Early Locomotor Training With Clonidine in Spinal Cats

1998 ◽  
Vol 79 (1) ◽  
pp. 392-409 ◽  
Author(s):  
Connie Chau ◽  
Hugues Barbeau ◽  
Serge Rossignol
Keyword(s):  
Locomotor Activity ◽  
Daily Injection ◽  
Emg Activity ◽  
Locomotor Training ◽  
Step Cycle ◽  
Locomotor Pattern ◽  
Video Images ◽  
Weight Support ◽  
Ankle Joints ◽  
Before And After

Chau, Connie, Hugues Barbeau, and Serge Rossignol. Early locomotor training with clonidine in spinal cats. J. Neurophysiol. 79: 392–409, 1998. Clonidine, a noradrenergic alpha-2 agonist, can initiate locomotion early after spinalization in cats. Because this effect lasts 4–6 h, we have injected clonidine daily, intraperitoneally or intrathecally, and intensively trained five spinal cats to perform hindlimb walking on a treadmill starting at day 3 and continuing until 10 days posttransection. Each day, clonidine was injected to induce locomotor activity and cats were trained to walk with as much weight support as possible and at different speeds during multiple (1–5) locomotor training sessions, each lasting from 10 to 20 min, until the effects of clonidine wore off. Electromyographic (EMG) activity synchronized to video images of the hindlimbs were recorded before and after each clonidine injection. The results showed, first, a day-to-day change of the locomotor pattern induced by clonidine from the 3rd to the 11th day including an increase in the duration of the step cycle, an increase in the duration of extensor EMG activity, and an increase in total angular excursion of the hip, knee, and ankle joints. Second, after 6–11 days of this regimen, there was an emergence of a coordinated locomotor pattern with weight support of the hindquarters that was visible even before that day's clonidine injection. The results suggested that daily injection of clonidine followed by early and daily interactive locomotor training can enhance the recovery of locomotion in spinal cats.

Locomotor activity in spinal cord-injured persons

2004 ◽  
Vol 96 (5) ◽  
pp. 1954-1960 ◽  
Author(s):  
V. Dietz ◽  
Susan J. Harkema
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Afferent Input ◽  
Walking Ability ◽  
Locomotor Training ◽  
Locomotor Pattern ◽  
Weight Support ◽  
Cord Injury ◽  
The Central Nervous System ◽  
Spinal Cord Injured

After a spinal cord injury (SCI) of the cat or rat, neuronal centers below the level of lesion exhibit plasticity that can be exploited by specific training paradigms. In individuals with complete or incomplete SCI, human spinal locomotor centers can be activated and modulated by locomotor training (facilitating stepping movements of the legs using body weight support on a treadmill to provide appropriate sensory cues). Individuals with incomplete SCI benefit from locomotor training such that they improve their ability to walk over ground. Load- or hip joint-related afferent input seems to be of crucial importance for both the generation of a locomotor pattern and the effectiveness of the training. However, it may be a critical combination of afferent signals that is needed to generate a locomotor pattern after severe SCI. Mobility of individuals after a SCI can be improved by taking advantage of the plasticity of the central nervous system and can be maintained with persistent locomotor activity. In the future, if regeneration approaches can successfully be applied in human SCI, even individuals with complete SCI may recover walking ability with locomotor training.

scholarly journals The role of the load-dependent sensory input in control of balance during gait

2021 ◽  
Author(s):  
Popov Alexander ◽  
Lyakhovetskii Vsevolod ◽  
Bazhenova Elena ◽  
Gorskii Oleg ◽  
Kalinina Daria ◽  
...  
Keyword(s):  
Locomotor Activity ◽  
Balance Control ◽  
Center Of Mass ◽  
Afferent Input ◽  
Hindlimb Unloading ◽  
Emg Activity ◽  
Control Mechanisms ◽  
Step Cycle ◽  
Hindlimb Muscle ◽  
Before And After

Locomotor activity requires fine balance control that strongly depends on the afferent input from the load receptors. Following hindlimb unloading (HU), the kinematic and EMG activity of the hindlimbs is known to change significantly. However, the effects of HU on the integrative control mechanisms of posture and locomotion are not clear. The goal of the present study was to evaluate the center of mass (CoM) dynamic stabilization and associated adaptive changes in the trunk and hindlimb muscle activity during locomotion after 7 days of HU. The EMG signals from the muscles of the low lumbar trunk (m. longissimus dorsi [VERT]) and the hind limb (m. tibialis anterior [TA], m. semitendinosus [ST], m. soleus [SOL]) were recorded together with the hindquarter kinematics during locomotion on a treadmill in 6 rats before and after HU. The CoM lateral shift in the step cycle significantly increased after HU and coincided with the enhanced activity of VERT. The mean EMG of the TA and the ST flexor activity increased significantly with reduction of their burst duration. These data demonstrate the disturbances of body balance after HU that can influence the basic parameters of locomotor activity. The load-dependent mechanisms resulted in compensatory adjustments of flexor activity toward a faster gait strategy, such as a trot or gallop, which presumably have supraspinal origin. The neuronal underpinnings of these integrative posture and locomotion mechanisms and their possible reorganization after HU are discussed.

Comparison of the Effect of Intrathecal Administration of Clonidine and Yohimbine on the Locomotion of Intact and Spinal Cats

2001 ◽  
Vol 85 (6) ◽  
pp. 2516-2536 ◽  
Author(s):  
Nathalie Giroux ◽  
Tomás A. Reader ◽  
Serge Rossignol
Keyword(s):  
Acid Methyl Ester ◽  
Intrathecal Administration ◽  
Cycle Duration ◽  
Descending Pathways ◽  
Step Cycle ◽  
Locomotor Pattern ◽  
Before And After ◽  
Spontaneous Expression ◽  
High Doses ◽  
Treadmill Locomotion

Several studies have shown that noradrenergic mechanisms are important for locomotion. For instance, L-dihydroxyphenylalanine (L-DOPA) can initiate “fictive” locomotion in immobilized acutely spinalized cats and α2-noradrenergic agonists, such as 2,6,-dichloro- N-2-imidazolidinylid-enebenzenamine (clonidine), can induce treadmill locomotion soon after spinalization. However, the activation of noradrenergic receptors may be not essential for the basic locomotor rhythmicity because chronic spinal cats can walk with the hindlimbs on a treadmill in the absence of noradrenergic stimulation because the descending pathways are completely severed. This suggests that locomotion, in intact and spinal conditions, is probably expressed and controlled through different neurotransmitter mechanisms. To test this hypothesis, we compared the effect of the α2 agonist, clonidine, and the antagonist (16α, 17α)-17-hydroxy yohimbine-16-carboxylic acid methyl ester hydrochloride (yohimbine), injected intrathecally at L3–L4before and after spinalization in the same cats chronically implanted with electrodes to record electromyograms (EMGs). In intact cats, clonidine (50–150 μg/100 μl) modulated the locomotor pattern slightly causing a decrease in duration of the step cycle accompanied with some variation of EMG burst amplitude and duration. In the spinal state, clonidine could trigger robust and sustained hind limb locomotion in the first week after the spinalization at a time when the cats were paraplegic. Later, after the spontaneous recovery of a stable locomotor pattern, clonidine prolonged the cycle duration, increased the amplitude and duration of flexor and extensor bursts, and augmented the foot drag at the onset of swing. In intact cats, yohimbine at high doses (800–1600 μg/100 μl) caused major walking difficulties characterized by asymmetric stepping, stumbling with poor lateral stability, and, at smaller doses (400 μg/100 μl), only had slight effects such as abduction of one of the hindlimbs and the turning of the hindquarters to one side. After spinalization, yohimbine had no effect even at the largest doses. These results indicate that, in the intact state, noradrenergic mechanisms probably play an important role in the control of locomotion since blocking the receptors results in a marked disruption of walking. In the spinal state, although the receptors are still present and functional since they can be activated by clonidine, they are seemingly not critical for the spontaneous expression of spinal locomotion since their blockade by yohimbine does not impair spinal locomotion. It is postulated therefore that the expression of spinal locomotion must depend on the activation of other types of receptors, probably related to excitatory amino acids.

Effects of Red Nucleus Microstimulation on the Locomotor Pattern and Timing in the Intact Cat: A Comparison With the Motor Cortex

1999 ◽  
Vol 81 (5) ◽  
pp. 2297-2315 ◽  
Author(s):  
Marie-Josée Rho ◽  
Sylvain Lavoie ◽  
Trevor Drew
Keyword(s):  
Motor Cortex ◽  
Red Nucleus ◽  
Emg Activity ◽  
Cycle Duration ◽  
Step Cycle ◽  
Rubrospinal Tract ◽  
Locomotor Pattern ◽  
Train Duration ◽  
Flexor Muscles ◽  
Cathodal Current

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex. To determine the extent to which the rubrospinal tract is capable of modifying locomotion in the intact cat, we applied microstimulation (cathodal current, 330 Hz; pulse duration 0.2 ms; maximal current, 25 μA) to the red nucleus during locomotion. The stimuli were applied either as short trains (33 ms) of impulses to determine the capacity of the rubrospinal tract to modify the level of electromyographic (EMG) activity in different flexors and extensors at different phases of the step cycle or as long trains (200 ms) of pulses to determine the effect of the red nucleus on cycle timing. Stimuli were also applied with the cat at rest (33-ms train). This latter stimulation evoked short-latency (average = 11.8–19.0 ms) facilitatory responses in all of the physiological flexor muscles of the forelimb that were recorded; facilitatory responses were also common in the elbow extensor, lateral head of triceps but were rare in the physiological wrist and digit extensor, palmaris longus. Responses were still evoked in most muscles when the current was decreased to near threshold (3–10 μA). Stimulation during locomotion with the short trains of stimuli evoked shorter-latency (average = 6.0–12.5 ms) facilitatory responses in flexor muscles during the swing phase of locomotion and, except in the case of the extensor digitorum communis, evoked substantially smaller responses in stance. The same stimuli also evoked facilitatory responses in the extensor muscles during swing and produced more complex effects involving both facilitation and suppression in stance. Increasing the duration of the train to 200 ms modified the amplitude and duration of the EMG activity of both flexors and extensors but had little significant effect on the cycle duration. In contrast, whereas stimulation of the motor cortex with short trains of stimuli during locomotion had very similar effects to that of the red nucleus, increasing the train duration to 200 ms frequently produced a marked reset of the step cycle by curtailing stance and initiating a new period of swing. The results suggest that whereas both the motor cortex and the red nucleus have access to the interneuronal circuits responsible for controlling the structure of the EMG activity in the step cycle, only the motor cortex has access to the circuits responsible for controlling cycle timing.

Effects of Intrathecal α1- and α2-Noradrenergic Agonists and Norepinephrine on Locomotion in Chronic Spinal Cats

1998 ◽  
Vol 79 (6) ◽  
pp. 2941-2963 ◽  
Author(s):  
Connie Chau ◽  
Hugues Barbeau ◽  
Serge Rossignol
Keyword(s):  
Time Course ◽  
Spinal Injury ◽  
Emg Activity ◽  
Cycle Duration ◽  
Flexor Muscle ◽  
Step Cycle ◽  
Differential Effects ◽  
Cutaneous Reflex ◽  
Weight Support ◽  
Locomotor Deficits

Chau, Connie, Hugues Barbeau, and Serge Rossignol. Effects of intrathecal α1- and α2-noradrenergic agonists and norepinephrine on locomotion in chronic spinal cats. J. Neurophysiol. 79: 2941–2963, 1998. Noradrenergic drugs, acting on α adrenoceptors, have been found to play an important role in the initiation and modulation of locomotor pattern in adult cats after spinal cord transection. There are at least two subtypes of α adrenoceptors, α1 and α2 adrenoceptors. The aim of this study was to investigate the effects of selective α1 and α2 agonists in the initiation and modulation of locomotion in adult chronic cats in the early and late stages after complete transection at T13. Five cats, chronically implanted with an intrathecal cannula and electromyographic (EMG) electrodes were used in this study. Noradrenergic drugs including α2 agonists (clonidine, tizanidine, and oxymetazoline) and an antagonist, yohimbine, one α1 agonist (methoxamine), and a blocker, prazosin, as well as norepinephrine were injected intrathecally. EMG activity synchronized to video images of the hindlimbs were recorded before and after each drug injection. The results show differential effects of α1 and α2 agonists in the initiation of locomotion in early spinal cats (i.e., in the first week or so when there is no spontaneous locomotion) and in the modulation of locomotion and cutaneous reflexes in the late-spinal cats (i.e., when cats have recovered spontaneous locomotion). In early spinal cats, all three α2 agonists were found to initiate locomotion, although their action had a different time course. The α1 agonist methoxamine induced bouts of nice locomotor activity in three spinal cats some hours after injection but only induced sustained locomotion in one cat in which the effects were blocked by the α1 antagonist prazosin. In late spinal cats, although α2 agonists markedly increased the cycle duration and flexor muscle burst duration and decreased the weight support or extensor activity (effects blocked by an α2 antagonist, yohimbine), α1 agonist increased the weight support and primarily the extensor activity of the hindlimbs without markedly changing the timing of the step cycle. Although α2 agonists, especially clonidine, markedly reduced the cutaneous excitability and augmented the foot drag, the α1 agonist was found to increase the cutaneous reflex excitability. This is in line with previously reported differential effects of activation of the two receptors on motoneuron excitability and reflex transmission. Noradrenaline, the neurotransmitter itself, increased the cycle duration and at the same time retained the cutaneous excitability, thus exerting both α1 and α2 effects. This work therefore suggests that different subclasses of noradrenergic drugs could be used to more specifically target aspects of locomotor deficits in patients after spinal injury or diseases.

scholarly journals Gait biometrics in children with cerebral palsy before and after robotic mechanotherapy

2020 ◽  
Vol 8 (2) ◽  
pp. 159-168
Author(s):  
Igor E. Nikityuk ◽  
Galina A. Ikoeva ◽  
Elizaveta L. Kononova ◽  
Irina Yu. Solokhina
Keyword(s):  
Cerebral Palsy ◽  
Motor Activity ◽  
Lower Extremities ◽  
Diagnostic Methods ◽  
Locomotor Training ◽  
Healthy Children ◽  
Step Cycle ◽  
Software Complex ◽  
Children With Cerebral Palsy ◽  
Before And After

Background. The improvement in existing methods and the development of new principles for treating children with cerebral palsy necessitates a quantitative assessment of the parameters of motor activity. However, because of the explicit and complex abnormalities in motor skills in patients with severe forms of cerebral palsy, an evaluation of their locomotor function dynamics using instrumental diagnostic methods remains a serious problem. Aim. This work aimed to study the walking function in patients with cerebral palsy before and after motor rehabilitation using a biomechanical method with biometric sensors. Materials and methods. We examined 14 patients with cerebral palsy aged 8 to 13 years with III level of restriction of motor activity according to the gross motor function classification system (GMFCS). All patients underwent rehabilitation in the Lokomat robotic simulator for three weeks. The course consisted of 15 sessions of 45 min each. The temporal and dynamic parameters of walking were studied in 14 patients with cerebral palsy before and after a course of locomotor training. The biometry of the step cycle was studied using the STEDIS hardware-software complex, including the Neurosens set of wireless biometric sensors. The temporal characteristics of the step cycle and the force interaction of the lower extremities with the supporting surface during walking were recorded. For comparison, we conducted a biomechanical examination of 18 healthy children of the same age who did not have signs of orthopedic disorders. Results. Although after a course of mechanotherapy, the indices of the support phases in biometry in children with cerebral palsy did not reach the level of healthy individuals, a physiological tendency to roll foot was observed in the phase of pushing and accelerating the foot. Active braking of the lower limb increased. The studied time parameters showed a relative improvement in the step structure because of the emerging tendency to normalize the ratio of the periods of the double support of the contralateral lower extremities. Conclusion. Robotic mechanotherapy helps to change the biomechanical pattern of walking of a child with a severe degree of cerebral palsy. An instrumental analysis of walking using wireless biometric sensors allows you to evaluate the results and effectiveness of rehabilitation measures in patients with severe motor impairment objectively.

scholarly journals Phase-Dependent Modulation of Percutaneously Elicited Multisegmental Muscle Responses After Spinal Cord Injury

2010 ◽  
Vol 103 (5) ◽  
pp. 2808-2820 ◽  
Author(s):  
Christine J. Dy ◽  
Yury P. Gerasimenko ◽  
V. Reggie Edgerton ◽  
Poul Dyhre-Poulsen ◽  
Grégoire Courtine ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Vastus Lateralis ◽  
Medial Gastrocnemius ◽  
Emg Activity ◽  
Step Cycle ◽  
Human Spinal Cord ◽  
Lumbosacral Spinal Cord ◽  
Weight Support ◽  
Cord Injury

Phase-dependent modulation of monosynaptic reflexes has been reported for several muscles of the lower limb of uninjured rats and humans. To assess whether this step-phase-dependent modulation can be mediated at the level of the human spinal cord, we compared the modulation of responses evoked simultaneously in multiple motor pools in clinically complete spinal cord injury (SCI) compared with noninjured (NI) individuals. We induced multisegmental responses of the soleus, medial gastrocnemius, tibialis anterior, medial hamstring, and vastus lateralis muscles in response to percutaneous spinal cord stimulation over the Th11–Th12 vertebrae during standing and stepping on a treadmill. Individuals with SCI stepped on a treadmill with partial body-weight support and manual assistance of leg movements. The NI group demonstrated phase-dependent modulation of evoked potentials in all recorded muscles with the modulation of the response amplitude corresponding with changes in EMG amplitude in the same muscle. The SCI group demonstrated more variation in the pattern of modulation across the step cycle and same individuals in the SCI group could display responses with a magnitude as great as that of modulation observed in the NI group. The relationship between modulation and EMG activity during the step cycle varied from noncorrelated to highly correlated patterns. These findings demonstrate that the human lumbosacral spinal cord can phase-dependently modulate motor neuron excitability in the absence of functional supraspinal influence, although with much less consistency than that in NI individuals.

Effects of bilateral lesions of the dorsolateral funiculi and dorsal columns at the level of the low thoracic spinal cord on the control of locomotion in the adult cat. I. Treadmill walking

1996 ◽  
Vol 76 (2) ◽  
pp. 849-866 ◽  
Author(s):  
W. Jiang ◽  
T. Drew
Keyword(s):  
Spinal Cord ◽  
The Other ◽  
Emg Activity ◽  
Step Cycle ◽  
Testing Period ◽  
Left Limb ◽  
Before And After ◽  
Dorsal Columns ◽  
The Right ◽  
Bilateral Lesions

1. A quantitative and longitudinal analysis of locomotion was made after bilateral lesions of the dorsolateral funiculi (DLF) and/or the dorsal columns (DC) in the lower thoracic cord (T12 or T13) in five adult cats. All cats were chronically implanted several weeks before the spinal cord lesion to permit the recording of electromyographic (EMG) activity from selected flexor and extensor muscles of the fore- and hindlimbs of each side. This allowed each cat to act as its own control when comparing the pattern and amplitude of EMG activity before and after the lesion. All experiments were also videotaped to allow an analysis of the kinematic changes before and after the lesions. Kinematic data were only analyzed for the side of the cat facing the camera; for all cats this was the left side. 2. After recovery periods of 2-5 mo, wheat-germ-agglutinated horseradish peroxidase (WGA-HRP) was injected caudal to the lesion site (normally at L2). The extent of the lesion was verified both histologically and by evaluating the number of HRP-labeled neurons in different supraspinal structures. These analyses showed that the cortico- and rubrospinal tracts (CST and RST, respectively) were completely interrupted, bilaterally, in two of five of the cats; in one of these cats the DCs were also interrupted. In the other three cats there was more variable damage, and the CST and RST were only completely interrupted on the right side of one of these animals. The DCs were completely sectioned in two of these cats. 3. During the 1st wk subsequent to the lesion, most cats had difficulty in supporting their weight and in walking. However, within 10 days all were able to walk, unaided, for extended periods on the treadmill at speeds of at least 0.35 m/s. In the two cats with the complete, bilateral DLF lesions, the animals dragged both their left and right hindpaws along the treadmill belt during the swing phase of the step cycle (paw drag) throughout the testing period of 3-5 mo. In the other three cats, paw drag in either hindlimb was only seen in the 1st 2-3 wk after the lesions, with the exception of the cat with the complete lesion of the DLF on the right side, which showed sustained paw drag in the right hindlimb throughout the testing period. 4. Significant increases in step cycle and swing duration following the lesion were observed only in the two cats with the largest lesions. In all five cats, statistical comparisons of the slopes from a linear regression analysis showed that the relationship between swing and step cycle duration was unchanged by the lesions. 5. Joint angles in the left hindlimb of the two cats with the largest lesions were generally smaller (more flexed) than in the prelesion controls. This was particularly true for the knee and ankle joints. The other three cats showed changed joint angle values for the hip, knee, and ankle only in the 1st 2-3 wk after the lesions. All of the cats, except the one with the least damage to the left DLF, exhibited increased joint excursions at the metatarsophalangeal (MTP) joint of the left limb throughout the recovery period. 6. There were sustained changes in the coupling between the hip and the knee of the left limb, together with smaller changes in the coupling of the knee and ankle in the two cats with the complete lesions of the DLF. In contrast to the prelesion controls, flexion at the ankle occurred before swing onset in these same two cats. The changes in the coordination between the hip and the knee were associated with changes in the temporal coupling between the hip flexor, sartorius (Srt), and the knee flexor, semitendinosus (St). Despite some improvement, the coupling between these two muscles never fully recovered to the prelesion values. Similar, but smaller, changes in the delay between Srt and St were also seen in two of the other three cats. (ABSTRACT TRUNCATED)

scholarly journals Rostrocaudal Distribution of the C-Fos-Immunopositive Spinal Network Defined by Muscle Activity during Locomotion

2021 ◽  
Vol 11 (1) ◽  
pp. 69
Author(s):  
Natalia Merkulyeva ◽  
Vsevolod Lyakhovetskii ◽  
Aleksandr Veshchitskii ◽  
Oleg Gorskii ◽  
Pavel Musienko
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Control Systems ◽  
Muscle Activity ◽  
Knee Extensors ◽  
Emg Activity ◽  
Lumbosacral Spinal Cord ◽  
Adductor Muscles ◽  
Spinal Network ◽  
Hip Flexor

The optimization of multisystem neurorehabilitation protocols including electrical spinal cord stimulation and multi-directional tasks training require understanding of underlying circuits mechanisms and distribution of the neuronal network over the spinal cord. In this study we compared the locomotor activity during forward and backward stepping in eighteen adult decerebrated cats. Interneuronal spinal networks responsible for forward and backward stepping were visualized using the C-Fos technique. A bi-modal rostrocaudal distribution of C-Fos-immunopositive neurons over the lumbosacral spinal cord (peaks in the L4/L5 and L6/S1 segments) was revealed. These patterns were compared with motoneuronal pools using Vanderhorst and Holstege scheme; the location of the first peak was correspondent to the motoneurons of the hip flexors and knee extensors, an inter-peak drop was presumably attributed to the motoneurons controlling the adductor muscles. Both were better expressed in cats stepping forward and in parallel, electromyographic (EMG) activity of the hip flexor and knee extensors was higher, while EMG activity of the adductor was lower, during this locomotor mode. On the basis of the present data, which showed greater activity of the adductor muscles and the attributed interneuronal spinal network during backward stepping and according with data about greater demands on postural control systems during backward locomotion, we suppose that the locomotor networks for movements in opposite directions are at least partially different.

Wipe and flexion reflexes of the frog. II. Response to perturbations

1993 ◽  
Vol 69 (5) ◽  
pp. 1736-1748 ◽  
Author(s):  
J. L. Schotland ◽  
W. Z. Rymer
Keyword(s):  
External Load ◽  
Hind Limb ◽  
Joint Angle ◽  
Activity Level ◽  
Temporal Organization ◽  
Emg Activity ◽  
Relative Timing ◽  
Before And After ◽  
Movement Segment ◽  
Initial Movement

1. To evaluate the hypothesis that the neural control of sensorimotor transformations may be simplified by using a single control variable, we compared the movement kinematics and muscle activity patterns [electromyograms (EMGs)] of the frog during flexion withdrawal and the hind limb-hind limb wipe reflex before and after adding an external load. In addition, the flexibility of spinal cord circuitry underlying the hind limb-hind limb wipe reflex was evaluated by comparing wipes before and after removal of one of the contributing muscles by cutting a muscle nerve. 2. The kinematics of the movements were recorded using a WATSMART infrared emitter-detector system and quantified using principal-components analysis to provide a measure of the shape (eigenvalues) and orientation (eigenvector coefficients) of the movement trajectories. The neural pattern coordinating the movements was characterized by the latencies and magnitudes of EMGs of seven muscles acting at the hip, knee, and ankle. These variables were compared 1) during flexion withdrawal and the initial movement segment of the limb during the hind limb-hind limb wipe reflex in both unrestrained movements and in movements executed when a load equal to approximately 10% of the animal's body weight was attached to a distal limb segment and 2) during the initial movement segment of the wipe reflex before and after cutting the nerve to the knee flexor-hip extensor, iliofibularis. 3. Addition of the load had no discernible effect on the end-point position of the foot during either reflex. However, during the loaded flexion reflex, the ankle joint did not move until after the hip and knee joints had moved to their normal positions. This delayed flexion of the ankle was accompanied by large increases in the magnitude of EMG activity in two ankle muscles that exceeded the levels found during unrestrained movements. Significant changes in the temporal organization of the EMG pattern accompanied the change in joint angle relations during flexion withdrawal. 4. Despite the addition of an external load, all animals successfully and reliably removed the stimulus during the wipe reflex, and the relative timing of both the EMG pattern and joint angle motion was preserved. 5. Immediately after section of the nerve to a single muscle (iliofibularis), all animals successfully and reliably removed the stimulus during the wipe reflex. The relative timing of muscle activation was preserved, accompanied by a reduction in the activity level of gluteus magnus, a muscle with action reciprocal to iliofibularis.(ABSTRACT TRUNCATED AT 400 WORDS)

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