Anterior Electromyography Research Articles

Changes in neural modulation and motor control during voluntary movement of older individuals.

Changes in the modulation of soleus alpha motoneuron excitability, as assessed by H reflexes, and temporal sequencing of the soleus and tibialis anterior muscles during voluntary ankle dorsiflexions and plantar flexions of young (24.7 +/- 11.5; n = 13) and older (68.7 +/- 5.4; n = 13) subjects were assessed to determine potential neural mechanisms that might contribute to motor control changes associated with aging. A repetitive stimulation (5 Hz) soleus H-reflex testing protocol and surface electromyography (EMG) were used to assess the latencies of soleus H-reflex changes in relation to tibialis anterior and soleus EMG activations of standing subjects during voluntary ankle dorsiflexions and plantar flexions at self-selected speeds. The pattern and latency of H-reflex changes in relation to EMG activity were compared between young and old subjects. There were no differences in the relative amount of antagonist muscle (soleus) inhibition during voluntary ankle dorsiflexions between young and old subjects (26.4% and 27.2% decrease from resting H-reflex values, respectively). Older subjects, however, required additional time to achieve these levels of inhibition. Delays in the activation of soleus H reflexes during the plantar flexion task were also observed in older subjects. Older subjects also had considerable intra- and intersubject variability in muscle temporal sequencing patterns during ankle plantar flexions. Although older subjects exhibited similar relative levels of alpha motoneuron inhibition and excitation during voluntary movements, this modulation was delayed when compared to younger subjects. Temporal sequencing of distal muscle activations also appears to undergo change with aging.

Hypoglossal neural activity during ingestion and rejection in the awake rat.

1. The activity of 34 hypoglossal (mXII) neurons was characterized during the ingestion and rejection of gustatory stimuli in the awake rat. Intraoral infusions of water, sucrose, sodium chloride, or hydrochloric acid initiated ingestion responses; infusions of quinine monohydrochloride initiated rejection responses. Electromyographic (EMG) activity from three oropharyngeal muscles monitored the occurrence of lick cycles and swallows (ingestion) and gape cycles (rejection). In addition, the orofacial region was videotaped to provide an independent assessment of lingual and jaw movements in relation to neural activity. 2. EMG activity during lick and gape cycles was quantified by calculating the duration, magnitude, and peak time of muscle contractions. Lick and gape cycles produced highly differentiated patterns of activity from jaw-opener (anterior digastric, AD), lingual protrudor (geniohyoid, GEN), and lingual retractor (styloglossus, STY) muscles. Lick cycles were characterized by an alternating two-phase sequence of protrusion-retraction; gape cycles by an initial coactivation of both lingual muscles (phase I), followed by a sequence of protrusion (phase II) and retraction (phase III). Contraction durations were significantly longer during gape cycles compared with lick cycles for the AD (Xlick +/- 59 ms; Xgape +/- 134 ms, means +/- SD), GEN (Xlick +/- 77 ms; Xgape +/- 200 ms), and STY (Xlick +/- 93 ms; Xgape +/- 220 ms) muscles. 3. Thirty-one out of 34 mXII neurons were functionally classified as protrudor- or retractor-related by cross-correlating anterior digastric EMG activity with neural activity during licking. Fourteen out of 34 neurons were protrudor-related, 17/34 were retractor-related. These classifications were largely consistent with the results from an analysis of a subset of cells (n = 14) that directly compared neural activity with videotaped records of visible tongue movements. 4. The magnitude of mXII activity during ingestion and rejection was compared by determining the mean number of spikes per lick, gape, and swallow for each neuron. Five out of 14 (36%) protrudor-related and 10/17 (59%) retractor-related cells had significant increases in activity during gape responses compared with the number of spikes per lick cycle. This increased activity of mXII neurons was consistent with the more robust lingual motor activity during the gape response. Two protrudor-related and three retractor-related neurons showed significant decreases in activity during gape responses. Although a similar proportion of mXII neurons exhibited decreases in activity during swallows compared with licks (3 protrudor- and 1 retractor-related), fewer mXII neurons (1 protrudor- and 1 retractor-related) showed increased activity during swallows.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of visuoproprioceptive mismatch on postural adjustments

The influence of visual input upon body stabilization was studied with subjects standing on a treadmill while a visual flow pattern was displayed. Both the treadmill and image were moved sinusoidally - backward/forward — at a frequency of 0.25 Hz. The effect of the presentation of the visual pattern was studied upon leg muscle electromyographic (EMG) activity and corresponding biomechanical signals for various phase shifts (45–360 degrees) between movements of the legs and the visual flow pattern. Around the posterior turning point of sinusoidal treadmill movement, i.e. at times when there is an anticipatory forward positioning of the body, a modulation of the tibialis anterior EMG was observed. The onset, duration, and amplitude of the latter were dependent upon the phase shift between the movements of the legs and the visual pattern. Maximum responses were recorded at phase shifts of 90270 degrees and minimum responses at phase shifts of 180360 degrees. Therefore a coincidence of fast velocities of the visual flow pattern with a phase of maximal body acceleration evoked the strongest tibialis anterior EMG responses. At times around the anterior turning point a modulation only of EMG amplitude occurred in the gastrocnemius muscle. This activity is believed to be linked to the preceding tibialis anterior EMG resulting in ‘resetting’ of the neutral body position. It is suggested that the tibialis anterior is more sensitive than the gastrocnemius muscle to a visual stimulus. The activity of the latter muscle with its antigravity function is more subject to proprioceptive input. Little adaptational changes in EMG pattern occurred between the second and fifth sway cycles after presentation of the optical flow pattern. It is assumed that task-specific factors act against early adaptation.

Masticatory electromyographic activity in healthy young adults and myogenous craniomandibular disorder patients.

The electromyographic (EMG) activity of the masseter and the anterior temporalis muscles were compared between 60 healthy controls and 61 myogenous craniomandibular disorder (CMD) patients. Subjects were asked to clench at 10% and at 50% of their maximum voluntary clenching level. The effects of CMD, age and gender were statistically analysed with the use of the analysis of covariance. The correlations between EMG asymmetries and the lateral slide from the retruded contact position to the intercuspal position and the asymmetry in the number of post-canine tooth contacts between the left and the right side were investigated. The CMD patients showed lower masseter EMG activities than the controls, whereas the anterior temporalis EMG activity was not different between the two groups. The activity index, relating the anterior temporalis EMG activity to the activity of the masseter muscles, confirmed the presence of a relatively high temporalis activity in the CMD group. No significant differences were found in the EMG asymmetries between the controls and the CMD patients. Males showed higher masticatory EMG activities than females. These gender effects were significant for the anterior temporalis at the 10% and 50% level and for the masseter muscle at the 10% level. The anterior temporalis EMG activity declined with age. No age related effects were observed in the masseter EMG. The lateral slide was larger and more prevalent in the CMD group. A significant correlation between the lateral slide and the anterior temporalis EMG was found for the CMD group at the 10% level. No correlation was found between the EMG asymmetry and the asymmetries in post-canine tooth contacts. significant CMD, age and gender effects were observed in the masticatory EMG activities of a group of myogenous CMD patients and a control group.

Performance of a Reservoir Nasal Cannula (Oxymizer) During Sleep in Hypoxemic Patients With COPD

To determine whether a reservoir nasal cannula (RNC) (Oxymizer) provides an arterial hemoglobin oxygen saturation as measured by pulse oximetry (SpO2) equivalent to that provided by the standard nasal cannula (SNC) during sleep in hypoxemic patients with COPD while reducing oxygen flow requirement and cost. The study took place in a sleep laboratory for three nights, with the first night for acclimatization to the new sleeping environment. In a repeated-measures design, on the second and third nights, subjects used the SNC for one night and the RNC on another night. The order in which they received the two devices was counterbalanced. The subjects were patients with COPD who had a stable PaO2 of 55 mm Hg or less or had a value of 56 to 59 mm Hg with evidence of cor pulmonale or polycythemia (or both) and an FEV1/FVC of less than 70 percent. A pulse oximeter was used to measure SpO2. An arterial blood gas measurement was taken on each night while the patients with COPD were receiving oxygen therapy via the assigned device. An EEG machine was used to record measurements of electro-oculography, chin electromyography (EMG), anterior tibialis EMG and EEG. There was a statistically significant difference between mean SpO2 during sleep (RNC, 91 percent; SNC, 93 percent; F = 7.89; p = 0.01). Nocturnal SpO2 was less than 90 percent for 24.2 percent of the time with the RNC and for 17.5 percent of the time with the SNC (F = 5.41; p = 0.03), but there was no significant difference in the amount of time that SpO2 was less than 85 percent. Compared to the SNC, in 4 of 26 patients with COPD, the RNC performed better; in 12 patients with COPD, the RNC performed the same, and in 10 patients with COPD the RNC performed worse during sleep. Sleep parameters were not significantly different between the two devices. The difference of 2 percent in mean SpO2 is within the range of SpO2 measurement error. Therefore, the two devices are equally effective when the sample is considered as a whole. Nighttime oximetry is necessary prior to prescription, since nighttime efficacy of the RNC cannot be predicted on the basis of daytime pulse oximetry.

Evaluation of methods to minimize cross talk in surface electromyography

The purposes of this study were to quantify the effectiveness of various methods to minimize cross talk in surface electromyography (EMG) using common recording equipment, and to compare the intra- and interday variabilities of signals recorded with these methods. Comparisons were made for signals recorded with the single differential (SD), double differential (DD) and branched electrode (BE) techniques with large and small electrodes and corresponding interelectrode distances. The amount of cross talk in tibialis anterior EMG signals during maximum voluntary effort (MVE) triceps surae excitation was estimated using a protocol involving electrical stimulation of the triceps surae via the tibial nerve. In SD signals, cross talk averaged 12.2 and 10.2 percent MVE, for the large and small interelectrode distances, respectively. DD and BE signals contained significantly less cross talk (approximately 5 percent MVE for both techniques and interelectrode distances) than SD signals. The intra- and interday variabilities associated with these methods were estimated by recording tibialis anterior EMG signals during maximum voluntary isometric dorsiflexion (3 trials on each of 2 days) and calculating coefficients of variation for average-rectified values and median frequencies. EMG signals recorded with the small interelectrode distance showed greater interday amplitude variability than those recorded with the large interelectrode distance. Intra- and interday amplitude variabilities were similar across SD, DD and BE recording techniques. Intra- and interday frequency variabilities were similar across all experimental conditions. Thus, the DD and BE techniques, in conjunction with the large interelectrode distance (and large electrodes), provide a signal which contains significantly less cross talk than the SD technique without sacrificing intra- and interday amplitude and frequency stability.

Hypoglossal neural activity during licking and swallowing in the awake rat.

1. Thirty-five neurons in the hypoglossal nucleus (mXII) of the rat were characterized during licking and swallowing in response to fluid stimulation in an awake, freely moving preparation. Simultaneously recorded electromyographic (EMG) recordings from a subset of oropharyngeal muscles were obtained to delineate both the lick cycle and the occurrence of swallows. Most mXII neurons discharged with rhythmic bursts in phase with licking. Twenty-six of the 35 mXII neurons had bimodal interspike interval (ISI) histograms, reflecting rhythmic bursts and the absence of spontaneous activity. Three mXII cells with unimodal ISI histograms were rhythmically active during licking but had some spontaneous activity. Of the remaining six cells with unimodal ISI histograms, five had nonbursting modes of activity. 2. Phase relationships between neural and EMG activity during licking were determined by cross-correlation and compared with distributions of cross-correlations between lingual and masticatory EMG activity. A bimodal distribution of cross-correlations was obtained by cross-correlating EMG activity between lingual protrudor muscles [genioglossus (GG) or geniohyoid (GH)] and masticatory jaw-opener activity [anterior digastric (AD)] and cross-correlating lingual retractor activity [styloglossus (STY)] with anterior digastric EMG. A similar bimodal distribution of cross-correlations obtained between mXII neuron activity and AD contractions suggested that the majority of mXII neurons (30/35) could be classified as protrudor- or retractor-related. Neurons classified as protrudor-related cells were located ventrally in mXII; cells classified as retractor-related were more dorsally located, consistent with anatomic and physiological descriptions of the myotopic organization of mXII. 3. Ten mXII protrudor-related neurons responded with a mean of 4.9 +/- 2.2 (SD) action potentials per lick cycle and preceded the peak jaw-opening phase of licking by a mean of 22.3 ms. In contrast, the activity of 20 retractor-related mXII neurons lagged the jaw-opening phase of licking by a mean of 55.9 ms, with a mean of 5.5 +/- 3.4 (SD) action potentials occurring per lick cycle. Five other mXII neurons exhibited nonrhythmic activity during licking and could not be classified as protrudor- or retractor-related on the basis of cross-correlations with the AD. 4. The occurrence of a swallow decreased the licking frequency by 21%, corresponding to an increase of approximately 43 ms in the period between AD contractions.(ABSTRACT TRUNCATED AT 400 WORDS)

Chapter 34 Significance of proprioceptive mechanisms in the regulation of stance

Compensatory electromyographic (EMG) responses and several biomechanical parameters were studied following impulsive disturbance of the limbs during stance of human volunteers on a treadmill. Treadmill acceleration impulses were backwards or forwards directed, or their initial direction was reversed after 30 ms. Backwards directed impulses were followed by gastrocnemius, forwards directed ones by tibialis anterior EMG responses (latency 65 to 75 ms) whose durations depended on impulse duration. When the direction of the impulse was reversed, the respective antagonistic leg muscles were activated again with a delay of 68 to 75 ms after onset of stretch of these muscles. The behaviour of the EMG responses could best be correlated to the displacement at the ankle joint and may be described in terms of a stretch reflex response. The results indicate that these stretch reflex responses help control of the body's centre of gravity thereby preventing falling. Head movements induced by the impulses showed little correlation with the appearance of the EMG responses, suggesting that the vestibular system is unlikely to be directly involved in the generation of these responses. Vestibular signals may, however, significantly contribute to slow body sway stabilization.

Involvement of different receptors in the regulation of human posture.

Compensatory electromyographic (EMG) responses and several biomechanical parameters were studied following impulsive disturbance of the lower limbs during stance on a treadmill. Treadmill acceleration impulses were backwards or forwards directed, or their direction was inverted after 30 ms. Backwards directed impulses were followed by gastrocnemius and forwards directed ones by tibialis anterior EMG responses (latency 65-75 ms) whose duration depended on impulse duration. When the direction of the impulse was inverted, the respective antagonistic leg muscles were activated, with a delay of 68 to 75 ms after onset of stretch of these muscles. The behaviour of the EMG responses could best be correlated to the displacement at the ankle joint and may be described in terms of a stretch reflex response. The function of this stretch reflex mechanism is suggested to be connected with the control of the body's centre of gravity in order to prevent falling. Head movements induced by the impulses showed little correlation with the appearance of the EMG responses, suggesting that the vestibular system is unlikely to be significantly involved in the generation of these responses.

Contour analysis of masticatory jaw movements and muscle activity in Macaca mulatta

AbstractFrontal plane mandibular movements during mastication and the associated electromyographic (EMG) activity for left and right superficial masseter, posterior temporalis, anterior temporalis, and anterior belly of the digastric (ABD) were studied for two adult male Macaca mulatta by the new technique of “contour” analysis. Contour analysis allowed graphic and quantitative portrayal of multiple chew cycle patterns of mandibular movement and EMG activity during active mastication. A series of computer programs (ATS, ATSED, ATSXYZ) facilitated the collection, editing and definition, and finally processing of these masticatory data into contour plots. These preliminary data indicated the essential symmetry of mandibular movement patterns, high chew cycle variability inferior to occlusion, multiple centers of intense EMG activity for balancing‐side superficial masseter, and no difference between working‐side anterior and posterior temporalis EMG patterns. Maximum EMG amplitude was found in the area of buccal phase power stroke (BPS). Maximum EMG amplitude for ABD was located medial and inferior to occlusion; all other muscle maximum amplitudes were buccal and inferior to occlusion. The location of maximum EMG amplitudes for superficial masseter and ABD were closer to occlusion (more superior) during mastication of carrot than were maximum amplitudes during biscuit mastication. The absence of any detectable shift of EMG maximum amplitude location between biscuit and carrot for posterior and anterior temporalis suggested, along with the continuous EMG activity of working‐side posterior temporalis, a secondary role for the temporalis (compensation for superficial masseter activity) during active mastication.

Incentives to enhance the effects of electromyographic Feedback Training in stroke patients

The use of monetary incentives to enhance the effects of electromyographic (EMG) feedback training was studied in five stabilized stroke patients with hemiplegia. The study was divided into Baseline, EMG Feedback Training, Feedback Training Plus Incentives, and Follow-up treatment conditions. Integrated EMG activity was recorded simultaneously from the anterior tibialis and medial gastrocnemius muscles during relaxation and dorsiflexion of the affected foot. Patients were instructed to try to increase anterior tibialis EMG activity while decreasing EMG activity in the medial gastrocnemius. Range of motion was measured both prior to and immediately following the Baseline and Feedback Training conditions. Results suggested that (a) EMG feedback training produced greater EMG control and range of motion than did unassisted practice, and (b) the addition of monetary incentives may enhance the effects of feedback training, possibly through its effect on patient motivation.