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Biomedical subjects

D M Corcos

Publications and source records attributed to D M Corcos.

54 records · Page 3Linked to original sources
PubMed1992

Organizing principles for single joint movements: V. Agonist-antagonist interactions.

1. Normal human subjects made discrete elbow flexions in the horizontal plane under different task conditions of initial or final position, inertial loading, or instruction about speed. We measured joint angle, acceleration, and electromyographic signals (EMGs) from two agonist and two antagonist muscles. 2. For many of the experimental tasks, the latency of the antagonist EMG burst was strongly correlated with parameters of the first agonist EMG burst defined by a single equation, expressed in terms of the agonist's hypothetical excitation pulse. Latency is proportional to the ratio of pulse duration to pulse intensity, making it proportional to movement distance and inertial load and inversely proportional to planned movement speed. However, these rules are not sufficient to define the timing of every possible single joint movement. 3. For movements described by the speed-insensitive strategy, the quantity of both antagonist and agonist muscle activity can be uniformly associated with selected kinetic measures that incorporate muscle force-velocity relations. 4. For movements collectively described by the speed-sensitive strategy, (i.e., that have direct or indirect constraints on speed), no single rule can describe all the combinations of agonist-antagonist coordination that are used to perform these diverse tasks. 5. Estimates of joint viscosity were made by calculating the amount of velocity-dependent torque used to terminate movements on target. These estimates are similar to those that have previously been made of limb viscosity during postural maintenance. They imply that a significant component of muscle activity must be used to overcome these forces. 6. These and previous results are all consistent with a dual-strategy hypothesis for those single-joint movements that are sufficiently fast to require pulse-like muscle activation patterns. The major features of such patterns (pulse intensities, durations, and latencies) are determined by central commands programmed in advance of movement initiation. The selection between speed-insensitive or speed-sensitive rules of motoneuron pool excitation is implicitly specified by the nature of speed constraints of the movement task.

Electromyography↗
PubMed1992

Intrathecal baclofen. Effects on nocturnal leg muscle spasticity.

Electromyographic activity was recorded from tibialis anterior during nocturnal polysomnography in six patients with severe spasticity of spinal origin. The patients had a baclofen reservoir system implanted subcutaneously into their lumbar subarachnoid space and were studied for two nights in a double-blind, placebo controlled, crossover design. Tibialis anterior electromyographic activity per hour of sleep was reduced on the night of baclofen infusion. In particular, less electromyographic activity occurred after arousal from sleep.

Adult↗
PubMed1991

Strategies underlying the control of disordered movement.

The purpose of this article is fourfold. First, a theory of motor control--the dual-strategy hypothesis--is outlined. Second, the methodologies and theoretical framework that are used to develop this theory are examined. Third, motor dysfunction is discussed in the context of this theory. In particular, Down syndrome, Parkinson's disease, cardiovascular accidents, and spasticity are discussed. Finally, potential applications of the theory to physical therapy are considered.

Biomechanical Phenomena↗
PubMed1991

Kinematic and electromyographic characteristics of single-joint movements of individuals with Down syndrome.

Single-joint elbow flexion movements over different distances were performed "as fast as possible" by 10 subjects with Down syndrome and 6 control subjects. Kinematic parameters and electromyograms (EMGs) of major muscle groups were recorded. Muscle reactions to unexpected perturbations were recorded under different instructions. Four of the subjects with Down syndrome were able to demonstrate kinematic and EMG patterns typical for one of the basic strategies observed in the general population. Only one of the subjects with Down syndrome was able to modulate the "pre-programmed" reactions to unexpected perturbations. We conclude that there are no major qualitative deficits in the motor control mechanisms of individuals with Down syndrome, but there might be problems with proper modulation of motor commands.

Adolescent↗
PubMed1990

Organizing principles for single joint movements. III. Speed-insensitive strategy as a default.

1. Human subjects made discrete elbow flexions in a horizontal plane over different distances, from a stationary initial position to a visually defined stationary target 9 degrees wide. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Subjects made movements over four different distances following one of four different instructions. The first instructed the subject simply to choose a comfortable speed. The other three explicitly emphasized either speed, accuracy, or maintenance of the "same" speed over different distances. These instructions produced a wide range of movement velocities. 3. The initial rises of the acceleration (and therefore of the inertial torque), as well as the initial slope of the agonist EMG, were all invariant over changes in the target distance for any single instruction but were all sensitive to the given instruction. 4. Our results demonstrate that the speed-insensitive strategy is a standard or default pattern for performing movements that may be carried out for different instructions over a wide range of speeds. A uniform intensity of excitation pulse is not a byproduct of moving at maximal speed. Submaximal intensities are associated with submaximal speeds and are a selected feature of the pattern of movement control.

Acceleration↗
PubMed1990

Organizing principles for single-joint movements. IV. Implications for isometric contractions.

1. Normal human subjects made isometric pulse and step contractions about the elbow to visually defined target torques of different amplitudes and at different rates. We measured joint torque and electromyograms (EMG) from two agonist and two antagonist muscles. 2. When the task specification requires that the subject explicitly alter the rate at which torque is increased, the rates of rise of the agonist and antagonist EMG bursts covary with the rate of rise of the torque. For pulses of torque the duration of motoneuron excitation varies with the duration of the task-defined contractile event. 3. When a subject is asked to generate torques of different amplitudes without specifying a time interval, torque amplitude is positively correlated with how long, and therefore how high, the EMG rose. Subjects usually proportionately covary the strength of the agonist and antagonist contractions but are not constrained to do so. Some subjects use a strategy of varying the antagonist inversely with the agonist contraction. 4. We extend the organizing principles for the control of movement about a single joint to the control of isometric torque. These rules state that control of torque about a single joint is exercised by one of two strategies: the speed-sensitive strategy modulates the rate at which contraction rises by varying the intensity of motoneuron-pool excitation. The speed-insensitive strategy varies the duration over which contraction rises but does not change the rate. These two respective patterns of torque emerge from pulse-height and pulse-width modulation of motoneuron-pool excitation. 5. The rules defining speed-sensitive and speed-insensitive strategies for movements are broadened for isometric contractions because of the wider range of torque patterns that we observe under these conditions. We propose a step-excitation component for prolonged isometric step contractions and slowly rising ramp patterns of excitation for contractions that develop over several hundreds of milliseconds. 6. The choice of strategies is based on task-specific torque requirements. The same two strategies that control torque to produce movement apply to the control of isometric torque. Unlike movements, however, isometric tasks are more often controlled by a blending of the two patterns. Possible reasons for this are discussed.

Electromyography↗
PubMed1990

Effects of intrathecal baclofen on voluntary motor control in spastic paresis.

Intrathecal baclofen injections were given to six patients with long-standing spastic paresis resistant to any nondestructive treatment, including oral baclofen. Attempts by the patients at voluntary muscle activation before intrathecal administration of baclofen led to considerable uncontrolled coactivation of antagonist and distant muscles. After the injection, dramatic suppression of the spastic signs was accompanied by more selective voluntary muscle activation. Tonic coactivation of the antagonists and distant muscle groups during voluntary contractions was decreased while the agonist level on electromyography (EMG) was not affected (three cases) or only slightly reduced (three cases). Furthermore, in one patient with sufficient residual motor control function, there was a considerable increase in the speed of fast isotonic movements, accompanied by the emergence of the ability to generate phasic muscle bursts on EMG that were characteristic of normal motor patterns. The results suggest that baclofen exerts different effects upon reflex pathways and descending motor pathways. This therapy appears to be a promising way for improving residual motor control in patients with increased muscle tone and/or reflexes.

Baclofen↗
PubMed1989

The relationship between muscle kinetic parameters and kinematic variables in a complex movement.

Kinematic variables of the vertical jump (jumping height, jump phase durations and joint angles) were measured on 39 male physical education students. In addition, kinetic parameters of the hip and knee extensors, and of the plantar flexors (maxima voluntary force and its rate of development) were recorded on the same subjects, in isometric conditions. The results demonstrated significant positive correlations between kinetic parameters of the active muscle groups and jumping height (r = 0.217-0.464). The dominant effect on these correlations was due to the knee extensors. Correlations between these parameters and the duration of the jump phases were much weaker. Correlation coefficients between kinetic parameters and limb angles in the lowest body position showed that fast force production in one muscle group was related to a significant decrease in the joint angles of distant body segments. Multiple correlation coefficients between leg extensor parameters and kinematic variables (ranging between 0.256 for the duration of the counter-movement phase and 0.616 for jump height) suggested that kinetic parameters could explain more than a quarter of the variability of this complex human movement. Therefore, the conclusion was drawn that an extended set of measurements of the relevant musculo-skeletal system parameters could predict a considerable amount of the variability of human movement. However, high correlation coefficients between the same kinetic parameters of different muscle groups suggest that not all active muscle groups have to be included in the measurements.

Adult↗
PubMed1989

Short-term effects of intrathecal baclofen in spasticity.

Six patients with long-lasting spasticity resistant to different drug therapies including oral baclofen received a bolus injection of lumbar intrathecal baclofen. Electromyographic (EMG) reactions of leg muscles (soleus, tibialis anterior, quadriceps, and hamstrings) to standard stimuli and during attempts at voluntary activation were recorded before the drug injection and up to 3 h after the injection. Responses to joint movements, H-reflexes, ankle clonus, and defensive reactions were noticeably suppressed within 30-45 min after the injection and had practically disappeared after 2 h. Ankle clonus was seen only in patients with H-reflexes, and clonus disappeared when the reflex responses to the n. tibialis stimuli were absent. A decrease in clonus EMG burst amplitudes was accompanied by a decrease in the clonus frequency. These observations favor the autooscillation hypothesis of clonus. Baclofen injection led to improvement in selective voluntary activation of leg muscles in patients with residual motor control. These results suggest that execution of voluntary motor commands in the patients suffered from functionally abnormal spinal circuitry rather than from changes in the descending motor commands. Intrathecal baclofen appears to be an effective way of eliminating increased muscle tone and spasms which can allow for voluntary motor function when it is present.

Administration, Oral↗
PubMed1989

Organizing principles for single-joint movements. I. A speed-insensitive strategy.

1. Normal human subjects made discrete elbow flexions and extensions in the horizontal plane from a stationary initial position to visually defined targets at different distances with a constant inertial load or made flexions to a visually defined target with different inertial loads. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Subjects were instructed to move their limbs accurately but quickly to the targets. Movements of greater distances or lesser loads were performed at higher velocities. 3. Peak inertial torque, acceleration and velocity, movement time, and integrated, rectified EMG were all highly correlated with the task variables, distance and inertial load. We show that peak inertial torque can be used as a linking variable that is almost sufficient to explain all correlations between the tasks, the EMG, and movement kinematics. 4. The rate at which subjects initially developed torque to accelerate their movements was invariant over changes in the value of either task variable. The rising phase of the agonist EMG was also independent of the distance or load moved. 5. Two components were distinguished in the antagonist EMG. The first had a relatively constant latency and amplitude. It terminated on the onset of the second and larger component at a latency that was delayed as both distance and load increased. 6. The integrated, rectified antagonist EMG was proportional to inertial load and peak decelerating torque for changes in inertial load. When target distance varied, proportionality between peak decelerating torque and antagonist EMG could be found if correction was made for the effects of muscle length on the torque-EMG relationship. 7. We propose organizing principles for the control of single-joint human movements in which tasks are performed by one of two strategies. These are called speed-insensitive and speed-sensitive strategies. 8. A model is described in which movements made under a speed-insensitive strategy are executed by controlling the duration and the relative timing of amplitude invariant patterns of activation to the spinal motoneuron pools.

Elbow Joint↗
PubMed1989

Organizing principles for single-joint movements. II. A speed-sensitive strategy.

1. Normal human subjects made discrete flexions of the elbow over a fixed distance in the horizontal plane from a stationary initial position to a visually defined target. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Changes in movement speed were elicited either by explicit instruction to the subject or by adjusting the target width. Instructions always required accurately stopping in the target zone. 3. Peak inertial torques and accelerations, movement times, and integrated EMGs were all highly correlated with speed. We show that inertial torque can be used as a linking variable that is almost sufficient to explain all correlations between the task, the EMG, and movement kinematics. 4. When subjects perform tasks that require control of movement speed, they adjust the rate at which torque is developed by the muscles. This rate is modulated by the way in which the muscles are activated. The rate at which joint torque develops is correlated with the rate at which the agonist EMG rises as well as with integrated EMG. 5. The antagonist EMG shows two components. The latency of the first is 30-50 ms and independent of movement dynamics. The latency of the second component is proportional to movement time. The rate of rise and area of both components scale with torque. 6. We propose organizing principles for the control of single-joint movements in which tasks are performed by one of two strategies. These are called speed-insensitive and speed-sensitive strategies. 7. A model is proposed in which movements made under a speed-sensitive strategy are executed by controlling the intensity of an excitation pulse delivered to the motoneuron pool. The effect is to regulate the rate at which joint torque, and consequently acceleration, increases. 8. Movements of variable distance, speed, accuracy, and load are shown to be controlled by one of two consistent sets of rules for muscle activation. These rules apply to the control of both the agonist and antagonist muscles. Rules of activation lead to distinguishable patterns of EMG and torque development. All observable changes in movement kinematics are explained as deterministic consequences of these effects.

Elbow Joint↗
PubMed1988

Practice improves even the simplest movements.

Three subjects practiced accurate, fast elbow flexions of 54 degrees to a 3 degrees wide target. Movements of 36 degrees, 54 degrees and 72 degrees were then tested. Comparison over the three distances showed that the normally monotonic relationship between movement distance and movement time is alterable by specific training. Subjects learn to go faster over the practiced distance by refining their neural commands to the muscles. The benefits of practice only partially transfer to other distances. We conclude that many of the relationships seen among movement variables in simple tasks are plastic in nature and affected by prior experience.

Adult↗
PubMed1988

Accuracy constraints upon rapid elbow movements.

Kinematic and myoelectric variables associated with rapid elbow-flexion movements of various distances to targets of various widths were studied. The movement time in these experiments conformed to Fitts' law: movement time increased with target distance and decreased with target width. Peak movement velocity, electromyograph (EMG) duration, and EMG quantity were poorly described by Fitts' law, for increases in target width were accompanied by increases in these variables. We show with regression equations, using separate weighting coefficients, that kinematic and myoelectric variables can be related to distance and target width. The use of distance and target width as independent variables allows us to suggest that the literature does not agree on the relation between EMG and distance moved partly because of the influences of the target on this relationship. We propose that human voluntary movement involves a subject "strategy," or set of internal constraints, that affect movement outcome. Significant elements of this strategy, such as how accurately to perform the task, may not be recognized or controlled in many movement paradigms, in spite of uniform instruction to subjects and similar apparatus.

Journal Article↗
PubMed1986

Movement deficits caused by hyperexcitable stretch reflexes in spastic humans.

Spastic patients were instructed to make accurate, rapid ankle dorsiflexion and plantarflexion movements over different distances to a target. Ankle position and surface electromyograms (EMGs) from tibialis anterior (TA) and soleus (SOL) muscles were recorded. In 3 of 8 spastic patients tested, dorsiflexion evoked velocity-dependent activation of the antagonist (SOL) muscle which impeded the movement to the extent that the limb unintentionally reversed movement direction. We propose that this activation is reflex in origin since it is tightly synchronized, has a large peak amplitude, occurs about 50 ms after the initiation of the movement, and is velocity dependent. One of the 3 patients who had reflex-induced antagonist activation in dorsiflexion also demonstrated sustained clonus during plantarflexion. This usually occurred only if the target had been overshot so that the return of the limb stretched the soleus muscle and triggered clonus. We conclude that in some patients, hyperactive stretch reflexes cause movement deficits.

Adult↗
PubMed1985

A note on accepting the null hypothesis: problems with respect to the mass-spring and pulse-step models of movement control.

Models are sometimes developed on the premise that there are no differences between two or more conditions regardless of experimental manipulation. This article argues that unless a very sensitive experiment (or series of experiments) was conducted, such conclusions are often premature. Design and statistical factors such as alpha level, variability, sample size, and treatment effect are all determinants of the sensitivity of the experiment. It is sometimes the case that an experiment produces differences between means and yet the null hypothesis is not rejected because of high variability within experimental conditions or because too few subjects were used. Unless the probability of detecting a difference between groups is known, it would seem unwise to conclude that no difference exists. Judgment on the model should be suspended. Examples are taken from the mass-spring and pulse-step models fro voluntary movement control to illustrate the problem.

Journal Article↗
PubMed1984

Electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions.

The purposes of this study were: a) to investigate electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions, and b) to investigate the role of antagonist coactivation under these same conditions. Five adult males performed maximal knee extensions and flexions on a modified Orthotron isokinetic dynamometer. Tests were done at four speeds (100-400 degrees/sec) and under two counterbalanced conditions: extension followed by flexion (E/F) and flexion followed by extension (F/E). Simultaneous recordings of torque, knee joint position and agonist/antagonist EMG changes from the quadriceps and hamstring musculature were collected and analyzed. No consistent EMG patterns emerged that inferred intermittent surges of muscular activity as the primary mechanism yielding double peaked torques that characteristically occur in isokinetic exercise. Further analyses revealed relatively small co-contractions of antagonists during the various phases of movement. The findings suggest that gravity and inertia of the limb/lever system were the major factors responsible for limb deceleration and substantive antagonist co-contraction was not required for braking. If isokinetic knee flexion and extension exercises are used for conditioning or developmental purposes of healthy subjects, any distraction of the co-contracting antagonist from the recorded force of the agonist appears to be small once the activity is learned.

Adolescent↗
PubMedDate not supplied

"Adequate control theory" for human single-joint elbow flexion on two tasks.

The control of distance and speed during single-joint human elbow flexion is accomplished by different models of activating the motoneuron pools. Distance is controlled by modulating the duration of activation, while speed is controlled by modulating the intensity. The experiments reported on here compare movements of different distances under two sets of instructions: subjects moved either as fast and accurately as possible or in a specified time. The first task showed duration modulation, whereas the second, which required simultaneous control of distance and speed, showed both duration and intensity modulation. These results are interpreted in the context of a model for motor control, predicated on the existence of movement plans that use prior knowledge of the dynamics of the movement task to generate muscle activation patterns that produce joint torques. These plans use a simple algorithm based upon parameters of the task such as distance, load, and speed. From this plan, the kinematic trajectory emerges.

Adult↗