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The purpose of this study was to investigate differences in passive muscular stiffness between the superficial multifidus (SM) and deep multifidus (DM), and to compare their passive and active stiffness in individuals with low back pain (LBP) and asymptomatic individuals. Fifteen LBP individuals and 15 asymptomatic individuals were recruited. Passive stiffness of the SM and DM was measured bilaterally using shear wave elastography (SWE) with participants lying prone. Active stiffness was measured for the SM during trunk extension, and the contraction ratio was calculated. DM displayed higher passive muscular stiffness than SM in both the asymptomatic and LBP groups (14.41 ± 2.62 and 15.40 ± 2.77 kPa respectively; p < 0.001). Individuals with LBP exhibited higher passive muscular stiffness of SM (LBP: 10.15 ± 4.21, asymptomatic: 6.84 ± 1.69 kPa; p < 0.005) and a lower contraction ratio (LBP: 1.54 ± 0.47, asymptomatic: 2.65 ± 1.36 kPa; p < 0.003) compared to the asymptomatic group. The findings support a differentiation in passive muscular stiffness between SM and DM and provide evidence for an alteration in muscular stiffness at rest in individuals with LBP. The lower increase of muscular stiffness with contraction observed for those with LBP may reflect a deficit in activation of the multifidus. [ABSTRACT FROM AUTHOR]

This study evaluates and compares the effects of strength and endurance training on motor unit discharge rate variability and force steadiness of knee extensor muscles. Thirty sedentary healthy men (age, 26.0±3.8yrs) were randomly assigned to strength training, endurance training or a control group. Conventional endurance and strength training was performed 3days per week, over a period of 6weeks. Maximum voluntary contraction (MVC), time to task failure (at 30% MVC), coefficient of variation (CoV) of force and of the discharges rates of motor units from the vastus medialis obliquus and vastus lateralis were determined as subjects performed 20% and 30% MVC knee extension contractions before and after training. CoV of motor unit discharges rates was significantly reduced for both muscles following strength training (P<0.001), but did not change in the endurance (P=0.875) or control group (P=0.995). CoV of force was reduced after the strength training intervention only (P<0.01). Strength training, but not endurance training, reduces motor unit discharge rate variability and enhances force steadiness of the knee extensors. These results provide new insights into the neuromuscular adaptations that occur with different training methods. [ABSTRACT FROM AUTHOR]

The purpose of this narrative review is to provide a critical reflection of how analytical machine learning approaches could provide the platform to harness variability of patient presentation to enhance clinical prediction. The review includes a summary of current knowledge on the physiological adaptations present in people with spinal pain. We discuss how contemporary evidence highlights the importance of not relying on single features when characterizing patients given the variability of physiological adaptations present in people with spinal pain. The advantages and disadvantages of current analytical strategies in contemporary basic science and epidemiological research are reviewed and we consider how analytical machine learning approaches could provide the platform to harness the variability of patient presentations to enhance clinical prediction of pain persistence or recurrence. We propose that machine learning techniques can be leveraged to translate a potentially heterogeneous set of variables into clinically useful information with the potential to enhance patient management. [ABSTRACT FROM AUTHOR]

Abstract: Due to the variations in morphological and architectural characteristics of fibers within a skeletal muscle, regions of a muscle may be differently affected by eccentric exercise. Although eccentric exercise may be beneficial for increasing muscle mass and can be beneficial for the treatment of tendinopathies, the non-uniform effect of eccentric exercise results in regional muscle damage and as a consequence, non-uniform changes in muscle activation. This regional muscle weakness can contribute to muscle strength imbalances and may potentially alter the load distribution on joint structures, increasing the risk of injury. In this brief review, the non-uniform effects of eccentric exercise are reviewed and their implications for training and sport are considered. [Copyright &y& Elsevier]

Abstract: The study compared the distribution of electromyographic (EMG) signal amplitude in the upper trapezius muscle in 10 women with fibromyalgia and in 10 healthy women before and after experimentally-induced muscle pain. Surface EMG signals were recorded over the right upper trapezius muscle with a 10×5 grid of electrodes during 90° shoulder abduction sustained for 60s. The control subjects repeated the abduction task following injections of isotonic and hypertonic (painful) saline into the upper trapezius muscle. The EMG amplitude was computed for each electrode pair and provided a topographical map of the distribution of muscle activity. The pain level rated by the patients at the beginning of the sustained contraction was 5.9±1.5. The peak pain intensity for the control group following the injection of hypertonic saline was 6.0±1.6. During the sustained contractions, the EMG amplitude increased relatively more in the cranial than caudal region of the upper trapezius muscle for the control subjects (shift in the distribution of EMG amplitude: 2.3±1.3mm; P <0.01). The patient group showed lower average EMG amplitude than the controls during the contraction (P <0.05) and did not show different changes in EMG amplitude between different regions of the upper trapezius. A similar behavior was observed for the control group following injection of hypertonic saline. The results indicate that muscle pain prevents the adaptation of upper trapezius activity during sustained contractions as observed in non-painful conditions, which may induce overuse of similar muscle compartments with fatigue. [Copyright &y& Elsevier]

Abstract: This study investigated whether pain-induced changes in cervical muscle activation affect myoelectric manifestations of cervical muscle fatigue. Surface EMG signals were detected from the sternocleidomastoid and splenius capitis muscles bilaterally from 14 healthy subjects during 20-s cervical flexion contractions at 25% of the maximal force. Measurements were performed before and after the injection of 0.5ml of hypertonic (painful) or isotonic (control) saline into either the sternocleidomastoid or splenius capitis in two experimental sessions. EMG average rectified value and mean power spectral frequency were estimated throughout the sustained contraction. Sternocleidomastoid or splenius capitis muscle pain resulted in lower sternocleidomastoid EMG average rectified value on the side of pain (P <0.01). However, changes over time of sternocleidomastoid EMG average rectified value and mean frequency (myoelectric manifestations of fatigue) during sustained flexion were not changed during muscle pain. These results demonstrate that pain-induced modifications of cervical muscle activity do not change myoelectric manifestations of fatigue. This finding has implications for interpreting the mechanisms underlying greater cervical muscle fatigue in people with neck pain disorders. [Copyright &y& Elsevier]

Abstract: The purpose of this brief review is to present evidence from experimental and clinical neck pain studies of pain-induced neuromuscular adaptations. It has been shown that clinical neck pain is associated with a substantial reorganization in the control strategies of cervical muscles during static and dynamic tasks. Experimental neck pain models allow local elicitation of nociceptive afferents, mimicking the sensory aspects of clinical pain, without major changes in muscle properties. These models may help understand the physiological mechanisms underlying the observations from clinical neck pain studies. The knowledge obtained from the interpretation of clinical findings with experimental pain models has relevance for the development of therapeutic interventions for the rehabilitation of patients with neck pain disorders. [Copyright &y& Elsevier]

Abstract: The deep cervical flexor (DCF) muscles are considered to be of substantial clinical importance in the management of neck pain. While conventional cervical flexion (CF) dynamometry methods have been used frequently to assess the capacity of the cervical flexor muscles, it has been suggested that cranio-cervical flexion (CCF) methods may provide a more specific test of DCF muscle performance. This study compared the activation of the deep and superficial cervical flexor muscles between tests of isometric cranio-cervical flexion (CCF) and conventional cervical flexion (CF) dynamometry. Normalised root-mean-square values were recorded for the deep cervical flexor (DCF), sternocleidomastoid (SCM), anterior scalene (AS), and sternohyoid (SH) muscles during isometric CCF and CF tests at maximal voluntary contraction (MVC), 50% MVC, and 20% MVC in ten healthy volunteers. The results demonstrated significantly greater electromyography (EMG) amplitude for the SCM (P <.001–.002) and AS (P <.001–.001) muscles in the CF test conditions (MVC, 20%MVC, and 50%MVC) compared to CCF test conditions. Moreover, the SH muscle demonstrated significantly greater EMG amplitude during CF compared to CCF but only in the 50% MVC and 20% MVC conditions (P =.007 and .02 respectively). These results demonstrate that dynamometry tests of CF result in greater activity of the superficial cervical flexor muscles compared to tests of CCF. As a result, CCF dynamometry may provide a more specific method to assess and retrain DCF muscle performance, compared to conventional CF in which superficial muscle activity may mask impaired performance of the DCF muscles. [Copyright &y& Elsevier]

The diversity in electromyography (EMG) techniques and their reporting present significant challenges across multiple disciplines in research and clinical practice, where EMG is commonly used. To address these challenges and augment the reproducibility and interpretation of studies using EMG, the Consensus for Experimental Design in Electromyography (CEDE) project has developed a checklist (CEDE-Check) to assist researchers to thoroughly report their EMG methodologies. Development involved a multi-stage Delphi process with seventeen EMG experts from various disciplines. After two rounds, consensus was achieved. The final CEDE-Check consists of forty items that address four critical areas that demand precise reporting when EMG is employed: the task investigated, electrode placement, recording electrode characteristics, and acquisition and pre-processing of EMG signals. This checklist aims to guide researchers to accurately report and critically appraise EMG studies, thereby promoting a standardised critical evaluation, and greater scientific rigor in research that uses EMG signals. This approach not only aims to facilitate interpretation of study results and comparisons between studies, but it is also expected to contribute to advancing research quality and facilitate clinical and other practical applications of knowledge generated through the use of EMG. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigate whether visual feedback on the spatial distribution of upper trapezius muscle activity can prolong time to task failure of sustained shoulder abduction. Surface electromyographic signals were acquired with a 13x5 grid of high-density electromyography (HDEMG) electrodes from the right upper trapezius muscle of 12 healthy volunteers as they performed sustained isometric shoulder abduction at 20% of their maximum voluntary contraction torque (MVC) until volitional exhaustion. Data were collected in two sessions; one with HDEMG visual feedback on the spatial distribution of upper trapezius activity and one without feedback. Although the HDEMG amplitude maps could be voluntarily modified by the participants during the feedback condition (significant shift in the barycenter of activity towards the cranial direction, P = 0.038), this did not influence endurance time (total endurance time with HDEMG feedback: 149.01 ± 77.07 s, no feedback 141.74 ± 60.93 s, P = 0.532). Future studies should assess whether endurance performance can be enhanced by allowing changes in arm position during the task (changing fiber tension-length relationships), by providing a more individual motor strategy, and/or by manipulating the colours used for the HDEMG maps (lighter colours for higher contraction intensities). [ABSTRACT FROM AUTHOR]

We investigate whether visual feedback on the spatial distribution of upper trapezius muscle activity can prolong time to task failure of sustained shoulder abduction. Surface electromyographic signals were acquired with a 13x5 grid of high-density electromyography (HDEMG) electrodes from the right upper trapezius muscle of 12 healthy volunteers as they performed sustained isometric shoulder abduction at 20% of their maximum voluntary contraction torque (MVC) until volitional exhaustion. Data were collected in two sessions; one with HDEMG visual feedback on the spatial distribution of upper trapezius activity and one without feedback. Although the HDEMG amplitude maps could be voluntarily modified by the participants during the feedback condition (significant shift in the barycenter of activity towards the cranial direction, P = 0.038), this did not influence endurance time (total endurance time with HDEMG feedback: 149.01 ± 77.07 s, no feedback 141.74 ± 60.93 s, P = 0.532). Future studies should assess whether endurance performance can be enhanced by allowing changes in arm position during the task (changing fiber tension-length relationships), by providing a more individual motor strategy, and/or by manipulating the colours used for the HDEMG maps (lighter colours for higher contraction intensities). [ABSTRACT FROM AUTHOR]

High intensity eccentric exercise induces muscle fiber damage and associated delayed-onset muscle soreness (DOMS) resulting in an impaired ability of the muscle to generate voluntary force. This study investigates the extent to which DOMS, induced by high intensity eccentric exercise, can affect the activation and performance of the non-exercised homologous muscle of the contralateral limb. Healthy volunteers performed maximal voluntary contractions of knee extension and sustained isometric knee extension at 50% of maximal force until task failure on both the ipsilateral exercised limb and the contralateral limb. Surface electromyography (EMG) was recorded from the ipsilateral and contralateral knee extensor muscles (vastus medialis, rectus femoris, and vastus lateralis). Maximal isometric knee extension force (13.7% reduction) and time to task failure (38.1% reduction) of the contralateral non-exercised leg decreased immediately after eccentric exercise, and persisted 24 h and 48 h later (p < 0.05). Moreover, the amplitude of muscle activity recorded from the contralateral knee extensor muscles was significantly lower during the post exercise maximal and submaximal contractions following high intensity eccentric exercise of the opposite limb (p < 0.05). Unilateral high intensity eccentric exercise of the quadriceps can contribute to reduced neuromuscular activity and physical work capacity of the non-exercised homologous muscle in the contralateral limb. [ABSTRACT FROM AUTHOR]

Low back pain (LBP) is a leading cause of disability in the workplace, often caused by manually lifting of heavy loads. Instrumental-based assessment tools are used to quantitatively assess the biomechanical risk of lifting activities. This study aims to verify that, during the execution of fatiguing frequency-dependent lifting, high-density surface electromyography (HDsEMG) allows the discrimination of healthy controls (HC) versus people with LBP and biomechanical risk levels. Fifteen HC and eight people with LBP performed three lifting tasks with a progressively increasing lifting index, each lasting 15 min. Erector spinae (ES) activity was recorded using HDsEMG and amplitude parameters were calculated to characterize the spatial distribution of muscle activity. LBP group showed a less ES activity than HC (lower root mean square across the grid and of the activation region) and an involvement of the same muscular area across the task (lower coefficient of variation of the center of gravity of muscle activity). The results indicate the usefulness of HDsEMG parameters to classify risk levels for both HC and LBP groups and to determine differences between them. The findings suggest that the use of HDsEMG could expand the capabilities of existing instrumental-based tools for biomechanical risk classification during lifting activities. [ABSTRACT FROM AUTHOR]

Changes in spinal kinematic variability have been observed in people with chronic non-specific LBP (CNSLBP) during the performance of various repetitive functional tasks. However, the direction of these changes (i.e., less or more kinematic variability) is not consistent. This study aimed to assess differences in kinematic variability of the 3D angular displacement of thoracic and lumbar spinal segments in people with CNSLBP compared to asymptomatic individuals during a repetitive lifting task. Eleven people with CNSLBP and 11 asymptomatic volunteers performed 10 cycles of multi-planar lifting movements while spinal kinematics were recorded. For the three planes of motion, point-by-point standard deviations (SDs) were computed across all cycles of lifting and the average was calculated as a measure of kinematic variability for both segments. People with CNSLBP displayed higher thoracic (F = 8.00, p = 0.010, ηp2 = 0.286) and lumbar kinematic variability (F = 5.48, p = 0.030, ηp2 = 0.215) in the sagittal plane. Moreover, group differences were observed in the transversal plane for thoracic (F = 7.62, p = 0.012, ηp2 = 0.276) and lumbar kinematic variability (F = 5.402, p = 0.031, ηp2 = 0.213), as well as in the frontal plane for thoracic (F = 7.27, p = 0.014, ηp2 = 0.267) and lumbar kinematic variability (F = 6.11, p = 0.022, ηp2 = 0.234), all showing higher variability in those with CNSLBP. A significant main effect of group was not detected (p > 0.05) for spinal range of motion (ROM). Thus, people with CNSLBP completed the lifting task with the same ROM in all three planes of motion as observed for asymptomatic individuals, yet they performed the lifting task with higher spinal kinematic cycle-to-cycle variation. [ABSTRACT FROM AUTHOR]

The Consensus for Experimental Design in Electromyography (CEDE) project is an international initiative which aims to guide decision-making in recording, analysis, and interpretation of electromyographic (EMG) data. The quality of the EMG recording, and validity of its interpretation depend on many characteristics of the recording set-up and analysis procedures. Different electrode types (i.e., surface and intramuscular) will influence the recorded signal and its interpretation. This report presents a matrix to consider the best electrode type selection for recording EMG, and the process undertaken to achieve consensus. Four electrode types were considered: (1) conventional surface electrode, (2) surface matrix or array electrode, (3) fine-wire electrode, and (4) needle electrode. General features, pros, and cons of each electrode type are presented first. This information is followed by recommendations for specific types of muscles, the information that can be estimated, the typical representativeness of the recording and the types of contractions for which the electrode is best suited. This matrix is intended to help researchers when selecting and reporting the electrode type in EMG studies. [ABSTRACT FROM AUTHOR]

High-density surface electromyography (HDsEMG) provides a detailed analysis of a muscle's spatial distribution of activity. We applied a Bayesian spatio-temporal statistical method to quantify how acute nociception and task repetition alters the upper trapezius instantaneous spatial distribution of activity during dynamic muscular contractions. Ten male adults performed repeated lifting of a 1 kg box between shelves positioned at hip and shoulder heights with a cycle time of 3 s for 50 cycles under four conditions: baseline, isotonic and hypertonic saline injections (nociception) to the right upper trapezius, and 15 min post injection. Activity of the right upper trapezius was measured using a 64-channel surface electrode grid. Statistical inference was performed using Integrated Nested Laplace Approximations (INLA), and significance was determined by a non-zero crossing of the Bayesian 95% credible intervals (CrI). The maximal decrease in activity after nociception was -38.1 µV [95% CrI -40.9 to -35.3] at 30% of the lift cycle when compared to baseline. The maximal reduction in muscle activity between the early and later phases of lifting in the presence of nociception was by 10.4 µV [95% CrI 8.2-12.6]. A more holistic understanding of muscle behaviour is achieved using spatio-temporal inference than traditional reductionist methods. [ABSTRACT FROM AUTHOR]

The analysis of single motor unit (SMU) activity provides the foundation from which information about the neural strategies underlying the control of muscle force can be identified, due to the one-to-one association between the action potentials generated by an alpha motor neuron and those received by the innervated muscle fibers. Such a powerful assessment has been conventionally performed with invasive electrodes (i.e., intramuscular electromyography (EMG)), however, recent advances in signal processing techniques have enabled the identification of single motor unit (SMU) activity in high-density surface electromyography (HDsEMG) recordings. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, provides recommendations for the recording and analysis of SMU activity with both invasive (needle and fine-wire EMG) and non-invasive (HDsEMG) SMU identification methods, summarizing their advantages and disadvantages when used during different testing conditions. Recommendations for the analysis and reporting of discharge rate and peripheral (i.e., muscle fiber conduction velocity) SMU properties are also provided. The results of the Delphi process to reach consensus are contained in an appendix. This matrix is intended to help researchers to collect, report, and interpret SMU data in the context of both research and clinical applications. [ABSTRACT FROM AUTHOR]

The current study aimed to investigate differences in activity of neck flexor and extensor muscles in women with migraine considering the chronicity of their condition. Thirty-one subjects with episodic migraine, 21 with chronic migraine and 31 healthy controls participated. Surface electromyography signals were recorded bilaterally from the sternocleidomastoid, anterior scalene, splenius capitis and upper trapezius muscles as subjects performed 5 stages of cranio-cervical flexion (CCF), representing a progressive increase in range of CCF motion. Comparison of normalized root-mean-square among groups was conducted with 3×5 ANCOVA with task level as the within-subject variable, group as the between-subject variable, and the presence of neck pain and disability as co-variates. The group with chronic migraine exhibited increased activity of their extensor muscles compared to the control and episodic migraine groups (splenius capitis: F=3.149, P=0.045; upper trapezius: F=3.369, P=0.041). No significant between-group differences were found for the superficial neck flexors (sternocleidomastoid: F=1.161, P=0.320; anterior scalene: F=0.135, P=0.874). In conclusion, women with chronic migraine exhibit increased activity of their superficial neck extensor muscles when acting as antagonists during low-load isometric CCF contractions in comparison to non-headache subjects. [ABSTRACT FROM AUTHOR]

Purpose: Lumbar multifidus is a complex muscle with multi-fascicular morphology shown to be differentially controlled in healthy individuals during sagittal-plane motion. The normal behaviour of multifidus muscle regions during walking has only received modest attention in the literature. This study aimed to determine activation patterns for deep and superficial multifidus in young adults during walking at different speeds and inclination.Methods: This observational cohort study evaluated ten healthy volunteers in their twenties (three women, seven men) as they walked on a treadmill in eight conditions; at 2km/h and 4km/h, each at 0, 1, 5, and 10% inclination. Intramuscular EMG was recorded from the deep and superficial multifidus unilaterally at L5. Activity was characterized by: amplitude of the peak of activation, position of peak within the gait cycle (0-100%), and duration relative to the full gait cycle.Results: Across all conditions superficial multifidus showed higher normalised EMG amplitude (p<0.01); superficial multifidus peak amplitude was 232±115% higher when walking at 4km/h/10%, versus only 172±77% higher for deeper region (p<0.01). The percentage of the gait cycle where peak EMG amplitude was detected did not differ between regions (49±13%). Deep multifidus duration of activation was longer when walking at the faster vs slower speed at all inclinations (p<0.01), which was not evident for superficial multifidus (p<0.05). Thus, a significantly longer activation of deep multifidus was observed compared to superficial multifidus when walking at 4km/h (p<0.05).Conclusions: Differential activation within lumbar multifidus was shown in young adults during walking. The prolonged, more tonic activation of deep relative to superficial regions of multifidus during gait supports a postural function of deeper fibres. [ABSTRACT FROM AUTHOR]

High-density surface electromyography (HDsEMG) can be used to measure the spatial distribution of electrical muscle activity over the skin. As this distribution is associated with the generation and propagation of muscle fiber action potentials, HDsEMG is processed to extract information on regional muscle activation, muscle fiber characteristics and behaviour of individual motor units. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, summarizes recommendations on the use of HDsEMG in experimental studies. For each application, recommendations are included regarding electrode montage, electrode type and configuration, electrode location and orientation, data analysis, and interpretation. Cautions and reporting standards are also included. The steps of the Delphi process to reach consensus are contained in an appendix. This matrix is intended to help researchers when collecting, reporting, and interpreting HDsEMG data. It is hoped that this document will be used to generate new empirical evidence to improve how HDsEMG is used in research and in clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: This study compares neck force steadiness in women with neck pain and controls and the way this is influenced by short term vibration of the neck. In the first experiment, 9 women with chronic neck pain and 9 controls performed 10-s isometric cervical flexion at 15N. Intramuscular EMG was recorded from the sternocleidomastoid muscle. In the second experiment, 10 women with neck pain and 10 controls performed 10-s isometric cervical flexion at 25% of their maximal force before and after vibration to the neck (bursts of 50Hz with duration 20, 40, 60 and 120s). Surface EMG was acquired from the sternocleidomastoid and splenius capitis. In both experiments, force steadiness was characterized by the coefficient of variation (CoV) and the relative power in three frequency subbands (low: 0–3Hz; middle: 4–6Hz; high: 8–12Hz) of the force signal. Women with neck pain exhibited decreased force steadiness (Exp 1: patients 3.9±1.3%, controls 2.7±0.9%, P <0.05; Exp 2: patients 3.4±1.2%, controls 1.7±0.6%, P <0.01) which was associated with higher power in the low-frequency band (patients 71.2±9.6%, controls 56.7±9.2%, P <0.01). Following vibration, CoV (2.6±1.1%, P <0.05) and the power in the low-frequency band of the force signal decreased (63.1±13.9%, P <0.05) in the patient group. These effects were not present in controls. Motor unit behavior and surface EMG amplitude were similar between groups. In conclusion, women with neck pain have reduced force steadiness, likely due to alterations in Ia afferent input. Vibration, which modulates Ia afferent input, increases force steadiness in patients with neck pain. [Copyright &y& Elsevier]

Abstract: The study investigates the effects of eccentric exercise of the quadriceps on proprioception of the knee in weight and non-weight bearing tasks. Proprioception of the exercised leg was assessed at 120° and 150° of knee extension in 15 healthy adults (age 25.0±3.6 yrs) before, immediately after, and 24h following eccentric exercise of the quadriceps. Three tests of proprioception were performed: 1. matching the position of the exercised leg (right leg) to the reference leg (left leg) in sitting (non-weight bearing matching task); 2. repositioning the exercised leg after active movement in sitting (non-weight bearing repositioning task); 3. repositioning the exercised leg after active movement in standing (weight bearing task). Maximum knee extension force was reduced by 77.0±12.3 % immediately after the exercise, and by 82.7±16.2% 24h post exercise, with respect to baseline (P <0.001). The absolute error in the non-weight bearing matching task at 120° of knee extension was greater immediately following eccentric exercise (12.3±5.6, P <0.001) and 24h after exercise (8.1±4.5, P <0.05) compared to baseline (5.8±2.7). Similarly, the absolute error in the non-weight bearing repositioning task at 120° was greater both immediately (5.9±3.1°, P <0.01) and 24h post exercise (5.2±3.0°, P <0.05) compared to baseline (4.5±2.6°). Therefore, in both non-weight bearing tasks, the subjects matched the position of their leg after eccentric exercise by adopting a more extended knee position of the exercised limb. Furthermore, the subjects showed higher variability in their performance immediately post exercise (P <0.05, compared to baseline) but not 24h after. In contrast, eccentric exercise did not affect the repositioning errors in the weight bearing task. In conclusion, eccentric exercise of the quadriceps impairs proprioception of the knee both immediately after and 24h post exercise, but only in non-weight bearing tasks. [Copyright &y& Elsevier]

Consensus on the definition of common terms in electromyography (EMG) research promotes consistency in the EMG literature and facilitates the integration of research across the field. This paper presents a matrix developed within the Consensus for Experimental Design in Electromyography (CEDE) project, providing definitions for terms used in the EMG literature. The definitions for physiological and technical terms that are common in EMG research are included in two tables, with key information on each definition provided in a comment section. A brief outline of some basic principles for recording and analyzing EMG is included in an appendix, to provide researchers new to EMG with background and context for understanding the definitions of physiological and technical terms. This terminology matrix can be used as a reference to aid researchers new to EMG in reviewing the EMG literature. [ABSTRACT FROM AUTHOR]

We investigated whether adaptations of quadriceps muscle activity to fatiguing exercise differs between sexes. Fifteen healthy men (age, mean ± SD; 22. ± 2.4 yr, body mass 70.5 ± 11.4 kg, height 1.72 ± 0.06 m) and 15 healthy women (age, mean ± SD; 21 ± 1.8 yr, body mass 60 ± 7.5 kg, height 1.62 ± 0.07 m), all right leg dominant, participated in the study. Participants performed a submaximal isometric knee extension contraction at 50% of the maximum voluntary contraction (MVC) sustained until task failure before and after a fatiguing exercise. Surface electromyography (EMG) was simultaneously recorded from nine regions distributed over the medial, middle and lateral locations of the quadriceps muscles in a longitudinal direction corresponding to the vastus medialis, rectus femoris (RF) and vastus lateralis muscle, respectively. A significant reduction in maximal force and time to task failure were observed after fatiguing exercise for both sexes (P < 0.001). However, women displayed greater myoelectric manifestations of fatigue specifically for the RF during the post-fatigue sustained contraction (P < 0.05). The RF is more susceptible to fatiguing exercise in women compared to men which may partly explain the higher risk of knee injuries among female athletes during competitive sports. [ABSTRACT FROM AUTHOR]

The general purpose of normalization of EMG amplitude is to enable comparisons between participants, muscles, measurement sessions or electrode positions. Normalization is necessary to reduce the impact of differences in physiological and anatomical characteristics of muscles and surrounding tissues. Normalization of the EMG amplitude provides information about the magnitude of muscle activation relative to a reference value. It is essential to select an appropriate method for normalization with specific reference to how the EMG signal will be interpreted, and to consider how the normalized EMG amplitude may change when interpreting it under specific conditions. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, presents six approaches to EMG normalization: (1) Maximal voluntary contraction (MVC) in same task/context as the task of interest, (2) Standardized isometric MVC (which is not necessarily matched to the contraction type in the task of interest), (3) Standardized submaximal task (isometric/dynamic) that can be task-specific, (4) Peak/mean EMG amplitude in task, (5) Non-normalized, and (6) Maximal M-wave. General considerations for normalization, features that should be reported, definitions, and "pros and cons" of each normalization approach are presented first. This information is followed by recommendations for specific experimental contexts, along with an explanation of the factors that determine the suitability of a method, and frequently asked questions. This matrix is intended to help researchers when selecting, reporting and interpreting EMG amplitude data. [ABSTRACT FROM AUTHOR]