (59%). Fabricated from readily available materials, our prototypes can quickly attenuate vibrations caused by impacts and absorb shock energy in 0.3 s. Furthermore, leveraging their 2-dimensional working mode and self-locking mechanism, a stiffness-changing muscle for a robotic arm and an active tensegrity device exemplify the potential applications of auxetic electrostatic actuators to a wide range of bionic robots. Electrostatic actuators can imitate muscle features, but they are limited for real applications. Here, the authors show auxetic electrostatic actuators, using elastomer-enhanced auxetics and electrostatic zipping mechanism, that demonstrate muscle-like performance. [ABSTRACT FROM AUTHOR]

The leading joint hypothesis (LJH), developed for planar arm reaching, proposes that the interaction torques experienced by the proximal joint are low compared to the corresponding muscle torques. The human central nervous system could potentially ignore these interaction torques at the proximal ( leading) joint with little effect on the wrist trajectory, simplifying joint-level control. This paper investigates the extension of the LJH to spatial reaching. In spatial motion, a number of terms in the governing equation (Euler's angular momentum balance) that vanish for planar movements are non-trivial, so their contributions to the joint torque must be classified as net, interaction or muscle torque. This paper applies definitions from the literature to these torque components to establish a general classification for all terms in Euler's equation. This classification is equally applicable to planar and spatial motion. Additionally, a rationale for excluding gravity torques from the torque analysis is provided. Subjects performed point-to-point reaching movements between targets whose locations ensured that the wrist paths lay in various portions of the arm's spatial workspace. Movement kinematics were recorded using electromagnetic sensors located on the subject's arm segments and thorax. The arm was modeled as a three-link kinematic chain with idealized spherical and revolute joints at the shoulder and elbow. Joint torque components were computed using inverse dynamics. Most movements were 'shoulder-led' in that the interaction torque impulse was significantly lower than the muscle torque impulse for the shoulder, but not the elbow. For the few elbow-led movements, the interaction impulse at the elbow was low, while that at the shoulder was high, and these typically involved large elbow and small shoulder displacements. These results support the LJH and extend it to spatial reaching motion. [ABSTRACT FROM AUTHOR]

The gastrocnemius muscle forms the belly of calf muscles in the posterior compartment of the leg. This paper reports a four-headed gastrocnemius (named quadriceps gastrocnemius) muscle as a new variant and when present can alter the anatomy and/or the boundaries of the popliteal fossa. The four heads are named as medial, intermedio-medial, intermedio-lateral and medial. The newly identified heads, intermedio-medial and intermedio-lateral heads form the inferior boundaries of the popliteal fossa. Clinical conditions like popliteal entrapment syndrome may arise because of distal fossa congestion created by the intermedio-medial and intermedio-lateral heads. This supernumerary heads may also be useful for grafting and they also provide bulkier mass for gastrocnemius proximal attachment. The knowledge of anatomical variants presented is useful to surgeons, prosectors and radiologists. [ABSTRACT FROM AUTHOR]

The effects of IT and R.I.C.E. treatment on arm muscle performance in overhead athletes with elbow pain (EP) have been partially validated. However, there is a lack of research evidence regarding the efficacy of these two methods on arm muscle performance among swimmers with EP. The aim of this study was to investigate the trends and differences in the effects of IT and R.I.C.E. treatment on arm muscle performance among swimmers with EP. The main outcomes were the time effects and group effects of interventions on muscle voluntary contraction (MVC). Sixty elite freestyle swimmers from Tianjin, China, voluntarily participated in the study and completed a 10-week intervention program. Swimmers with EP in the IT group showed a positive trend in MVC, with an approximately 2% increase, whereas the MVC of subjects in the R.I.C.E. treatment group and control group decreased by approximately 4% and 5%, respectively. In comparison, the effects of the IT intervention on the MVC of the triceps and brachioradialis muscles in swimmers with EP were significant (p = 0.042 < 0.05, p = 0.027 < 0.05). The mean MVC value of the IT group (0.60) was greater than that of the other two groups (0.51, 0.50). IT has a beneficial impact on the MVC performance of the triceps and brachioradialis muscles in swimmers with EP. It is recommended that professionals consider incorporating IT into regular training routines to mitigate the risk of EP issues. Future research should examine the effectiveness of both interventions on hand-grip strength and completion time in 50-m freestyle swim drills in order for swimmers with EP to return to this sport. [ABSTRACT FROM AUTHOR]

Functional Electrical Stimulation (FES) has demonstrated potential in clinical applications, but determining the optimal electrical current to stimulate muscles remains challenging due to the intricate coordination of various muscle groups during human movement. In this study, we introduce a novel approach to model and control human arm planar reaching movements. In terms of the model, a comprehensive human upper limb model is developed, taking into account the double-link structure, six muscles, and the connection points between muscles and the skeletal system. Regarding the control, a comprehensive sensorimotor control model emulating neural activities for human arm planar reaching movements is proposed. The control model effectively incorporates the imprecise nature of human visual sensory feedback for arm endpoint positioning and emulates the neural activities to determine appropriate stimulation levels for each of the six constituent muscles, inducing muscle contractions and guiding the skeletal systems to the target positions. The effectiveness of the proposed controller is demonstrated via numerical simulation experiments. Through comparisons with different controllers, it is shown that the proposed controller exhibits superior performance in tracking predefined motion trajectories and robustness in dealing with various skeletal muscle arm parameters. [ABSTRACT FROM AUTHOR]

Purpose: The current cadaveric case series evaluates the coracobrachialis muscle morphology, the related musculocutaneous nerve origin, course, and branching pattern, as well as associated adjacent neuromuscular variants. Materials and methods: Twenty-seven (24 paired and 3 unpaired) cadaveric arms were dissected to identify the coracobrachialis possible variants with emphasis on the musculocutaneous nerve course and coexisted neural variants. Results: Four morphological types of the coracobrachialis were identified: a two-headed muscle in 62.96% (17/27 arms), a three-headed in 22.2% (6/27), a one-headed in 11.1% (3/27), and a four-headed in 3.7% (1 arm). A coracobrachialis variant morphology was identified in 37.04% (10/27). A three-headed biceps brachii muscle coexisted in 23.53% (4/17). Two different courses of the musculocutaneous nerve were recorded: 1. a course between coracobrachialis superficial and deep heads (in cases of two or more heads) (100%, 24/24), and 2. a medial course in case of one-headed coracobrachialis (100%, 3/3). Three neural interconnections were found: 1. the lateral cord of the brachial plexus with the medial root of the median nerve in 18.52%, 2. the musculocutaneous with the median nerve in 7.41% and 3. the radial with the ulnar nerve in 3.71%. Duplication of the lateral root of the median nerve was identified in 11.1%. Conclusions: The knowledge of the morphology of the muscles of the anterior arm compartment, especially the coracobrachialis variant morphology and the related musculocutaneous nerve variable course, is of paramount importance for surgeons. Careful dissection and knowledge of relatively common variants play a significant role in reducing iatrogenic injury. [ABSTRACT FROM AUTHOR]

In cases where mobility and joint function are impaired after implantation of a THA, weakening of hip movement in both extension/flexion and adduction/abduction may play a role due to shortening of the physiological lever arm of the hip muscles. Mechanical factors of influence include the lateral femoral offset, which affects the lever arm, and the antetorsion angle of the hip prosthesis, which affects the anterior femoral offset. This study aimed to investigate the effect of an altered antetorsion angle of the implant on the hip moments and gait patterns of the patient. For this study, 13 patients with a conventional stem on one side and a calcar-guided short stem implanted on the contralateral side were included. To determine the maximum hip moment, tests were performed on a dynamometer in extension/flexion and adduction/abduction in addition to gait analysis. As a control, a comparison was made with data from a reference group of 30 healthy subjects. Both implants showed similar symmetry indices. There was a significant difference between the implants for adduction moments (p < 0.001). The ratios between the directions of moments showed no significant differences. The joint function measured by isokinetic measurements and gait analysis remains comparable to the healthy control group after short stem arthroplasty, but shows slight changes after conventional stem arthroplasty. [ABSTRACT FROM AUTHOR]

Surf wetsuits are made of foamed chloroprene (neoprene), a synthetic rubber that is hard to recycle. Thermoplastic elastomer foam (TPE) may be a more sustainable replacement for neoprene in wetsuit design, but its impact on human thermoregulation and movement has not been evaluated. The purpose of this study was to compare skin temperature, oxygen consumption, heart rate, muscle activation, and arm kinematics while paddling in a thermoplastic elastomer vs. standard neoprene wetsuit. Thirty-three experienced surfers participated in one of two studies: a 60 min simulated surf session in a freshwater swim flume designed to evaluate skin temperature (n = 18), or a dry-land ergometer session designed to evaluate physiological and biomechanical aspects of surfboard paddling (n = 15). Skin temperatures under neoprene were significantly warmer than under thermoplastic elastomer at several anatomical locations including the upper chest (p < 0.01, η partial 2 = 0.291), lower abdomen (p < 0.001, η partial 2 = 0.527), lower back (p < 0.005, η partial 2 = 0.416), lower arm (p < 0.001, η partial 2 =0.537), upper leg (p < 0.001, η partial 2 = 0.717), and lower leg (p < 0.001, η partial 2 = 0.802). However, most participants did not perceive any temperature differences (50%) or felt that the thermoplastic elastomer was warmer (19%). There were no significant differences for any of the other physiological and biomechanical variables analyzed here (p > 0.05). These results suggest that thermoplastic elastomer foam is the less efficient insulator when compared to neoprene, but this difference may be imperceptible to the average surfer. Further, the thermoplastic elastomer wetsuit does not appear to add resistance to or alter upper extremity motion while paddling a dry land ergometer. [ABSTRACT FROM AUTHOR]

Epidural electrical stimulation (EES) of lumbosacral sensorimotor circuits improves leg motor control in animals and humans with spinal cord injury (SCI). Upper-limb motor control involves similar circuits, located in the cervical spinal cord, suggesting that EES could also improve arm and hand movements after quadriplegia. However, the ability of cervical EES to selectively modulate specific upper-limb motor nuclei remains unclear. Here, we combined a computational model of the cervical spinal cord with experiments in macaque monkeys to explore the mechanisms of upper-limb motoneuron recruitment with EES and characterize the selectivity of cervical interfaces. We show that lateral electrodes produce a segmental recruitment of arm motoneurons mediated by the direct activation of sensory afferents, and that muscle responses to EES are modulated during movement. Intraoperative recordings suggested similar properties in humans at rest. These modelling and experimental results can be applied for the development of neurotechnologies designed for the improvement of arm and hand control in humans with quadriplegia. The efficacy of epidural electrical stimulation (EES) to engage arm muscles and improve movement after spinal cord injury is still unclear. Here, the authors investigated how EES can recruit upper-limb motor neurons by combining computational modelling with experiments in non-human primates. [ABSTRACT FROM AUTHOR]

A model of central commands (CCs) coming to the muscles during limb movements is proposed; it is based on experimental studies of the nonlinear dynamics of muscle contraction and of the parafrontal two-joint arm movements in humans. It is known that such CCs possess powerful hysteresis properties; levels of muscle activation rise within parts of the movement trajectories, where the muscles are actively shortened and overcome the action of an external force, but decrease during muscle stretching by the above force. Basing on an analogy with the classic thermodynamics, a "thermodynamic" model (T-model) is proposed, which allows one to predict the nonlinear functional interdependence of three basic parameters defining the muscle state, namely E (intensity of efferent activity), F (muscle force), and L (muscle length). The T-model includes the time-dependent integration of the equations defining the interrelations between infinitesimal changes of the above parameters, which are assumed to be the exact differentials. By inducing only one additional parameter, the hysteresis weight, the T-model can satisfactorily explain patterns of EMG records observed in real movements of the arm. [ABSTRACT FROM AUTHOR]

Purpose: Boys' lower-body muscle power generation (PO) recovers faster than men's following intensive exercise. The purpose of this study was to examine whether boys differ from adult men in recovering from upper-body muscle power generation following intensive exercise.Methods: Fifteen prepubertal boys (M ± SD age 10.6 ± 1.0 years) and 13 men (31.1 ± 5.0 years) performed two upper-body Wingate Anaerobic Tests (WAnT), separated by either 2-min or 10-min recovery intervals. WAnT parameters, pre-and post-WAnT heart rates (HR), and blood lactate ([La]) were measured during recovery from the WAnTs.Results: Boys' mean power (MP) of the repeated WAnT (WAnT2) following 2- and 10-min recoveries was 97.3 ± 7.2% and 99.4 ± 3.9%, respectively, compared to MP of the first test (WAnT1) (p > 0.05 for both tests). In contrast, in men's MP of the WAnT2 following the 2-min recovery, was significantly lower than that of the WAnT1 (84.4 ± 6.7%, p = 0.0001). While boys' and men's HR recovery after 2 min differed significantly (p = 0.046), no between-group differences were found following the 10-min recovery. Peak [La] in boys was 37-44% lower than that in men (p = 0.002).Conclusions: The faster recovery of PO in boys after supra-maximal upper-body exercise is partially explained by the lower power generated by boys, attributed in part to a lower anaerobic capacity and to the greater relative contribution of aerobic processes to performance and recovery from anaerobic-type tasks. Further research is needed to determine the physiologic, neurologic and biochemical basis of the rapid muscle power recovery in children. [ABSTRACT FROM AUTHOR]

Many researchers have recently focused on the functional properties of muscles, and on the mechanics and kinematics of flight, without being able to consult an anatomical database since such a database was either nonexistent or incomplete. In particular, the anatomy of the wing muscles of soaring birds of prey, such as Buteo buteo and Pernis apivorus, has not been examined in detail. The aim of this study was, therefore, to fill this gap in the avian literature and to provide a reference for future comparative and functional studies. Our results show a lesser degree of differentiation of the shoulder musculature as compared to other previously examined birds of prey. However, a few peculiarities were found. In particular, the M. rhomboideus superficialis only has a cranial and a caudal part instead of the typical three parts; the M. pectoralis exhibits a wide and robust fibrous sheet on the deep surface of the Pars sternobrachialis; the cranial head of the Pars propatagialis of the M. deltoideus is especially developed, whereas the tendon of the caudal head divides into two branches. The M. scapulotriceps possesses a humeral anchor and the M. humerotriceps originates from three heads. [ABSTRACT FROM AUTHOR]

An experiment using reciprocal arm and wrist aiming movements with an amplitude of 16 and target width of .5° (ID = 6) was conducted to determine the impact of adding external loads. We predicted that wrist and arm performance may be differentially impacted by the added mass. Participants were asked to flex/extend their limb/lever in a horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between the two targets as quickly and accurately as possible. External loads of 0, .568, or 1.136 kg were fixed at the distal end of the limb/lever. The targets and the current position of the limb were projected on the screen in front of the participant. The results indicated significant Group × Load interactions for movement time and percent time to peak velocity. Movement time decreased as load increased for the wrist but remained stable across loads for arm movements. Percent movement time utilized to accelerate the limb increased as load increased for wrist movements but only increased from 0 to .568 kg load for the arm movements. For both groups increased load had no significant effect on endpoint variability. The present findings suggest that the additional load allowed the control advantages of the wrist muscles to be exploited. [ABSTRACT FROM AUTHOR]