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   2017

Changes in tibialis anterior architecture affect the amplitude of surface electromyograms. Vieira TM, Bisi MC, Stagni R, Botter A. J Neuroeng Rehabil. 2017 Aug 14;14(1):81
2017 Aug 14;14(1):81. doi: 10.1186/s12984-017-0291-5.

Changes in tibialis anterior architecture affect the amplitude of surface electromyograms.

Author information
1
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy. taian.vieira@polito.it.
2
Department of Electrical, Electronic and Information Engineering “Guglielmo Marconi”, University of Bologna, Viale Risorgimento 2, Bologna, 40136, Italy.
3
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics and Telecommunication, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy.

Abstract

BACKGROUND:

Variations in the amplitude of surface electromyograms (EMGs) are typically considered to advance inferences on the timing and degree of muscle activation in different circumstances. Surface EMGs are however affected by factors other than the muscle neural drive. In this study, we use electrical stimulation to investigate whether architectural changes in tibialis anterior (TA), a key muscle for balance and gait, affect the amplitude of surface EMGs.

METHODS:

Current pulses (500 μs; 2 pps) were applied to the fibular nerve of ten participants, with the ankle at neutral, full dorsi and full plantar flexion positions. Ultrasound images were collected to quantify changes in TA architecture with changes in foot position. The peak-to-peak amplitude of differential M waves, detected with a grid of surface electrodes (16 × 4 electrodes; 10 mm inter-electrode distance), was considered to assess the effect of changes in TA architecture on the surface recordings.

RESULTS:

On average, both TA pennation angle and width increased by respectively 7 deg. and 9 mm when the foot moved from plantar to dorsiflexion (P < 0.02). M-wave amplitudes changed significantly with ankle position. M waves elicited in dorsiflexion and neutral positions were ~25% greater than those obtained during plantar flexion, regardless of where they were detected in the grid (P < 0.001). This figure increased to ~50% when considering bipolar M waves.

CONCLUSIONS:

Findings reported here indicate the changes in EMG amplitude observed during dynamic contractions, especially when changes in TA architecture are expected (e.g., during gait), may not be exclusively conceived as variations in TA activation.

KEYWORDS:

Electrical stimulation; Surface electromyograms; Tibialis anterior; Ultrasound

PMID:
28807025
DOI:
10.1186/s12984-017-0291-5
Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions? Cabral HV, de Souza LML, Mello RGT, Gallina A, de Oliveira LF, Vieira TM. Muscle Nerve. 2017 May 13
2017 May 13. doi: 10.1002/mus.25688. [Epub ahead of print]

Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions?

Abstract

INTRODUCTION:

Previous evidence suggests the fibers of different motor units reside within distinct vastus medialis (VM) regions. It remains unknown whether the activity of these motor units may be modulated differently. Herein we assess the discharge rate of motor units detected proximodistally from the VM to address this issue.

METHODS:

Surface electromyograms (EMGs) were recorded proximally and distally from the VM while 10 healthy subjects performed isometric contractions. Single motor units were decomposed from surface EMGs. The smoothed discharge rates of motor units identified from the same and from different VM regions were then cross-correlated.

RESULTS:

During low-level contractions, the discharge rate varied more similarly for distal (cross-correlation peak; interquartile interval: 0.27-0.40) and proximal (0.28-0.52) than for proximodistal pairs of VM motor units (0.20-0.33; P = 0.006).

CONCLUSIONS:

The discharge rates of motor units from different proximodistal VM regions show less similarity in their variations than those of pairs of units either distally or proximally. Muscle Nerve, 2017.

KEYWORDS:

compartmentalization; knee; motor unit; quadriceps; surface electromyography; vastus medialis

PMID:
28500671
DOI:
10.1002/mus.25688
Is heart rate variability affected by distinct motor imagery strategies? Peixoto Pinto T, Mello Russo Ramos M, Lemos T, Domingues Vargas C, Imbiriba LA. Physiol Behav. 2017 Aug 1;177:189-195.
2017 Aug 1;177:189-195. doi: 10.1016/j.physbeh.2017.05.004. Epub 2017 May 2.

Is heart rate variability affected by distinct motor imagery strategies?

Abstract

Although some studies have reported significant changes in autonomic responses according to the perspective-taking during motor imagery [first person perspective (1P) and third person perspective (3P)], investigations on how the strategies adopted to mentally simulate a given movement affect the heart rate variability (HRV) seem so far unexplored. Twenty healthy subjects mentally simulated the movement of middle-finger extension in 1P and 3P, while electrocardiogram was recorded. After each task, the level of easiness was self-reported. Motor imagery ability was also assessed through the revised version of Movement Imagery Questionnaire (MIQ-R) and a mental chronometry index. The traditional measures of HRV in the time- and frequency-domain were compared between 1P and 3P tasks by using Student’s t-test for dependent samples. The MIQ-R results showed that subjects had the same facility to imagine movements in 1P or 3P. The mental chronometry index revealed a similar temporal course only between 1P and execution, while the 3P strategy had a shorter duration. Additionally, the subjective report was similar between the experimental tasks. Regarding the HRV measures, the low frequency component, in log-transformed unit, was significantly higher (p=0.017) in 1P than 3P, suggesting a higher activity of the sympathetic system during 1P. This log-transformed HRV parameter seems to be more sensitive than normalized values for the assessment of the motor imagery ability, together with questionnaires, scales and mental chronometry.

KEYWORDS:

Autonomic nervous system; Heart rate variability; Motor imagery strategies

PMID:
28476285
DOI:
10.1016/j.physbeh.2017.05.004
Physiological arousal accompanying postural responses to external perturbations after stroke. Pollock CL, Carpenter MG, Hunt MA, Gallina A, Vieira TM, Ivanova TD, Garland SJ. Clin Neurophysiol. 2017 Jun;128(6):935-944
2017 Jun;128(6):935-944. doi: 10.1016/j.clinph.2017.03.008. Epub 2017 Mar 18.

Physiological arousal accompanying postural responses to external perturbations after stroke.

Author information

1
Department of Physical Therapy, University of British Columbia, Vancouver, Canada.
2
School of Kinesiology, University of British Columbia, Vancouver, Canada.
3
Department of Physical Therapy, University of British Columbia, Vancouver, Canada; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Italy.
4
Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Italy; Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
5
Faculty of Health Sciences, Western University, London, Canada.
6
Faculty of Health Sciences, Western University, London, Canada. Electronic address: jgarland@uwo.ca.

Abstract

OBJECTIVE:

The purpose of this study was to examine simultaneously the level of physiological arousal and the postural response to external perturbations in people post-stroke compared to age-matched controls to build a more comprehensive understanding of the effect of stroke on postural control and balance self-efficacy.

METHODS:

Participants stood with each foot on separate force platforms. Ten applications of loads of 2% body weight at the hips perturbed the participant anteriorly under two conditions: investigator-triggered or self-triggered (total 20). Electrodermal activity (EDA; measurement of physiological arousal), electromyography (EMG) of the ankle plantarflexor muscles and anterior-posterior center of pressure measurements were taken pre-perturbation (anticipatory) and post-perturbation (response) and compared between the initial (first two) and final (last two) perturbations.

RESULTS:

Participants post-stroke demonstrated significantly higher levels of anticipatory EDA and anticipatory paretic plantarflexor EMG during both self- and investigator-triggered conditions compared to controls. Anticipatory EDA levels were higher in the final perturbations in participants post-stroke in both conditions, but not in controls. Habituation of the EDA responses post-perturbation was exhibited in the self-triggered perturbations in controls, but not in participants post-stroke.

CONCLUSIONS:

Physiological arousal and postural control strategies of controls revealed habituation in response to self-triggered perturbations, whereas this was not seen in participants post-stroke.

SIGNIFICANCE:

Understanding the physiological arousal response to challenges to standing balance post-stroke furthers our understanding of postural control mechanisms post-stroke.

KEYWORDS:

External perturbation; Physiological arousal; Postural control; Stroke

PMID:
28407522
DOI:
10.1016/j.clinph.2017.03.008
Optimization of surface electrodes location for H-reflex recordings in soleus muscle. Botter A, Vieira TM. J Electromyogr Kinesiol. 2017 Jun;34:14-23
2017 Jun;34:14-23. doi: 10.1016/j.jelekin.2017.03.003. Epub 2017 Mar 16.

Optimization of surface electrodes location for H-reflex recordings in soleus muscle.

Author information

1
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. Electronic address: alberto.botter@polito.it.
2
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.

Abstract

The Hoffmann reflex (H reflex) is extensively used to investigate the spinal motor neuron excitability in healthy and pathological subjects. Obtaining a representative and robust amplitude estimation of the H reflex is of marked relevance in clinical as well as in research applications. As for the motor responses, this issue is strictly related to the electrode positioning, especially for large, pinnate muscles such as the triceps surae. In this study we investigated the effect of electrode position on soleus H-reflex amplitude. A grid of 96 electrodes was used to identify maximal H reflexes (Hmax) across the whole soleus region available for surface recording. The spatial distribution of Hmax amplitude detected in monopolar and single-differential derivations was used to determine where greatest reflex responses were detected from soleus. For both derivations and for all participants, largest Hmax were detected consistently over the central soleus region, in correspondence of the muscle superficial aponeurosis. Indeed, the amplitude of Hmax provided by conventional electrodes (1cm2 area, 2cm apart) located centrally was significantly greater (median: 35% for monopolar and 79% for single-differential derivations) than that obtained medially, where surface electromyograms are typically recorded from soleus. Computer simulations, used to assist in the interpretation of results, suggest the soleus pinnate architecture was the key determinant of the medio-lateral variability observed for the experimental Hmax. The presented results provide a clear indication for electrode positioning, of crucial relevance in applied studies aimed at eliciting H reflexes.

KEYWORDS:

Achilles tendon; EMG; Electrode positioning; H reflex; Soleus

PMID:
28342367
DOI:
10.1016/j.jelekin.2017.03.003
Is myoelectric activity distributed equally within the rectus femoris muscle during loaded, squat exercises? de Souza LM, da Fonseca DB, Cabral HD, de Oliveira LF, Vieira TM. J Electromyogr Kinesiol. 2017 Apr;33:10-19
2017 Apr;33:10-19. doi: 10.1016/j.jelekin.2017.01.003. Epub 2017 Jan 9.

Is myoelectric activity distributed equally within the rectus femoris muscle during loaded, squat exercises?

Author information

1
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
2
Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
3
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Electronic address: liliam@peb.ufrj.br.
4
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.

Abstract

Recent evidence suggests different regions of the rectus femoris (RF) muscle respond differently to squat exercises. Such differential adaptation may result from neural inputs distributed locally within RF, as previously reported for isometric contractions, walking and in response to fatigue. Here we therefore investigate whether myoelectric activity distributes evenly within RF during squat. Surface electromyograms (EMGs) were sampled proximally and distally from RF with arrays of electrodes, while thirteen healthy volunteers performed 10 consecutive squats with 20% and 40% of their body weight. The root mean square (RMS) value, computed separately for thirds of the concentric and eccentric phases, was considered to assess the proximo-distal changes in EMG amplitude during squat. The channels with variations in EMG amplitude during squat associated with shifts in the muscle innervation zone were excluded from analysis. No significant differences were observed between RF regions when considering squat phases and knee joint angles individually (P>0.16) while a significant interaction between phase and knee joint angle with detection site was observed (P<0.005). For the two loads considered, proximal RMS values were greater during the eccentric phase and for the more flexed knee joint position (P<0.001). Our results suggest inferences on the degree of RF activation during squat must be made cautiously from surface EMGs. Of more practical relevance, there may be a potential for the differential adaption of RF proximal and distal regions to squat exercises.

KEYWORDS:

Rectus femoris; Resistance training; Squat; Surface electromyography

PMID:
28110043
DOI:
10.1016/j.jelekin.2017.01.003
The Spatial Distribution of Ankle Muscles Activity Discriminates Aged from Young Subjects during Standing. Dos Anjos FV, Pinto TP, Gazzoni M, Vieira TM. Front Hum Neurosci. 2017 Apr 19;11:190
2017 Apr 19;11:190. doi: 10.3389/fnhum.2017.00190. eCollection 2017.

The Spatial Distribution of Ankle Muscles Activity Discriminates Aged from Young Subjects during Standing.

Author information

1
Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di TorinoTorino, Italy.

Abstract

During standing, age-related differences in the activation of ankle muscles have been reported from surface electromyograms (EMGs) sampled locally. Given though activity seems to distribute unevenly within ankle muscles, the local sampling of surface EMGs may provide a biased view on how often and how much elderly and young individuals activate these muscles during standing. This study aimed therefore at sampling EMGs from multiple regions of individual ankle muscles to evaluate whether the distribution of muscle activity differs between aged and young subjects during standing. Thirteen young and eleven aged, healthy subjects were tested. Surface EMGs were sampled at multiple skin locations from tibialis anterior, soleus and medial and lateral gastrocnemius muscles while subjects stood at ease. The root mean square amplitude of EMGs was considered to estimate the duration, the degree of activity and the size of the region where muscle activity was detected. Our main findings revealed the medial gastrocnemius was active for longer periods in aged (interquartile interval; 74.1-98.2%) than young (44.9-81.9%) individuals (P = 0.02). Similarly, while tibialis anterior was rarely active in young (0.7-4.4%), in elderly subjects (2.6-82.5%) it was often recruited (P = 0.01). Moreover, EMGs with relatively higher amplitude were detected over a significantly wider proximo-distal region of medial gastrocnemius in aged (29.4-45.6%) than young (20.1-31.3%) subjects (P = 0.04). These results indicate the duration and the size of active muscle volume, as quantified from the spatial distribution of surface EMGs, may discriminate aged from young individuals during standing; elderlies seem to rely more heavily on the active loading of ankle muscles to control their standing posture than young individuals. Most importantly, current results suggest different conclusions on the active control of standing posture may be drawn depending on the skin location from where EMGs are collected, in particular for the medial gastrocnemius.

KEYWORDS:

aging; electromyography; muscle activity; postural control; standing

PMID:
28469567
PMCID:
PMC5395606
DOI:
10.3389/fnhum.2017.00190
Spatial variation and inconsistency between estimates of onset of muscle activation from EMG and ultrasound. Dieterich AV, Botter A, Vieira TM, Peolsson A, Petzke F, Davey P, Falla D. Sci Rep. 2017 Feb 8;7:42011. doi: 10.1038/srep42011
2017 Feb 8;7:42011. doi: 10.1038/srep42011.

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

Author information

1
Pain Clinic, Anaesthesiology, University Medical Center, Göttingen, Germany.
2
Laboratory of Engineering of the Neuromuscular System and Motor Rehabilitation, Department of Electronics, Politecnico di Torino, Torino, Italy.
3
School of Physical Education and Sports, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
4
Department of Medical and Health Sciences, Physiotherapy, Linköping University, Linköping, Sweden.
5
School of Physiotherapy and Exercise Science, Faculty of Health Sciences, Curtin University, Perth, Australia.
6
Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.

Abstract

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.

   2016

Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing. Afsharipour B, Petracca F, Gasparini M, Merletti R. J Electromyogr Kinesiol. 2016 Dec;31:144-153
2016 Dec;31:144-153. doi: 10.1016/j.jelekin.2016.10.003. Epub 2016 Oct 31.

Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing.

Author information

1
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, United States; Department of Physical Medicine and Rehabilitation of Northwestern University, United States; Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: babak.afsharipour@northwestern.edu.
2
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: fra.petra.fp@gmail.com.
3
Department of Mathematical Sciences, Politecnico di Torino, Torino, Italy. Electronic address: mauro.gasparini@polito.it.
4
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: roberto.merletti@polito.it.

Abstract

Musicians activate their muscles in different patterns, depending on their posture, the instrument being played, and their experience level. Bipolar surface electrodes have been used in the past to monitor such activity, but this method is highly sensitive to the location of the electrode pair. In this work, the spatial distribution of surface EMG (sEMG) of the right trapezius and right and left erector spinae muscles were studied in 16 violin players and 11 cello players. Musicians played their instrument one string at a time in sitting position with/without backrest support. A 64 sEMG electrode (16×4) grid, 10mm inter-electrode distance (IED), was placed over the middle and lower trapezius (MT and LT) of the bowing arm. Two 16×2 electrode grids (IED=10mm) were placed on the left and right erector spinae muscles. Subjects played each of the four strings of the instrument either in large (1bow/s) or detaché tip/tail (8bows/s) bowing in two sessions (two days). In each of two days, measurements were repeated after half an hour of exercise to see the effect of exercise on the muscle activity and signal stability. A “muscle activity index” (MAI) was defined as the spatial average of the segmented active region of the RMS map. Spatial maps were automatically segmented using the watershed algorithm and thresholding. Results showed that, for violin players, sliding the bow upward from the tip toward the tail results in a higher MAI for the trapezius muscle than a downward bow. On the contrary, in cello players, higher MAI is produced in the tail to tip movement. For both instruments, an increasing MAI in the trapezius was observed as the string position became increasingly lateral, from string 1 (most medial) toward string 4 (most lateral). Half an hour of performance did not cause significant differences between the signal quality and the MAI values measured before and after the exercise. The MAI of the left and right erector spinae was smaller in the case of backrest support, especially for violin players. Back muscles of violin and cello players were activated asymmetrically, specifically in fast movements (detaché tip/tail). These findings demonstrate the sensitivity and stability of the technique and justify more extensive investigation following this proof of concept.

KEYWORDS:

Cello; Erector spinae; High density surface electromyography (HDsEMG); Musicians; String players; Surface EMG; Trapezius; Violin

PMID:
27835831
DOI:
10.1016/j.jelekin.2016.10.003
Does the type of visual feedback information change the control of standing balance? Dos Anjos F, Lemos T, Imbiriba LA. Eur J Appl Physiol. 2016 Sep;116(9):1771-9
2016 Sep;116(9):1771-9. doi: 10.1007/s00421-016-3434-7. Epub 2016 Jul 18.

Does the type of visual feedback information change the control of standing balance?

Abstract

PURPOSE:

The aim of this study was to evaluate whether different types of visual feedback influence the control of standing balance.

METHODS:

Twenty-six subjects performed three tasks on a force platform: (1) standing with eyes open; (2) maintaining the own center of pressure (COP) displacement (internal feedback) on a target; and (3) pointing with a handheld laser pointer (external feedback) on a target. The COP and ankle displacements were measured through a force platform and a biaxial electrogoniometer, respectively, during 60 s in each task. Global posturographic parameters were computed in the anterior-posterior and medial-lateral directions. In addition, the standard deviation and mean frequency of the ankle movements were also calculated in the sagittal plane.

RESULTS:

The sway area and standard deviation of COP differed between conditions, wherein smaller and higher values were typically observed during the internal and external feedback, respectively. Conversely, both the mean frequency and the mean velocity of COP were greater during internal feedback compared with other tasks, while external feedback usually leads to smaller values. Additionally, smaller and higher values for the ankle standard deviation and the ankle mean frequency, respectively, were observed during internal feedback, with the external feedback condition showing an opposite behavior.

CONCLUSIONS:

These results showed that the global postural sway and the postural adjustments at ankle during standing balance change depending on the type of visual feedback information.

KEYWORDS:

Ankle motion; Postural control; Posturography; Visual feedback

PMID:
27431210
DOI:
10.1007/s00421-016-3434-7
Is there sufficient evidence to claim muscle units are not localised and functionally grouped within the human gastrocnemius? Vieira TM, Wakeling JM, Hodson-Tole EF. J Physiol. 2016 Apr 1;594(7):1953-4.
2016 Apr 1;594(7):1953-4. doi: 10.1113/JP271866.

Is there sufficient evidence to claim muscle units are not localised and functionally grouped within the human gastrocnemius?

Author information

1
Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Politecnico di Torino, Torino, Italia. taian.vieira@polito.it.
2
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil. taian.vieira@polito.it.
3
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Canada.
4
School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
PMID:
27038106
PMCID:
PMC4818604
DOI:
10.1113/JP271866
Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance. Vieira TM, Baudry S, Botter A. Front Physiol. 2016 Apr 29;7:158. doi: 10.3389/fphys.2016.00158. eCollection 2016.
2016 Apr 29;7:158. doi: 10.3389/fphys.2016.00158. eCollection 2016.

Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance.

Author information

1
Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di TorinoTorino, Italia; Escola de Educação Física e Desportos, Departamento de Arte Corporal, Universidade Federal do Rio de JaneiroRio de Janeiro, Brasil.
2
Laboratory of Applied Biology and Neurophysiology, ULB Neuroscience Institute, Université libre de Bruxelles Brussels, Belgium.
3
Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino Torino, Italia.

Abstract

Recent evidence suggests the minimization of muscular effort rather than of the size of bodily sway may be the primary, nervous system goal when regulating the human, standing posture. Different programs have been proposed for balance training; none however has been focused on the activation of postural muscles during standing. In this study we investigated the possibility of minimizing the activation of the calf muscles during standing through biofeedback. By providing subjects with an audio signal that varied in amplitude and frequency with the amplitude of surface electromyograms (EMG) recorded from different regions of the gastrocnemius and soleus muscles, we expected them to be able to minimize the level of muscle activation during standing without increasing the excursion of the center of pressure (CoP). CoP data and surface EMG from gastrocnemii, soleus and tibialis anterior muscles were obtained from 10 healthy participants while standing at ease and while standing with EMG biofeedback. Four sensitivities were used to test subjects’ responsiveness to the EMG biofeedback. Compared with standing at ease, the two most sensitive feedback conditions induced a decrease in plantar flexor activity (~15%; P < 0.05) and an increase in tibialis anterior EMG (~10%; P < 0.05). Furthermore, CoP mean position significantly shifted backward (~30 mm). In contrast, the use of less sensitive EMG biofeedback resulted in a significant decrease in EMG activity of ankle plantar flexors with a marginal increase in TA activity compared with standing at ease. These changes were not accompanied by greater CoP displacements or significant changes in mean CoP position. Key results revealed subjects were able to keep standing stability while reducing the activity of gastrocnemius and soleus without loading their tibialis anterior muscle when standing with EMG biofeedback. These results may therefore posit the basis for the development of training protocols aimed at assisting subjects in more efficiently controlling leg muscle activity during standing.

KEYWORDS:

balance; biofeedback; electromyography; postural sway; standing

PMID:
27199773
PMCID:
PMC4850153
DOI:
10.3389/fphys.2016.00158
Between-day reliability of triceps surae responses to standing perturbations in people post-stroke and healthy controls: A high-density surface EMG investigation. Gallina A, Pollock CL, Vieira TM, Ivanova TD, Garland SJ. Gait Posture. 2016 Feb;44:103-9
2016 Feb;44:103-9. doi: 10.1016/j.gaitpost.2015.11.015. Epub 2015 Dec 7.

Between-day reliability of triceps surae responses to standing perturbations in people post-stroke and healthy controls: A high-density surface EMG investigation.

Abstract

The reliability of triceps surae electromyographic responses to standing perturbations in people after stroke and healthy controls is unknown. High-Density surface Electromyography (HDsEMG) is a technique that records electromyographic signals from different locations over a muscle, overcoming limitations of traditional surface EMG such as between-day differences in electrode placement. In this study, HDsEMG was used to measure responses from soleus (SOL, 18 channels) and medial and lateral gastrocnemius (MG and LG, 16 channels each) in 10 people after stroke and 10 controls. Timing and amplitude of the response were estimated for each channel of the grids. Intraclass Correlation Coefficient (ICC) and normalized Standard Error of Measurement (SEM%) were calculated for each channel individually (single-channel configuration) and on the median of each grid (all-channels configuration). Both timing (single-channel: ICC=0.75-0.96, SEM%=5.0-9.1; all-channels: ICC=0.85-0.97; SEM%=3.5-6.2%) and amplitude (single-channel: ICC=0.60-0.91, SEM%=25.1-46.6; ICC=0.73-0.95, SEM%=19.3-42.1) showed good-to-excellent reliability. HDsEMG provides reliable estimates of EMG responses to perturbations both in individuals after stroke and in healthy controls; reliability was marginally better for the all-channels compared to the single-channel configuration.

KEYWORDS:

High-density surface electromyography; Perturbation; Posture; Reliability; Stroke

PMID:
27004641
DOI:
10.1016/j.gaitpost.2015.11.015
Electrode position markedly affects knee torque in tetanic, stimulated contractions. Vieira TM, Potenza P, Gastaldi L, Botter A. Eur J Appl Physiol. 2016 Feb;116(2):335-42
2016 Feb;116(2):335-42. doi: 10.1007/s00421-015-3289-3. Epub 2015 Nov 2.

Electrode position markedly affects knee torque in tetanic, stimulated contractions.

Author information

1
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
2
Departamento de Arte Corporal, Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil.
3
Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino, Torino, Italy.
4
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. alberto.botter@polito.it.

Abstract

PURPOSE:

The purpose of this study was to investigate how much the distance between stimulation electrodes affects the knee extension torque in tetanic, electrically elicited contractions.

METHODS:

Current pulses of progressively larger amplitude, from 0 mA to maximally tolerated intensities, were delivered at 20 pps to the vastus medialis, rectus femoris and vastus lateralis muscles of ten, healthy male subjects. Four inter-electrode distances were tested: 32.5% (L1), 45.0% (L2), 57.5% (L3) and 70% (L4) of the distance between the patella apex and the anterior superior iliac spine. The maximal knee extension torque and the current leading to the maximal torque were measured and compared between electrode configurations.

RESULTS:

The maximal current tolerated by each participant ranged from 60 to 100 mA and did not depend on the inter-electrode distance. The maximal knee extension torque elicited did not differ between L3 and L4 (P = 0.15) but, for both conditions, knee torque was significantly greater than for L1 and L2 (P < 0.024). On average, the extension torque elicited for L3 and L4 was two to three times greater than that obtained for L1 and L2. The current leading to maximal torque was not as sensitive to inter-electrode distance. Except for L1 current intensity did not change with electrode configuration (P > 0.16).

CONCLUSIONS:

Key results presented here revealed that for a given stimulation intensity, knee extension torque increased dramatically with the distance between electrodes. The distance between electrodes seems therefore to critically affect knee torque, with potential implication for optimising exercise protocols based on electrical stimulation.

KEYWORDS:

Electrode configuration; Functional electrical stimulation; Quadriceps muscle; Stimulation parameters

PMID:
26526290
DOI:
10.1007/s00421-015-3289-3
The correct episiotomy: Does it exist? Merletti R, Riva D, Cescon C, Zacesta V. Int Urogynecol J. 2016 Jan;27(1):161-2. doi: 10.1007/s00192-015-2879-2. Epub 2015 Nov 12.
2016 Feb;116(2):335-42. doi: 10.1007/s00421-015-3289-3. Epub 2015 Nov 2.

Electrode position markedly affects knee torque in tetanic, stimulated contractions.

Author information

1
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
2
Departamento de Arte Corporal, Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil.
3
Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino, Torino, Italy.
4
Laboratory for Engineering of the Neuromuscular System (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy. alberto.botter@polito.it.

Abstract

PURPOSE:

The purpose of this study was to investigate how much the distance between stimulation electrodes affects the knee extension torque in tetanic, electrically elicited contractions.

METHODS:

Current pulses of progressively larger amplitude, from 0 mA to maximally tolerated intensities, were delivered at 20 pps to the vastus medialis, rectus femoris and vastus lateralis muscles of ten, healthy male subjects. Four inter-electrode distances were tested: 32.5% (L1), 45.0% (L2), 57.5% (L3) and 70% (L4) of the distance between the patella apex and the anterior superior iliac spine. The maximal knee extension torque and the current leading to the maximal torque were measured and compared between electrode configurations.

RESULTS:

The maximal current tolerated by each participant ranged from 60 to 100 mA and did not depend on the inter-electrode distance. The maximal knee extension torque elicited did not differ between L3 and L4 (P = 0.15) but, for both conditions, knee torque was significantly greater than for L1 and L2 (P < 0.024). On average, the extension torque elicited for L3 and L4 was two to three times greater than that obtained for L1 and L2. The current leading to maximal torque was not as sensitive to inter-electrode distance. Except for L1 current intensity did not change with electrode configuration (P > 0.16).

CONCLUSIONS:

Key results presented here revealed that for a given stimulation intensity, knee extension torque increased dramatically with the distance between electrodes. The distance between electrodes seems therefore to critically affect knee torque, with potential implication for optimising exercise protocols based on electrical stimulation.

KEYWORDS:

Electrode configuration; Functional electrical stimulation; Quadriceps muscle; Stimulation parameters

PMID:
26526290
DOI:
10.1007/s00421-015-3289-3

   2011-2015

. Territory and fiber orientation of vastus medialis motor units: A Surface electromyography investigation. Gallina A, Vieira T. Muscle Nerve. 2015 Dec;52(6):1057-65. doi: 10.1002/mus.24662. Epub 2015 Sep 8.
2015 Dec;52(6):1057-65. doi: 10.1002/mus.24662. Epub 2015 Sep 8.

Territory and fiber orientation of vastus medialis motor units: A Surface electromyography investigation.

Author information

1
Laboratorio per l’Ingegneria del Sistema Nuromuscolare, Dipartimento di Ingegneria Elettronica, Politecnico di Torino, Via Cavalli 22/h, 10138, Torino, Italy.
2
Graduate Program in Rehabilitation Sciences, Department of Physical Therapy, University of British Columbia, Vancouver (BC), Canada.
3
Escola de Educação Física e Desportos, Departamento de Arte Corporal, Universidade Federal do Rio de Janeiro, Rio di Janeiro, Brazil.

Abstract

INTRODUCTION:

The aim of this study was to determine whether muscle fibers innervated by single motor neurons are confined in small subvolumes of the vastus medialis (VM) and if motor unit fiber orientation depends on their position within the muscle.

METHODS:

Single motor units were identified from a grid of surface electrodes. The size of their surface representation and fiber orientation were extracted using an algorithm validated on simulated signals.

RESULTS:

The action potentials of 77 motor units were represented locally on the skin (10th-90th percentiles: 14-25 mm). According to simulations, this indicates territories smaller than 11.8-64.8 mm. Motor units in distal regions of VM had fibers at a greater angle than those in proximal regions (R = -0.54, P < 0.001).

CONCLUSION:

Motor units with small territories and varying fiber orientations may be an anatomical predisposition to regulate how regions within VM apply forces to the patella. This could help to redistribute loads within the joint in painful conditions.

KEYWORDS:

compartmentalization; electromyography; motor unit; quadriceps; surface EMG; territory

PMID:
25808985
DOI:
10.1002/mus.24662
Filtered Virtual Reference: A New Method for the Reduction of Power Line Interference With Minimal Distortion of Monopolar Surface EMG. Botter A, Vieira TM. IEEE Trans Biomed Eng. 2015 Nov;62(11):2638-47. doi: 10.1109/TBME.2015.2438335.
2015 Nov;62(11):2638-47. doi: 10.1109/TBME.2015.2438335.

Filtered Virtual Reference: A New Method for the Reduction of Power Line Interference With Minimal Distortion of Monopolar Surface EMG.

Abstract

GOAL:

This study tests and validates a new method to remove power line interference from monopolar EMGs detected by multichannel systems: the filtered virtual reference (FVR). FVR is an adaptation of the virtual reference (VR) method, which consists in referencing signals detected by each electrode in a grid to their spatial average. Signals may however be distorted with the VR approach, in particular when the skin region where the detection system is positioned does not cover the entire muscle.

METHODS:

Simulated and experimental EMGs were used to compare the performance of FVR and VR in terms of interference reduction and distortion of monopolar signals referred to a remote reference.

RESULTS:

Simulated data revealed the monopolar EMG signals processed with FVR were significantly less distorted than those filtered by VR. These results were similarly observed for experimental signals. Moreover, FVR method outperformed VR in removing power line interference when it was distributed unevenly across the signals of the grid.

CONCLUSION:

Key results demonstrated that FVR improves the VR method as it reduces interference while preserving the information content of monopolar signals.

SIGNIFICANCE:

Although the actual distribution of motor unit action potential is represented in monopolar EMGs, collecting high quality monopolar signals is challenging. This study presents a possible solution to this issue; FVR provides undistorted monopolar signals with negligible interference and is insensitive to muscle architecture. It is therefore relevant for EMG applications benefiting from a clean monopolar detection (e.g., decomposition, control of prosthetic devices, motor unit number estimation).

PMID:
26513767
DOI:
10.1109/TBME.2015.2438335
Spatial variability in cortex-muscle coherence investigated with magnetoencephalography and high-density surface electromyography. Piitulainen H, Botter A, Bourguignon M, Jousmäki V, Hari R. J Neurophysiol. 2015 Nov;114(5):2843-53. doi: 10.1152/jn.00574.2015. Epub 2015 Sep 9.
2015 Nov;114(5):2843-53. doi: 10.1152/jn.00574.2015. Epub 2015 Sep 9.

Spatial variability in cortex-muscle coherence investigated with magnetoencephalography and high-density surface electromyography.

Author information

1
Brain Research Unit, Department of Neuroscience and Biomedical Engineering, and MEG Core and Advanced Magnetic Imaging (AMI) Centre, Aalto NeuroImaging, Aalto University School of Science, Aalto, Espoo, Finland; and harri.piitulainen@aalto.fi.
2
Laboratory of Engineering of Neuromuscular System and Motor Rehabilitation, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Turin, Italy.
3
Brain Research Unit, Department of Neuroscience and Biomedical Engineering, and MEG Core and Advanced Magnetic Imaging (AMI) Centre, Aalto NeuroImaging, Aalto University School of Science, Aalto, Espoo, Finland; and.

Abstract

Cortex-muscle coherence (CMC) reflects coupling between magnetoencephalography (MEG) and surface electromyography (sEMG), being strongest during isometric contraction but absent, for unknown reasons, in some individuals. We used a novel nonmagnetic high-density sEMG (HD-sEMG) electrode grid (36 mm × 12 mm; 60 electrodes separated by 3 mm) to study effects of sEMG recording site, electrode derivation, and rectification on the strength of CMC. Monopolar sEMG from right thenar and 306-channel whole-scalp MEG were recorded from 14 subjects during 4-min isometric thumb abduction. CMC was computed for 60 monopolar, 55 bipolar, and 32 Laplacian HD-sEMG derivations, and two derivations were computed to mimic “macroscopic” monopolar and bipolar sEMG (electrode diameter 9 mm; interelectrode distance 21 mm). With unrectified sEMG, 12 subjects showed statistically significant CMC in 91-95% of the HD-sEMG channels, with maximum coherence at ∼25 Hz. CMC was about a fifth stronger for monopolar than bipolar and Laplacian derivations. Monopolar derivations resulted in most uniform CMC distributions across the thenar and in tightest cortical source clusters in the left rolandic hand area. CMC was 19-27% stronger for HD-sEMG than for “macroscopic” monopolar or bipolar derivations. EMG rectification reduced the CMC peak by a quarter, resulted in a more uniformly distributed CMC across the thenar, and provided more tightly clustered cortical sources than unrectifed sEMGs. Moreover, it revealed CMC at ∼12 Hz. We conclude that HD-sEMG, especially with monopolar derivation, can facilitate detection of CMC and that individual muscle anatomy cannot explain the high interindividual CMC variability.

KEYWORDS:

corticomuscular coherence; magnetoencephalography; multichannel EMG; sensorimotor cortex; spatial filter

PMID:
26354317
PMCID:
PMC4737422
DOI:
10.1152/jn.00574.2015
Spatial variation of compound muscle action potentials across human gastrocnemius medialis. Vieira TM, Botter A, Minetto MA, Hodson-Tole EF. J Neurophysiol. 2015 Sep;114(3):1617-27. doi: 10.1152/jn.00221.2015. Epub 2015 Jul 8.
2015 Sep;114(3):1617-27. doi: 10.1152/jn.00221.2015. Epub 2015 Jul 8.

Spatial variation of compound muscle action potentials across human gastrocnemius medialis.

Abstract

The massed action potential (M wave) elicited through nerve stimulation underpins a wide range of physiological and mechanical understanding of skeletal muscle structure and function. Although systematic approaches have evaluated the effect of different factors on M waves, the effect of the location and distribution of activated fibers within the muscle remains unknown. By detecting M waves from the medial gastrocnemius (MG) of 12 participants with a grid of 128 electrodes, we investigated whether different populations of muscle units have different spatial organization within MG. If populations of muscle units occupy discrete MG regions, current pulses of progressively greater intensities applied to the MG nerve branch would be expected to lead to local changes in M-wave amplitudes. Electrical pulses were therefore delivered at 2 pps, with the current pulse amplitude increased every 10 stimuli to elicit different degrees of muscle activation. The localization of MG response to increases in current intensity was determined from the spatial distribution of M-wave amplitude. Key results revealed that increases in M-wave amplitude were detected somewhat locally, by 10-50% of the 128 electrodes. Most importantly, the electrodes detecting greatest increases in M-wave amplitude were localized at different regions in the grid, with a tendency for greater stimulation intensities to elicit M waves in the more distal MG region. The presented results indicate that M waves recorded locally may not provide a representative MG response, with major implications for the estimation of, e.g., the maximal stimulation levels, the number of motor units, and the onset and normalization in H-reflex studies.

KEYWORDS:

M wave; electrical stimulation; medial gastrocnemius; motor units; surface EMG

PMID:
26156382
PMCID:
PMC4563026
DOI:
10.1152/jn.00221.2015
Examination of Poststroke Alteration in Motor Unit Firing Behavior Using High-Density Surface EMG Decomposition. Li X, Holobar A, Gazzoni M, Merletti R, Rymer WZ, Zhou P. IEEE Trans Biomed Eng. 2015 May;62(5):1242-52. doi: 10.1109/TBME.2014.2368514. Epub 2014 Nov 7.
2015 May;62(5):1242-52. doi: 10.1109/TBME.2014.2368514. Epub 2014 Nov 7.

Examination of Poststroke Alteration in Motor Unit Firing Behavior Using High-Density Surface EMG Decomposition.

Abstract

Recent advances in high-density surface electromyogram (EMG) decomposition have made it a feasible task to discriminate single motor unit activity from surface EMG interference patterns, thus providing a noninvasive approach for examination of motor unit control properties. In the current study, we applied high-density surface EMG recording and decomposition techniques to assess motor unit firing behavior alterations poststroke. Surface EMG signals were collected using a 64-channel 2-D electrode array from the paretic and contralateral first dorsal interosseous (FDI) muscles of nine hemiparetic stroke subjects at different isometric discrete contraction levels between 2 to 10 N with a 2 N increment step. Motor unit firing rates were extracted through decomposition of the high-density surface EMG signals and compared between paretic and contralateral muscles. Across the nine tested subjects, paretic FDI muscles showed decreased motor unit firing rates compared with contralateral muscles at different contraction levels. Regression analysis indicated a linear relation between the mean motor unit firing rate and the muscle contraction level for both paretic and contralateral muscles (p < 0.001), with the former demonstrating a lower increment rate (0.32 pulses per second (pps)/N) compared with the latter (0.67 pps/N). The coefficient of variation (averaged over the contraction levels) of the motor unit firing rates for the paretic muscles (0.21 ± 0.012) was significantly higher than for the contralateral muscles (0.17 ± 0.014) (p < 0.05). This study provides direct evidence of motor unit firing behavior alterations poststroke using surface EMG, which can be an important factor contributing to hemiparetic muscle weakness.

PMID:
25389239
PMCID:
PMC4406795
DOI:
10.1109/TBME.2014.2368514
Variations in the spatial distribution of the amplitude of surface electromyograms are unlikely explained by changes in the length of medial gastrocnemius fibres with knee joint angle. Avancini C, de Oliveira LF, Menegaldo LL, Vieira TM. PLoS One. 2015 May 22;10(5):e0126888. doi: 10.1371/journal.pone.0126888. eCollection 2015
2015 May 22;10(5):e0126888. doi: 10.1371/journal.pone.0126888. eCollection 2015.

Variations in the spatial distribution of the amplitude of surface electromyograms are unlikely explained by changes in the length of medial gastrocnemius fibres with knee joint angle.

Author information

1
Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
2
Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil; Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
3
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Politecnico di Torino, Torino, TO, Italia.

Abstract

This study investigates whether knee position affects the amplitude distribution of surface electromyogram (EMG) in the medial gastrocnemius (MG) muscle. Of further concern is understanding whether knee-induced changes in EMG amplitude distribution are associated with regional changes in MG fibre length. Fifteen surface EMGs were acquired proximo-distally from the MG muscle while 22 (13 male) healthy participants (age range: 23-47 years) exerted isometric plantar flexion at 60% of their maximal effort, with knee fully extended and at 90 degrees flexion. The number of channels providing EMGs with greatest amplitude, their relative proximo-distal position and the EMG amplitude averaged over channels were considered to characterise changes in myoelectric activity with knee position. From ultrasound images, collected at rest, fibre length, pennation angle and fat thickness were computed for MG proximo-distal regions. Surface EMGs detected with knee flexed were on average five times smaller than those collected during knee extended. However, during knee flexed, relatively larger EMGs were detected by a dramatically greater number of channels, centred at the MG more proximal regions. Variation in knee position at rest did not affect the proximo-distal values obtained for MG fibre length, pennation angle and fat thickness. Our main findings revealed that, with knee flexion: i) there is a redistribution of activity within the whole MG muscle; ii) EMGs detected locally unlikely suffice to characterise the changes in the neural drive to MG during isometric contractions at knee fully extended and 90 degrees flexed positions; iii) sources other than fibre length may substantially contribute to determining the net, MG activation.

PMID:
26001107
PMCID:
PMC4441502
DOI:
10.1371/journal.pone.0126888
The effect of lymph drainage on the myoelectric manifestation of vastus lateralis fatigue: Preliminary results. Vieira TM, Readi NG, Schwarcke L, Botter A. Conf Proc IEEE Eng Med Biol Soc. 2015;2015:6671-4. doi: 10.1109/EMBC.2015.7319923.
2015;2015:6671-4. doi: 10.1109/EMBC.2015.7319923.

The effect of lymph drainage on the myoelectric manifestation of vastus lateralis fatigue: Preliminary results.

Abstract

Variations in surface electromyograms (EMGs) collected from the vastus lateralis muscle during isometric fatiguing contractions were investigated pre-post lymphatic drainage (intervention group, N=3) and pre-post rest (control group, N=3). The slope of conduction velocity and of EMG amplitude and spectral descriptors was computed from the start to the failure time; the instant after which subjects could not endure contractions. When compared to subjects in the control group, those in the intervention group endured longer. Similarly, muscle fatigue affected to a lesser extent EMGs following lymphatic drainage than following rest. These preliminary results suggest the lymphatic drainage may potentially delay muscle fatigue.

PMID:
26737823
DOI:
10.1109/EMBC.2015.7319923
High Density EMG investigation of H-reflex distribution over the soleus muscle. Botter A, Vazzoler I, Vieira TM. Conf Proc IEEE Eng Med Biol Soc. 2015 Aug;2015:3460-3. doi: 10.1109/EMBC.2015.7319137
2015 Aug;2015:3460-3. doi: 10.1109/EMBC.2015.7319137.

High Density EMG investigation of H-reflex distribution over the soleus muscle.

Abstract

The spatial distribution of H-reflexes over soleus muscle was investigated through High-Density EMG in five healthy subjects. The posterior tibial nerve was stimulated with a staircase current envelope with 1mA steps. The regions where the incremental responses (incremental H-reflexes) occurred were identified for each stimulation step with a validated segmentation algorithm. The average centroid of the segmented areas was located over the Achilles tendon, 5 cm below the myo-tendinous junction of the medial gastrocnemius. The average dimension of these regions corresponded to 28% of the surface covered by the grid of electrodes. The amplitude of H-reflexes recorded in the segmented areas was higher than the average amplitude computed over the entire detection system as well as the H-reflex recorded by the electrode positioned according to SENIAM guidelines. These preliminary results suggest that: i) H-reflex detected from a specific soleus region unlikely reflects the whole muscle volume and ii) H-reflexes with greatest amplitude can be recorded over the Achilles tendon.

PMID:
26737037
DOI:
10.1109/EMBC.2015.7319137
Power line interference attenuation in multi-channel sEMG signals: Algorithms and analysis. Soedirdjo SD, Ullah K, Merletti R. Conf Proc IEEE Eng Med Biol Soc. 2015 Aug;2015:3823-6. doi: 10.1109/EMBC.2015.7319227.
2015 Aug;2015:3823-6. doi: 10.1109/EMBC.2015.7319227.

Power line interference attenuation in multi-channel sEMG signals: Algorithms and analysis.

Abstract

Electromyogram (EMG) recordings are often corrupted by power line interference (PLI) even though the skin is prepared and well-designed instruments are used. This study focuses on the analysis of some of the recent and classical existing digital signal processing approaches have been used to attenuate, if not eliminate, the power line interference from EMG signals. A comparison of the signal to interference ratio (SIR) of the output signals is presented, for four methods: classical notch filter, spectral interpolation, adaptive noise canceller with phase locked loop (ANC-PLL) and adaptive filter, applied to simulated multichannel monopolar EMG signals with different SIR. The effect of each method on the shape of the EMG signals is also analyzed. The results show that ANC-PLL method gives the best output SIR and lowest shape distortion compared to the other methods. Classical notch filtering is the simplest method but some information might be lost as it removes both the interference and the EMG signals. Thus, it is obvious that notch filter has the lowest performance and it introduces distortion into the resulting signals.

PMID:
26737127
DOI:
10.1109/EMBC.2015.7319227
Modulation of tibialis anterior muscle activity changes with upright stance width. Lemos T, Imbiriba LA, Vargas CD, Vieira TM. J Electromyogr Kinesiol. 2015 Feb;25(1):168-74. doi: 10.1016/j.jelekin.2014.07.009. Epub 2014 Aug 8.
2015 Feb;25(1):168-74. doi: 10.1016/j.jelekin.2014.07.009. Epub 2014 Aug 8.

Modulation of tibialis anterior muscle activity changes with upright stance width.

Author information

1
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, RJ, Brazil. Electronic address: lemoscarvalho.thiago@gmail.com.
2
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, RJ, Brazil.
3
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, RJ, Brazil.
4
Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, RJ, Brazil; Laboratorio di Ingegneria del Sistema Neuromuscolare, Politecnico di Torino, Torino, Italy.

Abstract

When individuals stand with their feet apart, activation of tibialis anterior (TA) muscle seems to slightly exceed rest levels. In narrow stances, conversely, the stabilization of body lateral sways may impose marked, active demand on ankle inversors/eversors. In this study we investigate how much the modulation in TA activity, associated to center of pressure (COP) lateral sways, changes when stance width reduces. Surface EMG and COP coordinates were collected from 17 subjects at three different stances: feet apart, feet together and tandem. Pearson correlation analysis was applied to check whether the expected greater modulations in TA activity corresponded to a stronger association between fluctuations in EMG amplitude and COP lateral sways. When standing at progressively narrower stances participants showed larger fluctuations in COP lateral sways (p<0.01) and higher EMG-COP association (p<0.01); marked increases in TA activity were only observed in tandem stance (p<0.001). Interestingly, more pronounced modulations in TA activity were observed for subjects showing greater association between EMG amplitude and COP sways in feet together and tandem stance (Pearson R>0.56, p<0.02), though not when standing with feet apart (R=-0.22, p=0.40). These results indicate that the contribution of TA activity to lateral sway control increases for narrower stances.

KEYWORDS:

Posture control; Stance width; Surface EMG; Tibialis anterior

PMID:
25156446
DOI:
10.1016/j.jelekin.2014.07.009

   2006-2010

Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing. Afsharipour B, Petracca F, Gasparini M, Merletti R. J Electromyogr Kinesiol. 2016 Dec;31:144-153
2016 Dec;31:144-153. doi: 10.1016/j.jelekin.2016.10.003. Epub 2016 Oct 31.

Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing.

Author information

1
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, United States; Department of Physical Medicine and Rehabilitation of Northwestern University, United States; Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: babak.afsharipour@northwestern.edu.
2
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: fra.petra.fp@gmail.com.
3
Department of Mathematical Sciences, Politecnico di Torino, Torino, Italy. Electronic address: mauro.gasparini@polito.it.
4
Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Politecnico di Torino, Torino, Italy. Electronic address: roberto.merletti@polito.it.

Abstract

Musicians activate their muscles in different patterns, depending on their posture, the instrument being played, and their experience level. Bipolar surface electrodes have been used in the past to monitor such activity, but this method is highly sensitive to the location of the electrode pair. In this work, the spatial distribution of surface EMG (sEMG) of the right trapezius and right and left erector spinae muscles were studied in 16 violin players and 11 cello players. Musicians played their instrument one string at a time in sitting position with/without backrest support. A 64 sEMG electrode (16×4) grid, 10mm inter-electrode distance (IED), was placed over the middle and lower trapezius (MT and LT) of the bowing arm. Two 16×2 electrode grids (IED=10mm) were placed on the left and right erector spinae muscles. Subjects played each of the four strings of the instrument either in large (1bow/s) or detaché tip/tail (8bows/s) bowing in two sessions (two days). In each of two days, measurements were repeated after half an hour of exercise to see the effect of exercise on the muscle activity and signal stability. A “muscle activity index” (MAI) was defined as the spatial average of the segmented active region of the RMS map. Spatial maps were automatically segmented using the watershed algorithm and thresholding. Results showed that, for violin players, sliding the bow upward from the tip toward the tail results in a higher MAI for the trapezius muscle than a downward bow. On the contrary, in cello players, higher MAI is produced in the tail to tip movement. For both instruments, an increasing MAI in the trapezius was observed as the string position became increasingly lateral, from string 1 (most medial) toward string 4 (most lateral). Half an hour of performance did not cause significant differences between the signal quality and the MAI values measured before and after the exercise. The MAI of the left and right erector spinae was smaller in the case of backrest support, especially for violin players. Back muscles of violin and cello players were activated asymmetrically, specifically in fast movements (detaché tip/tail). These findings demonstrate the sensitivity and stability of the technique and justify more extensive investigation following this proof of concept.

KEYWORDS:

Cello; Erector spinae; High density surface electromyography (HDsEMG); Musicians; String players; Surface EMG; Trapezius; Violin

PMID:
27835831
DOI:
10.1016/j.jelekin.2016.10.003