Accuracy and Precision of Three Acceleromyographs, Three Electromyographs, and a Mechanomyograph Measuring the Train-of-four Ratio in the Absence of Neuromuscular Blocking Drugs.

BACKGROUND: The accuracy and precision of currently available, widely used acceleromyograph and electromyograph neuromuscular blockade monitors have not been well studied. In addition, the normalization of the train-of-four ratio from acceleromyography (train-of-four ratio [T4/T1] divided by the baseline train-of-four ratio) has not been validated in comparison to mechanomyography. METHODS: Enrolled patients had surgery under general anesthesia with a supraglottic airway and without any neuromuscular blocking drugs. Three acceleromyograph monitors, three electromyograph monitors, and a mechanomyograph built in the authors' laboratory were tested. Most patients had an electromyograph and the mechanomyograph on one arm and a third monitor on the contralateral arm. Train-of-four ratios were collected every 12 to 20 s for the duration of the anesthetic. At least 1,000 train-of-four ratios were recorded for each device. Gauge repeatability and reproducibility analysis was performed. RESULTS: Twenty-eight patients were enrolled. In total, 9,498 train-of-four ratio measurements were collected. Since no neuromuscular blocking drugs were used, the expected train-of-four ratio was 1.0. All of the acceleromyograph monitors produced overshoot in the train-of-four ratio (estimated means, 1.10 to 1.13) and substantial variability (gauge SDs, 0.07 to 0.18). Normalization of the train-of-four ratio measured by acceleromyography improved the estimated mean for each device (0.97 to 1.0), but the variability was not improved (gauge SDs, 0.06 to 0.17). The electromyograph and the mechanomyograph monitors produced minimal overshoot (estimated means, 0.99 to 1.01) and substantially less variation (gauge SDs, 0.01 to 0.02). For electromyography and mechanomyography, 0.3% of all train-of-four ratios were outside of the range 0.9 to 1.1. For acceleromyography, 27 to 51% of normalized train-of-four ratios were outside the range of 0.9 to 1.1. CONCLUSIONS: Three currently available acceleromyograph monitors produced overshoot and substantial variability that could be clinically significant. Normalization corrected the overshoot in the average results but did not reduce the wide variability. Three electromyograph monitors measured the train-of-four ratio with minimal overshoot and variability, similar to a mechanomyograph.

AI-Enabled Soft Sensing Array for Simultaneous Detection of Muscle Deformation and Mechanomyography for Metaverse Somatosensory Interaction.

Motion recognition (MR)-based somatosensory interaction technology, which interprets user movements as input instructions, presents a natural approach for promoting human-computer interaction, a critical element for advancing metaverse applications. Herein, this work introduces a non-intrusive muscle-sensing wearable device, that in conjunction with machine learning, enables motion-control-based somatosensory interaction with metaverse avatars. To facilitate MR, the proposed device simultaneously detects muscle mechanical activities, including dynamic muscle shape changes and vibrational mechanomyogram signals, utilizing a flexible 16-channel pressure sensor array (weighing ≈0.38 g). Leveraging the rich information from multiple channels, a recognition accuracy of ≈96.06% is achieved by classifying ten lower-limb motions executed by ten human subjects. In addition, this work demonstrates the practical application of muscle-sensing-based somatosensory interaction, using the proposed wearable device, for enabling the real-time control of avatars in a virtual space. This study provides an alternative approach to traditional rigid inertial measurement units and electromyography-based methods for achieving accurate human motion capture, which can further broaden the applications of motion-interactive wearable devices for the coming metaverse age.

Local fat content and muscle quality measured by a new electrical impedance myography device: correlations with ultrasound variables.

AbstractThe present study investigated the relationship between local fat percentage (SKfat) and muscle quality (MQ) estimated by a new hand-held electrical impedance myography (hEIM) device or derived from ultrasound and strength assessments. The right anterior thigh of 90 healthy participants (mean ± SD; age=22.9 ± 2.9 years; 45 men: BMI = 23.9 ± 2.4 kgm-2; 45 women: BMI = 21.1 ± 1.9 kgm-2) was scanned by hEIM and ultrasound. Correlations between SKfat, local subcutaneous fat (SUBfat), and echo intensity (EIus) were explored. Correlations between MQ, EIus, quadriceps femoris anatomical cross-sectional area (ACSAQF), knee extensors maximum voluntary isometric torque (T), T/ACSAQF, EIus/SUBfat, and ACSAQF/SUBfat were also assessed. SKfat correlated with SUBfat (r = 0.88; p < 0.001) and EIus (r = 0.64; p < 0.001). MQ correlated with EIus (r = -0.66; p < 0.001), ACSAQF (r = 0.37; p < 0.001), EIus/SUBfat (r = 0.37; p < 0.001), and ACSAQF/SUBfat (r = 0.81; p < 0.001). Multiple regression analysis showed that SUBfat, EIus, and sex explained 86% of SKfat variance, whereas ACSAQF/SUBfat, sex and EIus explained 75% of MQ variance. In conclusion, high hEIM local fat percentage relates to greater subcutaneous fat and intramuscular non-contractile tissue content. High hEIM muscle quality relates to greater muscle-size:subcutaneous-fat ratio and contractile tissue content. Sex influences the prediction of both parameters. This hEIM device seems to be useful to estimate local thigh composition.

Invasive electrical impedance myography at different levels of contraction of gastrocnemius muscle of rat.

Electrical impedance myography (EIM) is as an experimental technique that associates muscle impedance with muscular activity. Changes in muscle impedance during contraction occur mainly due to changes in the morphological and physiological characteristics of muscles that lead to different impeditivities in comparison with the resting condition. There is no consensus on the details of muscular impedance during muscle activity. EIM measurements on humans are also influenced by factors such as the electrode-skin interface, layers of skin and fat, and the connective tissue that can generate undesirable effects in the impedance signal. These effects can be avoided if EIM measurements are carried out directly on the muscle by using the models of animals. This study investigates changes in the EIM signal in the gastrocnemius muscles of Wistar rats during different levels of muscular contraction. In vivo experiments were conducted on 19 male rats. The muscle was exposed, fixed on a load cell, and electrically stimulated to evoke different levels of muscle contraction. Signals of the components of impedance were analyzed against the muscular force signal. The results show moderate correlations (p < 0.05) among the impedance-related parameters of resistance (r = -0.76), reactance (r = 0.57), and phase (r = 0.53). In addition to providing an experimental protocol for the invasive collection of data on electrical impedance to minimize problems associated with surface electrodes, this study shows that of the components of impedance, resistance is most affected by the intensity of muscular contractions and that morphological changes influence impedance mainly at low intensities.

Intra- and inter-rater reliability of electrical impedance myography using adhesive electrodes in healthy volunteers.

In spite of the growing use of the electrical impedance myography (EIM) measures for clinical assessment and follow-up of diseased muscle tissue, reliability studies are scarce. We evaluate the reliability of the (EIM) technique using four adhesive electrodes over the muscle of interest. Intra- and inter-rater reliability was studied within the same session and between sessions. Thirty-one healthy and volunteer subjects aged between 20 and 26 years were recruited. Phase angle, reactance and resistance were assessed for each EIM measurement. Intraclass correlation coefficient (ICC) was used to determine the relative reliability. Absolute reliability was expressed as the standard error of measurement and the minimum detectable change. Relative reliability within the same session and between sessions for the EIM technique was excellent (ICCs > 0.9) concerning both intra- and inter-rater reliability, except for the component reactance. The absolute reliability was very high for the three EIM components. EIM measures using four adhesive electrodes over the area of interest is a reliable technique to assess muscle tissue status. This study confirms that these measurement results barely vary depending on the examiner and the moment. The present study also confirms phase angle as the least affected EIM component by examiner and evaluation moment.

Difficult extubation of a damaged neural integrity monitor electromyogram tracheal tube: A case report.

INTRODUCTION: The purpose of a neural integrity monitor electromyogram (EMG) tracheal tube is to reduce the risk of damage to the recurrent laryngeal nerves. Complications associated with the use of EMG tube are ventilatory failure, tracheal injury, and difficult extubation. PATIENT CONCERNS: We encountered a case of difficult extubation of an EMG tube after thyroidectomy and partial tracheal resection in a 73-year-old woman. DIAGNOSES: The cuff was torn intraoperatively; but, it was kept inflated to maintain the integrity of the ventilatory circuit. During extubation, the vocal cord blocked the torn hole on the shoulder of the cuff, which subsequently was filled with air, complicating the extubation. INTERVENTIONS: We extubated the EMG tube slowly with the help of videolaryngoscopy with a moderate amount of force and re-intubated with a 6.0-mm ID endotracheal tube. OUTCOMES: We examined the airway during and after re-intubation using videolaryngoscopy. The findings were normal and no bleeding or laceration was observed. The subsequent recovery and extubation occurred smoothly. CONCLUSIONS: Awareness of the characteristics and types of damage that can occur in an EMG tube is essential. Because it can be difficult to ascertain the type of damage before extubation, communication between the surgeon and anesthesiologist, along with the preparation for emergency airway management are necessary for cases of difficult extubation.

Wrist-worn wearables based on force myography: on the significance of user anthropometry.

BACKGROUND: Force myography (FMG) is a non-invasive technology used to track functional movements and hand gestures by sensing volumetric changes in the limbs caused by muscle contraction. Force transmission through tissue implies that differences in tissue mechanics and/or architecture might impact FMG signal acquisition and the accuracy of gesture classifier models. The aim of this study is to identify if and how user anthropometry affects the quality of FMG signal acquisition and the performance of machine learning models trained to classify different hand and wrist gestures based on that data. METHODS: Wrist and forearm anthropometric measures were collected from a total of 21 volunteers aged between 22 and 82 years old. Participants performed a set of tasks while wearing a custom-designed FMG band. Primary outcome measure was the Spearman's correlation coefficient (R) between the anthropometric measures and FMG signal quality/ML model performance. RESULTS: Results demonstrated moderate (0.3 ≤|R| < 0.67) and strong (0.67 ≤ |R|) relationships for ratio of skinfold thickness to forearm circumference, grip strength and ratio of wrist to forearm circumference. These anthropometric features contributed to 23-30% of the variability in FMG signal acquisition and as much as 50% of the variability in classification accuracy for single gestures. CONCLUSIONS: Increased grip strength, larger forearm girth, and smaller skinfold-to-forearm circumference ratio improve signal quality and gesture classification accuracy.

A comparison of a prototype electromyograph vs. a mechanomyograph and an acceleromyograph for assessment of neuromuscular blockade.

The extent of neuromuscular blockade during anaesthesia is frequently measured using a train-of-four stimulus. Various monitors have been used to quantify the train-of-four, including mechanomyography, acceleromyography and electromyography. Mechanomyography is often considered to be the laboratory gold standard of measurement, but is not commercially available and has rarely been used in clinical practice. Acceleromyography is currently the most commonly used monitor in the clinical setting, whereas electromyography is not widely available. We compared a prototype electromyograph with a newly constructed mechanomyograph and a commercially available acceleromyograph monitor in 43 anesthetised patients. The mean difference (bias; 95% limits of agreement) in train-of-four ratios was 4.7 (-25.2 to 34.6) for mechanomyography vs. electromyography; 14.9 (-13.0 to 42.8) for acceleromyography vs. electromyography; and 9.8 (-31.8 to 51.3) for acceleromyography vs. mechanomyography. The mean difference (95% limits of agreement) in train-of-four ratios between opposite arms when using electromyography was -0.7 (-20.7 to 19.3). There were significantly more acceleromyography train-of-four values > 1.0 (23%) compared with electromyography or mechanomography (2-4%; p < 0.0001). Electromyography most closely resembled mechanomyographic assessment of neuromuscular blockade, whereas acceleromyography frequently produced train-of-four ratio values > 1.0, complicating the interpretation of acceleromyography results in the clinical setting.

Preliminary Examination of the Ability of a New Wearable Device to Capture Functional Hand Activity After Stroke.

Background and Purpose- A reliable measure of movement repetitions is required to assist in determining the optimal dose for maximizing upper limb recovery after stroke. This study investigated the ability of a new wearable device to capture reach-to-grasp repetitions in individuals with stroke. Methods- Eight individuals with stroke wore an instrumented wrist bracelet while completing 12 upper limb activities. Participants completed 5 and 10 repetitions of each activity on 2 separate sessions (time 1 and time 2) and completed clinical assessments (Fugl-Meyer Upper Extremity Assessment and Action Research Arm Test). Mean reach-to-grasp counts (ie, hand counts) were compared across activities. Scaling properties were assessed by the ratio of 10 repetitions to 5 repetitions for the activities (ie, expected value of 2). Bland-Altman diagrams were used to examine agreement between time 1 and time 2 counts. Results- The wrist bracelet averaged 0 to 0.6 hand counts per repetition for the arm-only and hand-only activities and averaged 1 to 2 counts per repetition of the reach-to-grasp activities. The mean ratio of 10 repetition to 5 repetition counts was ≈2 for all of the reach-to-grasp activities. Mean differences from time 1 to time 2 were <0.3 counts/repetition for all activities except one. Conclusions- These preliminary results provide evidence that the wrist bracelet is able to capture hand counts over a variety of tasks in a consistent manner. This wrist bracelet could be further developed as a tool to record dose of upper limb practice for research or clinical practice, as well as providing motivation and accountability to patients participating in treatments requiring upper limb movement repetitions. Currently, there are limitations in interpreting the impact of impairment and common compensatory movements on hand counts, and it would be valuable for future studies to explore these effects.

A Review of Force Myography Research and Development.

Information about limb movements can be used for monitoring physical activities or for human-machine-interface applications. In recent years, a technique called Force Myography (FMG) has gained ever-increasing traction among researchers to extract such information. FMG uses force sensors to register the variation of muscle stiffness patterns around a limb during different movements. Using machine learning algorithms, researchers are able to predict many different limb activities. This review paper presents state-of-art research and development on FMG technology in the past 20 years. It summarizes the research progress in both the hardware design and the signal processing techniques. It also discusses the challenges that need to be solved before FMG can be used in an everyday scenario. This paper aims to provide new insight into FMG technology and contribute to its advancement.

Measurement of maximum tongue protrusion force (MTPF) in healthy young adults.

We propose that tongue protrusive strength and tone may be related to upper airway patency, and when protrusive strength is reduced, individuals are at higher risk of developing sleep apnea, or speech/swallow disorders. The goal of the current study was to determine normative values of maximum tongue protrusion force (MTPF) in healthy young adults, using a unique newly developed device. We hypothesized that MTPF would be greater in males than in females. One hundred and one healthy young adults (mean age: 22.99 years; male: 23, female: 78) participated in this study. The subjects pushed their tongue forward against the device's piston (protrusion) as hard as possible for 2-5 sec and MTPF was recorded in Newtons (N). A minimum of 5 MTPF measurements were obtained with 1-2 min rest between measurements. The average MTPF for all subjects was 15.4 N (SD: ±3.8), with a range of 8-29. The male average MTPF was higher than female (17.8 N, SD: ±3.7 vs. 14.7 N, SD: ±3.5; P = 0.001). There was no significant difference for age between males and females; males had significantly greater height and weight. The results demonstrate our novel device can effectively measure tongue protrusive force in healthy young adults. This study provides normative values for MTPF, and identified significant tongue protrusion strength differences between males and females.

FMG Versus EMG: A Comparison of Usability for Real-Time Pattern Recognition Based Control.

OBJECTIVE: Force myography (FMG), which measures the surface pressure profile exerted by contracting muscles, has been proposed as an alternative to electromyography (EMG) for human-machine interfaces. Although FMG pattern recognition-based control systems have yielded higher offline classification accuracy, comparatively few works have examined the usability of FMG for real-time control. In this work, we conduct a comprehensive comparison of EMG- and FMG-based schemes using both classification and regression controllers. METHODS: A total of 20 participants performed a two-degree-of-freedom Fitts' Law-style virtual target acquisition task using both FMG- and EMG-based classification and regression control schemes. Performance was evaluated based on the standard Fitts' law testing metrics throughput, path efficiency, average speed, number of timeouts, overshoot, stopping distance, and simultaneity. RESULTS: The FMG-based classification system significantly outperformed the EMG-based classification system in both throughput (0.902 ± 0.270) versus (0.751 ± 0.309), (ρ < 0.001) and path efficiency (87.2 ± 8.7) versus (83.2 ± 7.8), (ρ < 0.001). Similarly, FMG-based regression significantly outperformed EMG-based regression in throughput (0.871 ± 0.2) versus (0.69 ± 0.3), (ρ < 0.001) and path efficiency (64.8 ± 5.3) versus (58.8 ± 7.1), (ρ < 0.001). CONCLUSIONS: The FMG-based schemes outperformed the EMG-based schemes regardless of which controller was used. This provides further evidence for FMG as a viable alternative to EMG for human-machine interfaces. SIGNIFICANCE: This work describes a comprehensive evaluation of the online usability of FMG- and EMG-based control using both sequential classification and simultaneous regression control.

Optically Pumped Magnetometers for Magneto-Myography to Study the Innervation of the Hand.

The central nervous system exerts control over the activation of muscles via a dense network of nerve fibers targeting each individual muscle. There are numerous clinical situations where a detailed assessment of the nerve-innervation pattern is required for diagnosis and treatment. Especially, deep muscles are hard to examine and are as yet only accessible by uncomfortable and painful needle EMG techniques. Just recently, a new and flexible method and device became available to measure the small magnetic fields generated by the contraction of the muscles: optically pumped magnetometers (OPMs). OPMs are small devices that measure the zero-field level crossing resonance of spin-polarized rubidium atoms. The resonance is dependent on the local magnetic field strength, and therefore, these devices are able to measure small magnetic fields in the range of a few hundred femtoteslas. In this paper, we demonstrate as a proof of principle that OPMs can be used to measure the low magnetic fields generated by small hand muscles after electric stimulation of the ulnar or median nerve. We show that using this technique, we are able to record differential innervation pattern of small palmar hand muscles and are capable of distinguishing between areas innervated by the median or ulnar nerve. We expect that the new approach will have an important impact on the diagnosis of nerve entrapment syndromes, spinal cord lesions, and neuromuscular diseases.

An investigation of the accuracy and reliability of body composition assessed with a handheld electrical impedance myography device.

The purpose of this study was to compare the body fat per cent (BF%) assessed with a unique handheld electrical impedance myography (EIM) device, along with other popular methods, to dual-energy X-ray absorptiometry (DXA). Participants included 33 males (aged 24.3 ± 4.6 years) and 38 females (aged 25.3 ± 8.9 years) who completed 2 visits separated by 24-72 h. The assessments included DXA, bioelectrical impedance analysis (BIA), skinfold measures (SKF), and three separate EIM measurements. No significant differences in BF% (P > 0.05) were found between all EIM assessments when compared against DXA for both males and females for each visit. All methods showed no significant differences in BF% (P > 0.05) between days within themselves. Across both days, the standard error of the estimate (SEE) for the EIM measurements ranged from 2.66% to 3.15%, the SEE for BIA was 2.80 and 2.85, and for SKF was 2.90 and 2.82. The 95% limits of agreement ranged from ±5.34% to ±6.38% for EIM measurements and were highest for SKF (±7.42% and ±7.47%). The total error for both days was largest for SKF (5.20% and 5.35%) and lowest for the EIM measurements (2.48-3.24%). This investigation supports use of a handheld EIM device as an accurate and reliable method of estimating BF% compared to DXA in young, apparently healthy individuals with BF% in the range of 10-22% for males and 20-32% in females and suggests this EIM device be considered a viable alternative to other established field measurements in this population.

Precontractile optical response during excitation-contraction in human muscle revealed by non-invasive high-speed spatiotemporal NIR measurement.

During muscle contraction the excitation-contraction process mediates the neural input and mechanical output. Proper muscle function and body locomotion depends on the status of the elements in the same process. However, non-invasive and in-vivo methods to study this are not available. Here we show the existence of an optical response occurring during the excitation-contraction process in human biceps brachii muscle. We developed a non-invasive instrument from a photodiode array and light emitting diodes to detect spatially propagating (~5 m/s) and precontractile (~6 ms onset) optical signals closely related to the action potential during electrostimulation. Although this phenomenon was observed 60 years ago on isolated frog muscle cells in the lab, it has not been shown in-vivo before now. We anticipate our results to be a starting point for a new category in-vivo studies, characterising alterations in the excitation-contraction process in patients with neuromuscular disease and to monitor effects of therapy.

Assessing the viscoelastic properties of upper trapezius muscle: Intra- and inter-tester reliability and the effect of shoulder elevation.

BACKGROUND: Increasing stiffness in the upper trapezius muscle may contribute to imbalance of scapular motion, and result in shoulder and neck discomfort during shoulder flexion. Therefore, it is essential to quantify upper trapezius stiffness in various shoulder positions in order to aid in the prevention of these disorders and to optimize rehabilitation. OBJECTIVES: The objectives of the present study were to examine the intra and inter-tester reliability of MyotonPRO device in measuring upper trapezius stiffness and its ability to determine changes in stiffness during shoulder flexion. METHODS: Twenty healthy male subjects (mean age: 28.3±4.8 years) were studied. The stiffness of upper trapezius was quantified using the MyotonPRO device. RESULTS: The results revealed excellent intra and inter-tester reliability for measuring upper trapezius stiffness with the shoulder in a neutral position, and also found a 14.2% increase in stiffness upon shoulder flexion between 0° and 60° of flexion. Minimal detectable change (MDC) was 26.3 N/m. CONCLUSIONS: Our findings indicate that MyotonPRO device is a feasible tool to quantify upper trapezius stiffness as well as changes in muscle stiffness. Thus, it is important to assess the changes in upper trapezius muscle stiffness due to pathology or treatments for future studies.

Upper-limb prosthetic control using wearable multichannel mechanomyography.

In this paper we introduce a robust multi-channel wearable sensor system for capturing user intent to control robotic hands. The interface is based on a fusion of inertial measurement and mechanomyography (MMG), which measures the vibrations of muscle fibres during motion. MMG is immune to issues such as sweat, skin impedance, and the need for a reference signal that is common to electromyography (EMG). The main contributions of this work are: 1) the hardware design of a fused inertial and MMG measurement system that can be worn on the arm, 2) a unified algorithm for detection, segmentation, and classification of muscle movement corresponding to hand gestures, and 3) experiments demonstrating the real-time control of a commercial prosthetic hand (Bebionic Version 2). Results show recognition of seven gestures, achieving an offline classification accuracy of 83.5% performed on five healthy subjects and one transradial amputee. The gesture recognition was then tested in real time on subsets of two and five gestures, with an average accuracy of 93.3% and 62.2% respectively. To our knowledge this is the first applied MMG based control system for practical prosthetic control.

Quantitative assessment of swallowing activity by MMG measurement with PVDF film.

Difficulty of swallowing, called dysphagia, leads to aspiration pneumonia which is particularly a big health concern in aging societies. Therefore, prevention and treatment of dysphagia would contribute to extending healthy-life and QOL of elderly people and decreasing healthcare cost. Robotics technologies are expected as one of the effective methods to solve the problem in terms of detecting malfunction in swallowing and recovering swallowing function. The aim of this study is to investigate muscle activity during normal swallowing using mechanomyography (MMG) with PolyVinylidene DiFluoride (PVDF) film which is a ferroelectrics polymer. Measurement of MMG signal during voluntary isometric contraction of the biceps brachii muscle was conducted to confirm whether PVDF film can detect MMG signal. In the experiment, surface electromyography (sEMG) was also measured as a reference to estimate muscle activity for comparison. Then, activities of swallowing muscles during normal swallowing with different volume of bolus were measured using MMG signal. As the result, it was confirmed that swallowing activity can be quantified by the detected MMG signal from different region of neck.

Recording characteristics of electrical impedance myography needle electrodes.

OBJECTIVE: Neurologists and physiatrists need improved tools for the evaluation of skeletal muscle condition. Here we evaluate needle electrical impedance myography (EIM), a new minimally invasive approach to determine muscle status that could ultimately become a bedside tool for the assessment of neuromuscular disorders. APPROACH: We design and study the recording characteristics of tetrapolar EIM needle electrodes combining theory and finite-element model simulations. We then use these results to build and pilot in vivo an EIM needle electrode in the rat gastrocnemius muscle ([Formula: see text]). The dielectric properties of muscle are reported (mean ± standard deviation). RESULTS: The numerical simulations show that the contribution of subcutaneous fat and muscle tissues to needle EIM data is <3% and >97%, respectively, and the sensed volume is [Formula: see text] cm3. Apparent resistivity [Formula: see text] [Formula: see text] cm and relative permittivity [Formula: see text] (dimensionless) measured at 10 kHz are in good agreement with in vivo dielectric properties reported in the literature. SIGNIFICANCE: The results presented show the feasibility of measuring muscle impedivity in vivo using a needle electrode from 10 kHz to 1 MHz. The development of needle EIM technology can open up a new field of study in electrodiagnostic medicine, with potential applications to both disease diagnosis and biomarker assessment of therapy.

System identification of velocity mechanomyogram measured with a capacitor microphone for muscle stiffness estimation.

A mechanomyogram (MMG) measured with a displacement sensor (displacement MMG) can provide a better estimation of longitudinal muscle stiffness than that measured with an acceleration sensor (acceleration MMG), but the displacement MMG cannot provide transverse muscle stiffness. We propose a method to estimate both longitudinal and transverse muscle stiffness from a velocity MMG using a system identification technique. The aims of this study are to show the advantages of the proposed method. The velocity MMG was measured using a capacitor microphone and a differential circuit, and the MMG, evoked by electrical stimulation, of the tibialis anterior muscle was measured five times in seven healthy young male volunteers. The evoked MMG system was identified using the singular value decomposition method and was approximated with a fourth-order model, which provides two undamped natural frequencies corresponding to the longitudinal and transverse muscle stiffness. The fluctuation of the undamped natural frequencies estimated from the velocity MMG was significantly smaller than that from the acceleration MMG. There was no significant difference between the fluctuations of the undamped natural frequencies estimated from the velocity MMG and that from the displacement MMG. The proposed method using the velocity MMG is thus more advantageous for muscle stiffness estimation.