Subject's Muscle Research Articles

Physio-avatar EB: aftereffects in error learning with EMG manipulation of first-person avatar experience.

Many studies have investigated the manipulation of a virtual upper arm using electromyogram (EMG); however, these studies primarily used a machine learning model or trigger control for this purpose. Furthermore, most of them could only display the constant motion of the virtual arm because the motion to be displayed was selected by pattern recognition or trigger control. In addition, these studies did not examine changes in the electromyographic signals after experiencing the virtual arm. By contrast, we propose a real-time, continuous, learning-free avatar that manipulates the virtual arm with electromyogram signals or physio-avatar EMG biofeedback (EB). The goal of the physio-avatar EB system is to induce physiological changes through experiential interactions. We explored the possibility of changing motor control strategies by applying the system to healthy individuals as a case study. An intervention method that provided an experience of a body different from one's own was conducted on seven participants using a time-invariant calculation algorithm to determine the joint angles of the avatar. Control strategies for an indicator of the equilibrium point in the baseline and adaptation phases were determined to evaluate the physio-avatar EB intervention effect. The similarity of these BL and adaptation control strategies compared to those used during the washout period was assessed using the coefficient of determination. The accuracy and reliability of the virtual reality (VR) system were evaluated by comparison with existing studies and the required specs. Changes in motor control strategies due to the physio-avatar EB system were observed in four experiments, where the participants gradually returned to their pre-intervention control strategies. This result can be attributed to the aftereffects caused by error learning. This implies that the developed system influenced their motor control strategies. The number of EMG acquisition bits was 16 bits, and the sampling rate was 1,000 Hz. The refresh rate of the head-mounted display was 90 Hz, and its resolution was for a single eye. Additionally, the simulation frame rate was 30 FPS. These values were adequate compared to existing studies and required specs. The essential contribution of this study is the development of an avatar that is controlled by a different method than has been used in previous studies and the demonstration of changes in a subject's muscle activity after they experience an avatar. In the future, the clinical efficacy of the proposed system will be evaluated with actual patients.

Reduced muscle expression heterogeneity by categorising diabetic subjects resulted in improved statistical significance for trascriptome comparison

The information gained through studies investigating muscle gene expression profiles (GEPs) for diabetes biomarkers identification, has resulted in the general belief that muscle transcriptome is relatively unaltered while the subject gradually progresses from a healthy to a diabetic condition. In this study, we focused on identifying the diabetes subgroup based on the subject's muscle gene expression profile to reduce the expression heterogeneity and regain statistical significance in transcriptome comparison. Given the muscle GEPs of type-II diabetic (T2D) and normal glucose tolerant (NGT) subjects, the R-package WGCNA was used to identify a set of correlated genes termed a module. The Random Forest classifier trained over expression profiles of genes belonging to respective modules was used to classify subjects into subgroups. The study was able to categorize early-stage diabetic (ESD) and advance stage diabetic (ASD) subjects based on muscle gene expression profiles. The ASD subjects differed significantly from ESD subjects with respect to diabetes-related clinical traits. Comparison between ASD and NGT subjects showed significant up-regulation of muscle atrophy marker atrogin-1 along with the FOXO signaling pathway. The expression of PDK4, an important inhibitor of glycolytic flux was up-regulated whereas, glucose oxidation biomarkers, HK2 and LDHB were down-regulated in ASD subjects. The result obtained from this study highlights muscle-associated gene expression changes that could be used to categorize diabetic subjects into biologically relevant subgroups.

A DMP-Based Motion Generation Scheme for Robotic Mirror Therapy

Hemiparesis has become prevalent in recent years, and robot-assisted rehabilitation provides great therapeutic potential. Robotic mirror therapy is a promising approach for hemiplegic patients by transmitting the motion of the healthy limb (HL) to the impaired limb (IL), where the wearable robot assists the IL to mimic the HL's action to stimulate the active participation of the injured muscles. However, complete replication of the HL's movement trajectory without considering the IL's muscle strength is not satisfactory for rehabilitation. In this article, a motion generation scheme is proposed for robotic mirror therapy. The robot's movement trajectory is modeled with dynamic movement primitive (DMP), and the physical human–robot interaction is formulated as an impedance model and coupled with the DMP model. The subject's muscle strength is evaluated with skin surface electromyography signals and transferred to the robot's joint stiffness. In order to adapt the human–robot coupled DMP model parameters to varying subject performance, a reinforcement learning algorithm is designed to optimize the robot's movement trajectory and stiffness profile, where the training safety and rehabilitation improvement are both guaranteed. The proposed method is validated using a lower extremity rehabilitation robot, and experimental results demonstrate its feasibility and superiority.

Sting and evaluation of a prototype of a mobility trainer: Verticalizer for children (2 to 7 years) weighing up to 20 kg.

The prototype of mobility trainer-verticalizer (hereinafter - PMTV) is designed to develop existing movements caused by individual physical conditions and disease damage, as close as possible to the natural biomechanics of a healthy person. The aim is to make the equipment comfortable, simple, suitable for everyday use in a variety of environments, from medical institutions to the patient's home, and customizable according to the anthropometric data of the growing child. To investigate and evaluate the technical characteristics and feasibility of a PMTV for children (2 to 7 years) weighing up to 20 kg. Empirical research method (anthropometric measurements); quantitative research method (survey); qualitative research method (interviews). The PMTV is suitable for use with children aged 2 to 7 years, although children with various disabilities may have heights, weights and other anthropometric data that fall far below or exceed the healthy standard. The exercise with the use of a PMTV had a positive effect on muscle tone, with a decrease in muscle tone in both the upper and lower limbs. An increased range of motion (hereinafter - ROM) of shoulder flexion and abduction was observed. In the lower limb, there was an improvement in the ROM of hip internal and external rotation and the flexion and extension of knee. Physiotherapy using PMTV had a positive effect on the subject's limb volume and muscle tone, a positive effect on the subject's passive ROM, and a positive effect on the subject's gross motor function.

The development of split-treadmill with a fall prevention training function.

The weakening of the ability of the elderly to perform gait is becoming a major cause of the increase in the frequency of falls. In this study, we designed and manufactured a treadmill capable of restraining walking by providing a sudden repulsive force on the left and right legs of a pedestrian when walking for the fall prevention training of the elderly. Through this, it is possible for the elderly person to strengthen the lower extremity muscles to prevent and prepare for falling through the fall prevention training similar to the fall environment that may occur in daily life. The development system includes a motor for generating a driving force in the form of a left and a right driving system and a belt separated from each other, an electromagnetic clutch for rapidly stopping the running belt of the motor transmitted to the running belt to stop the running belt, and a controller for controlling the driver. In order to evaluate the development system, the motor driving ability test and the power transmission, connection and shut-off performance of the electromagnetic clutch were carried out. The subject's muscle activity of the lower extremity muscles was evaluated when the running belt stopped at the beginning of the right folding. It is expected that the developed dual function system would be helpful for the fall prevention exercise as well as the rehabilitation exercise for patients who have recovered from surgery or hemiplegic patients.

Pushing A Sled with Constant Resistance and Controlled Cadence Induces Lower Limb Musculature Quicker Activation Response and Prolongs Duration with Faster Speed

Physical inactivity is rising in both youthful and older people. Such inactivity is problematic for many reasons, primarily because it contributes to overall physical deconditioning. This study examines characteristics in lower extremity muscle adaptations while pushing a sled at constant resistance with three varying cadences. Twenty-one graduate school participants with an average age of 22.8 years consented to place electromyography (EMG) electrodes on their dominant leg. The targeted muscles for the EMG electrodes were over the gastrocnemius (GA), tibialis anterior (TA), and gluteus maximus (GMax). The subject's muscle activation was monitored over three different walking protocols at varying cadences. The protocols were: slow walk (SW, 80 bpm), intermediate walk (IW, 110 bpm), and fast walk cadence (FW, 140 bpm). The investigation results portrayed two main findings: the muscles studied exhibited faster muscle recruitment and a shorter duration of activation when cadence was increased from the IW to the FW cadence. The second discovery among the IW and FW protocols revealed that the GA and Gmax showed greater muscular adaptations than the TA. In conclusion, pushing the sled proves effective in recruiting lower extremity musculature, indicating it could be of great use in rehabilitating individuals deemed deconditioned.

Muscles Affecting Minimum Toe Clearance.

The aim of this study was to investigate how the anterior and posterior muscles in the shank (Tibialis Anterior, Gastrocnemius Lateralis and Medialis), influence the level of minimum toe clearance (MTC). With aging, MTC deteriorates thus, greatly increasing the probability of falling or tripping. This could result in injury or even death. For this study, muscle activity retention taping (MART) was used on young adults, which is an accepted method of simulating a poor MTC—found in elderly gait. The subject's muscle activation was measured using surface electromyography (SEMG), and the kinematic parameters (MTC, knee and ankle joint angles) were measured using an optical motion capture system. Our results indicate that MART produces significant reductions in MTC (P < α), knee flexion (P < α) and ankle dorsiflexion (P < α), as expected. However, the muscle activity increased significantly, contrary to the expected result (elderly individuals should have lower muscle activity). This was due to the subject's muscle conditions (healthy and strong), hence the muscles worked harder to counteract the external restriction. Yet, the significant change in muscle activity (due to MART) proves that the shank muscles do play an important role in determining the level of MTC. The Tibialis Anterior had the highest overall muscle activation, making it the primary muscle active during the swing phase. With aging, the shank muscles (specifically the Tibialis Anterior) would weaken and stiffen, coupled with a reduced joint range of motion. Thus, ankle-drop would increase—leading to a reduction in MTC.

Effect of Robotic Exoskeleton Motion Constraints on Upper Limb Muscle Synergies: A Case Study

Evidence exists that changes in composition, timing, and number of muscle synergies can be correlated to functional changes resulting from neurological injury. These changes can also serve as an indicator of level of motor impairment. As such, synergy analysis can be used as an assessment tool for robotic rehabilitation. However, it is unclear whether using a rehabilitation robot to isolate limb movements during training affects the subject's muscle synergies, which would affect synergy-based assessments. In this case study, electromyographic (EMG) data were collected to analyze muscle synergies generated during single degree-of-freedom (DoF) elbow and wrist movements performed by a single healthy subject in a four DoF robotic exoskeleton. For each trial, the subject was instructed to move a single DoF from a neutral position out to a target and back while the remaining DoFs were held in a neutral position by either the robot (constrained) or the subject (unconstrained). Four factorization methods were used to calculate muscle synergies for both types of trials: concatenation, averaging, single trials, and bootstrapping. The number of synergies was chosen to achieve 90% global variability accounted for. Our preliminary results indicate that muscle synergy composition and timing were highly similar for constrained and unconstrained trials, though some differences between the four factorization methods existed. These differences could be explained by higher trial-to-trial EMG variability for the unconstrained trials. These results suggest that using a robotic exoskeleton to constrain limb movements during robotic training may not alter a subject's muscle synergies, at least for healthy subjects.

Comparative Assessment of Central and Peripheral Chemoreceptor Reflex Regulation of Muscle Sympathetic Nerve Activity and Ventilation

We tested the hypothesis that central and peripheral chemoreceptor‐mediated sympathetic activation elicited by increases in CO2 tension (PCO2) mirror concurrent ventilatory responses. Twelve healthy young men (mean±SD; age: 24±4 yr; BMI: 24.5±1.3 kg·m−2) performed a modified rebreathing protocol designed to equilibrate central and peripheral chemoreceptor PCO2 tensions with end‐tidal PCO2 (PETCO2) at two isoxic end‐tidal PO2 (PETO2) tensions such that central chemoreceptor reflex responses (hyperoxia) can be isolated from additive peripheral responses (i.e., hypoxia minus hyperoxia). Subject's ventilation (volume turbine) and muscle sympathetic nerve activity (MSNA; microneurography, right fibular nerve) responses to rebreathing at isoxic PETO2 tensions of 150 mmHg (hyperoxia) and 50 mmHg (hypoxia) were recorded continuously. During rebreathing, the PETCO2 (mmHg) at which ventilation (L·min−1) and total MSNA (au) began to rise were identified as the PETCO2 recruitment thresholds (RT). Slopes of these responses above RT also were determined. In hyperoxic rebreathing (i.e., the central chemoreflex response), the mean RT for ventilation (46±3 mmHg) and MSNA (45±4 mmHg) did not differ (p&gt;0.05). Mean slopes were 2.3±0.9 L·min−1·mmHg−1 and 2.1±1.5 au·mmHg−1, respectively. In hypoxic rebreathing (i.e., the summed central and peripheral chemoreflex response), the RT for both ventilation and MSNA were not different (41±3 mmHg vs 41±3 mmHg, p&gt;0.05) but were lower (p&lt;0.05) compared to hyperoxia. Mean slopes for ventilation (4.0±1.8 L·min−1·mmHg−1) and MSNA (5.1±3.4 au·mmHg−1) in hypoxia were greater than in hyperoxia yielding a mean peripheral chemoreflex sensitivity (hypoxic slope minus hyperoxic slope) of 1.7±0.1 L·min−1·mmHg−1 for ventilation and 3.0±2.6 au·mmHg−1 for MSNA. The 95% limits of agreement of RT between ventilation and MSNA for the central chemoreflex were −7 to 6 mmHg (bias=−1 mmHg, p&gt;0.05) and −5 to 5 mmHg (bias=0 mmHg, p&gt;0.05) for the peripheral chemoreflex. There was no relationship (p&gt;0.05) between the ventilatory and MSNA sensitivity for either the central (r2=0.16) or peripheral (r2=0.01) chemoreceptor reflexes. These data highlight two novel findings: 1) ventilatory and sympathetic arms of the central and peripheral chemoreceptor reflexes are initiated at similar PETCO2 recruitment thresholds and 2) sympathetic responsiveness cannot be predicted from the sensitivities of the ventilatory central and peripheral chemoreceptor reflexes.Support or Funding InformationExperiments were funded by a Project Grant from the Canadian Institutes of Health Research (PJT 159491). Dr. Floras holds the Canada Research Chair in Integrative Cardiovascular Biology.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of Patient Body Mass Index on Laparoscopic Surgical Ergonomics.

Minimally invasive surgery may introduce new ergonomic challenges for surgeons. Increased patient body mass index (BMI) may further add to this ergonomic stress. The objective of this study was to quantify the ergonomic impact of patient BMI on surgeons during laparoscopic surgery. University Hospital, USA. This prospective cohort study analyzed five minimally invasive surgeons during 24 laparoscopic procedures. Each subject's muscle stress was assessed by recording surface electromyography (EMG) data from eight upper body muscle groups during laparoscopic procedures. EMG data was normalized against the maximal voluntary contraction (MVC) of each muscle measured before the start of surgery to create a percentage of the MVC value (%MVC). Subject workload was assessed through the NASA Task Load Index (NTLX). Statistical analysis was used to determine significance between surgeons operating on patients with or without obesity for %MVC and NTLX scores. There was no significant difference (p > 0.05) in both the average muscle activation of all eight muscle groups and NTLX scores during laparoscopic surgery in surgeons operating on patients with BMI > = 30 compared with patients with a BMI < 30. We detected no differences in ergonomic stress or workload for surgeons operating on patients with or without obesity. For surgeons, the laparoscopic approach may offer an additional advantage over open surgery in patients with obesity. This advantage may be due to an "equalizing effect" of laparoscopy-that surgical ergonomics are less affected by the BMI of the patient when using laparoscopic tools.

Tigecycline-induced inhibition of mitochondrial DNA translation may cause lethal mitochondrial dysfunction in humans

BackgroundA 65-year-old patient developed an unexplained and ultimately lethal metabolic acidosis under prolonged treatment with tigecycline. Tigecycline is known to have a selective inhibitory effect on eukaryotic mitochondrial translation. The underlying molecular mechanisms of the metabolic acidosis in this patient were explored. MethodsOxidative phosphorylation system (OXPHOS) analysis, blue native polyacrylamide gel electrophoresis followed by in-gel activity staining in mitochondria, molecular analysis of mitochondrial DNA (mtDNA) for genomic rearrangements and sequencing of the rRNA genes was performed on the subject's skeletal muscle. ResultsOXPHOS analysis revealed a combined deficiency of the complexes I, III, IV and V, with a preserved function of complex II (encoded by nuclear DNA), thus demonstrating a defective mtDNA translation. There were no known underlying mitochondrial genetic defects. The patient had a (m.1391T>A) variant within the 12SrRNA gene in heteroplasmy (50–60%). ConclusionsThis patient developed an ultimately lethal mitochondrial toxicity while receiving prolonged treatment with tigecycline, which was caused by a defective translation of the mtDNA. Tigecycline is known to suppress eukaryotic mitochondrial DNA translation, but until now this effect has been considered to be clinically insignificant. The observations in this patient suggest a clinically significant mitochondrial toxicity of tigecycline in this patient, and warrant further investigation.

1RM prediction: a novel methodology based on the force-velocity and load-velocity relationships.

This study aimed to evaluate the accuracy of a novel approach for predicting the one-repetition maximum (1RM). The prediction is based on the force-velocity and load-velocity relationships determined from measured force and velocity data collected during resistance-training exercises with incremental submaximal loads. 1RM was determined as the load corresponding to the intersection of these two curves, where the gravitational force exceeds the force that the subject can exert. The proposed force-velocity-based method (FVM) was tested on 37 participants (23.9±3.1year; BMI 23.44±2.45) with no specific resistance-training experience, and the predicted 1RM was compared to that achieved using a direct method (DM) in chest-press (CP) and leg-press (LP) exercises. The mean 1RM in CP was 99.5kg (±27.0) for DM and 100.8kg (±27.2) for FVM (SEE=1.2kg), whereas the mean 1RM in LP was 249.3kg (±60.2) for DM and 251.1kg (±60.3) for FVM (SEE=2.1kg). A high correlation was found between the two methods for both CP and LP exercises (0.999, p<0.001). Good agreement between the two methods emerged from the Bland and Altman plot analysis. These findings suggest the use of the proposed methodology as a valid alternative to other indirect approaches for 1RM prediction. The mathematical construct is simply based on the definition of the 1RM, and it is fed with subject's muscle strength capacities measured during a specific exercise. Its reliability is, thus, expected to be not affected by those factors that typically jeopardize regression-based approaches.

Relating Speech Production to Tongue Muscle Compressions Using Tagged and High-resolution Magnetic Resonance Imaging.

The human tongue is composed of multiple internal muscles that work collaboratively during the production of speech. Assessment of muscle mechanics can help understand the creation of tongue motion, interpret clinical observations, and predict surgical outcomes. Although various methods have been proposed for computing the tongue's motion, associating motion with muscle activity in an interdigitated fiber framework has not been studied. In this work, we aim to develop a method that reveals different tongue muscles' activities in different time phases during speech. We use four-dimensional tagged magnetic resonance (MR) images and static high-resolution MR images to obtain tongue motion and muscle anatomy, respectively. Then we compute strain tensors and local tissue compression along the muscle fiber directions in order to reveal their shortening pattern. This process relies on the support from multiple image analysis methods, including super-resolution volume reconstruction from MR image slices, segmentation of internal muscles, tracking the incompressible motion of tissue points using tagged images, propagation of muscle fiber directions over time, and calculation of strain in the line of action, etc. We evaluated the method on a control subject and two post-glossectomy patients in a controlled speech task. The normal subject's tongue muscle activity shows high correspondence with the production of speech in different time instants, while both patients' muscle activities show different patterns from the control due to their resected tongues. This method shows potential for relating overall tongue motion to particular muscle activity, which may provide novel information for future clinical and scientific studies.

Reference values for isometric muscle force among workers for the Netherlands: a comparison of reference values

BackgroundMuscle force is important for daily life and sports and can be measured with a handheld dynamometer. Reference values are employed to quantify a subject’s muscle force. It is not unambiguous whether reference values can be generalized to other populations. Objectives in this study were; first to confirm the reliability of the utilization of hand-held dynamometers for isometric strength measurement; second to determine reference values for a population of Dutch workers; third to compare these values with those of a USA population.Methods462 Healthy working subjects (259 male, 203 female) were included in this study. Their age ranged from 20 to 60 years with a mean (sd) of 41 (11) years. Muscle force values from elbow flexion and extension, knee flexion and extension, and shoulder abduction were measured with the break method using a MicroFet 2 hand-held dynamometer. Reliability was analyzed by calculating ICC’s and limits of agreement. Muscle force expressed in Newton, means, and confidence intervals were determined for males and females in age groups ranging from twenty to sixty years old. Regression equations and explained variances were calculated from weight, height, age, and gender. The mean values and 95% CI were compared to the results from other studies.ResultsReliability was good; the ICC ranged between 0.83 to 0.94. The explained variance ranged from 0.25 to 0.51. Comparison of data for the Dutch population mean muscle force values with those from the USA revealed important differences between muscle force reference values for the American and Dutch populations.ConclusionsMuscle force measurements demonstrate a sound reliability. Reference values and regressions equations are made available for the Dutch population. Comparison with other studies indicates that reference values differ between countries.

Altering length and velocity feedback during a neuro-musculoskeletal simulation of normal gait contributes to hemiparetic gait characteristics.

BackgroundSpasticity is an important complication after stroke, especially in the anti-gravity muscles, i.e. lower limb extensors. However the contribution of hyperexcitable muscle spindle reflex loops to gait impairments after stroke is often disputed. In this study a neuro-musculoskeletal model was developed to investigate the contribution of an increased length and velocity feedback and altered reflex modulation patterns to hemiparetic gait deficits.MethodsA musculoskeletal model was extended with a muscle spindle model providing real-time length and velocity feedback of gastrocnemius, soleus, vasti and rectus femoris during a forward dynamic simulation (neural control model). By using a healthy subject’s base muscle excitations, in combination with increased feedback gains and altered reflex modulation patterns, the effect on kinematics was simulated. A foot-ground contact model was added to account for the interaction effect between the changed kinematics and the ground. The qualitative effect i.e. the directional effect and the specific gait phases where the effect is present, on the joint kinematics was then compared with hemiparetic gait deviations reported in the literature.ResultsOur results show that increased feedback in combination with altered reflex modulation patterns of soleus, vasti and rectus femoris muscle can contribute to excessive ankle plantarflexion/inadequate dorsiflexion, knee hyperextension/inadequate flexion and increased hip extension/inadequate flexion during dedicated gait cycle phases. Increased feedback of gastrocnemius can also contribute to excessive plantarflexion/inadequate dorsiflexion, however in combination with excessive knee and hip flexion. Increased length/velocity feedback can therefore contribute to two types of gait deviations, which are both in accordance with previously reported gait deviations in hemiparetic patients. Furthermore altered modulation patterns, in particular the reduced suppression of the muscle spindle feedback during swing, can contribute largely to an increased plantarflexion and knee extension during the swing phase and consequently to hampered toe clearance.ConclusionsOur results support the idea that hyperexcitability of length and velocity feedback pathways, especially in combination with altered reflex modulation patterns, can contribute to deviations in hemiparetic gait. Surprisingly, our results showed only subtle temporal differences between length and velocity feedback. Therefore, we cannot attribute the effects seen in kinematics to one specific type of feedback.

Relationships of 35 lower limb muscles to height and body mass quantified using MRI

Skeletal muscle is the most abundant tissue in the body and serves various physiological functions including the generation of movement and support. Whole body motor function requires adequate quantity, geometry, and distribution of muscle. This raises the question: how do muscles scale with subject size in order to achieve similar function across humans? While much of the current knowledge of human muscle architecture is based on cadaver dissection, modern medical imaging avoids limitations of old age, poor health, and limited subject pool, allowing for muscle architecture data to be obtained in vivo from healthy subjects ranging in size. The purpose of this study was to use novel fast-acquisition MRI to quantify volumes and lengths of 35 major lower limb muscles in 24 young, healthy subjects and to determine if muscle size correlates with bone geometry and subject parameters of mass and height. It was found that total lower limb muscle volume scales with mass (R2=0.85) and with the height–mass product (R2=0.92). Furthermore, individual muscle volumes scale with total muscle volume (median R2=0.66), with the height–mass product (median R2=0.61), and with mass (median R2=0.52). Muscle volume scales with bone volume (R2=0.75), and muscle length relative to bone length is conserved (median s.d.=2.1% of limb length). These relationships allow for an arbitrary subject's individual muscle volumes to be estimated from mass or mass and height while muscle lengths may be estimated from limb length. The dataset presented here can further be used as a normative standard to compare populations with musculoskeletal pathologies.

Stability Radius as a Method for Comparing the Dynamics of Neuromechanical Systems

Robust motor behaviors emerge from neuromechanical interactions that are nonlinear, have delays, and contain redundant neural and biomechanical components. For example, in standing balance a subject's muscle activity (neural control) decreases as stance width (biomechanics) increases when responding to a lateral perturbation, yet the center-of-mass motion (behavior) is nearly identical regardless of stance width. We present stability radius, a technique from robust control theory, to overcome the limitations of classical stability analysis tools, such as gain margin, which are insufficient for predicting how concurrent changes in both biomechanics (plant) and neural control (controller) affect system behavior. We first present the theory and then an application to a neuromechanical model of frontal-plane standing balance with delayed feedback. We show that stability radius can quantify differences in the sensitivity of system behavior to parameter changes, and predict that narrowing stance width increases system robustness. We further demonstrate that selecting combinations of stance width (biomechanics) and feedback gains (neural control) that have the same stability radius produce similar center-of-mass behavior in simulation. Therefore, stability radius may provide a useful tool for understanding neuromechanical interactions in movement and could aid in the design of devices and therapies for improving motor function.

Mechanomyogram for muscle function assessment: a review.

BackgroundMechanomyography (MMG) has been extensively applied in clinical and experimental practice to examine muscle characteristics including muscle function (MF), prosthesis and/or switch control, signal processing, physiological exercise, and medical rehabilitation. Despite several existing MMG studies of MF, there has not yet been a review of these. This study aimed to determine the current status on the use of MMG in measuring the conditions of MFs.Methodology/Principal FindingsFive electronic databases were extensively searched for potentially eligible studies published between 2003 and 2012. Two authors independently assessed selected articles using an MS-Word based form created for this review. Several domains (name of muscle, study type, sensor type, subject's types, muscle contraction, measured parameters, frequency range, hardware and software, signal processing and statistical analysis, results, applications, authors' conclusions and recommendations for future work) were extracted for further analysis. From a total of 2184 citations 119 were selected for full-text evaluation and 36 studies of MFs were identified. The systematic results find sufficient evidence that MMG may be used for assessing muscle fatigue, strength, and balance. This review also provides reason to believe that MMG may be used to examine muscle actions during movements and for monitoring muscle activities under various types of exercise paradigms.Conclusions/SignificanceOverall judging from the increasing number of articles in recent years, this review reports sufficient evidence that MMG is increasingly being used in different aspects of MF. Thus, MMG may be applied as a useful tool to examine diverse conditions of muscle activity. However, the existing studies which examined MMG for MFs were confined to a small sample size of healthy population. Therefore, future work is needed to investigate MMG, in examining MFs between a sufficient number of healthy subjects and neuromuscular patients.

歩行訓練と下肢筋力トレーニングに伴う下腿義足歩行動作改善の 1 例

In order to examine the process of improvement in the walking ability of trans-tibia amputees fitted with lower-limb prostheses, this study carried out tests of free walking and fast walking movements in a man with a TSB trans-tibia prosthesis. The tests included measurements of hip flexion in a sitting position, walking speed, step length, step rate, supporting time and swing time. The measurements were carried out every two weeks, for a total of six times. Furthermore, in order to examine the connection between the subject's walking ability and his training programs, investigative records of the subject's muscle strengthening and rehabilitation with walking were also examined. The results showed that there were continuous improvements of muscle strength in both legs as a result of muscle training and rehabilitation during 11 weeks. An obvious improvement of walking ability was observed two weeks after the start of walking as muscle strength increased, and the differences between the two legs evident at the initial stage slowly decreased. This bilateral difference showed a conspicuous improvement from about the seventh week, and perfectly normal walking was achieved from the 11th week. However, these results need to be interpreted with caution because this was a case study involving only one subject with a lower-limb prosthesis, and was not a case in which the socket of the artificial leg had considerable non-conformity.

Impact of muscle contraction upon head stabilisation during forward acceleration

Introduction: The impact of muscle contraction upon head movements induced by a forward acceleration was studied as a model for low impact car-accidents. The purpose of our research is to examine: (i) whether and by which mechanism neck muscle contraction is induced after onset of the movement; and (ii) if voluntary neck muscle contraction prior to the movement affects head motion. Subjects and methods: Eight healthy volunteers (mean age 21.4 years) were included in this study. Volunteers were sitting on a standard car seat mounted on a sled. The computer-controlled, motor-driven sled was forward accelerated with 0.6 g. In test series 1, head and body movement were detected with a standard video camera (20 ms per frame) and accelerometers mounted on the head without interference with muscle activity. Muscle activation was detected by simultaneous measurement of surface EMG of m. splenius capitis, m. trapezius (descending part), m. scalenis medius, m. sternocleido mastoideus, m. digastricus (anterior belly), m. mylohyoideus, m. pectoralis major, m. quadriceps, tibialis anterior and triceps surae. The subject's movements and muscle activity were examined during forward sled acceleration when: (i) the subjects were relaxed and could not anticipate the precise start of sled acceleration; (ii) when they contracted all body muscles for about 4 s prior to and during the sled acceleration; and (iii) when head and trunk were fixed to the chair. The same subjects were accelerated in test series 2, but now head and trunk movements were measured with a better time resolution by use of a high-speed video camera (500 Hz) and accelerometers mounted on the head (bite board), body and sled. Head and body movements were measured under conditions 1 and 2 as described above. Reproducibility was tested by repeating each test condition once, including repositioning of the subjects, the accelerometers and body fixed sell spot markers. Results and conclusions: The current experimental set-up allows a low-cost evaluation of head and body movements induced by low impact velocity impulses. We observed that sudden whole body acceleration induces head accelerations that exceed the acceleration of the impact by a factor of 2–3-fold. After the impact, the head first remains stationary in space while the sled and trunk move forward (relative head and upper trunk translation). Subsequently, head and trunk rotate backwards, ultimately followed by an additional retroflexion of the head alone. Precontraction and anticipation of the impact leads to a faster increase of general muscle tone. It does not affect the initial translation but leads to a reduction of about 30–35% of head rotations and head angular velocities. The muscle contraction is most like a generalised alerting response. It should be noted that the current results were obtained at a loading level of 0.7 g, which is far below the 5–12 g levels observed in rear-end collisions. Since the current study shows only small influences of the muscle contraction, it is assumed that the contraction will not be strong enough to limit the larger head and trunk motion with greater impacts and does not reduce the probability of getting a whiplash injury.