Biomedical subjects

G L Almeida

Publications and source records attributed to G L Almeida.

15 recordsLinked to original sources

PubMed2006

Postural strategy to keep balance on the seesaw.

This work investigates the kinematic and electromyography (EMG) strategy used by the central nervous system (CNS) to keep equilibrium during anterior-posterior balance on seesaws with different degrees of instability. The movement of hip, knee, and ankle were reconstructed using a 3D motion-analysis system and the EMG activities of selected ankle, knee, and hip muscles were recorded. Balance was kept mainly at the ankle joint. The EMG patterns of the gastrocnemius and anterior tibialis alternated between agonist and antagonist bursts. The agonist burst started before the end of the lengthening phase and was prolonged until the end of the shortening phase. The EMG activities of the muscles crossing the knee and hip joints were characterized by a pattern of generalized co-activation. The movements at these two joints were very small, suggesting a neural or biomechanical constraint underlying the operations of the equilibrium control. Our results also indicate that the strategy to keep balance on the seesaw is qualitatively the same for the different levels of mechanical demands in terms of the seesaw's instability.

Adult↗

PubMed2005

Coupling between muscle activities and muscle torques during horizontal-planar arm movements with direction reversal.

In this study we investigated the hypothesis that the simple set of rules used to explain the modulation of muscle activities during single-joint movements could also be applied for reversal movements of the shoulder and elbow joints. The muscle torques of both joints were characterized by a triphasic impulse. The first impulse of each joint accelerated the limb to the target and was generated by an initial burst of the muscles activated first (primary mover). The second impulse decelerated the limb to the target, reversed movement direction and accelerated the limb back to the initial position, and was generated by an initial burst of the muscles activated second (secondary movers). A third impulse, in each joint, decelerated the limb to the initial position due to the generation of a second burst of the primary movers. The first burst of the primary mover decreased abruptly, and the latency between the activation of the primary and secondary movers varied in proportion with target distances for the elbow, but not for the shoulder muscles. All impulses and bursts increased with target distances and were well coupled. Therefore, as predicted, the bursts of muscle activities were modulated to generate the appropriate level of muscle torque.

Adaptation, Physiological↗

PubMed2000

Effect of age and gender in the control of elbow flexion movements.

In previous studies of rapid elbow movements in young healthy men, characteristic task-dependent changes in the patterns of muscle activation when movement speed or distance was varied have been reported. In the present study, the authors investigated whether age or gender is associated with changes in the patterns of muscle activity previously reported in young men. Arm movements of 10 healthy older and 10 healthy younger participants (5 men and 5 women in each group) were studied. Surface electromyograms (EMGs) from agonist (biceps) and antagonist (triceps) muscles, kinematic and kinetic parameters, as well as anthropometric and strength measures were recorded. All 4 groups of participants showed similar task- (distance or speed) dependent changes in biphasic EMG activity. Similar modulation of the initial rate of rise of the EMG, integrated agonist and antagonist EMG activity, as well as their relative timing were observed in all 4 groups. Those results suggest that older individuals of both genders retain the control strategies for elbow movements used by young individuals. Despite the qualitative similarities in the patterns of muscle activation, the men moved more quickly than the women, and younger participants moved more quickly than older participants. Those performance differences could not be explained in terms of differences in body size and strength alone.

Adult↗

PubMed2000

Horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with down syndrome.

We examined the systematic variation in shoulder and elbow torque, as well as movement kinematics, for horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with Down syndrome. Eight neurologically normal individuals and eight individuals with Down syndrome performed horizontal, planar reversal movements to four different target locations. The four locations of the targets were chosen such that there is a systematic increase in elbow interaction torque for each of the four different target locations. This systematic increase in interaction torque has previously been shown to lead to progressively larger movement reversal errors, and trajectories that do not show a sharp reversal of direction, for movements to and from the target in patients who have proprioceptive abnormalities. We computed joint torques at the elbow and shoulder and found a high correlation between elbow and shoulder torque for the neurologically normal subjects. The ratio of joint torques varied systematically with target location. These findings extend previously reported findings of a linear synergy between shoulder and elbow joints for a variety of point-to-point movements. There was also a correlation between elbow and shoulder torque in individuals with Down syndrome, but the magnitude of the correlation was less. The ratio of joint torques changed systematically with target direction in individuals with Down syndrome but was slightly different from the ratio observed for neurologically normal individuals. The difference in the ratio was caused by the generation of proportionately more elbow torque than shoulder torque. The fingertip path of individuals with Down syndrome showed a sharp reversal in moving toward and then away from the target. In this respect, they were similar to neurologically normal individuals but dissimilar to individuals with proprioceptive deficits. Finally, we observed that individuals with Down syndrome spend proportionately more time in the vicinity of the target than normal individuals. Collectively these results show that there is a systematic relationship between joint torques at the elbow and shoulder. This relationship is present for reversal movements and is also present in individuals with Down syndrome.

Adolescent↗

PubMed1999

Effects of direction and curvature on variable error pattern of reaching movements.

A number of studies have analyzed various indices of the final position variability in order to provide insight into different levels of neuromotor processing during reaching movements. Yet the possible effects of movement kinematics on variability have often been neglected. The present study was designed to test the effects of movement direction and curvature on the pattern of movement variable errors. Subjects performed series of reaching movements over the same distance and into the same target. However, due either to changes in starting position or to applied obstacles, the movements were performed in different directions or along the trajectories of different curvatures. The pattern of movement variable errors was assessed by means of the principal component analysis applied on the 2-D scatter of movement final positions. The orientation of these ellipses demonstrated changes associated with changes in both movement direction and curvature. However, neither movement direction nor movement curvature affected movement variable errors assessed by area of the ellipses. Therefore it was concluded that the end-point variability depends partly, but not exclusively, on movement kinematics.

Adult↗

PubMed1997

Multidimensional assessment of motor function in a child with cerebral palsy following intrathecal administration of baclofen.

This case report describes an 11-year-old boy with spastic diplegia whose reflex status, range of motion (ROM), strength, and motor performance were measured before and after implantation of an indwelling system for delivery of intrathecally administered baclofen. Before baclofen use, the subject experienced clonus that interfered with walking, needed assistance with transfers, and was unable to independently put on underwear and socks. Measures of spasticity, kinematics and electromyographic activity during voluntary movements, ROM, Gross Motor Function Measure (GMFM) scores, and self-reports of change were obtained at baseline, before and after bolus baclofen injection, during a double-blind placebo-controlled clinical trial of baclofen administration via an indwelling pump, and after 1 and 2 years of baclofen therapy. Spasticity, Babinski reflexes, clonus, strength, and coactivation of antagonist muscles during voluntary movement were decreased shortly after baclofen administration began. Hip and ankle ROM increased, upper-extremity movement speed increased, independence in dressing and transfers improved, and orthoses were discarded. After 1 and 2 years, GMFM scores were 7.8% and 6.4% above baseline, respectively; the subject won a fitness award. After 2 years, ROM was worse than at baseline and concerns regarding hip subluxation arose. Single-joint movement control and independence improved and spasticity decreased during baclofen administration.

Activities of Daily Living↗

PubMed1997

Directional control of planar human arm movement.

We examined the patterns of joint kinematics and torques in two kinds of sagittal plane reaching movements. One consisted of movements from a fixed initial position with the arm partially outstretched, to different targets, equidistant from the initial position and located according to the hours of a clock. The other series added movements from different initial positions and directions and >40-80 cm distances. Dynamic muscle torque was calculated by inverse dynamic equations with the gravitational components removed. In making movements in almost every direction, the dynamic components of the muscle torques at both the elbow and shoulder were related almost linearly to each other. Both were similarly shaped, biphasic, almost synchronous and symmetrical pulses. These findings are consistent with our previously reported observations, which we termed a linear synergy. The relative scaling of the two joint torques changes continuously and regularly with movement direction. This was confirmed by calculating a vector defined by the dynamic components of the shoulder and elbow torques. The vector rotates smoothly about an ellipse in intrinsic, joint torque space as the direction of hand motion rotates about a circle in extrinsic Cartesian space. This confirms a second implication of linear synergy that the scaling constant between the linearly related joint torques is directionally dependent. Multiple linear regression showed that the torque at each joint scales as a simple linear function of the angular displacement at both joints, in spite of the complex nonlinear dynamics of multijoint movement. The coefficients of this function are independent of the initial arm position and movement distance and are the same for all subjects. This is an unanticipated finding. We discuss these observations in terms of the hypothesis that voluntary, multiple degrees of freedom, rapid reaching movements may use rule-based, feed-forward control of dynamic joint torque. Rule-based control of joint torque with separate dynamic and static controllers is an alternative to models such as those based on the equilibrium point hypotheses that rely on a positionally based controller to produce both dynamic and static torque components. It is also an alternative to feed-forward models that directly solve the problems of inverse dynamics. Our experimental findings are not necessarily incompatible with any of the alternative models, but they describe new, additional findings for which we need to account. The rules are chosen by the nervous system according to features of the kinematic task to couple muscle contraction at the shoulder and elbow in a linear synergy. Speed and load control preserves the relative magnitudes of the dynamic torques while directional control is accomplished by modulating them in a differential manner. This control system operates in parallel with a positional control system that solves the problems of postural stability.

Arm↗

PubMed1996

Coordinating movement at two joints: a principle of linear covariance.

1. Six subjects performed fast, "single-joint" flexions at either the elbow or shoulder over three angular distances in a sagittal plane. Movement endpoints were located to require flexion of only a single, "focal" joint, without any external, mechanical constraint on the other, "nonfocal" joint. Three subjects performed another series of movements between two targets while moving along different paths and in which both joints were flexed. 2. We compared the torque patterns that were produced at the two joints. For single-joint movements, they were both biphasic pulses that accelerated and then decelerated the limb. 3. The torque at the nonfocal joint of a single joint movement was very close to linearly proportional to that at the focal joint throughout the movement. Elbow and shoulder torques differed by a linear scaling constant and went through extrema and zero crossings almost simultaneously. 4. In contrast, during movements in which subjects were explicitly instructed to use a hand path they would not naturally, use the linear interjoint torque scaling rule did not apply. This demonstrated that when we wish to move along a path between two targets that is not produced by linear torque covariation, we are able to modify that rule at will. 5. We speculate that linear, dynamic covariation of the torque patterns across two joints may be an important principle for reducing the number of degrees of freedom that the nervous system must independently control in performing unconstrained limb movements over naturally chosen paths.

Analysis of Variance↗

PubMed1996

Organization of a simple two-joint synergy in individuals with Down syndrome.

Subjects with Down syndrome and age- and gender-matched control subjects performed discrete elbow or wrist, flexion or extension movements in a sagittal plane, moving one of the joints as fast as possible. The hand was either pronated or supinated. In control subjects, alternating bursts of activity were seen in the agonist-antagonist muscle pair controlling the nonfocal joint. Subjects with Down syndrome, in most series, demonstrated simultaneous bursts of activity in the flexor and extensor muscles controlling both joints. This group difference was particularly pronounced for the muscles controlling the nonfocal joint. We assume that the central nervous system may use two strategies to avoid flapping of a postural joint. The more universal co-contraction strategy in Down syndrome may be viewed as an adaptive feature reflecting a general tendency of these persons to trade efficacy for safety.

Adult↗

PubMed1995

The effects of intrathecally administered baclofen on function in patients with spasticity.

The purpose of this article is to review the literature on the effects of intrathecally administered baclofen on impairment in spasticity and muscle activation patterns, on functional limitations in mobility and self-care, and on disability in daily life roles. We found plentiful evidence of improvement in spasticity, spasms, and bladder function and some reports of improved patterns of muscle activation and kinematics of single-joint movement. Improved ability to accomplish transfers, self-care, and locomotion is less consistently studied but has also been reported in about 60% to 70% of patients. Evidence of improved quality of life is primarily anecdotal but may be found in 10% to 30% of patients. We conclude that research protocols should be developed to clarify effects on control of voluntary movement, functional limitations, and quality of life.

Activities of Daily Living↗

PubMed1995

Organizing principles for voluntary movement: extending single-joint rules.

1. Four subjects performed fast flexions of the elbow or shoulder over three different distances. Elbow flexions were performed both in a horizontal, single-degree-of-freedom manipulandum and in a sagittal plane with the limb unconstrained. Shoulder flexions were only performed in the sagittal plane by the unconstrained limb. We simultaneously recorded kinematic and electromyographic (EMG) patterns at the "focal" joint, that which the subject intentionally flexed, and at the other, "nonfocal" joint that the subject had been instructed to not flex. 2. Comparisons of the elbow EMG patterns across tasks show that agonist and antagonist muscles were similar in pattern but not size, reflecting the net muscle torque patterns. Comparisons at the shoulder also revealed similar EMG patterns across tasks that reflected net muscle torques. 3. Comparisons of EMG patterns across joints show that elbow and shoulder flexors behaved similarly. This was not true of the extensors. The triceps EMG burst was delayed for longer distances but the posterior deltoid had an early, distance-invariant onset. 4. Similarities in EMG reflect torque demands required at the focal joint to produce flexion and at the nonfocal joint to reduce extension induced by dynamic interactions with the focal, flexing joint. These similarities appear despite very different kinematic intentions and outcomes. This argues against a strong role for length-sensitive reflexes in their generation. 5. These results support the hypothesis that movements are controlled by muscle activation patterns that are planned for the expected torque requirements of the task. This general rule is true whether we are performing single-joint or multiple-joint movements, with or without external constraints. The similarities between single-joint and multijoint movement control may be a consequence of ontogenetic development of multijoint movement strategies that prove useful and are therefore also expressed under the constrained conditions of specialized tasks such as those performed in single-joint manipulanda.

Adult↗

PubMed1995

Paradoxical effects of practice of fast single-joint movements.

We studied the effects of extensive practice of fast, unidirectional, single-joint elbow flexions against a small extending torque bias upon the kinematic and electromyographic (EMG) characteristics of the movements as well as upon the reconstructed hypothetical control patterns (equilibrium trajectories). The subjects were tested at different distances, both with and without the bias torque prior to and after the practice sessions. The basic finding was paradoxical: The subjects did not improve their performance at the practiced task (against the bias) and at other distances in the same condition; however, they showed an increase in movement speed and a decrease in movement time at all distances in unpracticed conditions (without the bias). Changes in the EMG patterns were similar in both conditions. We hypothesize that the principle of learning the dynamics of interaction with the experimental setup in combination with a very steep learning curve form the basis for the observed paradoxical effects of practice. The equilibrium-point hypothesis of movement control provides the least controversial description of these effects as compared to the force-control and EMG-control approaches.

Adult↗

PubMed1994

Practice and transfer effects during fast single-joint elbow movements in individuals with Down syndrome.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the effects of prolonged practice of a simple motor task (a fast, unidirectional single-joint movement) on different indexes of motor performance in individuals with Down syndrome. SUBJECTS: Eight individuals with Down syndrome were tested before and after practice involving 1,100 movements. METHODS: The test consisted of three series of elbow flexion movements. In the first series, the subjects were asked to move "as fast as possible" over four distances. In the second series, the subjects moved over one distance at a "comfortable speed." The initial position of the elbow joint for these two series of movements was 55 degrees into flexion (full elbow extension equals 0 degrees). In the third series, the subjects were also asked to move "as fast as possible" over two distances, but from another initial elbow position (73 degrees into flexion). RESULTS: After training over a 2-week period, all subjects improved their performance on all tasks as reflected by both kinematic and electromyographic data. In particular, they increased the quantity of the agonist activity, decreased the antagonist onset latency, and doubled their peak velocity. They were able to transfer the improvement in their performance to the nontrained distances and to the different starting position. Subjects decreased their movement time by proportionally decreasing both the acceleration and deceleration times. CONCLUSION AND DISCUSSION: This study supports the idea that subjects with Down syndrome can use patterns of muscle activation that are qualitatively indistinguishable from those used by individuals who are neurologically normal. With appropriate training, individuals with Down syndrome achieved similar levels of motor performance to that described in the literature for individuals who are neurologically normal.

Acceleration↗

PubMed1993

Kinematic description of variability of fast movements: analytical and experimental approaches.

Analysis of variability of fast aimed movements predicts the properties of trajectory variance. The analysis is based on a kinematic model with nonlinear changes in "internal time". The purpose of the work was to identify different sources of variability and their influence on the trajectory variance. An analytical expression for the speed-accuracy trade-off is introduced. Experiments were performed with subjects making single-joint elbow flexion movements over different distances as fast as possible with their eyes closed to memorized targets. Standard deviation of movement trajectory increased during the first part of the movement and subsequently decreased. The variance peaked after the time of peak velocity, close to the time of peak deceleration. A dependence of the trajectory variance on movement distance (speed-accuracy trade-off) was seen during the movement (at times of peak velocity and peak deceleration) but not after the movement termination. We conclude that the previously reported drop in the variability of movement trajectory during the deceleration phase does not necessarily mean a compensation by the control system but may result from purely kinematic properties of the movement. The importance of the time of measurement for analysis of the speed-accuracy trade-offs is emphasized.

Biomechanical Phenomena↗

PubMed1993

Preprogrammed reactions in individuals with Down syndrome: the effects of instruction and predictability of the perturbation.

Preprogrammed reactions to unexpected loadings and unloadings of an elbow joint resisting an extending bias load were studied in subjects with Down syndrome. The subjects were instructed to either "let go" or "return back as fast as possible." Both predictable and unpredictable perturbation directions were used. Integrated electromyograms of the two elbow flexors and two elbow extensors were used to characterize the preprogrammed reactions. All the subjects were able to modulate their preprogrammed reactions in response to a change in the instruction. They were also able to grade the preprogrammed responses corresponding to the magnitude of the perturbation. Two basic patterns of modulation were observed, "reciprocal" and "coactivation." There were no effects of the predictability of the perturbation direction. Reconstructed joint compliant characteristics suggested an unchanged gain in the arc of the tonic stretch reflex. We propose that there are no abnormalities in the preprogrammed reactions of some individuals with Down syndrome. The apparent "clumsiness" of individuals with Down syndrome in a changing environment is assumed to reflect an adaptation to their impaired decision-making ability. The high variability of motor performance in subjects with Down syndrome may result from mixing different strategies for solving motor tasks.

Adolescent↗