Physical and electrophysiological motor unit characteristics are revealed with simultaneous high-density electromyography and ultrafast ultrasound imaging

Electromyography and ultrasonography provide complementary information about electrophysiological and physical (i.e. anatomical and mechanical) muscle properties. In this study, we propose a method to assess the electrical and physical properties of single motor units (MUs) by combining High-Density surface Electromyography (HDsEMG) and ultrafast ultrasonography (US). Individual MU firings extracted from HDsEMG were used to identify the corresponding region of muscle tissue displacement in US videos. The time evolution of the tissue velocity in the identified region was regarded as the MU tissue displacement velocity. The method was tested in simulated conditions and applied to experimental signals to study the local association between the amplitude distribution of single MU action potentials and the identified displacement area. We were able to identify the location of simulated MUs in the muscle cross-section within a 2 mm error and to reconstruct the simulated MU displacement velocity (cc > 0.85). Multiple regression analysis of 180 experimental MUs detected during isometric contractions of the biceps brachii revealed a significant association between the identified location of MU displacement areas and the centroid of the EMG amplitude distribution. The proposed approach has the potential to enable non-invasive assessment of the electrical, anatomical, and mechanical properties of single MUs in voluntary contractions

Extracting Human-Exoskeleton Interaction Torque for Cable-Driven Upper-Limb Exoskeleton Equipped With Torque Sensors

Powered exoskeletons have global trends in broad applications, such as rehabilitation and human strength amplification in industry, military, and activities of daily livings. The motion intention of the exoskeleton wearer can be obtained using the interaction force at the physical human-machine interface. This article implements joint torque sensors in a custom-made cable-driven exoskeleton. The model of the torque sensor signal is established to extract the human-exoskeleton interaction (HEI) torque, which can be used to predict the human upper-limb motion intention. To accurately decouple the HEI torque from other components in the torque sensor signal, a nonlinear numerical friction model composed of the cable and joint parts is investigated based on the LuGre friction model. A protocol for parameter identification of the proposed friction model is verified experimentally. Furthermore, a coefficient combining the two friction models is designed for antagonistic directions in a joint to account for the bidirectional cable drive's backlash and hysteresis characteristics. Owing to this coefficient, the error of the friction model is reduced by approximately 90% during motion direction change. Finally, the accuracy of the torque sensor model is verified experimentally, and the root-mean-square error (RMSE) is about 0.038 N·m (2.8%). The RMSE of extracted interaction torque is about 0.25 N·m (8.1%). This article validates the feasibility of extracting HEI torque via a torque sensor implemented in the upper-limb exoskeleton, which can promote the development of new generations of upper-limb exoskeleton for active rehabilitation or assistance and research on intuitive control of exoskeleton in future.</p

Do changes in neuromuscular activation contribute to the knee extensor angle-torque relationship?

The influence of joint angle on knee extensor neuromuscular activation is unclear due in part due to the diversity of surface electromyography (sEMG) and/or interpolated twitch technique (ITT) methods employed. The aim of the study was to compare neuromuscular activation, using rigorous contemporary sEMG and ITT procedures, during isometric maximal voluntary contractions (iMVC) of the quadriceps femoris (Q) at different knee-joint angles and examine if activation contributes to the angle-torque relationship. Sixteen healthy active males completed two familiarization sessions and two experimental sessions of isometric knee extension and knee flexion contractions. The experimental sessions included the following at each of four joint angles (25°, 50°, 80° and 106°): iMVCs (with and without superimposed evoked doublets); submaximal contractions with superimposed doublets; evoked twitch and doublet contractions whilst voluntarily passive and knee flexion iMVC at the same knee joint positions. Absolute Q EMG was normalised to MMAX peak-to-peak amplitude and the doublet-voluntary torque relationship was used to calculate activation with the ITT (ACTITT ). Agonist activation, assessed with both normalised EMG and ACTITT , was reduced in the more extended compared to the more flexed positions (25 & 50 vs. 80 & 106°; P ≤ 0.016), whereas antagonist co-activation was greatest in the most flexed compared to the extended positions (106 vs. 25 & 50°; P ≤ 0.02). In conclusion, both agonist and antagonist activation differed with knee joint angle during knee extension iMVCs and thus both likely contribute to the knee extensor angle-torque relationship

Towards the Development of a Wearable Tremor Suppression Glove

Patients diagnosed with Parkinson’s disease (PD) often associate with tremor. Among other symptoms of PD, tremor is the most aggressive symptom and it is difficult to control with traditional treatments. This thesis presents the assessment of Parkinsonian hand tremor in both the time domain and the frequency domain, the performance of a tremor estimator using different tremor models, and the development of a novel mechatronic transmission system for a wearable tremor suppression device. This transmission system functions as a mechatronic splitter that allows a single power source to support multiple independent applications. Unique features of this transmission system include low power consumption and adjustability in size and weight. Tremor assessment results showed that the hand tremor signal often presents a multi-harmonics pattern. The use of a multi-harmonics tremor model produced a better estimation result than using a monoharmonic tremor model

Investigations of the Neuromuscular Response During and Following Elite Maximum Strength and Power Type Resistance Exercise

The thesis aimed to analyse the acute neuromuscular (NM) response during and following maximum strength and power training methods. The primary aim of study one was to establish the reliability of biomechanical and surface electromyographic (sEMG) measurements during barbell squat exercise. This would enable the subsequent studies to precisely assess muscle activity and mechanical power during barbell resistance exercise sessions. Nine male well-trained subjects performed squat exercise on three separate trial days. Each trial comprised one set of squat at 50, 75 and 100% of 3RM load. Synchronous recordings of knee joint kinematics from a flexible electrogoniometer, barbell displacement from a single linear position transducer and quadriceps sEMG amplitude were made. The mean maximum knee angle during squat was recorded at each load, and the overall inter-trial coefficient of variation (CV) was 5.5%. Mean concentric repetition power was processed from displacement data and derived into force and velocity values. The overall inter-trial CV for mean power was found to be 8.4%. The raw sEMG signal was processed into root mean square (RMS) amplitude and normalised to values taken from pre-trial knee extension maximum voluntary contractions (MVC). RMS amplitude was processed for the whole concentric phase and a 200 ms time interval at a knee angle of 70°, which matched the knee angle used during MVC. Inter-trial CV for RMS amplitude from the concentric phase and 70° knee angle were 7.2% and 16.4% respectively. There were no differences in RMS amplitude, maximum knee angle or mean power across trial days. It was concluded there was acceptable reliability for all three measurements (CV < 10%), if RMS amplitude was processed from the concentric phase. Based upon the measurement reliability, the analysis system was considered suitable for monitoring power and sEMG during barbell exercise. The second study aimed to establish the reliability of muscle fibre conduction velocity (MFCV) measurements during barbell squat. This was of interest, as MFCV may provide useful information of NM recruitment and fatigue processes during resistance exercise. The study was also used as a preliminary investigation of MFCV response, in comparison to RMS amplitude, to increasing fatigue and load during squat exercise. Nine well-trained male subjects performed a series of exercises on two separate trial days. Each trial comprised isometric knee extensions at 50, 75 and 100% of MVC force, followed by barbell squats at 50, 75 and 100% of 3RM, and then a maximal bout of squat jumps at 50% 3RM load, performed until failure. sEMG measurements were recorded from a four-electrode array, secured upon the vastus lateralis. Normalised RMS amplitude was processed as above, and MFCV was processed from the inter-electrode distance and time delay between two double differentiated and correlated signals, using bespoke software. The overall value of MFCV during squat was 5.8 m.s-1. The inter-trial CV for MFCV was 9.6% during squat and 12.1% during squat jump. Based upon acceptable reliability of 10%, MFCV measurements from barbell squats were considered reliable. As expected, MFCV significantly increased with each knee extension force level (4.7 ± 1.4, 5.6 ± 1.5 and 6.2 ± 1.8 m.s-1) (p<0.01), along with RMS amplitude (p<0.0001). No differences in MFCV were found between squat loads, whilst RMS amplitude significantly increased with load (p<0.0001). Power (1920 ± 143 versus 1407 ± 254 W) and MFCV (5.7 ± 1.4 versus 4.6 ± 1.0 m.s-1) significant decreased (p<0.001) from the start to the end of the squat jump trial, with RMS amplitude unchanged. Therefore, MFCV altered with increasing fatigue, but not load, during dynamic squat exercise. It was concluded that MFCV provides useful and reliable data for acute fatigue investigations of barbell resistance exercise, in addition to sEMG amplitude measures. The following three investigations compared NM responses during and following maximum strength and power type resistance exercise sessions with different exercises, loads and movement speeds. The sessions were designed to represent elite athlete training practices, to help inform the optimisation of resistance exercise programmes. The first of these studies aimed to compare NM response to a typical maximum strength session performed with barbell squat or deadlift exercise. The purpose was to assess if technical differences between the exercises, influenced the acute NM response. Nine elite trained weightlifters performed the trial sessions of five sets of five repetitions on separate days. Normalised RMS amplitude, MFCV and power was continually measured during exercise repetitions, using the methods established above. NM function was assessed pre- and post- sessions using MVC force, central activation ratio (CAR) from superimposed stimulation during MVC, and jump performance (CMJ). The exercises were performed with subjectively matched load levels, corresponding to active muscle RPE = 17 (Borg scale), and also with controlled lifting speed. However, the squat load was lowered and raised upon the lifter’s back, whilst deadlift load was grasped in the hands, raised from the floor and then dropped. Repetition mean power was unchanged within and across sets of both sessions. Repetition RMS amplitude significantly increased (p<0.001) within sets of squat and deadlift, whilst a significant interaction between sessions and set (p<0.001) demonstrated RMS increased more during squat. Furthermore, a significant reduction in repetition MFCV was found within sets of squat (p = 0.034), but not deadlift. This suggests that motor unit activation increased during both exercises, as a response to the task of maintaining power during repetitions of whole body lifting. However, acute fatigue within squat sets led to additional increased activation as a NM compensation strategy. No pre- versus post- session differences were found for MVC, CAR or CMJ; suggesting minimal change in NM function occurred following five sets of maximum strength type resistance exercise, in well-trained subjects. The primary aim of the second study was to compare NM response and 24-hour recovery following barbell exercise maximum strength and power type sessions. The purpose was to specifically establish the degree and nature of NM response, as previous findings were unclear and barbell exercise sessions of this type have not been compared. 10 elite sprint athletes performed sessions comprising squat, split squat and push press, with four sets x repetitions per exercise. The maximum strength session exercises involved loads corresponding to active muscle RPE = 17 (Borg scale) and metronome controlled movements. The power session exercises used 30% of the maximum strength barbell load, performed as fast as possible. Repetition sEMG and power was monitored throughout each session, as above. NM function was assessed, pre-, post- and 24-hour post- each session, using the same tests as above. However, evoked peak twitch force (Pt) was also included to the pre- and post- assessments. Overall, the maximum strength session involved greater total work (p = 0.008), but lower mean power during exercise repetitions (p<0.001) in comparison to the power session. MVC and Pt force values both significantly decreased (p<0.05) pre- versus post- both sessions. However, MVC reduced more following maximum strength session (p<0.01). CAR and CMJ were unchanged post-both sessions and no differences were found between pre and 24-hour post session NM tests. The decreased Pt but not CAR findings, suggest peripheral fatigue explains the reduced force generation capacity following maximum strength and power sessions, contrary to previous resistance exercise session findings. Up to 24-hours may be required to recover force generation capacity following this volume of resistance exercise. Additional analysis suggested strength levels influenced the degree of fatigue following the power session. This was because barbell exercises involve lifting body mass and bar mass. Therefore, stronger subjects lifted relatively lighter loads during a barbell power session using 30% of bar mass. This supports the use of system mass loads to determine relative load levels during power type sessions. The aim of the final study was to compare NM and hormonal response following high intensity ‘explosive’ squat at three load levels. This training method is specific to elite athletes and has not been previously assessed. The purpose was to further understanding of the load level of explosive exercise that provides the most effective training stimulus. 15 elite power athletes, from track and field and rugby, completed 10 sets of high intensity squat exercise on three separate days. The heavy session involved loads corresponding to active muscle RPE = 17 (Borg scale), as above. The moderate and light sessions were 75% and 50% system mass of heavy session load, respectively. The execution of every repetition was maximal in all three sessions. Methods followed previous studies with the addition of isometric knee extension rate of force development (RFD) and loaded squat jump (SJ) power to the NM function tests. Saliva samples were taken at baseline, mid-, and post- session for testosterone (T) and cortisol (C) assay analysis. Heavy session involved greatest repetition impulse in comparison to moderate and light sessions (p<0.001), whilst light session involved highest repetition power (p<0.001). Total work performed in each session was similar. MVC, RFD and Pt force values were significantly reduced post- sessions (p<0.01). However, MVC and RFD reduced most following heavy, then moderate and then light sessions. This corresponded to significantly reduced repetition power during sets of the heavy session only (p<0.001). Repetition RMS amplitude also increased most during sets of heavy session (p<0.001), followed by moderate, with no change during light session. These findings suggest NM response was greatest during heavy session, providing effective training stimulus, but so was acute NM fatigue. Moderate load explosive exercise may also provide sufficient NM stimulus, however with less fatigue. Decrement in RFD was significantly greater than MVC force (p<0.001), and was reduced mid- as well as post- session. This suggests high intensity squat training affects NM mechanisms related to RFD capacity. No significant changes in CAR, CMJ or loaded SJ were found. Significant reductions in C relative to baseline (p<0.001) occurred mid- and post all three sessions, as expected following circadian rhythms. A significant interaction between session and time (p<0.01) was found, where T was maintained relative to baseline following moderate and heavy sessions, but reduced following the light session. This also suggests heavy and moderate high intensity sessions may provide more effective training stimulus than light load. The findings of this thesis show that the NM response during maximum strength and power type resistance exercise sessions involves increased motor unit activation within exercise sets. This may occur without fatigue during exercise repetitions and indicates the NM stimulus for adaptation. The nature of NM fatigue following maximum strength and power training, in terms of reduced force generation, involves peripheral, and not central, mechanisms, contrary to previous conclusions and general belief amongst sports coaches. Importantly, stimulus may not be directly related to the degree of post-session NM fatigue, but instead the NM activation during exercise repetitions. The data implies certain exercises (e.g. deadlift and explosive moderate load squats) provide sufficient stimulus for adaptation, with a limited NM fatigue response. This informs training programme design for elite athletes completing diverse and concurrent training activities

Shear wave elastography to assess the effect of botulinum toxin in muscle hypertonia following stroke

Introduction Sonoelastography is a method capable of evaluating the mechanical properties of soft tissues by ultrasound (US). A further development of this technique is shear wave elastography (SWE), which provides a quantitative evaluation of the elastic properties - in terms of tissutal stiffness - by measuring the propagation velocities of the directional shear waves, produced by an ultrasound pulse. Spasticity often appears in stroke patients in the affected limbs. It corresponds to velocity-dependent muscle hypertonia in relation to the hyperexcitability of the stretch reflex. Over time, the paretic muscles develop intrinsic alterations with consequent muscle shortening and increased fibrosis related to reduced use and immobilization. Intramuscular injections of botulinum toxin A (BoNT-A) is an effective treatment which reduces muscle activity by inhibiting the release of acetylcholine at the neuromuscular junction level and is therefore able to reduce neuromediated muscle hypertonicity. The study aims to evaluate the effectiveness of SWE to appreciate changes in stiffness in spastic muscles after treatment with BoNT-A and possibly detect differences between affected muscles and unaffected contralateral ones related to fibrous-fatty remodeling. Materials &amp; Methods 14 adult patients (5F; age: 58,4\ub114,1 years, m\ub1SD; range:46-78) affected by spasticity were recruited after ischemic or hemorrhagic stroke diagnosed for at least 3 months and with a time interval from the last injection of at least 4 months, if already treated with BoNT-A. They patients underwent a physical examination in which muscle hypertonia was assessed using the modified Ashworth scale (MAS). The assessments were carried out on a sample muscle among the spastic ones favoring the greater volume and better accessibility to the ultrasound probe. SWE was also performed on the homologue non-paretic contralateral muscle. Spasticity was measured as the average electromyographic activity recorded during stretching (reflex by stretching) of the selected muscle at a reproducible speed, according to a previously validated methodology. The SWE evaluation was carried out with US scans across and along the direction of muscular fibers - as assessed by conventional US - covering the entire belly of the selected muscle to obtain a comprehensive estimate of the muscle stiffness both with the maximum shortened and elongated muscle position. Muscle fibrosis was also estimated on conventional B-mode US using the modified Heckmatt scale. All evaluations were performed shortly before botulinum toxin infiltration (T0) and one month later (T1). Clinical, electromyographic and ultrasound evaluation were performed by three different blinded examiners. Depending on data distribution, non-parametric statistical tests for paired data were performed for comparison; Spearman\u2019s r was calculated to assess data correlations. Results A total of 224 SWE values resulted considering both time points. Overall, SWE measurements on paretic muscles assessed with a longitudinal positioning of the probe showed statistically significant reduction at T1 versus T0 both in non stretched conditions (p=0.001) and in stretched conditions (p=0.0029). After BoNT-A injection, a significant reduction in MAS (p=0.009), spastic dystonia (p=0.0043), spasticity (p=0.0019) and longitudinal SWE measurements, both in non stretched conditions (p=0.001) and in stretched conditions (p=0.0029), was observed. No significant changes in SWE parameters were observed on non-paretic versus contralateral muscle . All SWE measurements were higher in the paretic limb than in the contralateral one (p&lt;0.01); higher SWE measurements resulted along the direction of muscular fibers versus across them (p&lt;0.01). Cohen\u2019s d estimate a larger effect on EMG values than longitudinal SWE ones (either in non stretched and in stretched condition), with narrower 95%CI for SWE measurements. No changes resulted by the modified Heckmatt scale US assessments; there was a positive correlation (r: 0.46-0.84) between MHS scores and SWE values. Conclusion This is the first study evaluating the effect of BoNT-A on muscle hypertonia following stroke, assessed by mean of SWE and compared with the stretch reflex. The treatment resulted in a reduction of MAS, stretch reflex and muscular stiffness, in relation to the reduction of the neuro-mediated hypertonia. We have therefore shown that SWE is able to appreciate a reduction in neuro-mediated stiffness. Abolishing the neuro-mediated contribution by keeping the limb in a shortened position and moreover after BoNT-A injection, the SWE values resulted higher in the paretic muscle than in the healthy muscle in the same position. Hence, SWE-driven comparison between the spastic muscle and the contralateral unaffected homologous one is able to disclose the amount of stiffness due only to intrinsic muscular involutive remodeling. Alongside sEMG, SWE could therefore constitute an added-value to clinicians who manage spasticity for the assessment of responses to treatments and monitoring therapeutic interventions

Theories for Skilled Limb Movements .

Some of the theories that have been advanced to perform skilled limb movements are reviewed in this paper. The aspects discussed in brief include alpha-gamma control, choice of control variables in limb movements, equilibrium point hypotheses, experimental observations from simple movement studies and explanations proposed, in particular the dual strategy hypothesis. The single mechanical degree-of-freedom movements may be controlled by one of two strategies: a speed-insensitive strategy or a speed-sensitive strategy. The term strategy implies a set of rules which specify in terms of task variables and subject instructions how to choose the excitation signal, the controlling signal at the alpha motoneuron level. The two strategies differ in that speed-insensitive strategy is a result of duration modulation of the excitation pulse, whereas the speed-sensitive strategy is a result from amplitude modulation. Finally, the problem of multi-degrees of freedom movements and the role of higher motor control centres are discussed in brief

Biomechanics

Biomechanics is a vast discipline within the field of Biomedical Engineering. It explores the underlying mechanics of how biological and physiological systems move. It encompasses important clinical applications to address questions related to medicine using engineering mechanics principles. Biomechanics includes interdisciplinary concepts from engineers, physicians, therapists, biologists, physicists, and mathematicians. Through their collaborative efforts, biomechanics research is ever changing and expanding, explaining new mechanisms and principles for dynamic human systems. Biomechanics is used to describe how the human body moves, walks, and breathes, in addition to how it responds to injury and rehabilitation. Advanced biomechanical modeling methods, such as inverse dynamics, finite element analysis, and musculoskeletal modeling are used to simulate and investigate human situations in regard to movement and injury. Biomechanical technologies are progressing to answer contemporary medical questions. The future of biomechanics is dependent on interdisciplinary research efforts and the education of tomorrow’s scientists

Rehabilitation Engineering

Population ageing has major consequences and implications in all areas of our daily life as well as other important aspects, such as economic growth, savings, investment and consumption, labour markets, pensions, property and care from one generation to another. Additionally, health and related care, family composition and life-style, housing and migration are also affected. Given the rapid increase in the aging of the population and the further increase that is expected in the coming years, an important problem that has to be faced is the corresponding increase in chronic illness, disabilities, and loss of functional independence endemic to the elderly (WHO 2008). For this reason, novel methods of rehabilitation and care management are urgently needed. This book covers many rehabilitation support systems and robots developed for upper limbs, lower limbs as well as visually impaired condition. Other than upper limbs, the lower limb research works are also discussed like motorized foot rest for electric powered wheelchair and standing assistance device

A Simulation Study of Functional Electrical Stimulation for An Upper Limb Rehabilitation Robot using Iterative Learning Control (ILC) and Linear models

A proportional iterative learning control (P-ILC) for linear models of an existing hybrid stroke rehabilitation scheme is implemented for elbow extension/flexion during a rehabilitative task. Owing to transient error growth problem of P-ILC, a learning derivative constraint controller was included to ensure that the controlled system does not exceed a predefined velocity limit at every trial. To achieve this, linear transfer function models of the robot end-effector interaction with a stroke subject (plant) and muscle response to stimulation controllers were developed. A straight-line point-point trajectory of 0 - 0.3 m range served as the reference task space trajectory for the plant, feedforward, and feedback stimulation controllers. At each trial, a SAT-based bounded error derivative ILC algorithm served as the learning constraint controller. Three control configurations were developed and simulated. The system performance was evaluated using the root means square error (RMSE) and normalized RMSE. At different ILC gains over 16 iterations, a displacement error of 0.0060 m was obtained when control configurations were combined.Comment: 15 pages, 16 Figure