Agonist Electromyographic Activity Research Articles

Motor 'surround inhibition' is not correlated with activity in surround muscles.

Surround inhibition (SI) is a neural process that has been extensively investigated in the sensory system and has been recently probed in the motor system. Muscle-specific modulation of corticospinal excitability at the onset of an isolated finger movement has been assumed to reflect the presence of SI in the motor system. This study attempted to characterise this phenomenon in a large cohort of normal volunteers and investigate its relationship with muscle activity in the hand. Corticospinal excitability of the pathways projecting to three hand muscles [first dorsal interosseus (FDI), abductor pollicis brevis (APB) and abductor digiti minimi (ADM)] and electromyographic (EMG) activity of the same muscles were assessed in 31 healthy volunteers during an isolated index finger movement. In the agonist FDI muscle both corticospinal excitability and EMG activity were found to be increased at the onset of the movement (P < 0.001 and P < 0.001, respectively). On the contrary, in the surround ADM, there was dissociation between the corticospinal excitability (decreased: P < 0.001) and EMG activity (increased: P < 0.001). Cross-correlation analysis of the EMG activity showed that neuronal signals driving the agonist and surround muscles are not synchronised when SI is present. The results suggest a distinctive origin of the neuronal signals driving the agonist and surround muscles. In addition, they indicate that cortical output might be simultaneously modulated by voluntary and non-voluntary activity, generated in cortical and subcortical structures, respectively.

Neuromuscular differences between boys with and without intellectual disability during squat jump

The purpose of this study was to identify the differences in vertical squat jump (SJ) between volunteers with and without intellectual disability (ID). Thirteen boys with ID (average intelligence quotient, estimated by Wisk III test: 55.6 ± 11.2) and 13 peers without disabilities performed maximal SJ on a force platform. Kinematic data were captured using a six-camera 3D motion analysis system and electromyographic (EMG) activity was recorded using surface electrodes. Unpaired T-test determined the statistical difference between the two groups. The obtained results indicated that the group with ID, jumped lower, developed lower vertical ground reaction forces, knee power output, knee angular velocity, and take-off velocity, and showed longer propulsion duration, decreased mean to maximum agonist EMG activity and higher antagonist/agonist activity ratio. The deficit in the SJ observed in individuals with ID was attributed to a deficit in the examined mechanical and neuromuscular parameters, and especially to the agonist and antagonist co-contraction.

Force variability during isometric wrist flexion in highly skilled and sedentary individuals

The association of expertness in specific motor activities with a higher ability to sustain a constant application of force, regardless of muscle length, has been hypothesized. Ten highly skilled (HS group) young tennis and handball athletes and 10 sedentary (S group) individuals performed maximal and submaximal (5, 10, 20, 50, and 75% of the MVC) isometric wrist flexions on an isokinetic dynamometer (Kin-Com, Chattanooga). The wrist joint was fixed at five different angles (230, 210, 180, 150, and 1300). For each position the percentages of the maximal isometric force were calculated and participants were asked to maintain the respective force level for 5 s. Electromyographic (EMG) activation of the Flexor Carpi Ulnaris and Extensor Digitorum muscles was recorded using bipolar surface electrodes. No significant differences were observed in maximal isometric strength between HS and S groups. Participants of HS group showed significantly (P < 0.05) smaller force coefficient of variability (CV) and SD values at all submaximal levels of MVC at all wrist angles. The CV and SD values remained unaltered regardless of wrist angle. No difference in normalized agonist and antagonist EMG activity was observed between the two groups. It is concluded that long-term practice could be associated with decreased isometric force variability independently from muscular length and coactivation of the antagonist muscles.

Incomplete functional subdivision of the human multitendoned finger muscle flexor digitorum profundus: an electromyographic study.

The human flexor digitorum profundus (FDP) sends tendons to all 4 fingers. One might assume that this multitendoned muscle consists of 4 discrete neuromuscular compartments each acting on a different finger, but recent anatomical and physiological studies raise the possibility that the human FDP is incompletely subdivided. To investigate the functional organization of the human FDP, we recorded electromyographic (EMG) activity by bipolar fine-wire electrodes simultaneously from 2 or 4 separate intramuscular sites as normal human subjects performed isometric, individuated flexion, and extension of each left-hand digit. Some recordings showed EMG activity during flexion of only one of the 4 fingers, indicating that the human FDP has highly selective core regions that act on single fingers. The majority of recordings, however, showed a large amount of EMG activity during flexion of one finger and lower levels of EMG activity during flexion of an adjacent finger. This lesser EMG activity during flexion of adjacent fingers was unlikely to have resulted from recording motor units in neighboring neuromuscular compartments, and instead suggests incomplete functional subdivision of the human FDP. In addition to the greatest agonist EMG activity during flexion of a given finger, most recordings also showed EMG activity during extension of adjacent fingers, apparently serving to stabilize the given finger against unwanted extension. Paradoxically, the functional organization of the human FDP-with both incomplete functional subdivision and highly selective core regions-may contribute simultaneously to the inability of humans to produce completely independent finger movements, and to the greater ability of humans (compared with macaques) to individuate finger movements.

Dependence of deltoid muscle activity upon initial angles of shoulder abduction prior to flexion.

The present study was undertaken to investigate the hypothesis that the direction and selectivity of an appropriately modified version of shoulder flexion is dependent upon initial angles of shoulder abduction. Analysis indicated that initial small angles of shoulder abduction were associated with longer electromyographic (EMG) durations of the agonist (anterior deltoid) muscle. Moreover, as initial angles became smaller, EMG onsets of the antagonist (posterior deltoid muscle) occurred nearer to those of the agonist. Modulations of duration of the agonist EMG activity can be explained by changes in amplitude of movement. Two possible interpretations of the changes of EMG onset of the antagonist in accordance with different initial angles of shoulder abduction are considered. One concerns the effect of the change on the load of the upper limb, dependent on different angles of shoulder abduction. The second concerns the changing role of the antagonist to a synergist, dependent upon decreased initial angles of shoulder abduction prior to the shoulder flexion. Based on the present findings, it is suggested that angles of shoulder abduction are an important determinant of agonist-antagonist muscle activity of the deltoid during flexion of the shoulder.

DEPENDENCE OF DELTOID MUSCLE ACTIVITY UPON INITIAL ANGLES OF SHOULDER ABDUCTION PRIOR TO FLEXION

The present study was undertaken to investigate the hypothesis that the direction and selectivity of an appropriately modified version of shoulder flexion is dependent upon initial angles of shoulder abduction. Analysis indicated that initial small angles of shoulder abduction were associated with longer electromyographic (EMG) durations of the agonist (anterior deltoid) muscle. Moreover, as initial angles became smaller, EMG onsets of the antagonist (posterior deltoid muscle) occurred nearer to those of the agonist. Modulations of duration of the agonist EMG activity can be explained by changes in amplitude of movement. Two possible interpretations of the changes of EMG onset of the antagonist in accordance with different initial angles of shoulder abduction are considered. One concerns the effect of the change on the load of the upper limb, dependent on different angles of shoulder abduction. The second concerns the changing role of the antagonist to a synergist, dependent upon decreased initial angles of shoulder abduction prior to the shoulder flexion. Based on the present findings, it is suggested that angles of shoulder abduction are an important determinant of agonist-antagonist muscle activity of the deltoid during flexion of the shoulder.

Effects of TRH on ballistic wrist movements in cerebellar cortical atrophy: improvement of two genuine deficiencies but not of the major one.

Thyrotropin-releasing hormone (TRH) has been claimed to improve cerebellar ataxia in patients with idiopathic sporadic cerebellar cortical atrophy (CCA). We analysed the effects of intravenous administration of TRH (1 mg) in ballistic wrist flexions movements in 10 healthy subjects and in eight patients with CCA. The associated agonist and antagonist electromyographic (EMG) activities were recorded. In healthy subjects, TRH did modify neither the movement amplitudes, nor the intensity of the agonist and antagonist EMG activities. Before TRH administration, patients with CCA exhibited a hypermetria which was associated with a delayed onset of the antagonist activity. Moreover, the intensity of EMG activity in both the agonist and the antagonist muscles were reduced. After TRH, the hypermetria and the delayed onset latencies of the antagonist EMG activities were unchanged but the intensity of both the agonist and the antagonist EMG activities increased. TRH could increase the magnitude of agonist and antagonist EMG activities in patients with CCA by exerting an excitatory effect directly on motoneurons or by modulating at the supraspinal level the central commands to agonist and antagonist motoneuron pools. Copyright Rapid Science Ltd

Analysis of ballistic movements in ataxic hemiparesis following a pontine stroke

Although cerebellar-like ataxia is a well known component of the ataxic hemiparesis (AH), the mechanism of hypermetria in AH has not been established. We describe a patient presenting a left AH following a right pontine infarction. We investigated the ballistic flexion movements of both wrists and the associated agonist and antagonist electromyographic (EMG) activities, before and after addition of inertial loads. At the time of motion analysis, neurological examination showed cerebellar-like dysmetria of the left side but the patient had recovered a normal strength. In the basal state (without addition of loads), movements of the left wrist were hypermetric. The duration of the agonist EMG activity was prolonged and the onset latency of the antagonist EMG activity was not delayed. Moreover, when a mass was added, the hypermetria was unchanged because the patient was unable to adapt appropriately neither the agonist, nor the antagonist EMG activity. We suggest that the hypermetria was due to an imbalance between the duration of the agonist EMG activity (the launching force) and the duration of the antagonist EMG activity (the braking force).

Analysis of ballistic movements in ataxic hemiparesis following a pontine stroke

Although cerebellar-like ataxia is a well known component of the ataxic hemiparesis (AH), the mechanism of hypermetria in AH has not been established. We describe a patient presenting a left AH following a right pontine infarction. We investigated the ballistic flexion movements of both wrists and the associated agonist and antagonist electromyographic (EMG) activities, before and after addition of inertial loads. At the time of motion analysis, neurological examination showed cerebellar-like dysmetria of the left side but the patient had recovered a normal strength. In the basal state (without addition of loads), movements of the left wrist were hypermetric. The duration of the agonist EMG activity was prolonged and the onset latency of the antagonist EMG activity was not delayed. Moreover, when a mass was added, the hypermetria was unchanged because the patient was unable to adapt appropriately neither the agonist, nor the antagonist EMG activity. We suggest that the hypermetria was due to an imbalance between the duration of the agonist EMG activity (the launching force) and the duration of the antagonist EMG activity (the braking force).

Recovery of hypermetria after a cerebellar stroke occurs as a multistage process.

In a prospective study, we repeatedly recorded fast goal-directed wrist movements of 8 patients who had experienced an acute cerebellar hypermetria due to a stroke and who had subsequently recovered clinically. Movements and the associated agonist and antagonist electromyographic (EMG) activities were recorded before and after addition of inertial loads. Four stages characterized the recovery process. At stage 1, hypermetria was present in the basal state and was not modified by the addition of inerital loads. At stage 2, hypermetria, which was present in the basal state, was enlarged by mass addition. At stage 3, hypermetria was absent in the basal state, but was revealed by an inertial load increase. At stage 4, as in healthy subjects, there was no hypermetria without or with addition of inertial loads. At stage 1, the patients presented several defects. (1) Facing an increased inertia, they could not increase their agonist EMG activity. (2) The onset latency of their antagonist EMG activity was delayed. (3) Facing an increased inertia, they could not increase their antagonist EMG activity. Among these three defects, the first disappeared at stage 2, the second at stage 3, and the third at stage 4.

Effect of taping the patella on concentric and eccentric torque and EMG of knee extensor and flexor muscles in patients with patellofemoral pain syndrome.

The acute effect of patella taping on torque and electromyographic (EMG) activity in maximal voluntary concentric and eccentric action of the knee extensor and flexor muscles in patients with patellofemoral pain syndrome was studied in 48 patients (62 knees). The patients (28 female, 20 male) were tested concentrically and eccentrically on a Kin-Com dynamometer with simultaneous EMG recording with the patella untaped and medially or laterally taped. Patients with clinically normal patellar mobility did not improve their quadriceps performance by taping of the patella; after medial taping they decreased their muscle torque during concentric work at 60 degrees/s (P < 0.05) and eccentric work at 180 degrees/s (P < 0.05). After lateral taping they decreased their muscle torque during concentric work at 60 degrees/s (P < 0.05) and eccentric work at both 60 degrees/s (P < 0.01) and 180 degrees/s (P < 0.05). Moreover, these patients also decreased their agonist EMG activity during concentric work at 60 degrees/s (P < 0.05) and 180 degrees/s (P < 0.05) and their antagonist EMG activity during eccentric work at 60 degrees/s (P < 0.01). Patients with a clinical lateral patellar hypermobility increased their knee extensor torque after medial taping at 60 degrees/s during both eccentric work (P < 0.01) and concentric work (P < 0.05). The greatest improvement in quadriceps performance, however, was in patients with a clinical medial patellar hypermobility. They increased their knee extensor torque after lateral taping during eccentric work at both 60 degrees/s (P < 0.001) and 180 degrees/s (P < 0.001) and during concentric work at 60 degrees/s (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Timing and magnitude of electromyographic activity for two-joint arm movements in different directions

1. We studied electromyographic (EMG) and kinematic features of self-paced human arm movements involving rotations about the shoulder and elbow joints. Movements were initiated from various positions and covered much of the reachable work space in the horizontal plane. The attempt was to characterize robust features of the relative timing and magnitude of the EMG activity at the two joints, and to correlate them with variables related to the initial and final positions. 2. The pattern of muscle activity at each joint was typically characterized by bursts of alternating agonist and antagonist activity, comparable with the three-burst pattern associated with single-joint movements. As the spatial direction of the target was altered, the magnitude of each burst was modulated over a continuous range. Modulation down to zero activity was observed, not only for later bursts, as has been shown in some cases of single-joint movements, but for the first agonist burst as well. 3. In the preceding paper we showed that the choice of agonists (i.e., flexors or extensors) at each joint is predictable on the basis of the target direction relative to the distal segment (psi). Here, we present quantitative analyses of initial agonist EMG activity at the shoulder and elbow, which reveal that the onset-time difference between agonists at the two joints also varied systematically with psi, and so did their relative magnitude. 4. For most target directions, initial EMG activity at the shoulder preceded that at the elbow by 5-40 ms. Exceptions were observed mainly for target directions near the transitions between initial flexor and initial extensor activity at the shoulder. In these cases the initial agonist activity at the shoulder was greatly reduced or, in some cases, appeared entirely suppressed, although the later bursts were present in their usual temporal alignment with the corresponding bursts at the elbow. 5. Antagonist onset at the elbow tended to precede antagonist onset at the shoulder, but the difference in timing did not vary consistently with psi. 6. Despite the consistency of initial agonist timing between the two joints, the agonist onset-time difference was poorly correlated with the apparent difference in the onset times of shoulder and elbow joint rotations. The latter difference, which is affected by mechanics, cannot therefore be imputed directly to the CNS.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebellar dysmetria at the elbow, wrist, and fingers

1. The objective was to investigate in cerebellar patients with dysmetria the kinematic and electromyographic (EMG) characteristics of large and small movements at the elbow, wrist, and finger and thereby to determine the nature of cerebellar dysmetria at distal as well as proximal joints. Flexions were made as fast as possible by moving relatively heavy manipulanda for each joint to the same end position through 5, 30, and 60 degrees. 2. In normal subjects flexions at all joints were accompanied by similar triphasic EMG activity. Movements of increasing amplitude were made with increasing movement durations and increasing durations and magnitudes of initial agonist EMG activity. Antagonist activity often appeared to have two components: one coactive with the initial agonist burst but starting later, the other reaching its peak at about peak velocity. 3. Cerebellar patients with dysmetria showed hypermetria followed by tremor at all three joints when movements were made with the manipulanda. Hypermetria was most marked for aimed movements of small amplitude (5 degrees) at all joints. 4. A characteristic of cerebellar disordered movements, which could be present at all amplitudes and all joints, was an asymmetry with decreased peak accelerations and increased peak decelerations compared to normal movements. Both the asymmetry and the hypermetria for small amplitude movements could be used clinically as sensitive indicators of cerebellar dysfunction. 5. The EMG abnormalities accompanying hypermetria and asymmetry were a more gradual buildup and a prolongation of agonist activity and delayed onset of antagonist activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist and Antagonist Muscle EMG Activity Pattern Changes with Skill Acquisition

Abstract The purpose of this research was to investigate the modifications in the control of the biceps brachii (agonist) and triceps brachii (antagonist) muscles during the learning of two elbow flexion tasks in sixteen college-age women. A positioning and a coincidence task were each performed at 40° and 200° per second angular velocity while bipolar surface electrodes recorded the electromyographic (EMG) activity of the muscles involved. Data on the EMG activity, angular kinematics, and timing and angular displacement error were quantified and subjected to statistical analyses. The results of the error analyses indicated that subjects did learn the various tasks over the 120 trials. Because there were no significant changes in the angular velocity patterns over trials, the EMG activity modifications are suggested to reflect differences in the control of the muscles monitored during the movements. In addition, EMG activity pattern modifications which occurred in discrete portions of the movements in bot...