Electromyographic Onset Research Articles

Adipose tissue thickness does not affect the electromechanical delay

During voluntary contractions in humans, the subcutaneous tissues between surface electrodes and active motor units have been shown to attenuate surface electromyographic (EMG) signal amplitude. The purpose of this investigation was to examine the relationship between adipose tissue thickness and the electromechnical delay (EMD) during maximal voluntary contractions (MVCs). Thirty-two healthy women (mean ± SD age = 21 ± 2 years; mass = 60.7 ± 11.5 kg; height = 161.7 ± 7.5 cm; dual-energy x-ray absorptiometry body-fat percentage = 33.1 ± 9.9%) performed MVCs of the right leg extensors while bipolar surface EMG signals were detected from the vastus lateralis muscle. EMD was calculated as the time (ms) between EMG and torque onsets. B-mode ultrasonography was used to determine adipose tissue thickness over the same location of the vastus lateralis where the EMG sensor was placed. Partial correlation was used to examine the relationship between adipose tissue thickness and EMD while statistically removing the influence of peak torque, EMG amplitude, and vastus lateralis muscle thickness. The partial correlation demonstrated no relationship between adipose tissue thickness and EMD (r = −0.010, p = 0.956). Collectively, these findings demonstrated that adiposity does not influence the estimation of EMD.

Core muscle recruitment pattern during voluntary heel raises is different between patients with patellofemoral pain and healthy individuals

BackgroundRecent studies suggest that the inconsistent outcomes of patellofemoral pain (PFP) treatment may result from the unclear understanding of changes in the structures remote from the knee joint. Due to the crucial influence of core stability on the knee function, this study aimed to evaluate the recruitment pattern of core muscles in individuals with and without PFP. MethodsSixty women aged 18 to 40years, including 30 subjects diagnosed with PFP and 30 healthy controls rose on to their toes as quickly and strongly as possible in response to a sound alarm in standing position. Electromyographic onsets of the transversus abdominis (TrA)/internal oblique (IO), erector spinae (ES), and gluteus medius (GM) muscles were expressed relative to the electromyographic onset of the prime mover (i.e. soleus). Independent t-tests were performed to compare the onsets of each muscle between the groups. The nonparametric Friedman test and the post-hoc of Wilcoxon signed-rank test were used to describe the muscle activation pattern within the groups. ResultsThe results revealed different recruitment patterns of the core muscles between the groups. In the healthy group the GM and TrA/IO contracted, almost simultaneously, in anticipation of the prime mover contraction (sol). However, in PFP subjects a significant delay in the contraction of TrA/IO changed the pattern of muscle activation. ConclusionThe findings demonstrate that muscular stabilization of spine is altered in the presence of PFP and suggest that treatment techniques aimed at improving core stability could be appropriate in the management of PFP.

The effects of dual-tasking on arm muscle responses in young and older adults

This study examined whether dual-tasking affects an individual’s ability to generate arm muscle responses following a loss of balance. Nineteen young and 16 older adults recovered their balance in response to a surface translation. This balance task was either completed on its own or while counting backwards by 2’s (easy counting difficulty) or 7’s (hard counting difficulty). With increasing counting difficulty, less attentional resources were assumed to be available for balance recovery. The ability to generate arm muscle responses was quantified through the measurement of electromyographic (EMG) onset latencies and amplitudes from three arm muscles. Results indicated that the attentional requirements of the counting task did not greatly affect EMG onset latencies or amplitudes for both young and older adults. Even when an effect was observed, the magnitude of change was small (e.g., ∼3ms earlier EMG onset and ∼2.0%MVC smaller EMG amplitude during the dual- compared to the single-task conditions). Thus, the generation of arm muscle responses do not appear to require a significant amount of attentional resources and the decreased ability to cope with cognitive interference with ageing is unlikely to explain why older adults have difficulty in generating arm responses following a loss of balance.

Characterization of ictal slow waves in epileptic spasms.

We characterized the clinico-neurophysiological features of epileptic spasms, particularly focusing on high-voltage slow waves during ictal EEG. We studied 22 patients with epileptic spasms recorded during digital video-scalp EEG, including five individuals who still had persistent spasms after callosotomy. We analysed the duration, amplitude, latency to onset of electromyographic bursts, and distribution of the highest positive and negative peaks of slow waves in 352 spasms. High-voltage positive slow waves preceded the identifiable muscle contractions of spasms. The mean duration of these positive waves was 569±228m, and the mean latency to electromyographic onset was 182±127m. These parameters varied markedly even within a patient. The highest peak of the positive component was distributed in variable regions, which was not consistent with the location of lesions on MRI. The peak of the negative component following the positivity was distributed in the neighbouring or opposite areas of the positive peak distribution. No changes were evident in the pre- or post-surgical distributions of the positive peak, or in the interhemispheric delay between both hemispheres, in individuals with callosotomy. Our data imply that ictal positive slow waves are the most common EEG changes during spasms associated with a massive motor component. Plausible explanations for these widespread positive slow waves include the notion that EEG changes possibly reflect involvement of both cortical and subcortical structures.

The effects of strengthening exercise, stretching and meditation on electromyography onset timing of the rectus femoris and gastrocnemius during vertical jump performance in healthy adults

Objective: Jump training helps increase the muscle power by improving the muscle strength and reaction time of the muscle in operation. The purpose of this study was to identify the effects of strengthening, stretching exercise and meditation on electromyographic (EMG) onset timing of rectus femoris and gastrocnemius muscle during vertical jump performance. Design: Cross-sectional study. Methods: Ten healthy adults (5 male and 5 female) who were familiar with the vertical jumping task and had no lower extremity injuries or any bone or joint disorders, were recruited for this study. Muscle onset timing was measured by surface EMG. After EMG onset timing were measured during performing three baseline vertical jump trials, strengthening and stretching exercises of the rectus femoris and gastrocnemius, and meditation were performed in random order. EMG onset timing was measured during vertical jump after intervention, respectively. EMG value was averaged for the three trials and analyzed using one-way repeated ANOVA. Results: During vertical jump, EMG onset timing of gastrocnemius was a significant difference after intervention (p

Preliminary investigation of onset of EMG (electromyographic) activation of selected hip muscles in persons with and without patellofemoral pain (PFP)

Preliminary investigation of onset of EMG (electromyographic) activation of selected hip muscles in persons with and without patellofemoral pain (PFP)

Muscle activation characteristics of the front leg during baseball swings with timing correction for sudden velocity decrease.

This study aimed to clarify the activation characteristics of the vastus lateralis muscle in the front leg during timing correction for a sudden decrease in the velocity of a target during baseball swings. Eleven male collegiate baseball players performed coincident timing tasks that comprised constant velocity of 8 m/s (unchanged) and a sudden decrease in velocity from 8 to 4 m/s (decreased velocity). Electromyography (EMG) revealed that the muscle activation was typically monophasic when responding unchanged conditions. The type of muscle activation during swings in response to decreased velocity condition was both monophasic and biphasic. When biphasic activation appeared in response to decreased velocity, the impact time and the time to peak EMG amplitude were significantly prolonged and the timing error was significantly smaller than that of monophasic activation. However, the EMG onset from the target start was consistent both monophasic and biphasic activation in response to conditions of decreased velocity. In addition, batters with small timing errors in response to decreased velocity were more likely to generate biphasic EMG activation. These findings indicated that timing correction for a sudden decrease in the velocity of an oncoming target is achieved by modifying the muscle activation characteristics of the vastus lateralis muscle of front leg from monophasic to biphasic to delay reaching peak muscle activation and thus prolong impact time. Therefore, the present findings suggests that the extent of timing errors in response to decreased velocity is influenced by the ability to correct muscle activation after its initiation rather than by delaying the initiation timing of muscle activation during baseball swings.

Bilateral force transients in the upper limbs evoked by single-pulse microstimulation in the pontomedullary reticular formation.

Neurons in the pontomedullary reticular formation (PMRF) give rise to the reticulospinal tract. The motor output of the PMRF was investigated using stimulus-triggered averaging of electromyography (EMG) and force recordings in two monkeys (M. fascicularis). EMG was recorded from 12 pairs of upper limb muscles, and forces were detected using two isometric force-sensitive handles. Of 150 stimulation sites, 105 (70.0%) produced significant force responses, and 139 (92.5%) produced significant EMG responses. Based on the average flexor EMG onset latency of 8.3 ms and average force onset latency of 15.9 ms poststimulation, an electromechanical delay of ∼7.6 ms was calculated. The magnitude of force responses (∼10 mN) was correlated with the average change in EMG activity (P < 0.001). A multivariate linear regression analysis was used to estimate the contribution of each muscle to force generation, with flexors and extensors exhibiting antagonistic effects. A predominant force output pattern of ipsilateral flexion and contralateral extension was observed in response to PMRF stimulation, with 65.3% of significant ipsilateral force responses directed medially and posteriorly (P < 0.001) and 78.6% of contralateral responses directed laterally and anteriorly (P < 0.001). This novel approach permits direct measurement of force outputs evoked by central nervous system microstimulation. Despite the small magnitude of poststimulus EMG effects, low-intensity single-pulse microstimulation of the PMRF evoked detectable forces. The forces, showing the combined effect of all muscle activity in the arms, are consistent with reciprocal pattern of force outputs from the PMRF detectable with stimulus-triggered averaging of EMG.

M-mode ultrasound used to detect the onset of deep muscle activity

M-mode ultrasound imaging (US) reflects motion of connective tissue within muscles. As muscle contraction is accompanied by motion of muscle tissue, M-mode US may be used to measure non-invasively the onset of deep muscle activity. Isometric hip abduction was measured on nine healthy subjects in the deep region of the gluteus medius muscle and in gluteus minimus by fine-wire electromyography (EMG) and M-mode US. Following signal transformation with the Teager–Kaiser Energy Operator, EMG and M-mode US onsets of muscle activity were computer-processed. Correlation between log-transformed EMG and M-mode high-energy onsets was higher in gluteus medius (r 0.93) than in gluteus minimus (r 0.86). M-mode high-energy onsets followed EMG onset by median 33 (IQR 53) ms in gluteus medius, and by 17 (IQR 63) ms in gluteus minimus. 4% of gluteus medius and 23% of gluteus minimus M-mode onsets were detected before EMG onset. Using a higher onset threshold reduced the rate of onsets detected before EMG but also prediction accuracy. In voluntary activation, M-mode US high-energy onsets were closely related to EMG-measured onsets, but the time interval between both measures varied. The relationship of electrical and mechanical activation onsets appears to be influenced by modifying factors which may differ between muscles.

Restoration of Central Programmed Movement Pattern by Temporal Electrical Stimulation-Assisted Training in Patients with Spinal Cerebellar Atrophy.

Disrupted triphasic electromyography (EMG) patterns of agonist and antagonist muscle pairs during fast goal-directed movements have been found in patients with hypermetria. Since peripheral electrical stimulation (ES) and motor training may modulate motor cortical excitability through plasticity mechanisms, we aimed to investigate whether temporal ES-assisted movement training could influence premovement cortical excitability and alleviate hypermetria in patients with spinal cerebellar ataxia (SCA). The EMG of the agonist extensor carpi radialis muscle and antagonist flexor carpi radialis muscle, premovement motor evoked potentials (MEPs) of the flexor carpi radialis muscle, and the constant and variable errors of movements were assessed before and after 4 weeks of ES-assisted fast goal-directed wrist extension training in the training group and of general health education in the control group. After training, the premovement MEPs of the antagonist muscle were facilitated at 50 ms before the onset of movement. In addition, the EMG onset latency of the antagonist muscle shifted earlier and the constant error decreased significantly. In summary, temporal ES-assisted training alleviated hypermetria by restoring antagonist premovement and temporal triphasic EMG patterns in SCA patients. This technique may be applied to treat hypermetria in cerebellar disorders. (This trial is registered with NCT01983670.)

Acute effects of passive stretching of the plantarflexor muscles on neuromuscular function: the influence of age.

The acute effects of stretching on peak force (Fpeak), percent voluntary activation (%VA), electromyographic (EMG) amplitude, maximum range of motion (MROM), peak passive torque, the passive resistance to stretch, and the percentage of ROM at EMG onset (%EMGonset) were examined in 18 young and 19 old men. Participants performed a MROM assessment and a maximal voluntary contraction of the plantarflexors before and immediately after 20 min of passive stretching. Fpeak (-11 %), %VA (-6 %), and MG EMG amplitude (-9 %) decreased after stretching in the young, but not the old (P > 0.05). Changes in Fpeak were related to reductions in all muscle activation variables (r = 0.56-0.75), but unrelated to changes in the passive resistance to stretch (P ≥ 0.24). Both groups experienced increases in MROM and peak passive torque and decreases in the passive resistance to stretch. However, the old men experienced greater changes in MROM (P < 0.001) and passive resistance (P = 0.02-0.06). Changes in MROM were correlated to increases in peak passive torque (r = 0.717), and the old men also experienced a nonsignificant greater (P = 0.08) increase in peak passive torque. %EMGonset did not change from pre- to post-stretching for both groups (P = 0.213), but occurred earlier in the old (P = 0.06). The stretching-induced impairments in strength and activation in the young but not the old men may suggest that the neural impairments following stretching are gamma-loop-mediated. In addition, the augmented changes in MROM and passive torque and the lack of change in %EMGonset for the old men may be a result of age-related changes in muscle-tendon behavior.

EMG onset detection and upper limb movements identification algorithm

Electromyography (EMG) consists of the measurement and recording of the electrical potential generated by the activation of muscle fibers when performing voluntary or involuntary movements. Therefore, electromyography signals (EMGs) are directly linked to the movement performed by a person. Hence, the study of surface EMGs to determine the movement a person is performing to control exoskeletons for post-stroke rehabilitation has become increasingly popular in recent years; particularly towards bilateral rehabilitation (BLR). Bilateral rehabilitation provides the patient the opportunity to control the intensity and frequency of the rehabilitation exercises. This paper introduces an onset detection method and a movement identification algorithm to differentiate (identify) among five different movements of the upper limb; abduction (AB), adduction (AD), flexion of the upper limb (FUL), extension of the upper limb (EUL) and AB followed by arm to the front (ABF). The movement identification algorithm focuses on the activation of muscle fibers within a single muscle when performing different movements; rather than a comparison between flexor and extensor muscles. This algorithm was evaluated using surface EMG recordings measured on healthy subjects at the Deltoid Muscle. Prior to the movement identification, the proper EMG preprocessing, feature extraction and onset detection of each EMGs recording was performed using Matlab. Two features were extracted from each channel, the root mean square (RMS) and the contractility characteristic of the muscle. An algorithm is then followed to identify the movement performed by a person. Results have shown a highly percentage of accuracy for both, the onset detection and movement identification algorithms.

Foot orthoses induce immediate changes in lower limb neuromotor control of gait in people with patellofemoral joint osteoarthritis: a pilot study

Foot orthoses induce immediate changes in lower limb neuromotor control of gait in people with patellofemoral joint osteoarthritis: a pilot study

Isotonic resistance jaw exercise alters jaw muscle coordination during jaw movements

The aim was to investigate the effects of isotonic resistance exercise on the electro-myographic (EMG) activity of the jaw muscles during standardised jaw movements. In 12 asymptomatic adults surface EMG activity was recorded from the anterior temporalis and masseter muscles bilaterally and the right anterior digastric muscle during right lateral jaw movements that tracked a target. Participants were randomly assigned to a Control group or an Exercise group. Jaw movement and EMG activity were collected (i) at baseline, before the exercise task (pre-exercise); (ii) immediately after the exercise task (isotonic resistance at 60% MVC against right lateral jaw movements); (iii) after 4 weeks of a home-based exercise programme; and, (iv) at 8-weeks follow-up. There were no significant within-subject or between-group differences in the velocity and amplitude of the right lateral jaw movements either within or between data collection sessions (P > 0.05). However, over the 8 weeks of the study, three of the tested EMG variables (EMG Duration, Time to Peak EMG from EMG Onset, and Time to Peak EMG activity relative to Movement Onset) showed significant (P < 0.05) differences in the five tested muscles. Many of the significant changes occurred in the Control group, while the Exercise group tended to maintain the majority of the tested variables at pre-exercise baseline values. The data suggest a level of variability between recording sessions in the recruitment patterns of some of the muscles of mastication for the production of the same right lateral jaw movement and that isotonic resistance exercise may reduce this variability.

The nociceptive withdrawal reflex does not adapt to joint position change and short-term motor practice

The nociceptive withdrawal reflex is a protective mechanism to mediate interactions within a potentially dangerous environment. The reflex is formed by action-based sensory encoding during the early post-natal developmental period, and it is unknown if the protective motor function of the nociceptive withdrawal reflex in the human upper-limb is adaptable based on the configuration of the arm or if it can be modified by short-term practice of a similar or opposing motor action. In the present study, nociceptive withdrawal reflexes were evoked by a brief train of electrical stimuli applied to digit II, 1) in five different static arm positions and, 2) before and after motor practice that was opposite (EXT) or similar (FLEX) to the stereotyped withdrawal response, in 10 individuals. Withdrawal responses were quantified by the electromyography (EMG) reflex response in several upper limb muscles, and by the forces and moments recorded at the wrist. EMG onset latencies and response amplitudes were not significantly different across the arm positions or between the EXT and FLEX practice conditions, and the general direction of the withdrawal response was similar across arm positions. In addition, the force vectors were not different after practice in either the practice condition or between EXT and FLEX conditions. We conclude the withdrawal response is insensitive to changes in elbow or shoulder joint angles as well as remaining resistant to short-term adaptations from the practice of motor actions, resulting in a generalized limb withdrawal in each case. It is further hypothesized that the multisensory feedback is weighted differently in each arm position, but integrated to achieve a similar withdrawal response to safeguard against erroneous motor responses that could cause further harm. The results remain consistent with the concept that nociceptive withdrawal reflexes are shaped through long-term and not short-term action based sensory encoding.

Detecting and correcting partial errors: Evidence for efficient control without conscious access.

Appropriate reactions to erroneous actions are essential to keeping behavior adaptive. Erring, however, is not an all-or-none process: electromyographic (EMG) recordings of the responding muscles have revealed that covert incorrect response activations (termed “partial errors”) occur on a proportion of overtly correct trials. The occurrence of such “partial errors” shows that incorrect response activations could be corrected online, before turning into overt errors. In the present study, we showed that, unlike overt errors, such “partial errors” are poorly consciously detected by participants, who could report only one third of their partial errors. Two parameters of the partial errors were found to predict detection: the surface of the incorrect EMG burst (larger for detected) and the correction time (between the incorrect and correct EMG onsets; longer for detected). These two parameters provided independent information. The correct(ive) responses associated with detected partial errors were larger than the “pure-correct” ones, and this increase was likely a consequence, rather than a cause, of the detection. The respective impacts of the two parameters predicting detection (incorrect surface and correction time), along with the underlying physiological processes subtending partial-error detection, are discussed.

Differences in muscle activation patterns during step recovery in elderly women with and without a history of falls

This study aimed at comparing the patterns of muscle activation used in stepping to regain balance during a forward fall between subjects with and without a history of falling and at identifying the causes of functional deficits in recovery stepping. Elderly women with and without a history of falling (fallers: n=12, mean age±SD=82.8±4.5years; non-fallers: n=17, age=81.4±3.4years) participated in the study. The subjects were suspended in a forward-leaning position by a lean-control cable with a load of 15% of body weight and instructed to regain standing balance upon release by taking a single step forward. Electromyography (EMG) data were obtained from five lower extremity muscles on the stepping side, and the muscle activation patterns were compared between fallers and non-fallers. Fallers had a shorter step length and slower step velocity than non-fallers. The EMG time-to-peak for the gastrocnemius muscle, which provides push-off prior to foot lift-off, was slower for fallers than for non-fallers, whereas the EMG onset times of the biceps femoris and gastrocnemius muscles were similar between the groups. The fallers exhibited significantly delayed muscle deactivation of the upper leg and increased co-contraction between the rectus femoris and biceps femoris during the stepping phase than did the non-fallers. These findings suggest that the muscle activation pattern during the regain balance may reflect an inability to step forward rapidly in elderly women with a history of falls.

Reorganised anticipatory postural adjustments due to experimental lower extremity muscle pain

Automated movements adjusting postural control may be hampered during musculoskeletal pain leaving a risk of incomplete control of balance. This study investigated the effect of experimental muscle pain on anticipatory postural adjustments by reaction task movements. While standing, nine healthy males performed two reaction time tasks (shoulder flexion of dominant side and bilateral heel lift) before, during and after experimental muscle pain. On two different days experimental pain was induced in the m. vastus medialis (VM) or the m. tibialis anterior (TA) of the dominant side by injections of hypertonic saline (1ml, 5.8%). Isotonic saline (1ml, 0.9%) was used as control injection. Electromyography (EMG) was recorded from 13 muscles. EMG onset, EMG amplitude, and kinematic parameters (shoulder and ankle joint) were extracted. During shoulder flexion and VM pain the onset of the ipsilateral biceps femoris was significantly faster than baseline and post injection sessions. During heels lift in the VM and TA pain conditions the onset of the contralateral TA was significantly faster than baseline and post injection sessions in bilateral side. VM pain significantly reduced m. quadriceps femoris activity and TA pain significantly reduced ipsilateral VM activity and TA activity during bilateral heel lift. The EMG reaction time was delayed in bilateral soleus muscles during heels lift with VM and TA pain. The faster onset of postural muscle activity during anticipatory postural adjustments may suggest a compensatory function to maintain postural control whereas the reduced postural muscle activity during APAs may indicate a pain adaptation strategy to avoid secondary damage.

P 184. Exercise-induced strengthening of inter-digital connections in musicians

To investigate whether finger exercise affects surround inhibition in professional musicians as it was previously observed in non-musicians, we performed a transcranial magnetic stimulation (TMS) study in 13 healthy right-handed professional musicians. TMS was set to be triggered by self-initiated flexion of the index finger at 3 ms after electromyography onset (self-triggered TMS). Motor evoked potentials (MEPs) of the abductor digiti minimi (ADM) were measured before and at 0, 10, 20 and 30 min after ‘single’ (little finger abduction) and ‘dual’ (both index finger flexion and little finger abduction) exercise at 0.5 Hz for 30 min. Control and self-triggered MEPs were not different between the two exercise sessions. MEP enhancements were significantly greater in self-triggered TMS than control TMS after single exercise as well as dual exercise. This result demonstrates that MEP enhancement in self-triggered TMS was comparable between two exercise sessions in professional musicians, a result different from that observed in healthy non-musicians. Enhanced self-triggered MEPs after isolated finger exercise suggest that inter-digital cortical connections are strengthened in musicians, presumably due to previous musical training. Inter-digital cortical connections are strengthened in musicians and are not differently modulated by different types of short-term finger exercise.

Adaptability of the nociceptive withdrawal reflex

The nociceptive withdrawal reflex is a protective mechanism to mediate interactions within a potentially dangerous environment. The reflex is formed by action-based sensory encoding during the early post-natal developmental period, and it is unknown if the protective motor function of the nociceptive withdrawal reflex in the human upper-limb is adaptable based on the configuration of the arm or if it can be modified by short-term practice of a similar or opposing motor action. In the present study, nociceptive withdrawal reflexes were evoked by a brief train of electrical stimuli applied to digit II, 1) in five different static arm positions and, 2) before and after motor practice that was opposite (EXT) or similar (FLEX) to the stereotyped withdrawal response, in 10 individuals. Withdrawal responses were quantified by the electromyography (EMG) reflex response in several upper limb muscles, and by the forces and moments recorded at the wrist. EMG onset latencies and response amplitudes were not significantly different across the arm positions or between the EXT and FLEX practice conditions, and the general direction of the withdrawal response was similar across arm positions. In addition, the force vectors were not different after practice in either the practice condition or between EXT and FLEX conditions. We conclude the withdrawal response is insensitive to changes in elbow or shoulder joint angles as well as remaining resistant to short-term adaptations from the practice of motor actions, resulting in a generalized limb withdrawal in each case. It is further hypothesized that the multisensory feedback is weighted differently in each arm position, but integrated to achieve a similar withdrawal response to safeguard against erroneous motor responses that could cause further harm. The results remain consistent with the concept that nociceptive withdrawal reflexes are shaped through long-term and not short-term action based sensory encoding.