Electromyographic Onset Research Articles

Influence of adiposity and fatigue on the scapular muscle recruitment order.

BackgroundSeveral authors have indicated that excess body weight can modify the electromyographic (EMG) amplitude due to the accumulation of subcutaneous fat. This accumulation of adipose tissue around the muscle would affect the metabolic capacity during functional activities. On the other hand, some authors have not observed differences in the myoelectric manifestations of fatigue between normal weight and obese people. Furthermore, these manifestations have not been investigated regarding EMG onset latency, which indicates a pattern of muscle activation between different muscles. The objective of this study was to determine whether an increase in body weight, skinfolds, and muscle fatigue modify the trapezius and serratus anterior (SA) onset latencies and to determine the scapular muscle recruitment order in fatigue and excess body weight conditions.MethodsThis cross-sectional study was carried out in a university laboratory. The participants were randomly assigned to the no-fatigue group (17 participants) or the fatigue (17 participants) group. The body mass index, skinfold thickness (axillary, pectoral, and subscapular), and percentage of body fat were measured. In addition, the onset latency of the scapular muscles [lower trapezius (LT), middle trapezius (MT), upper trapezius (UT), and SA] was assessed by surface EMG during the performance of a voluntary arm raise task. A multiple linear regression model was adjusted and analyzed for the additive combination of the variables, percentage body fat, skinfold thickness, and fatigue. The differences in onset latency between the scapular muscles were analyzed using a three-way repeated measure analysis of variance. In all the tests, an alpha level <0.05 was considered statistically significant.ResultsFor the MT, LT, and SA onset latencies, the body mass index was associated with a delayed onset latency when it was adjusted for the additive combination of percentage of body fat, skinfold thickness, and fatigue. Of these adjustment factors, the subscapular skinfold thickness (R2 = 0.51; β = 10.7; p = 0.001) and fatigue (R2 = 0.86; β = 95.4; p = 0.001) primarily contributed to the increase in SA onset latency. A significant muscle ×body mass index ×fatigue interaction (F = 4.182; p = 0.008) was observed. In the fatigue/excess body weight condition, the UT was activated significantly earlier than the other three scapular muscles (p < 0.001) and SA activation was significantly delayed compared to LT (p < 0.001).DiscussionExcess body weight, adjusted for skinfold thickness (axillary and subscapular) and fatigue, increases the onset latency of the MT, LT, and SA muscles and modifies the recruitment order of scapular muscles. In fact, the scapular stabilizing muscles (MT, LT, and SA) increase their onset latency in comparison to the UT muscle. These results were not observed when excess body weight was considered as an individual variable or when adjusted by the percentage body fat.

Comparison of neural excitation measures from the surface electromyogram during rate-dependent muscle contractions

Peak power and peak rate of isometric force development (RFD) predict performance and functional mobility. Surface electromyography (EMG) is used to quantify the amplitude and rate of neuromuscular excitation. To inform the selection of EMG measures in research on rate-dependent muscle contractions, this methodological study compared amplitude-, area- and rate-based measures based on their correlations with RFD. Considering populations in whom a quiet EMG baseline is challenging, we included measures that do not require the determination of EMG onset. Twenty-one young adults performed isometric dorsiflexion contractions to 40% of their maximal force at increasing RFD. EMG was recorded from tibialis anterior. Relationships between EMG measures and RFD were quantified with Spearman’s rho. RMS amplitude of the initial 75 ms of EMG had the strongest correlation with peak RFD (ρ = 0.80) among measures computed from EMG onset. Peak rate of EMG rise (RER) had the strongest relationship with peak RFD (ρ = 0.69) among measures that did not require determination of EMG onset. The strength of the relationship between RER and RFD and the strong correlation between RER and RMS75 during rapid contractions (ρ = 0.86) supports the use of RER in experiments where neural excitation might not be initiated from a quiet baseline.

Functional behaviour of spinal muscles after training with an exercise device developed to recruit and train postural muscles

This study investigated the effects of a single exercise session using a device developed for postural muscle training on the function of postural muscles in healthy, pain free individuals. During standardised rapid arm movements, timing of onset of electromyography (EMG) was measured using intramuscular and surface recordings of the transversus abdominis (TrA), obliquus internus abdominis (OI), obliquus externus abdominis (OE), lumbar multifidus (LM) and lumbar erector spinae (LES) muscles. A single exercise session with the device led to significantly (main effect of time: P = 0.03) earlier LES EMG onset in advance of the postural perturbation induced by rapid forward arm movements from -1 ms (SD: 32 ms) at baseline to -11 ms (SD: 27 ms) post-exercise and -16 ms (SD: 22 ms) at 10-min Wash-Out after the FRED exercise bout. The timing of EMG onset of the other trunk muscles was not affected by the single bout of exercise. A significant correlation was found between background activity and the EMG onset times of of TrA (r = 0.6; P < 0.001), OI (r = 0.59; P < 0.001), LES (r = 0.32; P = 0.046) and LMs (r = 0.77; P < 0.001). Higher levels of trunk muscle background activity were associated with later onset times. The present findings suggest that a single exposure to the postural training device can induce small changes in spinal muscle function in healthy pain free individuals.

Ankle perturbation generates bilateral alteration of knee muscle onset times after unilateral anterior cruciate ligament reconstruction.

BackgroundThe aim of this study was to compare muscle activation onset times of knee muscles between the involved and uninvolved knee of patients with unilateral anterior cruciate ligament reconstruction (ACLR), and the uninjured knees of healthy subjects after a controlled perturbation at the ankle level.MethodsFifty male amateur soccer players, 25 with unilateral ACLR using semitendinosus-gracilis graft (age = 28.36 ± 7.87 years; time after surgery = 9 ± 3 months) and 25 uninjured control subjects (age = 24.16 ± 2.67 years) participated in the study. Two destabilizing platforms (one for each limb) generated a controlled perturbation at the ankle of each participant (30°of inversion, 10°plantarflexion simultaneously) in a weight bearing condition. The muscle activation onset times of semitendinosus (ST) and vastus medialis (VM) was detected through an electromyographic (EMG) analysis to assess the neuromuscular function of knee muscles.ResultsSubjects with ACLR had significant delays in EMG onset in the involved (VM = 99.9 ± 30 ms; ST = 101.7 ± 28 ms) and uninvolved knee (VM = 100.4 ± 26 ms; ST = 104.7 ± 28 ms) when compared with the healthy subjects (VM = 69.1 ± 9 ms; ST = 74.6 ± 9 ms). However, no difference was found between involved and uninvolved knee of the ACLR group.DiscussionThe results show a bilateral alteration of knee muscles in EMG onset after a unilateral ACLR, responses that can be elicited with an ankle perturbation. This suggests an alteration in the central processing of proprioceptive information and/or central nervous system re-organization that may affect neuromuscular control of knee muscles in the involved and uninvolved lower limbs.

Analysis of skeletal muscle performance using piezoelectric film sensors.

A flexible piezoelectric thin film sensor has been proposed recently in several studies for detection of muscle movements. The objective of this study was to investigate the ability of this sensor to assess skeletal muscle performance and fatigue under isokinetic contractions. Simultaneous noninvasive measurements of muscles activity were done using surface electromyography (EMG) electrodes and two thin film piezoelectric sensors. Measurements were taken from the biceps during slow and fast elbow flexion with and without strong grip, during different weight lifting and from the gastrocnemius during treadmill marching at speeds of 4 and of 10 kph. The results shows correlation between the onset of EMG and the piezoelectric sensors (Piezo) signals during muscle contraction. Increasing contraction intensity increase significantly both EMG and Piezo signals. Higher contractions velocity increased Piezo signal. Opposite linear relation was found between the average maximal EMG envelope amplitudes and the average maximal Piezo peaks with increasing loads. The significant decrease in the maximal Piezo peaks with time of all 3 subjects during elbow flexion while holding weight suggests the ability of piezoelectric thin film sensor to track muscle fatigue during isokinetic contractions.

Shoulder Taping and Neuromuscular Control.

Scapular taping can offer clinical benefit to some patients with shoulder pain; however, the underlying mechanisms are unclear. Understanding these mechanisms may guide the development of treatment strategies for managing neuromusculoskeletal shoulder conditions. To examine the mechanisms underpinning the benefits of scapular taping. Descriptive laboratory study. University laboratory. A total of 15 individuals (8 men, 7 women; age = 31.0 ± 12.4 years, height = 170.9 ± 7.6 cm, mass = 73.8 ± 14.4 kg) with no history of shoulder pain. Scapular taping. Surface electromyography (EMG) was used to assess the (1) magnitude and onset of contraction of the upper trapezius (UT), lower trapezius (LT), and serratus anterior relative to the contraction of the middle deltoid during active shoulder flexion and abduction and (2) corticomotor excitability (amplitude of motor-evoked potentials from transcranial magnetic stimulation) of these muscles at rest and during isometric abduction. Active shoulder-flexion and shoulder-abduction range of motion were also evaluated. All outcomes were measured before taping, immediately after taping, 24 hours after taping with the original tape on, and 24 hours after taping with the tape removed. Onset of contractions occurred earlier immediately after taping than before taping during abduction for the UT (34.18 ± 118.91 milliseconds and 93.95 ± 106.33 milliseconds, respectively, after middle deltoid contraction; P = .02) and during flexion for the LT (110.02 ± 109.83 milliseconds and 5.94 ± 92.35 milliseconds, respectively, before middle deltoid contraction; P = .06). These changes were not maintained 24 hours after taping. Mean motor-evoked potential onset of the middle deltoid was earlier at 24 hours after taping (tape on = 7.20 ± 4.33 milliseconds) than before taping (8.71 ± 5.24 milliseconds, P = .008). We observed no differences in peak root mean square EMG activity or corticomotor excitability of the scapular muscles among any time frames. Scapular taping was associated with the earlier onset of UT and LT contractions during shoulder abduction and flexion, respectively. Altered corticomotor excitability did not underpin earlier EMG onsets of activity after taping in this sample. Our findings suggested that the optimal time to engage in rehabilitative exercises to facilitate onset of trapezius contractions during shoulder movements may be immediately after tape application.

The temporal relationship between activity of the pelvic floor muscles and motion of selected urogenital landmarks in healthy nulliparous women

AimsThe purpose of this study was to investigate the relationship between pelvic floor muscle (PFM) electromyographic (EMG) activation and urogenital landmark motion measured using 2D transperineal ultrasound (US) imaging. MethodsEight healthy, nulliparous women performed maximum voluntary PFM contractions while EMG and transperineal US images were acquired simultaneously. Changes in the levator plate length (LPL), bladder neck (BN) position and urethral position were determined by visual inspection. The relative timing of EMG onset and the onset of landmark motion, and the correlation coefficients between EMG activation and landmark motion were computed. Comparisons between the correlation coefficients and onset latencies of each landmark motion were made using one-way analysis of variance models. ResultsDespite generally good reliability metrics for the onset of EMG and the onset of landmark motion, the relative timing of EMG onset and the onset of landmark motion demonstrated no systematic patterns of activation onset. That said, the overall motion of the different urogenital landmarks throughout the MVC task was highly correlated with the PFM EMG data; correlation coefficients were generally good (>0.90) and highly significant (p < .001). The correlation between PFM EMG and LPL motion was significantly better than the correlation between PFM EMG and motion of the other landmarks. The relevance of one outlier is discussed. ConclusionsThe motion of all urogenital landmarks seen on US imaging is highly correlated with PFM EMG activation during maximum voluntary PFM contractions and may therefore be of value in the context of biofeedback training to infer that PFM activation has occurred. The motion of the BN, however, may require more cautious interpretation than the reduction of LPL. The timing of the onset of urogenital landmark motion on transperineal US imaging does not precede nor follow the timing of PFM activation, while the high variance of relative onset timing makes the onset of landmark motion of questionable value when training or evaluating co-ordination or motor control.

Spasm and flexion-relaxation phenomenon response to large lifting load during the performance of a trunk flexion-extension exercise

BackgroundThe flexion relaxation phenomenon (FRP) has been widely investigated. Nevertheless, no study has been reported on the FRP as well as spasm response to large lifting load. The aim of this study was to evaluate the effect of large lifting load on the FRP response and spasm during execution of a flexion-extension exercise.MethodsTwenty-two healthy male university students without low back pain history participated this study. Subjects randomly performed three trials of trunk flexion-extension cycles of 5 s flexion and 5 s extension in each of 4 conditions (three large lifting loads of 15, 20 and 25 kg and one lifting load of 0 kg for comparison). Surface EMG from bilateral erector spinae was recorded during the performance of a trunk anterior flexion-extension exercise. The relaxation phase was determined through the onset of electromyography (EMG) signals. Spasm was evaluated in the relaxation period. The mean normalized electromyography (NEMG) was derived from the raw EMG.ResultsSpasm was observed in more than 45% of the individuals and the intensity of muscle activation was increased by more than 78% in the relaxation phase.ConclusionsA large lifting load could lead to a high prevalence of spasms as well as a high intensity of muscle activations on erector spinae muscle in the relaxation period, which may be associated with the development of low back disorder during the performance of a flexion-extension exercise.

Developing control algorithms of a voluntary cough for an artificial bioengineered larynx using surface electromyography of chest muscles: A prospective cohort study.

This prospective cohort study investigates the prediction of a voluntary cough using surface electromyography (EMG) of intercostal and diaphragm muscles, to develop control algorithms for an EMG-controlled artificial larynx. The Ear Institute, London. Electromyography onset compared to voluntary cough exhalation onset and to 100ms (to give the artificial larynx the time to close the bioengineered vocal cords) before voluntary cough exhalation onset, in twelve healthy participants. In the 189 EMG of intercostal muscle-detected voluntary coughs, 172 coughs (91% CI 70-112) were detected before onset of cough exhalation and 128 coughs (67.6% CI 33.7-101.7) 100ms before onset of cough exhalation. In the 158 EMG of diaphragm muscle-detected voluntary coughs, 149 coughs (94.3% CI 76.3-112.3) were detected before onset of cough exhalation and 102 coughs (64.6% CI 26.6-102.6) 100ms before onset of cough exhalation. More coughs were detected before onset of cough exhalation when combining EMG activity of intercostal and diaphragm muscles and comparing this to intercostal muscle activity alone (183 coughs [96.8% CI 83.8-109.8] vs 172 coughs, P=.0294). When comparing the mentioned combination to diaphragm muscle activity alone, the higher percentage of detected coughs before cough exhalation onset was not found to be significant (183 coughs vs 149 coughs, P=.295). In addition, more coughs were detected 100ms before onset of cough exhalation with the mentioned combination of EMG activity and comparing this to intercostal muscles alone (149 coughs [78.8% CI 48.8-108.8] vs 128 coughs, P=.0198) and to diaphragm muscles alone (149 coughs vs 102 coughs, P=.0038). Most voluntary coughs can be predicted based on combined EMG signals of intercostal and diaphragm muscles, and therefore, these two muscle groups will be useful in controlling the bioengineered vocal cords within the artificial larynx during a voluntary cough.

Iterative Assessment of Statistically-Oriented and Standard Algorithms for Determining Muscle Onset with Intramuscular Electromyography.

The onset of muscle activity, as measured by electromyography (EMG), is a commonly applied metric in biomechanics. Intramuscular EMG is often used to examine deep musculature and there are currently no studies examining the effectiveness of algorithms for intramuscular EMG onset. The present study examines standard surface EMG onsetalgorithms (linear envelope, Teager-Kaiser Energy Operator, and sample entropy) and novel algorithms (time series mean-variance analysis, sequential/batch processing with parametric and nonparametric methods, and Bayesian changepoint analysis). Thirteen male and 5 female subjects had intramuscular EMG collected during isolated biceps brachii and vastus lateralis contractions, resulting in 103 trials. EMG onset was visually determined twice by 3 blinded reviewers. Since the reliability of visual onset was high (ICC(1,1): 0.92), the mean of the 6 visual assessments was contrasted with the algorithmic approaches. Poorly performing algorithms were stepwise eliminated via (1)root mean square error analysis, (2)algorithm failure to identify onset/premature onset, (3)linear regression analysis, and (4)Bland-Altman plots. The top performing algorithms were all based on Bayesian changepoint analysis of rectified EMG and were statistically indistinguishable from visual analysis. Bayesian changepoint analysis has the potential to produce more reliable, accurate, and objective intramuscular EMG onset results than standard methodologies.

Rate of Torque Development and Feedforward Control of the Hip and Knee Extensors: Gender Differences

ABSTRACTThe purpose of this study was to determine whether women demonstrate decreased rate of torque development (RTD) of the hip and knee extensors and altered onset timing of the vastus lateralis and gluteus maximus during a drop-jump task when compared with men. On average, women demonstrated significantly lower normalized RTD of the hip extensors (women: 11.6 ± 1.3 MVT.s−1, men: 13.1 ± 0.9 MVT.s−1; p ≤ .01); however, there was no significant difference in knee extensor RTD. Women also demonstrated significantly earlier activation of their vastus lateralis (women: 206.0 ± 130.6 ms, men: 80.9 ± 69.6 ms; p ≤ .01) and gluteus maximus (women: 85.7 ± 58.6 ms, men: 54.5 ± 35.4 ms; p = .02). In both men and women, there was a significant negative correlation between the hip extensor RTD and the vastus lateralis electromyographic onset time (men: r = –.386, p = .046; women: r = –.531, p = .008). The study findings suggest that women may utilize a feedforward control strategy in which they activate their knee extensors earlier than men to compensate for deficits in hip extensor RTD. The impaired capacity to rapidly stabilize the hip and knee joints during dynamic maneuvers may contribute to the increased risk of anterior cruciate ligament injury observed in women.

The effects of foot cooling on postural muscle responses to an unexpected loss of balance

The purpose of this study was to examine the role of foot sole somatosensory information during reactive postural control. Twenty young adults (22.0±1.4y) participated in this study. Baseline skin sensitivity from the foot sole was assessed using Semmes-Weinstein monofilaments. Postural muscle responses, in the form of electromyographic (EMG) onset latencies and amplitudes, were then obtained while participants recovered their balance while standing on a moveable platform that could translate in either the forward or backward direction. Following these baseline measures, the participant’s foot soles were immersed in a 0–2°C ice-water bath for 12min followed by a 3min re-immersion period. At the completion of foot cooling, foot sole sensitivity and postural muscle responses to the balance perturbations were re-assessed. Results indicated that the foot cooling protocol reduced foot sole sensitivity and remained reduced throughout the duration of the experiment (p<0.001). The reduction in foot sole somatosensation resulted in the soleus EMG onset latency being delayed by 3ms (p=0.041) and the soleus and medial gastrocnemius EMG amplitudes increasing by 14–23% (p=0.002–0.036) during the balance perturbation trials. While the magnitude of these results may suggest that foot cooling has a minor functional consequence on reactive postural control, it is likely that the results also reflect the ability of the central nervous system to rapidly adapt to situations with altered somatosensory feedback.

Classification of COPD and normal lung airways using feature extraction of electromyographic signals

Airway obstruction is a common component in Chronic Obstructive Pulmonary Disease (COPD). Detection of obstruction and its grading is very essential. Obstruction in the airways, forces the accessory muscles like sternomastoid muscle (SMM) of respiration to work. Normally, only essential muscles of respiration work. In the said paper electromyographic (EMG) analysis of SMM is done for COPD and Normal subjects. We have developed improved slope based onset detection algorithm to detect the onset and offset timing of EMG. Time domain features are extracted for COPD and normal subject. The onset detection algorithm reduces the number of computations by 32.96% and increases accuracy of feature calculation by 40.19%. Dominant time domain features are selected and applied to Support Vector Machine Classifier. The SVM classification algorithm is compared with Threshold and Naïve Bayes classification algorithm. SVM gives the highest accuracy of 87.80%, sensitivity of 89.65% and specificity of 83.33%. Results are also compared with previously used FEV1/FEV6 and Forced Oscillation Technique. The activity of SMM has a significant role in the classification of Normal and COPD subject. Further analysis of SMM can be done to find different grades of COPD.

Analysis of statistical and standard algorithms for detecting muscle onset with surface electromyography.

The timing of muscle activity is a commonly applied analytic method to understand how the nervous system controls movement. This study systematically evaluates six classes of standard and statistical algorithms to determine muscle onset in both experimental surface electromyography (EMG) and simulated EMG with a known onset time. Eighteen participants had EMG collected from the biceps brachii and vastus lateralis while performing a biceps curl or knee extension, respectively. Three established methods and three statistical methods for EMG onset were evaluated. Linear envelope, Teager-Kaiser energy operator + linear envelope and sample entropy were the established methods evaluated while general time series mean/variance, sequential and batch processing of parametric and nonparametric tools, and Bayesian changepoint analysis were the statistical techniques used. Visual EMG onset (experimental data) and objective EMG onset (simulated data) were compared with algorithmic EMG onset via root mean square error and linear regression models for stepwise elimination of inferior algorithms. The top algorithms for both data types were analyzed for their mean agreement with the gold standard onset and evaluation of 95% confidence intervals. The top algorithms were all Bayesian changepoint analysis iterations where the parameter of the prior (p0) was zero. The best performing Bayesian algorithms were p0 = 0 and a posterior probability for onset determination at 60–90%. While existing algorithms performed reasonably, the Bayesian changepoint analysis methodology provides greater reliability and accuracy when determining the singular onset of EMG activity in a time series. Further research is needed to determine if this class of algorithms perform equally well when the time series has multiple bursts of muscle activity.

The Difficulty Of EMG Burst Identification

Surface electromyography (EMG) is commonly used to add physiologic context to observed patterns of movement. The onset of the EMG is often used to determine when a person responds to stimuli or to identify maladaptive muscle coordination strategies. Our research group has previously shown that Bayesian Changepoint Analysis (BCP) is superior to the standard linear envelope methodologies when determining a single EMG onset in a data series. PURPOSE: Examine the effectiveness of visual inspection and the novel BCP algorithm to detect EMG bursts in multiple muscles during complex movements. METHODS: Muscle activity from 10 healthy subjects was collected from the gastrocnemius, biceps femoris, and vastus lateralis muscles using surface EMG electrodes (4kHz sampling rate). Subjects completed 4 minutes of exercise on three modalities: treadmill running, ergometer cycling and stair climbing. All exercises were performed at self-selected low-to-moderate intensities. Six to ten seconds of EMG was collected at 90 and 210 seconds into the exercise. Three researchers visually identified the number of bursts in a trial twice (randomized, double-blind methodology). The instances where all six identifications (three reviewers, twice) agreed on the number of bursts, were compared with the identification results from the BCP algorithm. RESULTS: While the within rater reliability (ICC: 0.85) and between rater reliability (ICC: 0.83) were good, the visual review only resulted in 111 trials (out of 180) where all raters agreed on the number of bursts (61.7% total agreement). The correlation between the number of bursts raters identified and the BCP algorithm was moderate (Pearson’s R: 0.52). Furthermore, across all trials, there was a difference of 711 EMG bursts between the two methods. CONCLUSIONS: While visual assessment of the EMG is the “gold standard” for burst detection, its reproducibility is generally poor in dynamic tasks. Despite initial success with the BCP algorithm in determining EMG onset, the current iteration of the algorithm is insufficient for EMG burst identification in complex waveforms. This work highlights the need for a standardized algorithm of EMG burst detection, but also indicates that further work is necessary to make algorithms of sufficient accuracy and reliability.

Changes in electromechanical delay during fatiguing dynamic muscle actions.

The onsets of the electromyographic (EMG) signal, mechanomyographic (MMG) signal, and force production were used to identify voluntary electromechanical delay (EMD) during maximal and submaximal leg extensions. Twelve men performed 30% 1-repetition-maximum concentric, dynamic constant external resistance leg extensions to failure. The time periods for the onsets of EMG to MMG (EMDE-M ), MMG to force (EMDM-F ), and EMG to force (EMDE-F ) were assessed before, during, and after testing. Pretest vs. posttest assessments indicated approximately equal contributions from excitation-contraction coupling (EMDE-M ) and series elastic component (EMDM-F ) to the overall EMDE-F . During the workbout, excitation-contraction coupling failure and increases in the compliance of the series elastic component began at 40% and 30% of the repetitions to failure, respectively, and continued to failure. Increases in the series elastic component (EMDM-F ) began to affect EMDE-F before excitation-contraction coupling failure (EMDE-M ), and both contributed to EMDE-F throughout the remainder of the fatiguing workbout. Muscle Nerve 56: 315-320, 2017.

Spatial variation and inconsistency between estimates of onset of muscle activation from EMG and ultrasound

Delayed onset of muscle activation can be a descriptor of impaired motor control. Activation onset can be estimated from electromyography (EMG)-registered muscle excitation and from ultrasound-registered muscle motion, which enables non-invasive measurements in deep muscles. However, in voluntary activation, EMG- and ultrasound-detected activation onsets may not correspond. To evaluate this, ten healthy men performed isometric elbow flexion at 20% to 70% of their maximal force. Utilising a multi-channel electrode transparent to ultrasound, EMG and M(otion)-mode ultrasound were recorded simultaneously over the biceps brachii muscle. The time intervals between automated and visually estimated activation onsets were correlated with the regional variation of EMG and muscle motion onset, contraction level and speed. Automated and visual onsets indicated variable time intervals between EMG- and motion onset, median (interquartile range) 96 (121) ms and 48 (72) ms, respectively. In 17% (computed analysis) or 23% (visual analysis) of trials, motion onset was detected before local EMG onset. Multi-channel EMG and M-mode ultrasound revealed regional differences in activation onset, which decreased with higher contraction speed (Spearman ρ ≥ 0.45, P < 0.001). In voluntary activation the heterogeneous motor unit recruitment together with immediate motion transmission may explain the high variation of the time intervals between local EMG- and ultrasound-detected activation onset.

前額面における立位姿勢の違いが腰部多裂筋深層線維および浅層線維の筋反応時間に及ぼす影響

〔目的〕前額面における骨盤アライメントの変化が腰部多裂筋深層線維および腰部多裂筋浅層線維の筋反応時間に与える影響を検証すること．〔対象と方法〕健常成人男性9名とした．運動課題は，聴覚刺激に対しできるだけ素早く肩関節を屈曲および伸展することとし，ワイヤ筋電図で腰部多裂筋深層線維および浅層線維，表面筋電図で三角筋前部および後部線維を測定した．三角筋の筋活動開始を基準とし，腰部多裂筋の筋反応時間を算出した．測定肢位は，骨盤水平位，左骨盤下制位，左骨盤挙上位の3条件とした．〔結果〕反復測定分散分析の結果，肩関節屈曲では立位姿勢に有意な主効果が認められたが，筋と立位姿勢の交互作用は有意でなかった．〔結語〕前額面における骨盤アライメントの変化は，腰部多裂筋の筋反応時間が変化することが示している．

Retraso de la latencia de activación de los músculos de cadera y rodilla en individuos con acortamiento de la banda iliotibial

ObjectiveTo determinate the onset latency of the hip and knee muscles in participants with iliotibial band (ITB) tightness. Material and methodsA case-control study. Twelve male participants whit ITB tightness and 12 male participants without ITB tightness performed a sudden lower limbs perturbation in anterior, posterior, ipsolateral and contralateral direction. The electromyographic onset latencies of the medial vastus (VM), vastus lateralis (VL), tensor fascia lata (TFL) and gluteus maximus (GM) were measured during this test. The statistical analysis was performed with t-student test. Significance level was established a priori at P<.05. ResultsA significant increase of the VM (P=.0001), VL (P=.0163), GM (P=.0036) and TFL (P<.0001) latency was observed in participants with ITB tightness during a sudden anterior perturbation. In a posterior perturbation, a significant increase in the GM (P=.0001) and TFL (P<.0001) latency was observed in participants with ITB tightness. A significant increase of the TFL (P<.0001) latency was observed in participants with ITB tightness during a contralateral limb evaluated perturbation. ConclusionsIndividuals with ITB tightness present a delay of knee and hip muscles latencies, mainly the TFL muscle.

Beyond decision! Motor contribution to speed-accuracy trade-off in decision-making.

Both in real life and experimental settings, increasing response speed typically leads to more error-prone actions. Processes underlying such a "speed-accuracy trade-off" (SAT) are usually assumed to be purely decisional: cautiousness would be determined only by the amount of sensory evidence required to select a response. The present data challenges this largely accepted view, by directly showing that motor processes are speeded up under time pressure. In a choice reaction time task where emphasis was put either on response speed or accuracy, motor processes were investigated through the analysis of muscular activity related to response execution. When response speed was emphasized, the time between electromyographic onset and behavioral response (motor time) was also speeded up (contributing to more than 20 % of the total effect on global reaction time). This speeded execution (likely due to a more efficient motor command) may also explain why participants are less able to interrupt incorrect response execution once started (Burle et al., Psychonomic Bulletin & Review, 21(4), 1003-1010, 2014), leading to more overt errors. Pointing to a speed-accuracy exchange within motor processes themselves, the present results call for a re-evaluation of widely accepted assumptions about SAT, and more generally, decision-making processes. They are discussed in the context of recent extensions of the drift diffusion model framework, questioning the strict separation between decisional and motor processes.