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R L Segal

Publications and source records attributed to R L Segal.

At least 19 recordsLinked to original sources
PubMed2006

Leg muscles differ in spatial activation patterns with differing levels of voluntary plantarflexion activity in humans.

BACKGROUND/AIMS: The purpose of this study was to investigate the differential activity between and within individual muscles commonly grouped as plantarflexors. Much of the previous information gathered on plantarflexor activity has been attained using electromyographic recordings. In this study, we used magnetic resonance imaging which allowed us to look at spatial differences in activation. METHODS: Twenty-two human subjects exercised under four different conditions - combinations of loads of 25 or 65% of maximum voluntary contraction (MVC) and the direction of plantarflexion at a sagittal and off-sagittal angle. Before and after each exercise condition, T2-weighted magnetic resonance images were collected. Regions of interest were drawn around the lateral gastrocnemius (LG), medial gastrocnemius (MG), soleus (SOL), peroneus longus (PER) and tibialis anterior (TA) muscles and analyzed for differences. RESULTS: Significant increases in T2 relaxation times during 25% MVC conditions were found for PER and, during the 65% MVC, for all four muscles considered plantarflexors (LG, MG, SOL, PER). No significant differences were found between sagittal and off-sagittal conditions. Within LG and MG, greater increases in T2 times with exercise were found in proximal regions compared with distal regions. CONCLUSION: These results are consistent with suggestions that individual members of muscle groups are capable of differential activity and that for at least some muscles, such differential activity may exist within subvolumes of individual muscles.

Adolescent↗
PubMed2001

Functional activation of the extensor carpi radialis muscles in humans.

OBJECTIVES: To assess activity of radial wrist extensors caused by isometric radial deviation and extension by using magnetic resonance imaging (MRI) and to assess measures that might be used to normalize T2-weighted data. DESIGN: Two-way analysis of variance (ANOVA) design. SETTING: Laboratory and children's hospital. PARTICIPANTS: Three healthy volunteers. INTERVENTIONS: Ten repetitions of 10-second randomly ordered 30% or 60% of maximum voluntary isometric contractions toward wrist extension or radial deviation. MAIN OUTCOME MEASURES: Average T2 values from T2-weighted MR images of the extensor carpi radialis brevis (ECRB) and the extensor carpi radialis longus (ECRL), flexor digitorum profundus (FDP), and radius marrow were determined across 7 sections and 4 exercise bouts and a preexercise condition. RESULTS: Significant differences across task and across sections were determined. Post hoc analysis revealed differences in activity between proximal and distal ECRB and ECRL during an exercise and differential activation of the same muscle across the 2 exercise tasks. Bone marrow and FDP did not show task-related changes. The range of average T2 values of bone marrow across sections was greater than a muscle (FDP) that was not the target of the exercise protocol. However, FDP did show small but significant differences across sections. CONCLUSIONS: T2-weighted MR images can be used to study muscle activation at 30% and 60% of maximum voluntary contractions. The use of inactive muscle and bone marrow for normalizing data requires further investigation.

Adult↗
PubMed1996

Determining consistency of elbow joint threshold angle in elbow flexor muscles with spastic hypertonia.

BACKGROUND AND PURPOSE: Threshold angle, the point in passive range of motion where a muscle response or torque change is elicited, may be a potentially valid measure of hypertonus. Because the relationship of initial muscle length to threshold angle has not been addressed previously, this preliminary study examined whether starting elbow joint position and speed of stretch to elbow flexor muscles affect threshold angle. SUBJECTS: Five subjects with stroke-induced hypertonia of the elbow flexor muscles participated. METHODS: Two starting angles and two designated stretch speeds were applied randomly by a torque motor at each of three testing sessions. RESULTS: Starting angle, subject, and session affected threshold angle. A 90-degree starting angle at a stretch speed of approximately 1.0 radian/s produced the most consistent threshold angles between sessions within subjects, and threshold angle was relatively consistent for some subjects, irrespective of speed. CONCLUSION AND DISCUSSION: If future research indicates that these data can be generalized, the use of threshold angle as a consistent measure of hypertonia will require comparison within individuals, use of a consistent starting angle, and a movement condition of a 90-degree starting angle and an approximate movement speed of 1.0 radian/s across sessions.

Adult↗
PubMed1996

Long latency ankle responses to dynamic perturbation in older fallers and non-fallers.

OBJECTIVE: The purpose of this study was to examine the effects of falling history and aging on the latency and magnitude of long latency responses in the lateral gastrocnemius (LG) and tibialis anterior (TA) muscles of older adults. DESIGN: Single observation study. SETTING: Emory University School of Medicine, Center for Rehabilitation Medicine, serving the greater Atlanta, Georgia, area. PARTICIPANTS: There were 62 community-dwelling adults aged 60 or older, 32 with a history of two or more unexplained falls in the past year and 30 with no history of falls in the past year. MEASUREMENTS: The electromyographic activity of the gastrocnemius and tibialis anterior muscles was recorded bilaterally during repeated 10 degree dorsiflexion perturbations to standing subjects at the acceleration of gravity and a velocity of approximately 100 deg/sec. The latency and magnitude of the long latency EMG responses (LLR) of both muscles were determined and compared between individuals by falls history and by decades of age. MAIN RESULTS: No significant differences between falls status groups existed for mean LLR latencies or magnitudes of either LG or TA. Attenuation of the LLR throughout the trials was significantly different between groups. Non-fallers demonstrated attenuation of the LG magnitude over the first five stretches. Fallers showed maladaptation of the LG response, with the latency becoming shorter over 25 trials. More than half of the subjects in both groups had one or more instances of temporal reversal of the response latencies, with the TA response occurring earlier than the LG response during the first five stretches. No differences existed in the LLR between age decades within faller or non-faller groups. A timed measure of mobility (Up & Go) showed a significant difference between falls status, but not between age decades in either group. CONCLUSIONS: Lack of differences between falls status and age decade groups over all trials suggests that LLRs remain intact between older fallers and non-fallers and between older age groups. The mechanism of perturbation is a distinguishing feature of this study and probably contributes to our findings. The appearance of an atypical response strategy in both groups, where the TA response often occurs before the LG response, has raised the question of whether there is always a stereotypical pattern of LLRs during postural perturbations outside the experimental setting.

Accidental Falls↗
PubMed1996

Reducing human biceps brachii spinal stretch reflex magnitude.

1. Nine subjects received 6 baseline and 24 training sessions, each consisting of 250 elbow joint stretch perturbations into extension. The training sessions were designed to reduce the subjects' biceps brachii spinal stretch reflexes (SSR). Changes in longer-latency responses and short-latency brachioradialis responses were also monitored. Background electromyogram activity was recorded from the lateral head of triceps brachii during the biceps sampling intervals. These data were compared with those form 12 control subjects who received equal numbers of stretches over an extended baseline (i.e., without application of a training paradigm). 2. Training subjects reduced their mean biceps SSR responses by 24%, whereas control subjects increased their responses by 12% When changes in activity were grouped by sets of six consecutive sessions following the baseline interval, group-by-time interaction was observed. Training subjects showed significant reductions from baseline after the first raining set. The increased magnitude of biceps SSR for control subjects was significantly larger than baseline in sets 2-5. After the first training interval, all subsequent differences between groups were statistically significant. 3. The brachioradialis showed greater response variability, but these responses paralleled those seen in biceps brachii. The training group reduced their brachioradialis responses by 18%, whereas the control group increased their responses by 12%. Background activity recorded over the lateral head of triceps brachii during the biceps brachii SSR window became smaller in both groups. 4. Comparison of data between control subjects and subjects who had undergone biceps SSR up-training in previous studies suggests that the small increase seen among the present control subjects was probably not the result of a direct training effect. 5. Baseline differences in longer-latency response onset time were seen between groups. Over extended baseline sessions, longer-latency responses showed only a 1% onset, representing a change of 0.3 ms, in the control group. A 1.3% later onset, equaling a change of 1.1 ms, was observed over conditioning sessions in the training group. When analyzed by sets following baseline, neither group showed significant within- or between-group changes over time. 6. The magnitude of the longer-latency biceps brachii response showed 7% and 37% reductions for the control and training groups, respectively. No difference in set averages was seen within groups, but a significant difference was measured over sets 2-4 between groups. Reductions in the magnitude of longer-latency responses in training subjects were more obvious in later training sessions. 7. These data suggest that 1) the biceps brachii SSR can be reduced in human subjects; 2) concurrent changes are often observed in the synergist brachioradialis; and 3) the reduced biceps SSR magnitude is not linked to a compensatory increase in antagonist muscle activity. Reductions in the magnitude of longer-latency biceps brachii activity seen in parallel with the decreased SSR may imply that some degree of supraspinal processing is required to achieve this task.

Adolescent↗
PubMed1995

Contralateral and long latency effects of human biceps brachii stretch reflex conditioning.

Results from previous studies on monkeys and human subjects have demonstrated that the biceps brachii spinal stretch reflex (SSR) can be operantly conditioned. The extent to which conditioning paradigms influence contralateral SSRs or longer latency responses in the same limb has not been examined. Nine subjects were given 10 training sessions to either increase or decrease the size of their biceps brachii SSR. Group changes were compared to the mean of six baseline (control) sessions. Both groups showed progressive SSR changes over the training sessions. Up-trained subjects increased their SSR responses by an average of 135.3% above baseline, with the last three sessions showing a 237.5% increase, while down-trained subjects reduced their average SSR responses by 43.4%, with a 52.7% reduction over the last three sessions. ipsilateral longer latency responses showed average changes of 68.9% and -68.7% for up- and down-trainers, respectively. As in the case of SSRs, these responses changed progressively over sessions, with a 131.5% increase seen in the last three up-training sessions and an 82.4% reduction over the same period for down-trainers. Correlation coefficients between SSR and longer latency responses were high (R = 0.90, up-trainers; R = 0.87, down-trainers). Contralateral SSR and longer latency responses, measured in the absence of feedback and at least 10 min after ipsilateral conditioning, showed directional changes that were similar to the trained side, but their magnitudes were not as profound. Collectively, these data suggest that unilateral SSR conditioning affects spinal circuits controlling contralateral SSRs and influences longer latency responses.

Adult↗
PubMed1994

Operant conditioning of spinal stretch reflexes in patients with spinal cord injuries.

Hyperactive spinal stretch reflexes (SSRs) often occur with spinal cord injuries (SCI). These altered SSRs may impair movement. Recent studies in monkeys and human subjects have indicated that the magnitude of SSRs can be modulated using operant conditioning. The purpose of this study was to determine whether hyperactive biceps brachii SSRs could be operantly conditioned downward. Seventeen chronic (> 1 year postlesion) spinal cord-injured patients participated. Subjects were trained to keep biceps background (prestretch) electromyographic (EMG) activity and elbow angle at predetermined levels prior to having the elbow rapidly extended by a torque motor to elicit the biceps SSR. All subjects participated in six baseline sessions over a 2-week period. Then, subjects were randomly assigned to either control or training groups for the next 24 sessions over an 8-week period. By the end of the study, training subjects had significantly reduced biceps SSRs (t test, P < 0.001), while control subjects SSRs were not significantly reduced (t test, P > 0.05). The reduced SSRs persisted for up to 4 months following cessation of training. The results of this study support the hypothesis that hyperactive SSRs can be operantly conditioned downward in SCI patients.

Adolescent↗
PubMed1994

Immediate effects of the toe spreader on the tonic toe flexion reflex.

BACKGROUND AND PURPOSE: The purpose of the study was to determine whether the use of a toe spreader to inhibit the tonic toe flexion reflex (TTFR) immediately alters temporal-distance gait characteristics, plantar surface contact, or muscle activity in the limb exhibiting the TTFR of subjects with hemiparesis secondary to supraspinal lesion. SUBJECTS: Eighteen adults with hemiparesis secondary to supraspinal lesions served as subjects for the standing portion of the study. Sixteen of the subjects participated in the gait portion of the study. METHODS: The study was a randomized, within-subject, between-conditions comparison consisting of standing and gait phases, with four conditions for each phase (shoe off, toe spreader off/on, shoe on, toe spreader off/on). Measures performed were ink footprint gait analysis and integrated electromyography from the limb exhibiting the TTFR. RESULTS: Presence of the TTFR was reduced significantly with the use of the toe spreader. Velocity and cadence were increased significantly by use of the toe spreader. CONCLUSION AND DISCUSSION: The toe spreader may be a useful treatment option for improving gait. The clinical significance of these findings, however, will depend on the functional context of toe-spreader use.

Adult↗
PubMed1993

Genioglossi muscle activity in response to changes in anterior/neutral head posture.

Clinicians have acknowledged swallowing, tongue activity, and head posture as interdependent variables that must be concurrently examined. The purpose of this study was to evaluate genioglossus activity during swallowing, rest, and maximal tongue protrusion in two head positions (HPs) with a noninvasive recording device. Eight Angle Class I subjects were evaluated. Repeated measures were performed in a single session to record surface intraoral electromyographic (EMG) activity of the genioglossus muscles. Head position was measured in angular degrees from photographs. Three variables were measured in both the neutral-head position (NHP) and anterior-head position (AHP): (1) duration of genioglossus EMG during swallowing, (2) genioglossus EMG with the tongue at rest, and (3) genioglossus EMG during maximal isometric tongue protrusion. A Wilcoxin matched-pair signed-rank statistic was used for EMG analysis, and a paired sample t test statistic was used for head posture analysis. The angles measured for NHP and AHP within each subject were significantly different verifying two different head positions. Duration of swallowing was not significantly different between head positions. Resting genioglossus EMG and maximal isometric genioglossus EMG were statistically greater in the AHP. The data suggest that head positional changes may have an effect on genioglossus muscle activation thresholds. However, small differences in resting EMG activity between head positions suggests that the clinical significance needs further investigation.

Adult↗
PubMed1993

Compartmentalization of muscles and their motor nuclei: the partitioning hypothesis.

This review article is designed to expose physical therapists to an examination of muscle organization and the implications that this organization has for therapeutic applications. The partitioning hypothesis is based on the fact that an individual muscle is arranged in a more complex array than simply fibers attaching at aponeuroses, tendons, or bones with a single muscle nerve innervation. Neuromuscular compartments, which are distinct subvolumes of a muscle, each innervated by an individual muscle nerve branch and each containing motor unit territories with a unique array of physiological attributes, are described. In addition, the organization of individual muscles into these subunits is paralleled by the organization of their parent motoneurons within the spinal cord. These notions are detailed in a review of data derived from studies performed primarily in cat and rat models. Recent data derived from morphological and anatomical study of human muscles support the existence of similar neuromuscular partitions. These data are complemented by physiological studies, the results from which suggest that partitions may have functional or task-oriented roles; that is, different portions of one muscle may be called into play depending on the task demands of the situation. The importance of these observations for reconsidering how we provide clinical applications, such as neuromuscular stimulation or kinesiological monitoring, is discussed.

Animals↗
PubMed1992

Neuromuscular compartments in the human biceps brachii muscle.

Electrophysiological evidence suggests that the human biceps brachii muscle is organized into functional neuromuscular compartments. The purpose of this study was to determine whether there was an anatomical basis for these compartments. Dissection of the biceps revealed both architectural and nerve branching pattern compartmentalization within the muscle. Although the biceps brachii is grossly subdivided into long and short heads, these heads are further subdivided into roughly parallel architectural compartments. Moreover, these architectural compartments usually receive a private nerve branch, thus supporting the notion that the human biceps brachii has neuromuscular compartments.

Aged↗
PubMed1991

Anatomical partitioning of three multiarticular human muscles.

To examine neuromuscular partitioning within human muscles, the innervation patterns and muscle fiber architecture of the flexor carpi radialis (FCR), extensor carpi radialis longus (ECRL) and lateral gastrocnemius (LG) muscles were examined. Consistent patterns of innervation between specimens were found within each of the three muscles. The nerve to the FCR clearly innervates three major architectural divisions of the muscle. The ECRL is innervated by two different muscle nerves. Branches of these nerves innervate at least two distinct anatomical subvolumes. However, the subvolumes of the ECRL defined by muscle architecture are not totally congruent with those defined by the innervation pattern. In the LG, the single muscle nerve branches into two main divisions, and these subsequently divide into branches which supply the three heads. However, each head does not receive a completely private nerve. These results indicate that human muscles are partitioned in a manner roughly similar to the divisions of the same muscles in cats and rats, but with less congruency of architecture and innervation.

Hand↗
PubMed1991

Quantitative analysis of surface and percutaneous electromyographic activity in lumbar erector spinae of normal young women.

Bilateral surface and fine-wire electromyographic activity from the erector spinae at the L4-5 interspace was recorded from 10 female subjects during flexion, extension, rotation to right/left, and sidebending to right/left. Fine-wire electrodes demonstrated significant left-right electromyographic differences during terminal flexion. Surface and fine-wire electromyographic recordings demonstrated a symmetric pattern of activity during extension. A symmetric pattern of erector spinae activity was observed during rotation using fine-wire electrodes but not from surface electrodes. Increased electromyographic activity from the contralateral erector spinae was detected by the surface electrodes during sidebending to neutral movements.

Adult↗
PubMed1991

Wrist movements in able-bodied and brain injured individuals.

The purpose of this study was to compare movement velocity characteristics during targeted wrist movements between able-bodied individuals and a sample of individuals with spasticity secondary to closed head injury. Two amplitudes (30 degrees and 60 degrees) of movement were performed at slow and fast velocities, with the forearm either passively supported or actively supported by elbow extension and shoulder flexion. Variables measured were the following: (1) average velocity of entire movement, (2) velocity for 10 degrees increments of a movement, and (3) ratio of average peak 10 degrees increment velocity to average velocity. In addition, qualitative examination of velocity profiles was performed. Slow movements were performed in a discontinuous manner by both groups; however, observable differences in peak/average velocity were noted between groups in the unsupported position during slow and fast movements. Able-bodied individuals performed seven of eight fast movements with greater velocity (p less than .05) than brain injured individuals, and the fast movements of the able-bodied subjects were continuous.

Adult↗
PubMed1990

Conditioning of the spinal stretch reflex: implications for rehabilitation.

The purpose of this article is to describe a new technique that can potentially be applied to patients with hyperactive spinal stretch reflexes (SSRs). The progression of clinical research from conditioning of individual muscles or muscle groups (electromyographic biofeedback) to conditioning SSRs is explained. Research data from subhuman primates in addition to the first human experiments are reviewed. Potential applications of SSR conditioning are discussed, as are the issues requiring further delineation and research before the specificity of a training effect can be ascertained.

Animals↗
PubMed1989

Modification of human spinal stretch reflexes: preliminary studies.

Modulation of the human spinal stretch reflex (SSR) may be important in treating hyperactive reflexes or may be a tool to enhance normal performance. Eight of 9 subjects given feedback of biceps brachii SSR amplitude and instructed to increase (uptrain) or decrease (downtrain) this response were able to do so in the appropriate direction. These results imply that, as in non-human primates, SSR amplitude can be modified.

Adult↗
PubMed1989

Distribution of corticotectal axons from the caudal part of the anterior ectosylvian sulcus in the cat.

Axonal projections from cells in cortex surrounding the caudal part of the anterior ectosylvian sulcus (AES) to the superior colliculus (SC) were examined using anterograde tracers. The projection terminates in the medial two-thirds of the deep layers of SC bilaterally, and appears to be topographically organized, perhaps according to the sensory modality (auditory and visual) represented in the caudal part of AES.

Animals↗