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Biomedical subjects

M Latash

Publications and source records attributed to M Latash.

7 recordsLinked to original sources
PubMed2000

The effects of instability and additional hand support on anticipatory postural adjustments in leg, trunk, and arm muscles during standing.

We investigated the role of additional perceptual information (finger touch) and additional mechanical support (hand grasp) on the anticipatory postural adjustments (APAs) associated with fast arm movements performed by standing subjects. The subjects performed fast, unilateral shoulder ante-flexion movements while standing on a stable force platform or on an unstable board with instability in a sagittal or in a frontal plane. Changes in the background activity of leg, trunk, and arm muscles and displacements of the center of pressure were quantified within time intervals typical for APAs. Leg and trunk muscles showed a significant drop in APAs with added finger touch and no further changes when the touch was substituted with hand grasp. Arm muscles showed no changes or a small drop in APAs with touch and a significant increase in APAs with grasp. These changes were seen during both stable and unstable standing. We conclude that APAs can show changes associated not only with mechanical aspects of a task, but also with its perceptual aspects. Based on the equilibrium-point hypothesis of motor control, an additional analysis of APAs was performed. With additional support, we observed a significant modulation of an index related to the co-activation of agonist-antagonist muscle pairs, while no changes in reciprocal activation were found. A similar analysis performed across all the leg and trunk muscles with respect to control of the center of mass lead to similar results. We conclude that the central nervous system seems to simplify adjustments of control patterns to changes in task parameters by modulation of only one of the two major central commands.

Adult↗
PubMed2000

The roles of proximal and distal muscles in anticipatory postural adjustments under asymmetrical perturbations and during standing on rollerskates.

OBJECTIVES: The study addresses two controversial issues surrounding the nature of anticipatory postural adjustments (APAs). The first deals with the reproducible APA patterns in proximal postural muscles and variable APA patterns reported for the muscles controlling the ankle joint (TA-SOL). We hypothesized that the TA-SOL muscles participate mainly in the compensation of lateral and rotational perturbations, in particular those associated with asymmetrical movements. The second issue deals with decreased APAs reported during both very stable and unstable standing. We hypothesized that APA changes during unstable standing might depend on the actual mechanical nature of instability. METHODS: Eight healthy subjects were recruited who had had no prior experience with rollerskates. They performed series of bilateral and unilateral, flexion and extension movements during regular standing and bilateral movements during standing on rollerskates. EMG changes and shifts of the center of pressure were analyzed within a time window typical of APAs. RESULTS: We found that APAs in proximal muscles were decreased during unilateral shoulder movements as compared to APAs during bilateral movements but did not show right-left differences. In contrast, the distal muscles (TA-SOL) showed little involvement during bilateral movements, while a clear right-left asymmetry was seen during unilateral movements. Bilateral movements performed while standing on rollerskates were accompanied by unchanged APAs in the proximal muscle pairs and increased APAs in the TA-SOL pair. CONCLUSIONS: We conclude that the proximal muscles provide a general pattern counteracting expected perturbations in the anterior-posterior direction while the distal muscles deal with asymmetrical perturbations and the modulation of APAs in unusual conditions such as standing on rollerskates. There seems to be no unambiguous relation between the magnitude of APAs and the stability of standing: Depending on the exact mechanical nature of postural instability, it could be associated with qualitatively different changes in the APAs.

Adult↗
PubMed1996

Myogenic and central neurogenic factors in fatigue in multiple sclerosis.

Short episodes of electrical stimulation were applied to the right quadriceps muscle of patients with multiple sclerosis (MS) and healthy subjects at different times during 60 sec sustained voluntary muscle contractions at 0 to 100% levels of maximal voluntarily generated joint torque. The amplitude of electrically induced increments of torque (delta T) has been shown to depend upon both the level of muscular contraction and time from the beginning of the contraction. The dependence of delta T upon the time from the beginning of contraction has been assumed to reflect muscle fatigue. Patients with MS demonstrated an apparent involvement of central neurogenic mechanisms in fatigue manifested as a drop in muscle torque during sustained contractions at 75 and 100% levels when electrical stimulation was able to induce considerable increments in muscle torque. These patients also demonstrated a dependence of delta T upon the contraction level suggesting that they did not produce maximal voluntary contraction torque in the pre-trial. Fatigue in MS is due to central, neurogenic factors and does not seem to involve any myogenic factors such as might be related to secondary muscle changes due to the long-standing disorder. The subjective feeling of tiredness ('fatigue') may be related to a dissociation between central motor commands ('effort') and their mechanical consequences.

Adult↗
PubMed1989

Intrathecal baclofen for severe spinal spasticity.

We studied the effect of the intrathecal infusion of baclofen, an agonist of gamma-aminobutyric acid, on abnormal muscle tone and spasms associated with spinal spasticity, in a randomized double-blind crossover study. Twenty patients with spinal spasticity caused by multiple sclerosis or spinal-cord injury who had had no response to treatment with oral baclofen received an intrathecal infusion of baclofen or saline for three days. The infusions were administered by means of a programmable pump implanted in the lumbar subarachnoid space. Muscle tone decreased in all 20 patients (mean [+/- SD] Ashworth score for rigidity, from 4.0 +/- 1.0 to 1.2 +/- 0.4; P less than 0.0001), and spasms were decreased in 18 of the 19 patients who had spasms (mean [+/- SD] score for spasm frequency, from 3.3 +/- 1.2 to 0.4 +/- 0.8; P less than 0.0005). Tests for motor function, neurologic examination, and assessments by the patients correctly indicated when baclofen was being infused in all cases. All patients were then entered in an open long-term trial of continuous infusion of intrathecal baclofen. During a mean follow-up period of 19.2 months (range, 10 to 33), muscle tone has been maintained within the normal range (mean Ashworth score, 1.0 +/- 0.1) and spasms have been reduced to a level that does not interfere with activities of daily living (mean spasm score, 0.3 +/- 0.6). No drowsiness or confusion occurred, one pump failed, and two catheters became dislodged and had to be replaced. No infections were observed. Our observations suggest that intrathecal baclofen is an effective long-term treatment for spinal spasticity that has not responded to oral baclofen.

Adult↗
PubMedDate not supplied

[Hypothesis on the equilibrium point and variability of amplitude, speed and time of single-joint movement].

Problems of single-joint movement variability are analysed in the framework of the equilibrium-point hypothesis (the lambda-model). Control of the movements is described with three parameters related to movement amplitude speed, and time. Three strategies emerge from this description. Only one of them is likely to lead to a Fitts' type speed-accuracy trade-off. Experiments were performed to test one of the predictions of the model. Subjects performed identical sets of single-joint fast movements with open or closed eyes and some-what different instructions. Movements performed with closed eyes were characterized with higher peak speeds and unchanged variability in seeming violation of the Fitt's law and in a good correspondence to the model.

Humans↗