Surface EMG based muscle fatigue evaluation in biomechanics

In the last three decades it has become quite common to evaluate local muscle fatigue by means of surface electromyographic (sEMG) signal processing. A large number of studies have been performed yielding signal-based quantitative criteria of fatigue in primarily static but also in dynamic tasks. The non-invasive nature of this approach has been particularly appealing in areas like ergonomics and occupational biomechanics, to name just the most prominent ones. However, a correct appreciation of the findings concerned can only be obtained by judging both the scientific value and practical utility of methods while appreciating the corresponding advantages and limitations. The aim of this paper is to serve as a state of the art summary of this issue. The paper gives an overview of classical and modern signal processing methods and techniques from the standpoint of applicability to sEMG signals in fatigue-inducing situations relevant to the broad field of biomechanics. Time domain, frequency domain, time–frequency and time-scale representations, and other methods such as fractal analysis and recurrence quantification analysis are described succinctly and are illustrated with their biomechanical applications, research or clinical alike. Examples from the authors’ own work are incorporated where appropriate. The future of this methodology is projected by estimating those methods that have the greatest chance to be routinely used as reliable muscle fatigue measures.     

Construct validity of myotonometric measurements of muscle compliance as a measure of strength

Myotonometric measurement of muscle compliance represents new technology that quantifies muscle tone. Compliance change during muscle contraction might provide an indirect measure of strength. The purpose of this study was to determine relationships among myotonometric measurements of muscle compliance, surface electromyographic (sEMG) measurements of muscle activation and joint force production during voluntary isometric knee extensions. The level of relationship will contribute to the construct validity of use of muscle compliance as an indirect strength measurement. Thirteen male subjects, mean age 25 +/- 1.5 years, participated. Simultaneous recordings of myotonometric, sEMG of the rectus femoris and isometric knee extension force measurements were taken at rest, during maximal voluntary contraction (MVC), and during 33% and 66% MVC contractions. Relationships among the three measurement procedures were calculated using correlation and regression analyses. Myotonometric measures of muscle compliance, sEMG and force measurements were highly correlated. Myotonometric measurements were best represented by a curvilinear (quadratic) relationship to sEMG (r = 0.82, p < 0.001) and joint force (r = 0.83, p < 0.001). The present experiments establish the construct validity of myotonometric measurements of muscle compliance as an indirect means of quantifying muscle strength and activation levels. This method, therefore, offers a possible alternative for cases in which direct measurement of joint force or sEMG is difficult or inappropriate.     

双关节运动的局部肌肉疲劳与肌电变化

目的：以腕-肘关节为例，探讨不同水平运动负荷诱发尺侧腕屈肌（FCU）和肱二头肌（BB）疲劳过程中sEMG信号与各关节最大屈肌肌力的关系。方法：采集10名青年男性受试者在不同负荷水平（30％、55％、80％MVC）下疲劳过程中尺侧腕屈肌（FCU）和肱二头肌（BB）的表面肌电信号和各关节在疲劳前后的MVC。结果：不同运动负荷强度分别诱发前臂和上臂肌肉疲劳过程中，腕、肘关节最大屈肌肌力明显下降且具有明显负荷强度效应：BB和FCU的MPF与MF单调递减且下降率具有明显的负荷强度效应；不同负荷强度下BB和FCU的MPF和MF下降斜率与肘、腕关节最大屈肌肌力的下降比值之间有明显相关。结论：局部肌肉疲劳过程中MPF和MF下降率变化能够对相应关节最大肌力变化作出比较准确预测。     

Mechanical force spinal manipulation increases trunk muscle strength assessed by electromyography: a comparative clinical trial

OBJECTIVE: The objective of this study was to determine whether mechanical force, manually-assisted (MFMA) spinal manipulative therapy (SMT) affects paraspinal muscle strength as assessed through use of surface electromyography (sEMG). DESIGN: Prospective clinical trial comparing sEMG output in 1 active treatment group and 2 control groups. SETTING: Outpatient chiropractic clinic, Phoenix, AZ. SUBJECTS: Forty subjects with low back pain (LBP) participated in the study. Twenty patients with LBP (9 females and 11 males with a mean age of 35 years and 51 years, respectively) and 20 age- and sex-matched sham-SMT/control LBP subjects (10 females and 10 males with a mean age of 40 years and 52 years, respectively) were assessed. METHODS: Twenty consecutive patients with LBP (SMT treatment group) performed maximum voluntary contraction (MVC) isometric trunk extensions while lying prone on a treatment table. Surface, linear-enveloped sEMG was recorded from the erector spinae musculature at L3 and L5 during a trunk extension procedure. Patients were then assessed through use of the Activator Methods Chiropractic Technique protocol, during which time they were treated through use of MFMA SMT. The MFMA SMT treatment was followed by a dynamic stiffness and algometry assessment, after which a second or post-MVC isometric trunk extension and sEMG assessment were performed. Another 20 consecutive subjects with LBP were assigned to one of two other groups, a sham-SMT group and a control group. The sham-SMT group underwent the same experimental protocol with the exception that the subjects received a sham-MFMA SMT and dynamic stiffness assessment. The control group subjects received no SMT treatment, stiffness assessment, or algometry assessment intervention. Within-group analysis of MVC sEMG output (pre-SMT vs post-SMT sEMG output) and across-group analysis of MVC sEMG output ratio (post-SMT sEMG/pre-SMT sEMG output) during MVC was performed through use of a paired observations t test (POTT) and a robust analysis of variance (RANOVA), respectively. MAIN OUTCOME MEASURES: Surface, linear-enveloped EMG recordings during isometric MVC trunk extension were used as the primary outcome measure. RESULTS: Nineteen of the 20 patients in the SMT treatment group showed a positive increase in sEMG output during MVC (range, -9.7% to 66.8%) after the active MFMA SMT treatment and stiffness assessment. The SMT treatment group showed a significant (POTT, P < 0.001) increase in erector spinae muscle sEMG output (21% increase in comparison with pre-SMT levels) during MVC isometric trunk extension trials. There were no significant changes in pre-SMT vs post-SMT MVC sEMG output for the sham-SMT (5.8% increase) and control (3.9% increase) groups. Moreover, the sEMG output ratio of the SMT treatment group was significantly greater (robust analysis of variance, P = 0.05) than either that of the sham-SMT group or that of the control group. CONCLUSIONS: The results of this preliminary clinical trial demonstrated that MFMA SMT results in a significant increase in sEMG erector spinae isometric MVC muscle output. These findings indicate that altered muscle function may be a potential short-term therapeutic effect of MFMA SMT, and they form a basis for a randomized, controlled clinical trial to further investigate acute and long-term changes in low back function.     

Ultrasound Elastography: The New Frontier in Direct Measurement of Muscle Stiffness

The use of brightness-mode ultrasound and Doppler ultrasound in physical medicine and rehabilitation has increased dramatically. The continuing evolution of ultrasound technology has also produced ultrasound elastography, a cutting-edge technology that can directly measure the mechanical properties of tissue, including muscle stiffness. Its real-time and direct measurements of muscle stiffness can aid the diagnosis and rehabilitation of acute musculoskeletal injuries and chronic myofascial pain. It can also help monitor outcomes of interventions affecting muscle in neuromuscular and musculoskeletal diseases, and it can better inform the functional prognosis. This technology has implications for even broader use of ultrasound in physical medicine and rehabilitation practice, but more knowledge about its uses and limitations is essential to its appropriate clinical implementation. In this review, we describe different ultrasound elastography techniques for studying muscle stiffness, including strain elastography, acoustic radiation force impulse imaging, and shear-wave elastography. We discuss the basic principles of these techniques, including the strengths and limitations of their measurement capabilities. We review the current muscle research, discuss physiatric clinical applications of these techniques, and note directions for future research.     

肌电生物反馈联合康复训练对脊髓损伤患者运动功能及功能独立性的影响

目的:观察肌电生物反馈疗法联合康复训练对脊髓损伤(SCI)患者运动功能障碍的康复疗效。方法:60例胸腰段不完全性脊髓损伤患者随机分为观察组和对照组,每组30例。2组均进行常规康复治疗,观察组加用双下肢肌电生物反馈治疗。治疗前及治疗后8周、12周进行下肢肌肉最大收缩时表面肌电(sEMG)信号采集、运动功能评定及功能独立性(FIM)评定,比较临床疗效。结果:治疗8周后,2组患者股四头肌、胫前肌最大收缩时的sEMG信号均较治疗前明显提高(P0.05),治疗后12周继续提高(P0.01);观察组sEMG信号增幅高于对照组(P0.05)。治疗8周后,2组患者ASIA运动功能评分及FIM评分亦较治疗前提高(P0.05),组间比较差异无统计学意义;治疗12周后,2组ASIA运动功能及FIM评分较治疗8周后提高更明显(P0.01),观察组更高于对照组(P0.05)。结论:肌电生物反馈疗法联合康复训练对胸腰段不完全性脊髓损伤患者运动功能有促进作用,能明显提高患者的股四头肌、胫前肌表面肌电信号及肌力,并能提高功能独立水平,减少并发症。     

Effect of tonic muscle pain on short-latency jaw-stretch reflexes in humans

The modulation of human jaw-stretch reflexes by experimental muscle pain was studied in three experiments. Short-latency reflex responses were evoked in the masseter and temporalis muscles by fast stretches (1 mm displacement, 10 ms ramp time) before, during and 15 min after a period with tonic pain. In Expt. I, a dose of 5.8% hypertonic or 0.9% isotonic (control) saline was infused in random order into the left masseter for up to 15 min (n=12). The level of excitation of the left masseter was kept constant at 15% of maximal effort by visual feedback and on-line calculation of the root-mean-square value of the surface electromyogram (sEMG). In Expt. II, a dose of 5.8% saline was infused into the left masseter but with feedback from the right masseter sEMG (n=12). In Expt. III, both sEMG and intramuscular (im) EMG was recorded from the left and right masseter muscles. The feedback was from either the sEMG or imEMG of the left masseter in which 5.8% saline was infused (n=12). In all experiments, subjects continuously rated their perceived pain intensity on a 10-cm visual analogue scale (VAS). Infusion of 5.8% saline caused moderate levels of pain (mean VAS 4.9-5.0 cm) whereas infusion of 0.9% saline was almost pain-free (mean VAS 0.3 cm). The pre-stimulus EMG activity in the masseter, which served as the feedback muscle during the recording, was constant across the different conditions. During painful infusion of 5.8% saline in Expts. I and III, the pre-stimulus sEMG activity in the non-painful masseter was significantly higher than baseline when the sEMG on the painful side was used as feedback signal, and in Expt. II significantly lower on the painful side when the non-painful side served as feedback signal (Student-Newman-Keuls: P<0.05). Isotonic saline did not affect the pre-stimulus sEMG activity or the jaw-stretch reflex parameters. The peak-to-peak amplitude of the stretch reflex in the painful masseter normalized to the pre-stimulus EMG activity was significantly higher during the pain conditions compared with the pre- and post-infusion conditions in all experiments. These results indicate that experimental jaw-muscle pain facilitates the short-latency (8-9 ms), probably monosynaptic, jaw-stretch reflex as revealed by both sEMG and imEMG. This effect could not be accounted for by variability in pre-stimulus EMG activity. An increased sensitivity of the fusimotor system at this level of static muscle excitation is suggested as a possible mechanism, which could contribute to an increased stiffness of the jaw-muscles during pain.     

Scapular muscle tests in subjects with shoulder pain and functional loss: reliability and construct validity

BACKGROUND AND PURPOSE: Scapular muscle performance evaluated with a handheld dynamometer (HHD) has been investigated only in people without shoulder dysfunction for test-retest reliability of data obtained with a single scapular muscle test. The purpose of this study was to assess the reliability, error, and validity of data obtained with an HHD for 4 scapular muscle tests in subjects with shoulder pain and functional loss. SUBJECTS AND METHODS: Subjects (N=40) with shoulder pain and functional loss were tested by measuring the kilograms applied with an HHD during 3 trials for muscle tests for the lower trapezius, upper trapezius, middle trapezius, and serratus anterior muscles. Concurrently, surface electromyography (sEMG) data were collected for the 4 muscles. The same procedures were performed 24 to 72 hours after the initial testing by the same tester. Muscle tests were performed 3 times, and the results were averaged for data analysis. RESULTS: Intraclass correlation coefficients for intratester reliability of measurements of isometric force obtained using an HHD ranged from .89 to .96. The standard error of the measure (90% confidence interval [CI]) ranged from 1.3 to 2.7 kg; the minimal detectable change (90% CI) ranged from 1.8 to 3.6 kg. Construct validity assessment, done by comparing the amounts of isometric muscle activity (sEMG) for each muscle across the 4 muscle tests, revealed that the muscle activity of the upper trapezius and lower trapezius muscles was highest during their respective tests. Conversely, the isometric muscle activity of the middle trapezius and serratus anterior muscles was not highest during their respective tests. DISCUSSION AND CONCLUSION: In people with shoulder pain and functional loss, the intrarater reliability and error over 1 to 3 days were established using an HHD for measurement of isometric force for the assessment of scapular muscle performance. Error values can be used to make decisions regarding individual patients. Construct validity was established for the lower and upper trapezius muscle tests; therefore, these tests are advocated for use. However, construct validity was not demonstrated for the serratus anterior and middle trapezius muscle tests as performed in this study. Further investigation of these muscle tests is warranted.     

Altered motor control and spasticity after spinal cord injury: subjective and objective assessment

This study of measures of spasticity, or altered motor control, compares the clinically used Ashworth scale with a method based on surface electromyographic (sEMG) recordings called brain motor control assessment (BMCA) in a group of 97 subjects with spinal cord injury (SCI) and varying levels of motor dysfunction. In this paper, we describe how sEMG-derived scores relate to the severity of spasticity as judged clinically. When sEMG data from passive movements from the BMCA were analyzed by Ashworth category, we found that when the sEMG data were averaged for a limb, there was a significant difference between scores for those with Ashworth 0 vs. 2 and 3, and 1 vs. 2 and 3 (p<0.001), but not between 0 and 1. Analysis of the individual muscle scores improved the discrimination between Ashworth categories. Superiority of sEMG data over Ashworth category as an objective quantification of altered motor control ("spasticity") is argued.     

Cervical flexion: a study of dynamic surface electromyography and range of motion

BACKGROUND: In the comprehensive assessment of painful conditions, dynamic surface electromyography (sEMG) and range of motion (ROM) recordings can provide information regarding muscle spasm, antalgic postures, fear of pain (protective guarding), muscle injury, and disordered movement caused by pain. This study examines ROM and sEMG patterns observed during cervical flexion. OBJECTIVE: To demonstrate 2 distinctive sEMG recruitment and dynamic ROM patterns observed during cervical flexion and return to mid-line. DESIGN: Single-subject design with independent measurement of dynamic ROM and sEMG. SETTING: Applied clinical setting. PARTICIPANTS: Two subjects with normal ROM and cervical muscles were studied. MAIN OUTCOME MEASURE: One subject was studied with sEMG. looking at the cervical paraspinals and sternocleidomastoid muscles; the other subject was studied with an active ROM device. Three cervical movements were studied: lower cervical flexion, atlantoaxial (upper) cervical flexion, and a combination upper/lower cervical flexion. RESULTS: The active ROM device indicates larger movements (higher degrees of flexion) for the lower cervical flexion compared with upper flexion. The combined movement indicates a differential movement from 2 spinal segments. The sEMG recordings indicated differential recruitment patterns. The sternocleidomastoid recruits briskly during the flexion phase of the upper cervical flexion movement, whereas the cervical paraspinals recruit briskly during return to mid-line when the lower cervical flexion is used. The combined upper then lower cervical flexion movement recruits both sets of muscles. CONCLUSIONS: The results of the study indicate 2 distinct movement patterns associated with upper versus lower cervical flexion and 2 distinct sEMG recruitment patterns. The study suggests that these 2 distinct movements involve 2 distinct cervical segments and are associated with recruitment of different muscle groups. Applied clinical research on the cervical spine should use sEMG recordings to assess both the upper and lower flexion movements as the standard for the study of cervical flexion.     

Reduced complexity of force and muscle activity during low level isometric contractions of the ankle in diabetic individuals

BackgroundThis study evaluated the structure and amount of variability of surface electromyography (sEMG) patterns and ankle force data during low-level isometric contractions in diabetic subjects with different degrees of neuropathy.MethodsWe assessed 10 control subjects and 38 diabetic patients, classified as absent, mild, moderate, or severe neuropathy, by a fuzzy system based on clinical variables. Multichannel sEMG (64-electrode matrix) of tibialis anterior and gastrocnemius medialis muscles were acquired during isometric contractions at 10%, 20%, and 30% of the maximum voluntary contraction, and force levels during dorsi- and plantarflexion were recorded. Standard deviation and sample entropy of force signals were calculated and root mean square and sample entropy were calculated from sEMG signals. Differences among groups of force and sEMG variables were verified using a multivariate analysis of variance.FindingsOverall, during dorsiflexion contractions, moderate and severe subjects had higher force standard deviation and moderate subjects had lower force sample entropy. During plantarflexion, moderate subjects had higher force standard deviation and all diabetic subjects had lower entropy. Tibialis anterior presented higher root mean square in absent group and lower entropy in mild subjects. For gastrocnemius medialis, entropy was higher in severe and lower in moderate subjects.InterpretationDiabetic neuropathy affects the complexity of the neuromuscular system during low-level isometric contractions, reducing the system's capacity to adapt to challenging mechanical demands. The observed patterns of neuromuscular complexity were not associated with disease severity, with the majority of alterations recorded in moderate subject.     

Lower extremity applications of functional neuromuscular stimulation

Functional electrical stimulation (FES) applications in the lower extremity are common in research laboratories, but clinical applications are minimal. This review summarizes current knowledge with respect to clinical application. When electrical stimulation is used in clinical applications for functional movement such as standing and walking, it is typically applied in an open-loop manner; a predetermined stimulus pattern is delivered regardless of the consequences of the actual movement. Few clinical applications of FES involve closed-loop control because of the numerous difficulties involved in its application. As with any volitional muscle contraction, electrically stimulated muscle contractions will exhibit fatigue. Although the dynamics of fatigue may differ, electrically stimulated muscle contractions cannot be continuously sustained, and if the duty cycle is too severe, even alternating periods of rest and contraction cannot be sustained at a constant force level. The exact nature of fatigue is highly specific to the past history of the individual muscle and to the individual subject. Despite their intricate detail, quantitative modeling studies have not yet been applied extensively to clinical applications. Present implantable systems are not yet a viable option for clinical application. It is not clear whether more success with surface or percutaneous systems must first be achieved to justify implantation or whether greater improvements in implantable technology and surgical protocols are needed before implantable systems will become practical. It is clear that almost any reasonably designed stimulation protocol will increase muscle bulk. The existence of other therapeutic benefits and their cost/benefit ratios remain to be fully established. It is possible to stand through bilateral stimulation of the quadriceps. Using surface electrodes, this technique is achievable in any physical therapy clinic having minimal expertise in neuromuscular stimulation. FES-aided standing must be conducted as a research project with a protocol approved by the local institutional review board, as there are currently no FDA-approved stimulation devices for standing. Multichannel FES systems are not currently available for clinical application in the United States. This may change if the "Parastep" system receives FDA approval. Percutaneous and implanted systems are years away from commercialization and clinical availability. Hybrid systems, based primarily on the reciprocating gait orthosis (RGO), are presently the only clinically available form of walking that includes some form of FES assistance. The costs and benefits of adding FES to the RGO and the long-term user acceptance rate for these systems remain to be determined.     

A review on muscle activation behaviour during gait in shallow water and deep-water running and surface electromyography procedures

BackgroundSurface electromyography (sEMG) can provide information on muscle activation patterns during gait.ObjectivesTo characterize electromyographic activity during gait in shallow water and during deep-water running compare to on land and to review and analyse underwater surface-electromyographic (sEMG) procedures.Search methodsEight databases (MEDLINE, EMBASE, WEB OF SCIENCE, SPORT Discus, CINAHL, SCOPUS, SCIELO, and LILACS) were searched from their inception to the December of 2019.Selection criteriaThe selected studies had to be related to electromyographic analysis of gait in an aquatic environment.Data collection and analysisThe studies that met the inclusion criteria were reviewed by two independent reviewers and divided into four groups.ResultsTen studies met the inclusion criteria. Lower muscle activation was found with treadmill water walking compared to treadmill land walking. With deep-water running, the leg muscles (tibialis anterior and gastrocnemius lateralis) have lower muscle activation when compared to on land running, but the trunk and thigh muscles have higher activation.ConclusionIf gait is performed on an aquatic treadmill, the muscles assessed had lower muscle activation when compared to land. During deep-water running activities, lower activation of the distal leg muscles and a higher activation thigh muscles were found when compared to on land. Studies did not follow standard processes in sEMG procedures.     

Decoding subtle forearm flexions using fractal features of surface electromyogram from single and multiple sensors

Background  

Identifying finger and wrist flexion based actions using a single channel surface electromyogram (sEMG) can lead to a number of applications such as sEMG based controllers for near elbow amputees, human computer interface (HCI) devices for elderly and for defence personnel. These are currently infeasible because classification of sEMG is unreliable when the level of muscle contraction is low and there are multiple active muscles. The presence of noise and cross-talk from closely located and simultaneously active muscles is exaggerated when muscles are weakly active such as during sustained wrist and finger flexion. This paper reports the use of fractal properties of sEMG to reliably identify individual wrist and finger flexion, overcoming the earlier shortcomings.     

恢复期脑卒中患者膝关节拮抗肌群在动态运动负荷下对协同收缩率的影响

目的观察动态运动负荷对脑卒中患者膝关节拮抗肌群协同收缩率变化的影响。方法11例脑卒中患者(偏瘫组)和14例正常人(正常组)利用动态运动负荷诱发双侧下肢屈伸膝关节,采用表面电极引导和记录肌电信号并进行线性时、频分析。结果偏瘫组与正常组组内中位频率(MF)、平均功率频率(MPF)、平均肌电值(AEMG)膝关节拮抗肌群协同收缩率均值变化无显著性差异(P>0.05);组间比较,MF膝关节拮抗肌群协同收缩率均值变化无显著性差异(P>0.05);偏瘫组MPF膝关节拮抗肌群协同收缩率明显增高,AEMG膝关节拮抗肌群协同收缩率明显降低(均P<0.01)。结论MPF、AEMG膝关节拮抗肌群协同收缩率能反映动态运动负荷下脑卒中患者下肢肌肉表面肌电信号变化,而MF膝关节拮抗肌群协同收缩率并不能很好地反映动态运动负荷下脑卒中患者下肢肌肉表面肌电信号变化。     

表面肌电图在神经肌肉功能评定中的应用

表面肌电图（sEMG）是一种无创功能测评方法，通过记录运动时肌肉肌电图的振幅、频率等指标的变化，反映肌肉功能的水平。笔者对脑卒中患者运动时sEMG信号的研究进行综述，旨在为选择脑卒中后神经肌肉康复训练的方法提供科学依据。     

Size and shape of the posterior neck muscles measured by ultrasound imaging: normal values in males and females of different ages

Measurements of muscle strength or size are valuable indicators of muscle status in health and disease. When force cannot be measured directly, due to a particular muscle being one of a functional group or because of pain, size measurements may be the only option. For such data to be useful, normal values for age and gender are necessary. Procedures for scanning and measuring semispinalis capitis and the deep posterior neck muscles (semispinalis cervicis, multifidus and rotatores) using ultrasound imaging are described and normal data provided on size, shape and symmetry of these muscles from a sample of 99 healthy subjects (46 males aged 20-72 years and 53 females aged 18-70 years). Significant gender differences were found (P<0.001) but muscle size did not alter significantly with age. Between-side symmetry can be used to assess abnormality of the deep neck muscle group but not semispinalis capitis. A regression equation is provided for predicting the cross-sectional area (CSA) of the deep neck muscles from spinous process length in males. Clinically, linear measurements can be used to predict the neck muscle CSAs (r=0.66-0.84, P<0.001). The method described for assessing the neck muscles is a potentially valuable tool in clinical practice.     

Muscle tone in different joint positions and at submaximal isometric torque levels

The aim was to evaluate the tone and electric activity of the quadriceps muscle at rest and different torque levels. The second aim was to study whether thickness of soft tissues and change in the joint position would affect muscle tone. Eighteen healthy subjects participated. Computerized muscle tonometer (CMT) and surface electromyography (sEMG) measurements were performed: seated, first at rest with leg straight and then with the knee at 60 degrees . Thereafter measurements were obtained at levels of 80, 60, 40 and 20% of the maximum isometric torque at the same knee angle. Thickness of skin, subcutis and muscle was measured by ultrasound. The CMT values taken were the depth the indenter travelled and the work it did while compressing the right rectus femoris and vastus intermedius muscles. Expressed as mean (SD) depth the change in muscle tone changed from 29.2 (3.6) mm in the relaxed position to 16.9 (5.2) mm at 80% of maximal torque, and expressed as work the values were from 1589 (150) mJ to 739 (149) mJ respectively. The correlation between CMT, sEMG and torque measurements varied from r = -0.52 to -0.71 (p < 0.01). CMT was able to detect a change of 20% in torque production and 4% in tone. Tone values, at each torque level, were significantly separate from the values at the other force levels (p < 0.001-0.04). Soft tissue thickness explained most of the tone results at rest (57%). The repeatability of the CMT measures was good (ICCs 0.75-0.99). Both depth and work correlated with electric activity and muscle torque, but the correlation with work was higher. In conclusion, muscle activity, length and thickness have to be taken into account when evaluating muscle tone.     

Model-based estimation of muscle forces exerted during movements

Estimation of individual muscle forces during human movement can provide insight into neural control and tissue loading and can thus contribute to improved diagnosis and management of both neurological and orthopaedic conditions. Direct measurement of muscle forces is generally not feasible in a clinical setting, and non-invasive methods based on musculoskeletal modeling should therefore be considered. The current state of the art in clinical movement analysis is that resultant joint torques can be reliably estimated from motion data and external forces (inverse dynamic analysis). Static optimization methods to transform joint torques into estimates of individual muscle forces using musculoskeletal models, have been known for several decades. To date however, none of these methods have been successfully translated into clinical practice. The main obstacles are the lack of studies reporting successful validation of muscle force estimates, and the lack of user-friendly and efficient computer software. Recent advances in forward dynamics methods have opened up new opportunities. Forward dynamic optimization can be performed such that solutions are less dependent on measured kinematics and ground reaction forces, and are consistent with additional knowledge, such as the force-length-velocity-activation relationships of the muscles, and with observed electromyography signals during movement. We conclude that clinical applications of current research should be encouraged, supported by further development of computational tools and research into new algorithms for muscle force estimation and their validation.     

人体上肢表面肌电反馈康复训练系统的研制

目的：研究临床康复训练中急需解决的肌肉疲劳的保护问题。方法：开发了一种采用功能电刺激方式和表面肌电反馈控制的康复训练系统。该系统由功能电刺激器、被动训练发生器、表面肌电信号放大器及管理控制软件4部分组成。管理控制软件控制表面肌电信号放大器、功能电刺激器和被动训练发生器3部分的协调运作。结果：该系统可以实时分析康复训练过程中采集到的表面肌电信号，并以此判定肌肉是否疲劳，亦可设定功能电刺激系统的刺激参数，通过控制电路控制训练发生器运动参数等功能。结论：该系统可以有效地防止主动训练过程中因肌肉过度疲劳而造成的损伤。