Elbow Extension Movements Research Articles

On-Line Control of a Speeded Motor Response

Evidence for a point of no return in a motor act has been reported to occur very late in its preparation and even to the point at which the response is executed. We report a qualitative example from electromyographic (EMG) data of an elbow-extension movement from 1 of 12 adults which suggests that the response can be stopped at any time up to its production, from which we conclude that the response is subject to on-line control at all times.

Velocity-dependent activation of postural muscles in a simple two-joint synergy

A simple two-joint synergy was studied over a range of movement velocities. We hypothesized that focal and postural components of the synergy are consequences of a single control process and, as such, will demonstrate similar scaling with movement velocity. Healthy subjects performed discrete elbow or wrist flexion or extension movements in a sagittal plane under the instruction to move one of the joints at different speed in different trials of a series. Joint angles and electromyographic (EMG) signals from two flexor and two extensor muscles were recorded and analyzed. Irrespective whether the focal movement took place in the elbow or in the wrist joint, and irrespective of the movement direction and velocity, the elbow flexor and the wrist flexor tended to demonstrate simultaneous EMG bursts, while the elbow extensor and the wrist extensor also showed similar patterns of activation. During flexion (extension) movements in either joint, the latencies of both elbow and wrist extensors (flexors) decreased with velocity of the focal movement. Integrals of the EMG bursts in all the muscles increased with movement speed in all the series. Typically, there was a close to linear relation between the integral EMG indices for the elbow and wrist flexors as well as for the elbow and wrist extensors. We conclude that there exists a simple, scalable synergy which is used by the central nervous system in a wide range of movement velocities to simplify control of the postural component of a motor task.

Role of agonist and antagonist muscle strength in performance of rapid movements.

Six subjects performed rapid self-terminated elbow movements under different mechanical conditions prior to, and 5 weeks after an elbow extensor strengthening programme. Despite the large difference in the strengths of elbow flexors and extensors, the pretest did not demonstrate significant differences between the movement time of flexion and extension movements performed under the same mechanical conditions. The results obtained in the posttest demonstrated a decrease in movement time (i.e. an increase in movement speed) in both elbow flexion and extension movements under some mechanical conditions. In addition, flexion movements demonstrated a relative increase in the acceleration time (acceleration time as a proportion of the movement time). It was concluded that the strength of both the agonist and antagonist muscles was important for the performance of rapid movements. Stronger agonists could increase the acceleration of the limb being moved, while stronger antagonists could facilitate the arrest of the limb movement in a shorter time, providing a longer time for acceleration.

Brain mechanisms of the mind: information synthesis in dominant cortical areas

Eight elderly subjects (aged 68–95 years) and 6 young adults (aged 21–24 years) performed elbow flexion and extension movements in a visual step-tracking paradigm. Movement amplitudes ranging from 10°–80° were made under two instructions: “move at own speed” and “move fast and accurate.” In a second experiment, 5 elderly subjects practiced 30° movements for a total of 180 flexion and 180 extension movements under the instruction to increase movement speed, while maintaining accuracy, during practice. Movement trajectories became more variable as both movement amplitude and speed increased. Trajectory variability was greater in the elderly subjects for both the acceleratory and deceleratory phases of movements. This was due primarily to a greater rate of increase in trajectory variability during the acceleration phase in the elderly. With practice, elderly subjects could substantially reduce trajectory variability with little change in movement speed. The agonist burst initiating movements was qualitatively normal in the elderly subjects. However, there was considerable tonic cocontraction of agonist and antagonist muscles prior to and during movement. Phasic antagonist EMG activity was obviously abnormal in many elderly subjects. There was often no clear antagonist burst associated with deceleration of the movements or, if present, it was timed inappropriately early. With practice, combined agonist-antagonist EMG variability decreased. A clear antagonist burst also developed during practice in most elderly subjects, but its inappropriate timing remained in all but one subject. The results show that movement trajectories are less accurately controlled in the elderly. This greater movement variability may result from: 1) changes in motor neuron population and motor unit properties with aging and the associated effects on muscle force output and joint torques and 2) abnormal control of phasic and tonic antagonist muscle activity. The ability to improve performance with practice, however, is clearly not lost in the elderly.

EMG activities of mono- and bi-articular muscles during goal-directed ballistic movement

Eight subjects, who were seated with the upper arm supported in a horizontal position, performed a series of elbow flexion and extension movements in which a visual target was provided together with an elbow angle signal by vertically moving horizontal lines on an oscilloscope. Five loading conditions were employed, which differed in the number of steel plates attached to the subject's wrist: 0, 0.65, 1.30, 1.95 and 2.60 kg. The electromyographic (EMG) activity of the bi-articular biceps brachii (BB) was compared with the mono-articular brachioradialis (BR) for each of three EMG components; the first and the second agonist burst (AG1, AG2) during flexion movements, and the antagonist burst (ANT) during extension movements. The magnitude relations for each EMG component between the two muscles were evaluated by the BR/BB ratio. The results showed that there were significant differences ( p < 0.05) among the three EMG components in all but the no-loading condition. Further a post-hoc test revealed that there were significant BR/BB differences ( p < 0.05) between AG1 vs. AG2 in 0.65 and 1.3 kg loading conditions and between AG1 vs. ANT in all but the no-loading condition. These results may suggest that different neural processes underlie the activation of mono- and bi-articular muscles in the organization and the control of movements.

Lack of task-related motor unit activity in human triceps brachii muscle during elbow movements

Surface electromyographic (EMG) recordings have been associated with the acceleration and deceleration characteristics of single joint elbow movements [J. Neurophysiol., 63 (1990) 465–472]. To explore further the neural control of single joint movements, we investigated the behavior of motor units in triceps brachii muscle during elbow flexion and extension movements. In this communication, we provide evidence that individual motor units can contribute to each of the surface EMG bursts. This finding suggests that the nervous system can use the same motor units during movement regardless of whether the muscle is acting as an agonist or antagonist or functioning to initiate or terminate the movement.

Muscle tone in Huntington's disease

Tone was evaluated quantitatively in 39 patients with Huntington's disease (HD) by measuring resistance to passive elbow flexion and extension movements on a hydraulic testing device. A velocity dependent increase in resistance to passive elbow flexion and to a lesser extent in resistance to passive extension was found in 10 patients. Increase in muscle tone was related to disease duration but not to the age of the patients nor to the severity of choreatic movements or the amount of cognitive impairment. A hypertonic pattern could be observed also in patients without any medication, and seemed not to be related to neuroleptic treatment. The pattern of tone change in HD is compared to the pattern of hemispasticity in upper motor neuron syndrome and to that of Parkinson's disease. It appears that an increase in muscle tone, with a velocity dependent resistance to flexion more than extension movements, is a frequent feature in advanced stages of Huntington's disease.

Control of rapid elbow extension movement

Normal human subjects made rapid extensions of the elbow from an initial position to visual targets at different angular distances (9°–54°). We recorded joint angle, acceleration, and surface electromyograms (EMGs) with a monopolar electrode from the triceps and the biceps brachii muscles. Both the agonist triceps and antagonist biceps initiated their activation with a slow EMG wave (AGslw and ANTslw). The amplitude of the AGslw increased with angular distance moved, but its duration remained constant. The amplitude of the ANTslw varied among subjects with distance moved. The duration of the ANTslw was approximately constant but more variable than that of the AGslw. The onset of the ANTslw was delayed with increasing movement distance. Our results indicate that movement distance is controlled, at the motoneuron pool level, by the interval of a set of pulses sent to the agonist and antagonist muscles in association with pulse amplitude modulation to the agonist muscle.

Analysis of kinesthetic sensation: the influence of m. deltoid, m. forearm extensor and flexor on sensory information of reproductive elbow movements

The effect of muscle vibration during voluntary self-paced elbow movements were studied in normal human subjects. Vibrations (10Hz, 30Hz, 50Hz, 70Hz) were applied to the m. deltoid, m. forearm extensor and flexor: vibration was turned off between movements. During non-visually guided (eyes closed) movements (reproductive movements), an undershoot of the required movement was observed in cases where vibration (30Hz, 50Hz, 70Hz) was applied to the m. forearm extensor and flexor. On the contrary, no effect was observed in cases where vibration (80Hz) was applied to the m. deltoid. These findings suggest that sensory information from the m. forearm extensor and flexor might play a role in reproductive elbow extension and flexion movements.

Transition from slow to ballistic movement: development of triphasic electromyogram patterns

The purpose of this investigation was to determine how the triphasic electromyogram (EMG) pattern of muscle activation developed from the agonist muscle only pattern as movement time (tmov) decreased. Six adult women produced a series of 30 degrees elbow extension movements in the horizontal plane at speeds ranging from ballistic (less than 400-ms tmov) to very slow (greater than 800-ms tmov). Surface EMG from triceps brachii (agonist) and biceps brachii (antagonist) muscles were recorded, together with elbow angle, on a microcomputer. The results showed that triphasic EMG patterns developed systematically as tmov decreased from 1000 ms to less than 200 ms. In trials with very long tmov, many elbow extension movements were produced by a single continuous activation of the agonist triceps brachii muscle. As tmov decreased however, agonist activation became predominantly burst-like and other components of the triphasic EMG pattern [activation of the antagonist (Ant) and second agonist activation (Ag2)] began to appear. At the fastest movement speeds, triphasic EMG patterns (Ag1-Ant-Ag2, Ag1 being first activation of agonist muscle) were always present. This data indicated that the triphasic pattern of muscle activation was not switched on when a particular tmov was achieved. Rather, each component systematically developed until all were present, as distinctive bursts of activity, in most trials with tmov less than 400 ms.

Fractionated Reaction Times and Movement Times of Down Syndrome and Other Adults with Mental Retardation

A fractionation technique was employed to determine the locus of reaction time delay in Down syndrome (DS) and other adult subjects with mental retardation (MH). Twenty-three subjects (8 nondisabled, 8 MH, and 7 DS) responded to a light, sound, and combination light/sound signal. Dependent measures of premotor time, motor time, total reaction time, and movement time were obtained during a 20° elbow extension movement and were analyzed separately. As expected, both MH and DS subjects were slower and more variable in their responses than the subjects without disabilities. In turn, DS subjects were significantly slower but not more variable than the MH subjects. There were no significant differences between the DS and MH subjects on movement times. Evidence for both a specific (premotor) and a generalized (both premotor and motor) locus of delay was found. Some difference in signal effect was also found for the DS subjects.

Control of simple arm movements in elderly humans

Eight elderly subjects (aged 68–95 years) and 6 young adults (aged 21–24 years) performed elbow flexion and extension movements in a visual step-tracking paradigm. Movement amplitudes ranging from 10°–80° were made under two instructions: “move at own speed” and “move fast and accurate.” In a second experiment, 5 elderly subjects practiced 30° movements for a total of 180 flexion and 180 extension movements under the instruction to increase movement speed, while maintaining accuracy, during practice. Movement trajectories became more variable as both movement amplitude and speed increased. Trajectory variability was greater in the elderly subjects for both the acceleratory and deceleratory phases of movements. This was due primarily to a greater rate of increase in trajectory variability during the acceleration phase in the elderly. With practice, elderly subjects could substantially reduce trajectory variability with little change in movement speed. The agonist burst initiating movements was qualitatively normal in the elderly subjects. However, there was considerable tonic cocontraction of agonist and antagonist muscles prior to and during movement. Phasic antagonist EMG activity was obviously abnormal in many elderly subjects. There was often no clear antagonist burst associated with deceleration of the movements or, if present, it was timed inappropriately early. With practice, combined agonist-antagonist EMG variability decreased. A clear antagonist burst also developed during practice in most elderly subjects, but its inappropriate timing remained in all but one subject. The results show that movement trajectories are less accurately controlled in the elderly. This greater movement variability may result from: 1) changes in motor neuron population and motor unit properties with aging and the associated effects on muscle force output and joint torques and 2) abnormal control of phasic and tonic antagonist muscle activity. The ability to improve performance with practice, however, is clearly not lost in the elderly.

Effects of upper limb immobilization on isometric muscle strength, movement time, and triphasic electromyographic characteristics.

The effects of short-term immobilization on isometric muscle strength, movement time, and triphasic integrated electromyographic characteristics were assessed during a simple ballistic elbow flexion and extension movement. The nondominant upper limbs in six subjects (two female, four male) were immobilized in a plaster cast for 14 days. Testing consisted of isometric muscle strength output of elbow flexors and extensors; movement time; and IEMG output of the agonist, antagonist, and second agonist contractions during the ballistic movements. An analysis of variance revealed a decrease in flexor strength of the casted limb (p less than .05). Movement time was not significantly slowed. Antagonist IEMG amplitude was decreased (p less than .01) during flexion, and agonist IEMG amplitude (p less than .05) and antagonist IEMG amplitude (p less than .05) were diminished during extension of the casted limb. In conclusion, short-term upper limb immobilization affects primarily elbow flexion strength and some IEMG characteristics during a ballistic forearm movement, suggesting an influence on the neuromuscular aspects of the affected muscles.

Cerebellar nuclear activity in relation to simple movements.

Single unit activity in the fastigial, interpositus and dentate cerebellar nuclei was recorded in relation to simple elbow flexion and extension movements in two macaque monkeys. In common with proximal muscle activity, 94% of the task-related neurons had qualitatively similar discharge patterns for both directions of forearm movement. In many cases the flexion and extension discharge was virtually identical, but some cells had a distinct directional bias. The very few neurons which were directionally specific were located in the dentate and interpositus. Two had tonic activity well correlated to elbow angle. Task-related changes in discharge rate occurred earliest in dentate and latest in fastigial, but almost always during the period of concomitant proximal and elbow EMG changes. Correlations of phasic activity with movement velocity were uniformly weak. Many eye movement-related neurons were encountered in the fastigial, dentate and y-group nuclei. Fastigial eye cells, both bursting and tonic, tended to be highly direction specific, whereas dentate eye cells were usually omnidirectional and variable. For both arm and eye cerebellar cells, the directional preferences of phasic and tonic discharge, in the same neuron, could be opposed to one another.

Temporal pattern of agonist-antagonist EMG activity during rapid limb movements in man.

Analysis of elbow-extension movements, executed at maximal velocity, show positive correlations of timing of agonist-antagonist EMG activity with both movement velocity and displacement. Results indirectly support the notion that the antagonist musculature provides a braking force to arrest rapid limb movements.

Changes in the Variability of Movement Trajectories With Practice

We studied variability in movement phase plane trajectories (velocity-position relation) during movement. Human subjects performed 10 degrees and 30 degrees elbow flexion and extension movements in a visual step tracking paradigm. The area of ellipses with radii equal to one standard deviation in position and velocity was taken as a measure of trajectory variability. Trajectory variability was determined at 10-ms intervals throughout movements. Trajectory variability in both the acceleration and deceleration phases of movement decreased with practice. The average trajectory variability during deceleration was greater than that during acceleration even after extended practice (1000 trials). During practice, subjects usually increased movement speed while maintaining end-position accuracy. Trajectory variability was also related to movement speed when equal amounts of practice were given. Short duration (fast) movements had greater trajectory variability than long duration movements. Thus there is a tradeoff between movement speed and trajectory variability similar to the classical speed-accuracy tradeoff. Trajectory variability increased rapidly during the acceleratory phase of movement. The rate of increase was positively related to both movement amplitude and speed. Thus, the forces producing limb acceleration were variable and this variability was more marked in faster and larger movements. In contrast, trajectory variability increased more slowly or actually decreased during the deceleratory phase of movements. Forces involved in limb deceleration thus appeared to compensate to a greater or lesser degree for the variability in accelerative forces. The experiments indicate that the entire trajectory of simple limb movements is controlled by the central nervous system. Variations in accelerative forces may be compensated for by associated variations in decelerative forces. The linkage between accelerative and decelerative forces is progressively refined with practice resulting in decreased variability of the movement trajectory.

Variability of Positioning Accuracy following a Maximum Isometric Contraction

The purpose of this study was to examine the effects of different contraction times and delay times prior to a positioning task. While blindfolded, each of 25 subjects learned to produce elbow-extension movements to a short and a long target using a kinesthesiometer. The subject then produced 30 trials without feedback to each target. These control trials were preceded by a foreperiod of 0-, 3-, or 6-sec. delay. The 60 experimental trials were identical to control trials except the subject isometrically contracted elbow extensor muscles for 3 or 6 sec. prior to each trial. Following each isometric contraction the subject delayed movement for 0, 3, or 6 sec. The 3-sec. and 6-sec. prepositioning contractions produced greater undershooting and variability than no prepositioning contractions, and the 0-sec. delay produced less constant error than either the 3- or 6-sec. delay. It was concluded that following isometric contraction, undershooting a target occurred and this effect did not dissipate within a 6-sec. period.

Interlimb coordination in cat locomotion investigated with perturbation. I. Behavioral and electromyographic study on symmetric limbs of decerebrate and awake walking cats.

During locomotion of decerebrate and awake walking cats, perturbation (mechanical tap) was applied to the paw dorsum of the left forelimb (LF), and the responses of both forelimbs were recorded cinematographically and electromyographically (EMG). When the tap was applied during the LF stance phase, the duration of the ongoing LF stance was shortened by 10%; in the right forelimb (RF), the duration of the concomitant swing was shortened by 32%. A tap during the LF swing phase prolonged the duration of the ongoing LF swing phase and the concomitant RF stance phase by 55 and 15%, respectively. Analysis of RF joint angle excursions showed that the shortening of the RF swing phase was related mainly to acceleration of extension movement in the late swing phase; the prolongation of the RF stance phase was related to prolonged extension movement in the late stance phase. While EMG activities were relevant to these limb movements, a notable observation was that, by tapping the LF during the LF stance phase, EMG activity in the RF extensor started well before onset of the elbow extension movement to place down the limb; without the tap, the extensor activity started shortly after onset of the extension. Closely related to changes in phase durations of each forelimb, the period of bisupport phase where both forelimbs were in stance, was retained for more than 40% of that of unperturbed steps, even when the RF or LF made the first touchdown after the tap. The rostrocaudal level at RF touchdown after the tap was comparable to unperturbed steps. These findings on interlimb relation suggest that neural control ensures coordinated movements between symmetric limbs during locomotion.

A Discrete Step Goniometer for the Human Elbow

A discrete step goniometer has been developed which measures the total integrated angle of elbow flexion and extension movements. It is compact, comfortable and convenient to wear and use. Preliminary results have shown that it is sufficiently accurate for most clinical applications if calibration is carried out prior to the experiments and it should prove to be a useful device in diagnosis, evaluation of treatment and normal data collection.