Intralimb Coupling Research Articles

Delayed and reduced intralimb muscular coupling during postural reactions in individuals with incomplete spinal cord injury.

Postural strategies are enabled by rapid muscle activation sequences to prevent a fall. Intralimb muscular couplings underlie these postural strategies are likely impaired after incomplete spinal cord injury (iSCI), leading to inappropriate postural reactions and increased fall risk; yet, the nature of these changes is unknown. Identify changes occurring in intralimb coupling following a perturbation in individuals with iSCI. Ten men with iSCI and eight age-matched controls (CTRL) stood on a force-platform that was randomly tilted forward or backward. Electromyographic (EMG) activity of the lower limb muscles was recorded, and coactivation or simultaneous facilitation/suppression between pairs of muscles was analyzed. Onset and duration of coupling latency, intralimb coupling delay, and amplitude ratios were measured in the distal (soleus [SOL]/tibialis anterior [TA]), proximal (biceps femoris [BF]/vastus lateralis [VL]), anterior (TA-VL), and posterior (SOL-BF) muscle couplings. In forward tilt, the main coupling was TA-SOL co-contraction for both groups, but the latency was longer and the duration shorter in SCI participants. In backward tilt, the TA-VL co-activation was the main coupling in CTRL (88 %), although it was also expressed by 60 % of SCI participant with a delayed latency. The facilitation/suppression of TA-SOL was the main coupling in SCI group (80 % vs 63 % in CTRL). Delayed coupling latencies were more pronounced in individuals with cervical iSCI and were correlated with the strength of lower limbs. Similar muscular couplings are present in both groups but are delayed, which might contribute to postural reaction deficits in individuals with iSCI.

Influence of Custom Foot Orthotic Intervention on Lower Extremity Intralimb Coupling during a 30-Minute Run

The purpose of this study was to analyze the influence of a custom foot orthotic (CFO) intervention on lower extremity intralimb coupling during a 30-min run in a group of injured runners and to compare the results to a control group of healthy runners. Three-dimensional kinematic data were collected during a 30-min run on healthy female runners (Shoe-only) and a group of female runners who had a recent history of overuse injury (Shoe-only and Shoe with custom foot orthoses). Results from the study revealed that the coordination variability and pattern for the some couplings were influenced by history of injury, foot orthotic intervention and the duration of the run. These data suggest that custom foot orthoses worn by injured runners may play a role in the maintenance of coordination variability of the tibia (transverse plane) and calcaneus (frontal plane) coupling during the Early Stance phase. In addition, it appears that the coupling angle between the knee (transverse plane) and rearfoot (frontal plane) joints becomes more symmetrical in the late stance phase as a run progresses.

Can children with developmental coordination disorder adapt to task constraints when catching two-handed?

Purpose. To compare the nature and extent of inter and intralimb coupling during two-handed catching and the effect of manipulating task constraints in children with Developmental Coordination Disorder (DCD) and their typically developing peers (AMC).Method. Twenty children aged 7 – 10 years, ten with DCD and 10 AMC attempted to catch a ball ten times in condition 1 (C1), ball to the midline; condition 2 (C2), ball to the left shoulder and condition 3 (C3), ball to the right shoulder. Both 3D kinematic data and video data were collected.Results. Children with DCD caught fewer balls than the AMC children, regardless of age or condition (p ≤ 0.001). Children with DCD demonstrated a higher degree of linkage between limbs in C1 and a lower degree of between limb coupling in C2 and C3 when compared to the AMC (p ≤ 0.05). Differences between the AMC7 – 8 and AMC9 – 10 group were found with respect to interlimb coupling.Conclusions. The influence of manipulating task constraints and the individual nature of children with DCD must be considered by those involved in rehabilitation. By doing so, children with DCD may search for appropriate motor solutions to many functional movement tasks required for everyday life.

Two-Handed Catching in Children with Developmental Coordination Disorder

This study investigated the nature and extent of inter and intralimb coupling of the upper limbs in children with developmental coordination disorder (DCD) and their age-matched controls (AMC) when catching a ball two-handed. Sixteen children (8 DCD, 8 AMC) volunteered for the study; parental consent was gained for each child. Using standard video analysis and 3D kinematic analysis, all children were examined performing 30 two-handed catches. Video analysis showed that the AMC children caught more balls than the DCD children (p< .005). Analyses of the kinematic data showed DCD participants exhibit a greater degree of linkage both between and within limb than the AMC participants (p < .01), but the AMC participants demonstrate more intra individual variability in these linkages (p < .01). The data shows that both DCD and AMC children couple their limbs to exert control over redundant degrees of freedom when catching a ball two-handed. However, DCD children show little capacity to vary their motor behavior exhibiting a less adaptable movement system, which in turn affects their success at the task.

Altered timing of postural reflexes contributes to falling in persons with chronic stroke

The purpose of this study was to determine differences in the timing of postural reflexes and changes in kinematics between those who fell (fallers) in response to standing platform translations and those who did not (non-fallers). Forty-four persons with stroke were exposed to unexpected forward and backward platform translations while standing. Surface electromyography from bilateral tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris were recorded along with kinematic data. Those that fell in response to the translations were compared to those who did not fall in terms of (1) postural reflex onset latency, (2) the time interval between the activation of distal and proximal muscles (i.e. intralimb coupling), and (3) changes in joint angles and trunk motion. Approximately 85% of falls occurred in response to the forward translations. Postural reflex onset latencies were delayed and intralimb coupling durations were longer in the faller versus non-faller group. At the time that the platform completed the translating motion (300 ms), the faller group demonstrated higher trunk velocity, greater change in paretic ankle angle, and the trunk was further behind the ankle compared to the non-faller group. This study suggests that following platform translations, delays in the timing of postural reflexes and disturbed intralimb coupling result in changes in kinematics, which contribute to falls in persons with stroke.

Performance of locomotion and foot grasping following a unilateral thoracic corticospinal tract lesion in monkeys (Macaca mulatta)

Six adult monkeys (Macaca mulatta) received a unilateral lesion of the lateral corticospinal tract (CST) in the thoracic spinal cord. Prior to surgery, the animals were trained to perform quadrupedal stepping on a treadmill, and item retrieval with the foot. Whole body kinematics and electromyogram (EMG) recordings were made prior to, and at regular intervals over a period of 12 weeks after the CST lesion. After 1 week of recovery, all monkeys were able to walk unaided quadrupedally on the treadmill. The animals, however, dragged the hindpaw ipsilateral to the lesion along the treadmill belt during the swing phase and showed a significant reorganization of the spatiotemporal pattern of hindlimb (HL) and forelimb (FL) displacements. The inability to appropriately trigger the swing phase resulted in an increase in the cycle duration and stride length of both HLs. The stance duration decreased in the ipsilateral HL, and increased in the contralateral HL and both FLs. Consequently, there was a dramatic disruption of interlimb and intralimb coupling that was reflected in the limb kinematic and EMG patterns. The CST lesion completely abolished the ability of the monkeys to retrieve items with the foot ipsilateral to the lesion and significantly disrupted the level of performance of the contralateral HL during the first 2 weeks post-lesion. Interestingly, selected HL muscles remained almost quiescent when the monkeys attempted to retrieve items, but were unsuccessful with the affected foot at 1 week post-lesion, whereas the capacity to activate the same muscles was preserved, although reduced, during stepping. Spatial and temporal parameters of gait, kinematics, and EMG patterns recorded during locomotion generally converged toward control values over time, but significant differences persisted up to 12 weeks post-lesion. Although some control was recovered over the distal foot musculature, fine foot grasping remained significantly impaired at the end of the testing period. These findings demonstrate that the CST pathway from the brain normally makes an important contribution to interlimb and intralimb coordination during basic locomotion, and to muscle activation to produce dexterous foot digit movements in the monkey. Furthermore, the present study indicates that the primate has the ability to rapidly accommodate locomotor performance, and to a lesser degree fine foot motor skills, to a reduction in supraspinal control. Identification of the neural substrates mediating the rapid recovery of motor function following injury to the primate spinal cord could provide insight into developing repair strategies to augment functional recovery from neuromotor impairments.

Inter- and intralimb oscillator coupling in parkinsonian tremor.

This study reports the findings of an analysis of temporal correlation between tremor of different muscles of the same and different limbs in four patients with Parkinson's disease. Spectral coherence methods were used for determining whether simultaneously occurring oscillations in the electromyograms of different muscles are statistically coupled. The incidence of significant coherence was considerably higher for muscle pairs in the same limb than for pairs in different limbs; Parkinson's disease tremor is coupled within but not between limbs. Because the characteristics of tremor are known to vary under different behavioral situations, the intralimb coupling was examined for different tasks. A mental arithmetic task resulted in an increase in the coherence between muscles of the same limb, whereas the finger-to-nose task decreased the coherence. No significant change in coherence was found for a postural task. The amplitude and regularity of tremor electromyography showed changes analogous to those in coherence. These results support the hypothesis that tremor in different limbs results from the activity of several neural circuits oscillating independently. The results also emphasize the value of these methods for rigorously characterizing tremor, in relation to disease state, behavioral conditions, and the selection of treatment strategies.

Inter- and intralimb oscillator coupling in Parkinsonian tremor

This study reports the findings of an analysis of temporal correlation between tremor of different muscles of the same and different limbs in four patients with Parkinson's disease. Spectral coherence methods were used for determining whether simultaneously occurring oscillations in the electromyograms of different muscles are statistically coupled. The incidence of significant coherence was considerably higher for muscle pairs in the same limb than for pairs in different limbs; Parkinson's disease tremor is coupled within but not between limbs. Because the characteristics of tremor are known to vary under different behavioral situations, the intralimb coupling was examined for different tasks. A mental arithmetic task resulted in an increase in the coherence between muscles of the same limb, whereas the finger-to-nose task decreased the coherence. No significant change in coherence was found for a postural task. The amplitude and regularity of tremor electromyography showed changes analogous to those in coherence. These results support the hypothesis that tremor in different limbs results from the activity of several neural circuits oscillating independently. The results also emphasize the value of these methods for rigorously characterizing tremor, in relation to disease state, behavioral conditions, and the selection of treatment strategies.

Limb stiffness and postural tremor in the arm.

The relation between limb stiffness and postural tremor in the upper arm was investigated during a pointing task. The task goal was to minimize the amount of motion (tremor) at the index finger under levels of increasing limb stiffness. This study investigated the influence of increasing limb stiffness on the pattern of intra- and interlimb dynamics. The frequency profile of the tremor for all limb segments across all conditions displayed two peaks, one between 2-4 Hz and another between 8-12 Hz. A third, higher frequency component (20-22 Hz) was present in the index finger. Increasing limb stiffness through voluntary co-contraction of antagonistic muscle pairs effectively constrained the segments of the upper limb to increasingly operate as a single biomechanical degree of freedom. Higher levels of limb stiffness typically led to an increase in the frequency and power of the 2-4 and 8-12 Hz peaks. There was also a decrease in the frequency of the 20-22 Hz component of finger tremor. The act of reducing the effective degrees of freedom in joint space through voluntarily stiffening of the upper limbs also resulted in decreased performance as determined by an increase in finger tremor. In the preferred, natural level of limb stiffness, specific intralimb segment relations were observed but there was no significant interlimb coupling. The intralimb segment correlations were characterized by compensatory (out of phase) coupling between the upper arm/forearm and hand/index finger segment pairs of each limb that were organized about the action of the wrist joint. Increasing the degree of limb stiffness led to a decrease in the level of intralimb coupling. The findings suggest that the most efficient mechanism for reducing tremor at the periphery is that of compensatory coupling between relevant intralimb segments with a low level of limb stiffness.

Recovery of locomotion after ventral and ventrolateral spinal lesions in the cat. I. Deficits and adaptive mechanisms.

The recovery of treadmill locomotion of eight adult cats, subjected to chronic ventral and ventrolateral spinal lesions at low thoracic levels (T11 or T13), preserving at least one dorsolateral funiculus and the dorsal columns, was documented daily using electromyographic (EMG) and kinematic methods. The data show that all cats eventually recovered quadrupedal voluntary locomotion despite extensive damage to important pathways (such as the reticulospinal and the vestibulospinal) as verified by injection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) caudal to the site of lesion. Initially (in the early period after the spinal lesion), all the cats suffered from pronounced locomotor and postural deficits, and they could not support their hindquarters or walk with their hindlimbs. Gradually, during the recovery period, they regained quadrupedal walking, although their locomotion was wobbly and inconsistent, and they suffered from poor lateral stability. EMG and kinematic data analyses showed a tendency for an increase in the variability of the step cycle duration but no major changes in the step cycle structure or in the intralimb coupling of the joints. However, the homolateral fore- and hindlimb coupling was highly perturbed in cats with the largest lesions. Although the general alternating pattern of extensor and flexors was maintained, there were various changes in the duration and amplitude of the EMG bursts as well as a lack of amplitude modulation during walking uphill or downhill on the treadmill. In cats with larger lesions, the forelimbs also seem to take a greater propulsive role than usual as revealed by a consistent increase of the activity of the triceps. In cats with smaller lesions, these deficits were transient, but, for the most extensively lesioned cats, they were pronounced and lasted long term postlesion even after reaching a more or less stable locomotor behavior (plateau period). It is concluded that recovery of quadrupedal locomotion is possible even after a massive lesion to ventral and ventrolateral quadrants, severing the vestibulospinal pathway and causing severe, although incomplete, damage to the reticulospinal tract. The quick recovery in the less lesioned cats can be attributed to remaining pathways normally implicated in locomotor function. However, in the most extensively lesioned cats, the long period of recovery and the pronounced deficits during the plateau period may indicate that the compensation, attributed to remaining reticulospinal pathways, is not sufficient and that other pathways in the dorsolateral funiculi, such as the corticospinal, can sustain and adapt, up to a certain extent, the voluntary quadrupedal walking.

Kinematic variability and relationships characterizing the development of walking

The purposes of this study were: (1) to determine the pattern of variability and relationships in joint kinematics characterizing the development of walking and (2) to determine whether controlling for postural stability in new walkers results in less variability. The variability and relationships among hip, knee, and ankle motions were measured during 10 gait cycles of new walkers, supported new walkers, two-year-olds and seven-year-olds. Fourier series were generated for each joint motion and standard deviations were compared across groups. An age-related decline in variability was evident in select portions of the cycle. Stance and swing phase duration correlated with cycle duration for all ages. Postural support did not lessen variability in joint rotations for new walkers. Cross-correlations for hip-knee, knee-ankle, and hip-knee rotations were strong across all groups. These results suggest that a coordinative structure for walking produces strong intralimb coupling early in development, despite variability in select portions of joint motions.