EMG Output Research Articles

Effector dynamics of rhythmic wrist activity and its implications for (modeling) bimanual coordination

To examine the role of the effector dynamics of the wrist in the production of rhythmic motor activity, we estimated the phase shifts between the EMG and the task-related output for a rhythmic isometric torque production task and an oscillatory movement, and found a substantial difference (45–52°) between the two. For both tasks, the relation between EMG and task-related output (torque or displacement) was adequately reproduced with a physiologically motivated musculoskeletal model. The model simulations demonstrated the importance of the contribution of passive structures to the overall dynamics and provided an account for the observed phase shifts in the dynamic task. Additional simulations of the musculoskeletal model with added load suggested that particular changes in the phase relation between EMG and movement may follow largely from the intrinsic muscle dynamics, rather than being the result of adaptations in the neural control of joint stiffness. The implications of these results are discussed in relation to (models of) interlimb coordination in rhythmic tasks.

The effects of intraoral splints on the masticatory system of pigs.

While evidence exists to support the effectiveness of splints on conditions involving the masticatory musculature, few research projects have examined the results of long-term splint wear. The purpose of this study was to examine the function of the masticatory system over a 2-month time period of splint wear. Young adult female miniature pigs were divided into three groups: a control (C) group that wore no intraoral splint, a control splint (CS) group that wore a splint increasing bite height, and a protrusive splint (PS) group that wore a splint increasing bite height and moving the mandible anteriorly. Splints were worn constantly. Fine-wire needle EMG was performed prior to splint delivery and at 1 and 2 months post-splint delivery. Bilateral superficial masseters and zygomaticomandibularis (ZM, equivalent to deep masseter) muscles were monitored during normal feeding. Absolute EMG output, percentage output, and cycle timing were unaffected by chronic splint wear. However, chewing coordination was significantly changed in the splinted groups in both sessions post-splint delivery relative to baseline readings and to the C group (P < 0.005). Trends indicate that the coordination of the PS group was more greatly altered than that of the CS group.

オンオフ型およびバイオミメティック型筋電義手の3D-CGシミュレータの開発

Some kinds of myoelectric prosthetic hand, which use myoelectric signals (EMGs) of muscles as control signals for opening and closing, are used to replace the functions of a natural hand lost by amputation. Chances for an amputee to watch, touch, and use a myoelectric hand are very rare in Japan, because few hospitals give information on them and are provided with actual myoelectric hands. A simulator of a myoelectric hand can enable an amputee to use myoelectric hands virtually. The purpose of this study is to develop a 3 D-CG (three-dimensional computer graphics) simulator of an on-off control myoelectric hand and a biomimetic myoelectric hand. The former is produced by Otto Bock, and the latter was developed by our group. Both prosthetic hands are one-degree-of-freedom units with simultaneous opening and closing of thumb, index, and middle fingers. In the on-off control hand, either opening or closing is determined by the EMG amplitudes of flexor and extensor muscles. In the biomimetic hand, both the finger angle and the compliance are controlled by the EMGs. First, in this simulator, the EMGs are detected with special surface electrodes used for each hand. Second, the finger angle of the prosthetic hand is calculated from the EMGs with the model. Third, positions of the subject's upper limb are measured. Finally, the hand and the upper limb are displayed with 3 D-CG. It was found, in the on-off control hand, that the rate of change of finger angle was dependent on the finger angle. We constructed a model of the on-off control hand; the rate of angle change was determined from the output of the EMG electrode and the present finger angle. Using this model, the finger angle was calculated from the EMG electrode output and the initial finger angle. In the model of the biomimetic hand, an ideal relation between EMG input and finger angle output was utilized, although the real biomimetic myoelectric hand had complex nonlinear properties, such as friction and saturation. Using the model, the finger angle was calculated from the EMG output of the surface electrode. The positions of shoulder, elbow, and wrist were observed with a three-dimensional position sensor, and the posture of the upper limb was calculated. In this simulator, the posture of the upper limb was drawn with a stick picture and the orientation of the prosthetic hand was displayed with 3 D-CG. The experiment was conducted on normal subjects. Watching the 3D-CG of the simulator, they could easily control the finger angle and orientation of the hand.

Human Cerebral Potentials During Motor Training Under Different Forms of Sensory Feedback

Abstract In two experiments with four and two groups of healthy subjects, a novel motor task, the voluntary abduction of the right big toe, was trained. This task cannot usually be performed without training and is therefore ideal for the study of elementary motor learning. A systematic variation of proprioceptive, tactile, visual, and EMG feedback was used. In addition to peripheral measurements such as the voluntary range of motion and EMG output during training, a three-channel EEG was recorded over Cz, C3, and C4. The movement-related brain potential during distinct periods of the training was analyzed as a central nervous parameter of the ongoing learning process. In experiment I, we randomized four groups of 12 subjects each (group P: proprioceptive feedback; group PT: proprioceptive and tactile feedback; group PTV: proprioceptive, tactile, and visual feedback; group PTEMG: proprioceptive, tactile, and EMG feedback). Best training results were reported from the PTEMG and PTV groups. The movement-preceding cortical activity, in the form of the amplitude of the readiness potential at the time of EMG onset, was greatest in these two groups. Results of experiment II revealed a similar effect, with a greater training success and a higher electrocortical activation under additional EMG feedback compared to proprioceptive feedback alone. Sensory EMG feedback as evaluated by peripheral and central nervous measurements appears to be useful in motor training and neuromuscular re-education.

A Longitudinal Study of the Upper Airway Negative Pressure Reflex in Newborn Lambs. 1498

It has been previously shown that the activity of the neonatal Genioglossus(GG) muscle reflexly increases only in response to large amounts of upper airway negative pressure (UANP) in lambs (Duara, Ped Res: 4:331A,1994), in comparison to the small amounts needed to activate the GG in adults. In order to evaluate maturation of the UANP reflex in lambs, we hypothesized that onset of the adult pattern would coincide with the onset of another developmental marker, namely rumination, at 3-4 weeks of age. Because hypoxia increases respiratory muscles activity, we also hypothesized that hypoxia would potentiate the UANP reflex. Therefore, we studied seven chronically instrumented lambs shortly after birth (study 1: mean±SD age 10.6±0.48 days & weight 5.47±0.43 kg) and again at approximately 1 month of age (study 2: mean±SD age 25.1 ± 0.7 days & weight 8.14 ± 0.43 kg). During surgery, EMG wires were placed in the diaphragm and GG and a mid-cervical tracheal stoma was created. The animals were allowed to recover for 24-48 hours prior to study 1. Isolated upper airways (UA) were evaluated while awake lambs were allowed to breathe through tracheostomies. End-expiratory NP of different magnitudes (-5, -10,-20, -40 cm H2O) were randomly applied to the isolated UA for 3 breaths, or 3 seconds if apnea was induced, in room air (RA) and hypoxia (10% O2 through the tracheostomy for 7-10 min). EMG activity of the GG was quantified as average activity (AvAc, area under the curve/duration) derived from the moving time average of phasic EMG output. Results revealed that there was a significant increase in the GG response in relationship to increasing magnitudes of UANP in both study 1 and study 2 (p<0.05). Hypoxia induced a significant increase in GG activity in both studies (<0.05). However, there was no significant increase in GG activity with small amounts of NP (-5 cm H2O) in either study, and hypoxia did not potentiate augmentation of GG at this level of NP. We conclude that the UANP reflex remains relatively immature in ruminating lambs, and that the adult response to low magnitude NP must occur later in development. Hypoxia augmented GG muscle activity above basal values in both studies, but did not potentiate its response to low magnitude NP. We speculate that the immature UANP reflex in neonates contributes to impaired oropharyngeal airway reopening in the event of its closure, and the failure to augment reflex activation with hypoxia may be a contributory factor in certain instances of SIDS.

Influence of muscle length on diphragm EMG and mechanical output

Influence of muscle length on diphragm EMG and mechanical output

Trunk Muscle Activation

This study was performed to quantify the electromyographic trunk muscle activities in response to variations in moment magnitude and direction while in forward-flexed postures. Recordings were made over eight trunk muscles in 19 subjects who maintained forward-flexed postures of 30 degrees and 60 degrees. In each of the two flexed postures, external moments of 20 Nm and 40 Nm were applied via a chest harness. The moment directions were varied in seven 30 degrees increments to a subject's right side, such that the direction of the applied load ranged from the upper body's anterior midsagittal plane (0 degree) to the posterior midsagittal plane (180 degrees). Statistical analyses yielded significant moment magnitude by moment-direction interaction effects for the EMG output from six of the eight muscles. Trunk flexion by moment-direction interactions were observed in the responses from three muscles. In general, the primary muscle supporting the torso and the applied load was the contralateral (left) erector spinae. The level of electromyographic activity in the anterior muscles was quite low, even with the posterior moment directions.

Patterns of neck muscle activation in cats during reflex and voluntary head movements.

When the head rotates, vestibulocollic reflexes counteract the rotation by causing contraction of the neck muscles that pull against the imposed motion. With voluntary head rotations, these same muscles contract and assist the movement of the head. The purpose of this study was to determine if an infinite variety of muscle activation patterns are available to generate a particular head movement, of if the CNS selects a consistent and unique muscle pattern for the same head movement whether performed in a voluntary or reflex mode. The relationship of neck muscle activity to reflex and voluntary head movements was examined by recording intramuscular EMG activity from six neck muscles in three alert cats during sinusoidal head rotations about 24 vertical and horizontal axes. The cats were trained to voluntarily follow a water spout with their heads. Vestibulocollic reflex (VCR) responses were recorded in the same cats by rotating them in an equivalent set of planes with the head stabilized to the trunk so that only the vestibular labyrinths were stimulated. Gain and phase of the EMG responses were calculated, and data analyzed to determine the directions of rotation for which specific muscles produced their greatest EMG output. Each muscle exhibited preferential activation for a unique direction of rotation, and weak responses during rotations orthogonal to that preferred direction. The direction of maximal activation could differ for reflex and voluntary responses. Also, the best excitation of the muscle was not always in the direction that would produce a maximum mechanical advantage for the muscle based on its line of pull. The results of this study suggest that a unique pattern of activity is selected for VCR and tracking responses in any one animal. Patterns for the two behaviors differ, indicating that the CNS can generate movements in the same direction using different muscle patterns.

Developmental Changes in the Response of the Newborn to Sustained Ventilatory Elastic Loads

Postnatal development of the steady-state response to inspiratory elastic loading was studied in eight 48-h-old and eight 24-day-old unanesthetized, tracheostomized monkeys. Both age groups exhibited a fall in minute ventilation (VE) with loads of two to five times baseline respiratory elastance. There was no statistical difference in the ventilatory response between age groups. The response patterns of both groups were characterized by a fall in both tidal volume (VT) and mean inspiratory flow (VT/TI) associated with a prolongation of TI and TI/Ttot. All subjects demonstrated a significant load compensatory response both in terms of neural drive (diaphragmatic EMG output) and force output (inspiratory work production). Arterial CO2 increased significantly during loading in the older subjects in linear correlation with the decline in VE, but the newborns did not exhibit a statistically significant alteration in PaCO2 throughout the range of elastic loads. These data indicate that normal newborns are capable of responding to an external elastic load and that the newborn response is comparable to that of more mature subjects.

Neck muscle activation patterns in humans during isometric head stabilization.

A musculoskeletal system with more muscles than there are motions could be programmed in alternative ways to produce a single movement. In this case, the muscles would have the potential to be maximally responsive in multiple directions rather than responding preferentially in a single direction. To determine the response patterns of muscles in the head-neck motor system, the simultaneous activation of four of the 23 neck muscles acting on the head was recorded with both surface and intramuscular electrodes. Fifteen human subjects were tested during an isometric head stabilization task. When the EMG response patterns were plotted, each muscle demonstrated a preferred direction of activation. This preferred activation direction was consistent in all of the subjects for three of the muscles tested. The fourth muscle, splenius, was preferentially activated during neck flexion in half of the subjects and during neck extension in the other half. Increasing the force parameters of the task suggested a linear relationship between force and the EMG output in the preferred response directions. Responses in the nonpreferred directions were produced by a nonlinear change in EMG activation of the muscle. This finding could have implications for theories of how reciprocal activation and cocontraction patterns of response are elicited. Results from this study, that the CNS programs neck muscles to respond in specific orientations rather than generating an infinite variety of muscle patterns, are in agreement with our findings in the cat.

Effect of Reaction Time Condition on EMG Activities of the Biceps Brachii Muscle in Elbow Flexion and Forearm Supination

Under simple- and choice-RT conditions, the biceps brachii muscle was examined in 8 healthy male subjects to determine how the temporal and spatial characteristics of elbow flexion and forearm supination differed at the initial phase of EMG activity and whether preparation or the presence of response uncertainty influenced the EMG outputs of the two movements. In the simple-RT condition, RT of supination was significantly faster than that of flexion but EMG activity of supination was less than that of flexion. In contrast, in the choice-RT condition, RT of flexion was significantly faster than that of supination but EMG activity of flexion was significantly reduced compared to supination. These findings indicate that advanced preparation or motor set facilitates the differentiation of RTs and EMG activities of the response movements and that response uncertainty causes a significant change in the temporal and spatial specificity of both elbow flexion and forearm supination.

Chapter 14 Dynamic and kinematic properties of the vestibulocollic and cervicocollic reflexes in the cat

In situations where the body and head can move independently, the VCR and CCR must work together to stabilize the head with respect to space and with respect to the body. The dynamic and kinematic properties of these two reflexes appear to be organized to promote relatively simple, linear interactions between them over a wide range of head movement frequencies. Neck EMG outputs produced by both reflexes exhibit nearly identical second-order lead characteristics as stimulus frequencies increase from 0.5 to 5.0 Hz. Their input/output curves are matched so that the threshold of the VCR is offset by the high sensitivity of the CCR at low stimulus amplitudes. In addition, the patterns of muscle activation produced by the two reflexes in the decerebrate cat are quite similar. Direct evidence of linear summation of the VCR and CCR has been obtained in situations where the head rotates with respect to a stationary trunk [16, 22] and where animals make head motions to compensate for rotation of the trunk [3, 22], In the latter situation, the two reflexes appear to play an important role in stabilizing the head of the cat at frequencies below about 3 Hz [3]. In primates, however, voluntary head movements may override this reflex stabilization [1, 25].

Evoked potentials from passive elbow movements. II. Modification by motor intent

Subjects were instructed to remain passive or to react to a forearm perturbation by opposing the imposed movement. Evoked potentials (EPs) were recorded at 8 scalp sites in both conditions. In the React condition, reflexes were observed in the EMG (mean onsets of 67 and 81 msec) and the EP was modified. Source derivation techniques revealed that the earliest cortical response (31 msec) across the central sulcus was not changes. Therefore the intention to react did not seem to affect afferent transmission to the primary sensorimotor cortex. Two periods of modulation were observed. In both, parietal and frontal potentials were modulated together, prior to the reflex components. After 70 msec, the pattern of potential gradients which occurred in the Passive case was accelerated and intensified in the React condition. The overall effect was to focus a larger zone of negativity over motor cortex at the time of triggered EMG output (109 msec). The earlier changes in cortical activity could be causally related to the appearance of the late stretch reflex. Since parietal and frontal areas were principally involved and not the motor area, it is suggested that the former exert a modulatory influence on spinal and brain-stem reflex centres.

The influence of clenching level on the post-stimulus EMG complex, including silent periods, of the masseter muscles in man

Standardized mechanical taps were delivered on an upper central incisor, while the nine subjects investigated maintained constant clenching levels of 5, 10, 20, 40 and 60 per cent of their maximal EMG outputs. Using statistical criteria, a computer program enabled an objective determination of the interaction between the clenching level and the sequence of upward and downward going waves following the stimulus in full-wave rectified and superimposed EMG, called a post-stimulus EMG complex (PSEC). The morphology of the PSEC, including one or two silent periods, was subject-specific and reproducible over one year. The surfaces of the waves were greatly influenced by the clenching level. In general, their total surface decreased as a function of the clenching level. However, the individual waves decreased selectively. The results suggest that the sequence of waves results from overlapping of inhibitory and excitatory inputs. The inhibitory waves, constituting the silent periods, are largely cancelled by the excitatory reflexes of the PSEC.

Electromyographic biofeedback applications to the hemiplegic patient. Changes in lower extremity neuromuscular and functional status.

The efficacy of EMG biofeedback in improving neuromuscular and functional measures of involved lower extremities in an Experimental Group of chronic stroke patients (n = 7) was examined. Differences in pretreatment-posttreatment measures of the Experimental Group were compared with those of groups of chronic stroke patients receiving no treatment (n = 6), biofeedback treatment of the involved upper extremity only (n = 16), and general relaxation training (n = 8). All examinations were performed in a blind fashion. The Experimental Group showed significant improvement in active range of motion at the knee and ankle that appeared to result from increases in EMG output to muscles governing these movements. Experimental patients did not improve substantially in walking speed over different terrains but did require significantly fewer or less complex assistive devices to walk. Limitations in the design and implementation of this study are provided, and suggestions for future investigation are offered.

Electromyographic biofeedback applications to the hemiplegic patient. Changes in upper extremity neuromuscular and functional status.

The effect of a specific EMG biofeedback treatment protocol on quantified changes in neuromuscular measures and functional activities was examined among the upper extremities of 22 chronic stroke patients who each received 60 feedback training sessions. These data were compared with changes measured from a Control Group of 9 (no treatment) patients. Those patients receiving feedback training showed significant improvements in numerous neuromuscular measures but not in functional measures. When the Experimental Group was subdivided into two groups (hand, n = 5; no hand, n = 17) on the basis of acquiring a specific hand function, significant pretreatment differences in neuromuscular status emerged. Based upon these pretreatment differences and outcome measures, characteristics possibly predictive of beneficial outcomes from EMG biofeedback training were exposed. Chronic stroke patients who gained maximal functional benefits from the biofeedback intervention initially had greater active range of motion at all major upper extremity joints and comparatively less hyperactivity within typically "spastic" muscles. Electromyographic biofeedback can lead to substantial improvements among select chronic stroke patients and can be of considerable functional benefit to others.

Forearm tension and change of finger temperature.

10 adult subjects were provided EMG feedback from the forearm and relaxed until integrated EMG output fell below 5 µV. The temperature of the index finger of the same limb was simultaneously monitored, and when it had stabilized, a baseline measurement was taken. Subjects then performed a tonic contraction of the forearm, maintaining a specified EMG output for three minutes. No movements of the hand, fingers, or arm were permitted during this period. Finger temperatures were again measured at the end of the contraction period and had decreased significantly in proportion to sustained EMG output. It is concluded that covert changes in tonic forearm EMG activity have a substantial effect on finger temperature.

Autoregulation of skin temperature with feedback-assisted relaxation of the target limb, and controlled variation in local air temperature.

The primary aim of this study was to determine whether feed-back-assisted skin temperature regulation can be demonstrated when skeletomuscular mediation, in the form of altered local EMG activity, is prevented. A second aim was to determine whether the success of such regulation is affected by the basal temperature of the skin. 30 adult subjects were asked to increase or decrease the temperature of the index finger of the dominant hand, while the local musculature was kept in a relaxed state using EMG feedback. The local ambient air temperature surrounding the limb was set at either 10 degrees C, 24 degrees C, or 38 degrees C, resulting in large differences in basal skin temperature. Subjects were successful at both increasing and decreasing skin temperature while maintaining an integrated EMG output below 75 muV in the target limb. The magnitude of change, much smaller than those commonly reported in this field, did not vary across the air temperature levels, indicating that skin temperature autoregulation under these conditions does not conform to the law of initial value. It was concluded that autoregulation of skin temperature can be demonstrated in a virtually flaccid limb, and that the amount of temperature change achieved is not a function of basal skin temperature.

Input-output properties of motor unit responses in muscles stretched by imposed displacements of the monkey wrist

Reflex responses are "servo-like" where the output is graded with the input or are "triggered" where the output is independent of input once an input threshold is exceeded. Imposed displacements of monkey or human upper limb joints result in prolonged EMG output in the muscles stretched by the displacements. The longer-latency portions of the prolonged output have been variously reported to be servo-like or to be triggered in nature. In monkeys and humans, angular wrist displacements imposed by step loads result in three peaks (M1, M2 and M3) in the gross EMG recorded from the stretched muscles. Each gross EMG peak largely results from the firing of a separately-responding subpopulation of single motor units (SMUs). We studied the responses of SMUs to loads that were presented to the monkeys in a random order as to magnitude, duration and onset time. Average response histograms were constructed for the SMU responses for individual step load magnitudes. Averages were also constructed for the simultaneously-recorded gross EMG responses for each step load magnitude. The input parameters used were the initial velocity of displacement or the magnitude of step load, while the output was taken as the probability of firing/millisecond/presentation above baseline for the SMUs or the area under the response peaks above baseline for gross EMG. The results establish: 1) That it is not possible to unambiguously determine the input-output properties of the responses to imposed displacements utilizing the analysis of gress EMG activity due to the response characteristics of the various subpopulations of motor units contributing to the gross response. 2) That the SMU activity during all of the peak intervals is monotonically graded with increases in magnitude of the step load or the initial velocity of displacement. Hence, the long-latency portions of the EMG responses are servo-like in nature and are not preprogrammed or triggered responses. 3) That the gain (output/input) of the gross EMG responses almost entirely reflects the variation in the number of motoneurons recruited by changes in magnitude of the step loads rather than variation in the firing rates of motoneurons during the reflex responses.

Electromyographic study of local and generalized muscular impairment.

A study was made of a) the effects of magnitude and duration of sustained isometric muscular contractions voluntarily maintained until ‘exhaustion’ on the surface electromyogram of active and inactive muscle and b) of the residual effects of an original contraction on the EMG obtained during a succeeding contraction. It was found that the EMG progressively increases with time in both active and passive muscle during sustained contraction, the rate being proportional to magnitude of contraction, and that the initial, average and final EMG levels relate positively to contraction magnitude, while the total EMG output and duration of contraction varies inversely and exponentially with contraction magnitude. The surface EMG appears to be related to impairment through an intermediary variable, voluntary effort. Submitted on June 8, 1959