Assessing the validity of surface electromyography for recording muscle activation patterns from serratus anterior

PurposeNo direct evidence exists to support the validity of using surface electrodes to record muscle activity from serratus anterior, an important and commonly investigated shoulder muscle. The aims of this study were to determine the validity of examining muscle activation patterns in serratus anterior using surface electromyography and to determine whether intramuscular electromyography is representative of serratus anterior muscle activity.MethodsSeven asymptomatic subjects performed dynamic and isometric shoulder flexion, extension, abduction, adduction and dynamic bench press plus tests. Surface electrodes were placed over serratus anterior and around intramuscular electrodes in serratus anterior. Load was ramped during isometric tests from 0% to 100% maximum load and dynamic tests were performed at 70% maximum load. EMG signals were normalised using five standard maximum voluntary contraction tests.ResultsSurface electrodes significantly underestimated serratus anterior muscle activity compared with the intramuscular electrodes during dynamic flexion, dynamic abduction, isometric flexion, isometric abduction and bench press plus tests. All other test conditions showed no significant differences including the flexion normalisation test where maximum activation was recorded from both electrode types. Low correlation between signals was recorded using surface and intramuscular electrodes during concentric phases of dynamic abduction and flexion.ConclusionsIt is not valid to use surface electromyography to assess muscle activation levels in serratus anterior during isometric exercises where the electrodes are not placed at the angle of testing and dynamic exercises. Intramuscular electrodes are as representative of the serratus anterior muscle activity as surface electrodes.     

Establishment of a recording method for surface electromyography in the iliopsoas muscle

We examined the availability and reliability of surface electromyography (EMG) signals from the iliopsoas muscle (IL). Using serial magnetic resonance images from fifty healthy young males, we evaluated whether the superficial region of IL was adequate for attaching surface EMG electrodes. Subsequently, we assessed EMG cross-talk from the sartorius muscle (SA)—the nearest to IL—using a selective cooling method in fourteen subjects. The skin above SA was cooled, and the median frequencies of EMG signals from IL and SA were determined. The maximum voluntary contraction during isometric hip flexion was measured before and after selective cooling, and surface EMG signals from SA and IL were measured. The superficial area of IL was adequately large (13.2 ± 2.7 cm²) for recording surface EMG in all fifty subjects. The maximum perimeter for the medial–lateral skin facing IL was noted at a level 3–5 cm distal to the anterior superior iliac spine. Following cooling, the median frequency for SA decreased significantly (from 70.1 to 51.9 Hz, p < 0.001); however, that for IL did not alter significantly. These results demonstrated that EMG cross-talk from SA was negligible for surface EMG signals from IL during hip flexion.     

Use of surface electromyography to estimate neck muscle activity

This paper reviews the literature concerning the use of surface electromyography (sEMG) for the study of the neck musculature in response to work and workplace design during light work and semi-static tasks. The paper also draws upon basic research and biomechanical modeling in order to provide methodological recommendations for the use of surface electromyography in this region of the body and to identify areas which require further investigation. The paper includes review and discussion of electrode site location, methods of normalization, data reliability, and factors that can affect sEMG signals from this region, including noise, physiologic artifact, stress, visual deficiencies, and pain. General guidance for maximum exertions with the neck musculature, for sEMG normalization or other purposes, is also included.     

表面肌电信号的肌肉疲劳判别研究进展

肌肉在周期的收缩或静态的拉伸过程中,会渐渐进入疲劳状态,肌肉疲劳特性的研究在康复医学、运动医学领域具有重要作用。表面肌电信号是从肌肉表面通过电极记录下来的反映神经肌肉系统活动的一维时间序列非平稳生物电信号,是评价局部肌肉疲劳的有效工具。本研究从时域和频域、时频域线性方法下的测量指标和非线性方法下的指标来综述表面肌电信号的疲劳研究进展,同时比较各种方法的优缺点,并对使用表面肌电信号来判别疲劳研究做了进一步的展望。     

Evaluation of upper limb muscle fatigue based on surface electromyography

Fatigue is believed to be a major contributory factor to occupational injuries in machine operators. The development of accurate and usable techniques to measure operator fatigue is therefore important. In this study, we used a novel method based on surface electromyography (sEMG) of the biceps brachii and the Borg scale to evaluate local muscle fatigue in the upper limb after isometric muscle action. Thirteen young males performed isometric actions with the upper limb at different force levels. sEMG activities of the biceps brachii were recorded during the actions. Borg scales were used to evaluate the subjective sensation of local fatigue of the biceps brachii after the actions. sEMG activities were analyzed using the one-third band octave method, and an equation to determine the degree of fatigue was derived based on the relationship between the variable and the Borg scale. The results showed that the relationship could be expressed by a conic curve, and could be used to evaluate muscle fatigue during machine operation.     

Shoulder muscle recruitment patterns during a kayak stroke performed on a paddling ergometer.

Precise muscle co-ordination is required to maintain normal shoulder function and alterations in synchrony between shoulder muscles can result in loss of full range of movement and pain. Although shoulder pain in kayakers is high with 53% of elite international paddlers reporting shoulder injuries, little information is available regarding the pattern of shoulder muscle recruitment during paddling. The aim of this study was to investigate the normal recruitment pattern of shoulder muscles during the kayak stroke. Nine recreational paddlers without shoulder pain were examined. EMG data from eight shoulder muscles of the dominant arm were collected simultaneously with video data during simulated paddling on an ergometer. EMG data was normalized to time and peak amplitude. Intersubject consistency was evaluated using Pearson correlation analysis. The results of this study indicated a fair to high correlation in at least one phase of the kayak stroke in five of the muscles examined: upper trapezius, supraspinatus, latissimus dorsi, serratus anterior and rhomboid major. This normative data will enable comparisons with the shoulder muscle recruitment patterns in kayakers with shoulder pain in order to determine the role of altered motor control in the painful kayaking shoulder.     

Kinesiological research: The use of surface electromyography for assessing the effects of spinal manipulation

Decreasing an elevated muscle tone is an often cited benefit of spinal manipulation. Spinal manipulation is theorized to disrupt an assumed pain-spasm-pain cycle that sufferers of low back pain may be experiencing. The current research has mostly investigated the short term influence of a single spinal manipulation on paraspinal muscle activity either at rest (e.g. standing or prone) or during simple movements (e.g. forward bend). The higher quality experiments to date have typically reported both reductions in muscle activity during lying prone or during the fully flexed position of forward bend. The only study measuring the long term influence of spinal manipulation has failed to document any change in muscle activity as measured with surface electromyography. Both manually delivered manipulations and manipulations delivered via a mechanical adjusting device have been associated with changes in muscle activation. Changes in muscle activity at muscles distant from the spinal joints manipulated (e.g. muscles in the upper limbs) have been documented following a single spinal manipulation however rather than the typical reduction in muscle activity an increase in resting activation has been reported. The state of muscle dysfunction (e.g. palpably tender or subjectively taut) may be a factor in achieving a myoelectric response to spinal manipulation. Currently, the clinical significance of short term changes in electromyographic amplitude following manipulation is unknown.     

New insights into pain-related changes in muscle activation revealed by high-density surface electromyography

High-density surface electromyography (HDEMG) is an electrophysiological technique that can be used to quantify the spatial distribution of activity within muscles. When pain-free individuals perform sustained or repetitive tasks, different regions within a muscle become progressively more active; this is thought to reflect a strategy to redistribute the load to different regions, thus limiting localised muscle fatigue. The use of HDEMG has revealed that when people with musculoskeletal pain perform the same tasks, the distribution of activity within the same muscle is usually different, and the same muscle region tends to be active throughout the whole task without progressive activation of different muscle regions. This potentially results in a focal overload of a muscle region, and may contribute to fatigue, localised muscle pain and potentially pain persistence and/or recurrence over time. Interestingly, not all patients with musculoskeletal pain present with this regional alteration in muscle activation, reflecting the heterogeneity of patient presentations. This article will briefly review the technique of HDEMG followed by a review of studies demonstrating spatial redistribution of muscle activity in asymptomatic people during both isometric and dynamic conditions, including functional tasks. Lastly, the article will provide a review of HDEMG studies with a focus on changes in the behaviour of the lumbar erector spine and upper trapezius in people with spinal pain. These studies have revealed subtle changes in the distribution of muscle activity in people with spinal pain, which may have relevance for onset, persistence or recurrence of symptoms and could become a target of novel therapeutic approaches.     

Velocity of isokinetic trunk exercises influences back muscle recruitment patterns in healthy subjects

Isokinetic exercises at different angular velocities on Cybex devices are often used for assessment and therapy in chronic low back pain patients. Little is known about the effect of velocity of movement on the muscle activity during these exercises. The purpose of this study was to investigate both relative muscle activity and ratios of local to global muscle activity at the different velocities of isokinetic movements on a Cybex dynamometer. Fifty-three healthy employees of Belgian Defence (26 male and 27 female) aged between 20 and 57 years old voluntarily performed isometric and isokinetic exercises at four different velocities. Surface electromyographic signals of different abdominal and back muscles were recorded on both sides. Both the relative muscle activity and the local to global muscle activity ratio of the back muscles were affected by changes in velocities of isokinetic exercises. The global muscle system was more influenced by changes in velocity, than the local muscle system. Abdominal relative muscle activity and ratios were not influenced by velocity of movement. This study revealed that the velocity of isokinetic extension exercises influences the recruitment of the back muscles, meaning that protocols of training programs should be adapted in function of the focus of the therapy.     

Evolution of surface electromyography: From muscle electrophysiology towards neural recording and interfacing

Surface electromyography (EMG) comprises a recording of electrical activity from the body surface generated by muscle fibres during muscle contractions. Its characteristics depend on the fibre membrane potentials and the neural activation signal sent from the motor neurons to the muscles. EMG has been classically used as the primary investigation tool in kinesiology studies in a variety of applications. More recently, surface EMG techniques have evolved from single-channel methods to high-density systems with hundreds of electrodes. High-density EMG recordings can be deconvolved to estimate the discharge times of spinal motor neurons innervating the recorded muscles, with algorithms that have been developed and validated in the last two decades. Within limits and with some variability across muscles, these techniques provide a non-invasive method to study relatively large populations of motor neurons in humans. Surface EMG is thus evolving from a peripheral measure of muscle electrical activity towards a neural recording and neural interfacing signal. These advances in technology have had a major impact on our fundamental understanding of the neural control of movement and have exposed new perspectives in neurotechnologies. Here we provide an overview and perspective of modern EMG technology, as derived from past achievements, and its impact in neurophysiology and neural engineering.     

No evidence of expertise-related changes in muscle synergies during rowing

The purpose of the present study was to determine whether expertise in rowing is driven by a specific structure in muscular coordination. We compared seven experienced rowers and eight untrained (i.e., inexperienced) subjects during rowing on an ergometer. Both surface electromyography activity and mechanical patterns (forces exerted at the handle and the foot-stretcher) were recorded during a high intensity rowing exercise. A non-negative matrix factorization was applied to 23 electromyographic patterns to differentiate muscle synergies. Results showed that expertise was not associated with different dimensionality in the electromyographic data and that three muscle synergies were sufficient to explain the majority of the variance accounted for (i.e., >90% of the total variance) in the two populations. The synergies extracted were similar in the two populations, with identical functional roles. While the temporal organization of the propulsive synergies was very similar, slight differences were found in the composition of the muscle synergies (muscle synergy vectors) between the two populations. The results suggests that rowing expertise would not require the development of novel muscle synergies but would imply intrinsic synergies already used in different behaviors. Performance in rowing is more probably linked to adjustments in the mechanical output of the muscle synergies rather than to differences in the shape and timing of their activations.     

Heterogeneity of muscle activation in relation to force direction: A multi-channel surface electromyography study on the triceps surae muscle

Several skeletal muscles can be divided into sub-modules, called neuromuscular compartments (NMCs), which are thought to be controlled independently and to have distinct biomechanical functions. We looked for distinct muscle activation patterns in the triceps surae muscle (TS) using surface electromyography (EMG) during voluntary contraction. Nine subjects performed isometric and isotonic plantar flexions combined with forces along pre-defined directions. Besides the forces under the ball of the foot, multi-channel surface EMG was measured with electrodes homogeneously distributed over the entire TS. Using principal component analysis, common (global) components were omitted from the EMG signals, thereby estimating muscle activity sufficiently accurate to track fine fluctuations of force during an isotonic contraction (r = 0.80 ± 0.09). A subsequent cluster analysis showed a topographical organization of co-activated parts of the muscle that was different between subjects. Low and negative correlations between the EMG activity within clusters were found, indicating a substantial heterogeneity of TS activation. The correlations between cluster time series and forces at the foot in specific directions differed substantially between clusters, showing that the differentially activated parts of the TS had specific biomechanical functions.     

Red muscle recruitment during steady swimming correlates with rostral-caudal patterns of power production in trout

Rainbow trout (Oncorhynchus mykiss) and brook trout (or charr, Salvelinus fontinalis) display different rostral-caudal patterns of power production by the red or aerobic muscle during steady swimming. The anterior muscle of rainbow trout produces much less power for swimming than the posterior, while in brook trout there is no variation in power output. To determine if red muscle recruitment is associated with anterior-posterior patterns of power production, electromyography (EMG) was used to record red muscle activity at three body positions across a range of swimming speeds in fish of each species. The initial recruitment of the anterior red muscle in swimming rainbow trout was predicted to lag behind, i.e. occur at higher speeds, that of the posterior due to the variation in power production, but no variation in recruitment was expected for brook trout. Burst of red muscle EMG activity occurring with each tailbeat was analyzed for frequency (tailbeat frequency), duty cycle (DC) (duration of burst relative to the period of the tailbeat) and burst intensity (BI) (magnitude of the measured EMG activity). Brook trout swam with higher tailbeat frequencies and longer values of DC than rainbow trout. Both species showed a pattern of longitudinal variation in DC, with longer DC values in the anterior red muscle. BI also differed significantly along the length of rainbow trout but not brook trout. In the former, BI of anterior muscle was significantly less than the posterior at lower steady swimming speeds. The EMG data suggest that power production and muscle recruitment are related. In rainbow trout, where there is longitudinal variation in muscle power output, there are also significant rostral-caudal differences in red muscle recruitment.     

Reliability of high-density surface electromyography for assessing characteristics of the thoracic erector spinae during static and dynamic tasks

PurposeTo establish intra- and inter-session reliability of high-density surface electromyography (HDEMG)-derived parameters from the thoracic erector spinae (ES) during static and dynamic goal-directed voluntary movements of the trunk, and during functional reaching tasks.MethodsTwenty participants performed: 1) static trunk extension, 2) dynamic trunk forward and lateral flexion, and 3) multidirectional functional reaching tasks on two occasions separated by 7.5 ± 1.2 days. Muscle activity was recorded bilaterally from the thoracic ES. Root mean square (RMS), coordinates of the barycentre, mean frequency (MNF), and entropy were derived from the HDEMG signals. Reliability was determined with intraclass correlation coefficient (ICC), coefficient of variation, and standard error of measurement.ResultsGood-to-excellent intra-session reliability was found for all parameters and tasks (ICC: 0.79-0.99), whereas inter-session reliability varied across tasks. Static tasks demonstrated higher reliability in most parameters compared to functional and dynamic tasks. Absolute RMS and MNF showed the highest overall reliability across tasks (ICC: 0.66-0.98), while reliability of the barycentre was influenced by the direction of the movements.ConclusionRMS and MNF derived from HDEMG show consistent inter-session reliability in goal-directed voluntary movements of the trunk and reaching tasks, whereas the measures of the barycentre and entropy demonstrate task-dependent reliability.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Detection of surface electromyography recording time interval without muscle fatigue effect for biceps brachii muscle during maximum voluntary contraction

The effects of fatigue on maximum voluntary contraction (MVC) parameters were examined by using force and surface electromyography (sEMG) signals of the biceps brachii muscles (BBM) of 12 subjects. The purpose of the study was to find the sEMG time interval of the MVC recordings which is not affected by the muscle fatigue. At least 10 s of force and sEMG signals of BBM were recorded simultaneously during MVC. The subjects reached the maximum force level within 2 s by slightly increasing the force, and then contracted the BBM maximally. The time index of each sEMG and force signal were labeled with respect to the time index of the maximum force (i.e. after the time normalization, each sEMG or force signal’s 0 s time index corresponds to maximum force point). Then, the first 8 s of sEMG and force signals were divided into 0.5 s intervals. Mean force, median frequency (MF) and integrated EMG (iEMG) values were calculated for each interval. Amplitude normalization was performed by dividing the force signals to their mean values of 0 s time intervals (i.e. ?0.25 to 0.25 s). A similar amplitude normalization procedure was repeated for the iEMG and MF signals. Statistical analysis (Friedman test with Dunn’s post hoc test) was performed on the time and amplitude normalized signals (MF, iEMG). Although the ANOVA results did not give statistically significant information about the onset of the muscle fatigue, linear regression (mean force vs. time) showed a decreasing slope (Pearson-r = 0.9462, p < 0.0001) starting from the 0 s time interval. Thus, it might be assumed that the muscle fatigue starts after the 0 s time interval as the muscles cannot attain their peak force levels. This implies that the most reliable interval for MVC calculation which is not affected by the muscle fatigue is from the onset of the EMG activity to the peak force time. Mean, SD, and range of this interval (excluding 2 s gradual increase time) for 12 subjects were 2353, 1258 ms and 536–4186 ms, respectively. Exceeding this interval introduces estimation errors in the maximum amplitude calculations of MVC–sEMG studies for BBM. It was shown that, simultaneous recording of force and sEMG signals was required to calculate the maximum amplitude of the MVC–sEMG more accurately.     

Seedling recruitment patterns in a tropical dry forest in Ghana

Abstract. Studies of seedling demography and dynamics were carried out in a dry forest at Pinkwae, Ghana (rainfall 1100 mm). Seedlings of tree and liana species in permanent transects were tagged, identified, measured and recensused at bimonthly intervals. A total of 1931 seedlings in 53 species were followed over 14 censuses during a 2-yr period. Germination and mortality were seasonal in their distribution; mortality was highest in dry periods. Seedling density varied seasonally, with the highest densities in comparatively wet periods. Diversity of seedlings was low, corresponding to that of the adult assemblage. Survivorship of tagged seedlings was recorded during the study period. The cohort tagged at the first census, comprising 1033 individuals of mixed ages and species, lost 61.9% during a 24-month period. Many seedlings were found to be rather large at the initial post-germination stage, with strong root development. Vegetative reproduction by root suckers or epicormic shoots was quite common at the site, although the majority of regeneration was by seeds. The current seedling assemblage appears to be representative, in terms of composition and diversity, of the adult species assemblage at Pinkwae.     

A new surface electromyography analysis method to determine spread of muscle fiber conduction velocities.

Muscle fiber conduction velocity (MFCV) estimation from surface signals is widely used to study muscle function, e.g., in neuromuscular disease and in fatigue studies. However, most analysis methods do not yield information about the velocity distribution of the various motor unit action potentials. We have developed a new method-the interpeak latency method (IPL)-to calculate both the mean MFCV and the spread of conduction velocities in vivo, from bipolar surface electromyogram (sEMG) during isometric contractions. sEMG was analyzed in the biceps brachii muscle in 15 young male volunteers. The motor unit action potential peaks are automatically detected with a computer program. Associated peaks are used to calculate a mean MFCV and the SD. The SD is taken as a measure of the MFCV spread. The main finding is that the IPL method can derive a measure of MFCV spread at different contraction levels. In conclusion, the IPL method provides accurate values for the MFCV and additionally gives information about the scatter of conduction velocities.