Biomedical subjects

Brian D Schmit

Publications and source records attributed to Brian D Schmit.

At least 19 recordsLinked to original sources

PubMed2006

Exaggerated interlimb neural coupling following stroke.

The patterns of interlimb coupling were examined in 10 stroke survivors with chronic hand impairment. In particular, the potential roles of postural state and motor tasks in promoting the flexed posture of the upper extremity were assessed. Through the use of electromyography analysis, joint angle measurements and a novel biomechanical apparatus to perturb the digits of the hand into extension, measurements of muscle activity and joint position were compared during multiple postural states, locomotion and voluntary muscle activity. The results demonstrated a significant increase in flexion of the digits (P < 0.001) and elbow (P < 0.005), during walking as compared with standing, sitting or laying supine. These results were indicative of an overall excessive activation coupling between the upper and lower extremities after stroke. Indeed both voluntary finger flexion and voluntary leg extension produced significant activity in the other impaired extremity, leg and arm, respectively, in the stroke as compared with the control subjects. Thus, rectus femoris in the impaired leg was active during finger flexion of the impaired hand in the stroke survivors and all four tested muscles in the impaired arm were active during extension of the legs (P < 0.05). These findings suggest an interlimb coupling related to active motor tasks, contributing to an upper extremity flexion bias following stroke.

Adult↗

PubMed2006

Spastic reflexes triggered by ankle load release in human spinal cord injury.

The rapid decrease in firing of load-sensitive group Ib muscle afferents during unloading may be particularly important in triggering the swing phase of gait. However, it still remains unclear whether load-sensitive muscle afferents modulate reflex activity in human spinal cord injury (SCI), as suggested by studies in the cat. The right hip of 12 individuals with chronic SCI was subjected to ramp (60 degrees /s) and hold (10 s) movements over a range from 40 degrees flexion to 0-10 degrees extension using a custom servomotor system. An ankle dorsiflexion load was imposed and released after the hip reached a targeted position using a custom-designed pneumatic motor system. Isometric joint torques of the hip and knee, reaction torque of the ankle, and surface electromyograms (EMGs) from eight muscles of the leg were recorded following the imposed hip movement and ankle load release. Reflexes, characterized by hip flexion torque, knee extension, and coactivation of ankle flexors and extensors, were triggered by ankle load release when the hip was in an extended position. The ankle load release was observed to enhance the reflexes triggered by hip extension itself, suggesting that ankle load afferents play an important role in spastic reflexes in human SCI and that the reflex pathways associated with ankle load afferents have important implications in the spinal reflex regulation of human movement. Such muscle behaviors emphasize the role of ankle load afferents and hip proprioceptors on locomotion. This knowledge may be especially helpful in the treatment of spasms and in identifying rehabilitation strategies for producing functional movements in human SCI.

Adult↗

PubMed2006

Pre- and post-alpha motoneuronal control of the soleus H-reflex during sinusoidal hip movements in human spinal cord injury.

The aim of this study was to establish the contribution of hip-mediated sensory feedback to spinal interneuronal circuits during dynamic conditions in people with incomplete spinal cord injury (SCI). Specifically, we investigated the effects of synergistic and antagonistic group I afferents on the soleus H-reflex during imposed sinusoidal hip movements. The soleus H-reflex was conditioned by stimulating the common peroneal nerve (CPN) at short (2, 3, and 4 ms) and long (80, 100, and 120 ms) conditioning test (C-T) intervals to assess the reciprocal and pre-synaptic inhibition of the soleus H-reflex, respectively. The soleus H-reflex was also conditioned by medial gastrocnemius (MG) nerve stimulation at C-T intervals ranging from 4 to 7 ms to assess changes in autogenic Ib inhibition during hip movement. Sinusoidal hip movements were imposed to the right hip joint at 0.2 Hz by the Biodex system while subjects were supine. The effects of sinusoidal hip movement on five leg muscles along with hip, knee, and ankle joint torques were also established during sensorimotor conditioning of the reflex. Phase-dependent modulation of antagonistic and synergistic muscle afferents was present during hip movement, with the reciprocal, pre-synaptic, and Ib inhibition to be significantly reduced during hip extension and reinforced during hip flexion. Reflexive muscle and joint torque responses--induced by the hip movement--were entrained to specific phases of hip movement. This study provides evidence that hip-mediated input acts as a controlling signal of pre- and post-alpha motoneuronal control of the soleus H-reflex. The expression of these spinal interneuronal circuits during imposed sinusoidal hip movements is discussed with respect to motor recovery in humans after SCI.

Adult↗

PubMed2006

Temporal facilitation of spastic stretch reflexes following human spinal cord injury.

Recent evidence suggests that alterations in ionic conductances in spinal motoneurones, specifically the manifestation of persistent inward currents, may be partly responsible for the appearance of hyperexcitable reflexes following spinal cord injury (SCI). We hypothesized that such alterations would manifest as temporal facilitation of stretch reflexes in human SCI. Controlled, triangular wave, ankle joint rotations applied at variable velocities (30-120 deg s(-1)) and intervals between stretches (0.25-5.0 s) were performed on 14 SCI subjects with velocity-dependent, hyperexcitable plantarflexors. Repeated stretch elicited significant increases in plantarflexion torques and electromyographic (EMG) activity from the soleus (SOL) and medial gastrocnemius (MG). At higher velocities (> or = 90 deg s(-1)), reflex torques declined initially, but subsequently increased to levels exceeding the initial response, while mean EMG responses increased throughout the joint perturbations. At lower velocities (< or = 60 deg s(-1)), both joint torques and EMGs increased gradually. Throughout a range of angular velocities, reflex responses increased significantly only at intervals < or = 1 s between stretches and following at least four rotations. Ramp-and-hold perturbations used to elicit tonic stretch reflexes revealed significantly prolonged EMG responses following one or two triangular stretches, as compared to single ramp-and-hold excursions. Post hoc analyses revealed reduced reflex facilitation in subjects using baclofen to control spastic behaviours. Evidence of stretch reflex facilitation post-SCI may reflect changes in underlying neuronal properties and provide insight into the mechanisms underlying spastic reflexes.

Adult↗

PubMed2006

Stimulation parameter optimization for functional electrical stimulation assisted gait in human spinal cord injury using response surface methodology.

BACKGROUND: The aims of this study were to identify the reflex moment induced by flexion withdrawal reflex and to optimize stimulation parameters for restoring swing motion with respect to initial kinematic conditions in human with spinal cord injury. METHODS: The influence of hip position and passive movement in the reflex moment were tested in six subjects with chronic spinal cord injury. The two-dimensional dynamic models consisted of thigh, shank and foot segments were developed to compute the swing-phase response and the response surface method was also used to optimize stimulation parameters for restoration of gait by functional electrical stimulation. FINDINGS: At three different hip positions, significant linear relationship was found between the reflex moment and hip angle (P < 0.05) and hip movement also increased the reflex moment compare to isometric conditions. The hip and knee flexion velocities significantly contributed to the hip and knee flexion angle during the swing-phase (P < 0.05) and increase of initial joint velocity resulted in a decrease of the burst frequency and duration time for optimal swing motion in spinal cord injured patients. INTERPRETATION: From dynamic simulation, we concluded that optimal solutions of pulse amplitude, frequency and duration time of burst for electrical stimulation assisted gait were influenced by initial kinematic conditions at toe-off. The reflex model and the results of this study can be applied to the design and control strategies of neuroprosthetic devices using functional electrical stimulation for spinal cord injured patients.

Adult↗

PubMed2006

Hip joint position modulates volitional knee extensor muscle activity after stroke.

Evidence from animal and human models has demonstrated the importance of hip proprioceptors and vestibular inputs in modulating lower-extremity muscle activity through reflex pathways. Comprehension of the role of these sensory inputs following stroke may be important in understanding pathological muscle activity during functional activities. We therefore examined the influence of both hip and head/trunk position on volitional quadriceps activity in chronic stroke and control subjects. With the knee held at 60 degrees, maximal voluntary isometric quadriceps contractions were elicited with trunk orientation (head position) and hip angle systematically positioned at 0 degrees, 45 degrees, and 90 degrees. Integrated electromyographic activity from the quadriceps was compared between groups and conditions. Vasti activity in the stroke group was greater in a seated upright posture (hip flexed) than supine (hip neutral). Controlling for vestibular input, the stroke group demonstrated greater quadriceps activity (VL and RF) with a neutral hip compared to flexion. Such findings may have implications for understanding inappropriate muscle activity during walking after stroke, as hip extension occurs immediately prior to toe off, when inappropriate quadriceps activity is commonly observed.

Adult↗

PubMed2006

A new technique for imaging the human spinal cord in vivo.

Diffusion tensor imaging has been used extensively in the brain for identifying morphological characteristics based on gray and white matter structures; however, similar applications in the spinal cord have not been as successful. Spatial resolution and limited contrast have undermined accurate delineation between gray and white matter in the spinal cord. This study applied fuzzy logic to diffusion tensor images of the human spinal cord to discriminate between gray and white matter. The technique used common anisotropy indices and newly developed indices based on properties of the diffusion ellipsoid. Preliminary applications to subjects with varying levels of spinal cord injury are also presented in this study. Results indicated larger contrast between gray and white matter compared to the traditional fractional anisotropy index and thus presents a superior technique for determining precise morphology of the spinal cord.

Adult↗

PubMed2005

Flexor reflex responses triggered by imposed knee extension in chronic human spinal cord injury.

Hypersensitivity of the flexor reflex pathways to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injury (SCI). In this study, we triggered flexor reflexes with constant velocity knee movements in 15 subjects with SCI. Ramp and hold knee extension perturbations were imposed on one leg while the hip and ankle were held in an isometric position using an instrumented leg brace. Knee, ankle and hip torque responses and electromyograms from six muscles of the leg were recorded following controlled knee extension at four different velocities. Tests were conducted with the hip in both flexed and extended positions. During the movement into knee extension, a velocity-dependent stretch reflex, represented by a progressively increasing knee flexion torque, was observed. In addition, another type of reflex that resembled a flexor reflex (flexion of the hip and ankle) was also triggered by the imposed knee extension. The magnitude of the ankle dorsiflexion torque responses was significantly correlated to the stretch reflex torque at the knee in 9 of the 15 subjects. We concluded that stretch reflexes initiate a muscle contraction that then can contribute to a flexor reflex response, possibly through muscle group III/IV afferent pathways. These results suggest that spasticity in SCI consists of a myriad of complex reflex responses that extend beyond stretch reflexes.

Adult↗

PubMed2005

The intralimb coordination of the flexor reflex response is altered in chronic human spinal cord injury.

The current study compared the intralimb coordination of flexor reflex responses in spinal intact and complete chronic spinal cord injured (SCI) individuals. Noxious electrocutaneous stimulation was applied at the apex of the medial arch of the foot (50 mA, 500 Hz, 1 ms pulse width, 20 ms) in 21 complete chronic SCI and 19 spinal intact volunteers and the flexor reflex response was quantified by measuring the isometric joint torques at the ankle, knee and hip. The results showed that SCI individuals had significantly smaller peak knee and hip joint flexion torques, often exhibited a net knee extension torque, and produced a much smaller hip joint flexion torque during the flexor reflex response in contrast to the spinal intact individuals. The latency of the reflex response, measured from the tibialis anterior electromyogram, was comparable in both test populations. These findings indicate that the intralimb coordination of the flexor reflex response of chronic complete SCI individuals is altered, possibly reflecting a functional reorganization of the flexion pathways of the spinal cord.

Chronic Disease↗

PubMed2005

A physiologically based clinical measure for spastic reflexes in spinal cord injury.

OBJECTIVE: To test the validity of the Spinal Cord Assessment Tool for Spastic reflexes (SCATS), a clinical tool intended to rate spastic motor behavior after spinal cord injury (SCI). DESIGN: By using correlational analyses, the SCATS was validated using concurrent measurements of kinematics and electromyograms and traditional assessments of spasms and spastic hypertonia. SETTING: Research laboratory (kinematics and electromyography) and outpatient medical clinic (traditional measures of spastic hypertonia). PARTICIPANTS: Eleven people with SCI were used for kinematic and electromyographic measurements. Seventeen people with SCI were used for comparison with other clinical scales. INTERVENTIONS: Not applicable. Main outcome measures Kinematic and surface electromyographic measurements of the tested lower extremity were used to quantify magnitude and/or duration of motor behaviors, and the Penn Spasm Frequency Scale (PSFS) and the Ashworth Scale were used to measure spasm frequency and resistance to joint movement for the hip flexors, knee flexors, and ankle plantarflexors, respectively. Concurrently, the SCATS was used to assess the clonus response to an imposed ankle dorsiflexion, the flexion response to a stimulus to the foot, and the knee extensor activity in response to an imposed leg extension. Each component of the SCATS was compared with the Ashworth Scale, the PSFS, and kinematic and electromyographic measurements by using the Spearman rank correlation test. RESULTS: Clonus, flexor spasm, and extensor spasm responses measured by using the SCATS correlated significantly with kinematic and electromyographic recordings (P<.01). Significant correlations were also observed between the SCATS extensor spasms and the Ashworth scores for hip and knee flexors and for ankle plantarflexors (rho=.98, .88, .61, respectively). Also, SCATS flexor spasms and SCATS clonus scores correlated significantly with some of the Ashworth scores. Only SCATS clonus scores correlated significantly with spasm frequency measures (rho=.59, P<.05). CONCLUSIONS: The SCATS produced a valid measure of 3 distinct types of spastic motor behaviors in SCI and may provide a complementary tool for measuring spastic hypertonia. Such a measure is valuable because current assessment tools do not differentiate between the different types of spastic motor behaviors that manifest after SCI. Distinguishing the 3 spastic reactions using an efficient and valid clinical tool may help guide management of spastic hypertonia in SCI.

Adolescent↗

PubMed2005

Reliability of biomechanical spasticity measurements at the elbow of people poststroke.

OBJECTIVE: To determine the minimum number of measurements required to obtain a reliable estimate of upper-extremity spasticity using biomechanic assessment across multiple testing trials and dates. DESIGN: Single-center, longitudinal study with repeated measurements of spastic upper-extremity torque measures taken 1 week apart. SETTING: A hospital-based laboratory with an isokinetic testing system. PARTICIPANTS: Sixteen subjects more than 6 months poststroke with upper-extremity spasticity. INTERVENTION: Elbow flexor hypertonia was assessed with a custom-made manipulandum attached to a 6-axis load cell and a Biodex System 3 isokinetic testing machine. Movements into extension were imposed at 4 speeds: 6 degrees /s, 30 degrees /s, 60 degrees /s, and 90 degrees /s. MAIN OUTCOME MEASURES: The resistive torque and electromyographic response to these imposed movements were measured. The torque response at the slowest speed (6 degrees /s) was attributed solely to the passive elements of the elbow and was subtracted from the torque response at the higher speeds (30 degrees /s, 60 degrees /s, 90 degrees /s), leaving only reflex torque. The reflex torques at 30 degrees /s, 60 degrees /s, and 90 degrees /s were used for further analysis. Peak torque, peak joint stiffness, and onset angle of reflex torque responses were found; repeatability and daily variability of these measures were statistically examined. The variabilities due to the subject, test day, and trial number were computed. The overall reliability of each parameter at the 3 higher test speeds using different testing schemes was also calculated. RESULTS: Ninety percent reliability in the measurement of all parameters was obtained after at least 2 days of testing during which 3 tests a day were performed. The variability in between-subjects measurements was at least 4 times greater than the intertrial variability when testing at the highest speeds; daily variability that was up to 50% of the intersubject variability was also observed. The biomechanic measures correlated well with the Ashworth Scale (Spearman rho=.84, P<.005), a clinical measure of hypertonia. CONCLUSIONS: We recommend at least 2 test dates to account for the daily variability in the spastic reflex response and to ensure reliable spasticity measurements.

Adult↗

PubMed2004

Length-tension properties of ankle muscles in chronic human spinal cord injury.

Contracture, or loss of range of motion (ROM) of a joint, is a common clinical problem in individuals with spinal cord injury (SCI). In order to measure the possible contribution of changes in muscle length to the loss of ankle ROM, the active force vs. angle curves for the tibialis anterior (TA) and gastrocnemiussoleus (GS) were measured in 20 participants, 10 with SCI, and 10 gender and age matched, neurologically intact (NI) individuals. Electrical stimuli were applied to the TA and GS motor nerves at incremented angles of the entire ROM of the ankle and the resulting ankle and knee torques were measured using a multi-axis load cell. The muscle forces of the TA and GS were calculated from the torque measurements using estimates of their respective moment arms and the resulting forces were plotted against joint angle. The force-angle relation for the GS at the ankle (GSA) was significantly shifted into plantar flexion in SCI subjects, compared to NI controls (t-test, p<0.001). Similar results were obtained based upon the GS knee (GSK) force-angle measurements (p<0.05). Conversely, no significant shift in the force-angle relation was found for the TA (p=0.138). Differences in the passive ROM were consistent with the force-angle changes. The ROM in the dorsiflexion direction was significantly smaller in SCI subjects compared to NI controls (p<0.05) while the plantar flexion ROM was not significantly different (p=0.114). Based upon these results, we concluded that muscle shortening is an important component of contracture in SCI.

Adult↗

PubMed2004

Extensor spasms triggered by imposed knee extension in chronic human spinal cord injury.

Extensor spasms, which are a significant component of spasticity in spinal cord injury (SCI), are still incompletely understood. In this study, contributions of knee proprioceptors to the origination of extensor spasms were examined in fifteen subjects with SCI. Ramp and hold knee extension perturbations were imposed to one leg while the hip and ankle were held in an isometric position using an instrumented leg brace. Isometric joint torques of knee, ankle and hip, and electromyograms (EMGs) from six muscles of the leg were recorded following controlled knee extension at four different velocities. Tests were conducted with the hip in both flexed and extended positions. A stereotypical torque response consisting of hip flexion, knee extension, and ankle plantar flexion was observed following knee perturbations, although not all components were demonstrated in every subject. During the hold periods with the knee extended, EMG activity recorded from the vastus medialis, medial gastrocnemius and rectus femoris demonstrated patterns consistent with clinical observations of extensor spasms. Furthermore, larger responses were observed with the hip in the extended vs. flexed position (p<0.05). Such behaviors emphasize the role of knee and hip proprioceptors in the initiation of extensor spasms in human SCI. This knowledge may be especially helpful in identifying rehabilitation strategies for producing functional movements in human SCI.

Adult↗

PubMed2004

Modulation of coordinated muscle activity during imposed sinusoidal hip movements in human spinal cord injury.

Individuals with chronic spinal cord injury (SCI) often demonstrate multijoint reflex activity that is clinically classified as an extensor spasm. These responses are commonly observed in conjunction with an imposed extension movement of the hips, such as movement from a sit to a supine position. Coincidentally, afferent feedback from hip proprioceptors has also been implicated in the control of locomotion in the spinalized cat. Because of this concurrence, we postulated that extensor spasms that are triggered by hip extension might involve activation of organized interneuronal circuits that also have a role in locomotion. If true, imposed oscillations of the hip would be expected to produce activity of the leg musculature in a locomotor pattern. Furthermore, this muscle activity would be entrained to the hip movement. The right hip joints of 10 individuals with chronic SCI, consisting of both complete [American Spinal Injury Association (ASIA) A] and incomplete (ASIA B,C) injuries, were subjected to ramp and hold (10 s) movements at 60 degrees /s and sinusoidal oscillations at 1.2, 1.88, and 2.2 rad/s over ranges from 40 to -15 degrees (+/-5 degrees ) using a custom servomotor system. Surface EMG from seven lower extremity muscles and sagittal-plane joint torques were recorded to characterize the response. Ramp and hold perturbations produced coactivation at the hip, knee, and ankle joints, with a long duration (5-10 s). Sinusoidal perturbations yielded consistent muscle timing patterns that resulted in alternating flexor and extensor joint torques. EMG and joint torques were commonly entrained to the frequency of movement, with rectus femoris, vastus medialis, and soleus activity coinciding with hip extension and medial hamstrings activity occurring during hip flexion. Individual muscle timing patterns were consistent with hip position during normal gait, except for the vastus medialis. These results suggest that reflexes associated with extensor spasms may occur through organized interneuronal pathways, such as spinal centers for locomotion.

Adult↗

PubMed2004

Mechanical measurements of the effects of intrathecal baclofen dosage adjustments in cerebral palsy: a pilot study.

OBJECTIVE: The purpose of this pilot study was to determine the feasibility of using mechanical measures of stretch reflexes to monitor spasticity after intrathecal baclofen dosage changes. DESIGN: Mechanical measures were made in studying six participants with cerebral palsy who were undergoing treatment for spasticity using intrathecal baclofen therapy. Mechanical measurements of stretch reflexes were made before and after pump implant in four of the six participants and after dosage changes in all participants, for a period of up to 2 yrs. The measurements comprised electromyograms and resistive torque responses to movement of the ankle, imposed with an isokinetic dynamometer. For each test session, random movements were applied to the ankle at each of four to seven speeds, repeated three or five times. RESULTS: Stretch reflex excitability decreased in three of four participants after initiation of intrathecal baclofen therapy and decreased with increasing dosages in three of the six participants. Broken catheters coincided with heightened mechanical measures in two cases. CONCLUSION: Mechanical measures of stretch reflexes change after intrathecal baclofen dosage adjustments, reflecting the clinical course of intrathecal baclofen therapy.

Adolescent↗

PubMed2004

Evidence for force-feedback inhibition in chronic stroke.

The presence of force-feedback inhibition was explored during reflex responses in five subjects with known incidence of stroke. Using constant velocity stretches, it was previously found that after movement onset, active reflex force progressively increases with increasing joint angle, at a rate proportional to a fractional exponent of the speed of stretch. However, after the reflex force magnitude exceeds a particular level, it begins rolling off until maintaining a steady-state value. The magnitudes of these force plateaus are correlated with the speed of stretch, such that higher movement speeds result in higher steady-state forces. Based upon these previous studies, we hypothesized that force plateau behavior could be explained by a force-feedback inhibitory pathway. To help facilitate an understanding of this stretch reflex force roll off, a simple model representing the elbow reflex pathways was developed. This model contained two separate feedback pathways, one representing the monosynaptic stretch reflex originating from muscle spindle excitation, and another representing force-feedback inhibition arising from force sensitive receptors. It was found that force-feedback inhibition altered the stretch reflex response, resulting in a force response that followed a sigmoidal shape similar to that observed experimentally. Furthermore, simulated reflex responses were highly dependent on force-feedback gain, where predicted reflex force began plateauing at decreasing levels with increases in this force-feedback gain. The parameters from the model fits indicate that the force threshold for force-sensitive receptors is relatively high, suggesting that the inhibition may arise from muscle free nerve endings rather than Golgi tendon organs. The experimental results coupled with the simulations of elbow reflex responses suggest the possibility that after stroke, the effectiveness of force-feedback inhibition may increase to a level that has functional significance. Practical implications of these findings are discussed in relation to muscle weakness commonly associated with stroke.

Chronic Disease↗

PubMed2003

Absence of local sign withdrawal in chronic human spinal cord injury.

Local sign withdrawal, a reflex to direct the limb away from noxious cutaneous stimuli, is thought to be indicative of a modular organization of the spinal cord. To assess the integrity of such an organization of the spinal cord in chronic human spinal cord injury (SCI), we tested the electromyogram (EMG) and joint torque responses to cutaneous stimuli applied to 6 locations of the leg in 10 SCI volunteers and 3 spinal-intact controls. The 6 locations included the medial arch of the foot, the second metatarsal, the dorsum, the region over the sural nerve at the lateral malleolus, and the anterior and posterior aspects of the lower leg. Although spinal-intact subjects demonstrated local sign withdrawal, the data from SCI subjects indicated that an invariant flexion response pattern was produced regardless of stimulus location. Ankle dorsiflexion and hip flexion were produced in all subjects at all locations and no difference in the ratio of hip:ankle torques could be detected for the 6 test locations. A windup-crossover test, employing a sequence of 6 stimuli at 1-s intervals was used to assess whether common neuronal pathways were responsible for the loss of modular organization. An additional 10 SCI volunteers were tested using stimuli in which the stimulus location was switched between the 2nd and 3rd stimulus of the test sequence. The response to the crossover stimulus more closely resembled the response to the 3rd stimulus of a windup sequence than a response without conditioning stimuli. These results indicate that increased excitability produced by windup at one stimulus site is maintained at the 2nd site. This observation suggests that deep dorsal horn neurons, typically associated with musculotopic mapping, may be reorganized in chronic spinal cord injury.

Adult↗

PubMed2002

Extensor reflexes in human spinal cord injury: activation by hip proprioceptors.

Extensor spasms, which are a significant component of spasticity in spinal cord injury (SCI), were investigated in an attempt to identify the role that hip proprioceptors play in triggering an extensor reflex response. In ten SCI subjects, a controlled hip extension movement was imposed on one leg while the knee and ankle were held in an isometric position using an instrumented leg brace. Isometric joint torques of the hip, knee, and ankle were measured following a constant velocity (30 degrees /s), 45 degrees -75 degrees extension movement of the hip that was applied using the motor of a Biodex rehabilitation/testing system. Electromyograms (EMGs) from four to eight muscles were also recorded during the ten movement trials. The stereotypical torque response to an imposed hip extension consisted of hip flexion, knee extension, and ankle plantarflexion, although all components were not observed in every subject. EMGs indicated coactivation at the knee and ankle joints, with extensor activity generally outlasting flexor activity. These observations are consistent with clinical descriptions of extensor spasms. In contrast, the response to imposed hip flexion, which was observed in six of the ten subjects, comprised hip extension, knee flexion and ankle extension. This difference between the response to hip flexion and the response to extension indicates a specificity of the reflex, suggesting that organized pathways for coordinating leg movements are involved.

Adolescent↗