-
[show abstract]
[hide abstract]
ABSTRACT: To determine whether trunk position sense is impaired in people with poststroke hemiparesis.
Good trunk stability is essential for balance and extremity use during daily functional activities and higher level tasks. Dynamic stability of the trunk requires adequate flexibility, muscle strength, neural control, and proprioception. While deficits of trunk muscle strength have been identified in people post-stroke, it is not clear whether they have adequate postural control and proprioception to ensure a stable foundation of balance to enable skilled extremity use. Trunk position sense is an essential element of trunk postural control. Even a small impairment in trunk position sense may contribute to trunk instability. However, a specific impairment of trunk position sense has not been reported in people post-stroke.
Twenty subjects with chronic stroke and 21 nonneurologically impaired subjects participated in the study.
Trunk repositioning error during sitting forward flexion movements was assessed using an electromagnetic movement analysis system, Flock of Birds. Subjects post-stroke were also evaluated with clinical measures of balance (Berg Balance Scale), postural control (Postural Assessment Scale for Stroke), and extremity motor impairment severity (Fugl-Meyer Assessment-Motor Score).
There were significant differences in absolute trunk repositioning error between stroke and control groups in both the sagittal (P = 0.0001) and transverse (P = 0.0012) planes. Mean sagittal plane error: post-stroke: 6.9 +/- 3.1 degrees, control: 3.2 +/- 1.8 degrees; mean transverse plane error: post-stroke 2.1 +/- 1.3 degrees, control: 1.0 +/- 0.6 degrees. There was a significant negative correlation between sagittal plane absolute repositioning error and the Berg Balance Scale score (r = -0.49, P = 0.03), transverse plane absolute repositioning error and Berg Balance Scale score (r = -0.48, P = 0.03), and transverse plane repositioning error and the Postural Assessment Scale for Stroke score (r = -0.52, P = 0.02)
Subjects with poststroke hemiparesis exhibit greater trunk repositioning error than age-matched controls. Trunk position sense retraining, emphasizing sagittal and transverse movements, should be further investigated as a potential poststroke intervention strategy to improve trunk balance and control.
Journal of neurologic physical therapy: JNPT 04/2008; 32(1):14-20.
-
[show abstract]
[hide abstract]
ABSTRACT: The goal of this study was to determine whether acute stroke survivors demonstrate abnormal synergy patterns in their affected lower extremity. During maximum isometric contractions with subjects in a standing position, joint torques generated simultaneously at the knee and hip were measured, along with associated muscle activation patterns in eight lower limb muscles. Ten acute stroke survivors and nine age-match controls participated in the study. For all joints tested, stroke subjects demonstrated significantly less maximum isometric torque than age-matched control subjects. However, the synergistic torques generated in directions different than the direction that was being maximized were not significantly different between the two groups. According to electromyography (EMG) data, it was found that stroke subjects activated antagonistic muscle groups significantly higher than the control group subjects, suggesting that deficits in joint torque may be at least partially attributable to co-contraction of antagonistic muscles. Our findings suggest that a primary contributor to lower limb motor impairment in acute hemiparetic stroke is poor volitional torque generating capacity, which is at least partially attributable to co-contraction of antagonistic muscles. Furthermore, while we did not observe abnormal torque synergy patterns commonly found in the upper limbs, muscle activation patterns differed between groups for many of the directions tested indicating changes in the motor control strategies of acute stroke survivors.
IEEE Transactions on Neural Systems and Rehabilitation Engineering 01/2008; 15(4):526-34. · 3.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study investigated differences in adaptation to a novel dynamic environment between the dominant and nondominant arms in 16 naive, right-handed, neurologically intact subjects. Subjects held onto the handle of a robotic manipulandum and executed reaching movements within a horizontal plane following a pseudo-random sequence of targets. Curl field perturbations were imposed by the robot motors, and we compared the rate and quality of adaptation between dominant and nondominant arms. During the early phase of the adaptation time course, the rate of motor adaptation between both arms was similar, but the mean peak and figural error of the nondominant arm were significantly smaller than those of the dominant arm. Also, the nondominant limb's aftereffects were significantly smaller than in the dominant arm. Thus, the controller of the nondominant limb appears to have relied on impedance control to a greater degree than the dominant limb when adapting to a novel dynamic environment. The results of this study imply that there are differences in dynamic adaptation between an individual's two arms.
Experimental Brain Research 11/2007; 182(4):567-77. · 2.39 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A technique for analyzing and comparing the dynamic properties of electromyographic (EMG) patterns collected during gait is presented. A gait metric is computed, consisting of both magnitude (amplitude) and phase (timing) components. For the magnitude component, the processed EMG pattern is compared to a normative EMG pattern obtained under similar walking conditions, where the metric is incremented if the muscle is firing during expected active regions or is silent during expected inactive regions. The magnitude metric is penalized when the EMG is silent during phases of expected activity or when the EMG is active in regions of expected inactivity. The phase component of the metric computes the percentage of the gait cycle when the muscle is firing appropriately, that is, active in expected active regions and silent in expected inactive regions. The magnitude and phase components of the metric are normalized and combined to yield the EMG pattern that demonstrates the closest characteristics compared to normative gait data collected under similar walking conditions. Using experimental data, the proposed gait metric was tested and accurately reflects the observed changes in the EMG patterns. Clinical uses for the gait metric are discussed in relation to gait therapies, such as determining optimal gait training conditions in individuals following stroke and spinal cord injury.
Journal of Electromyography and Kinesiology 09/2005; 15(4):384-92. · 1.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The goal of this study was to compare the muscle activation patterns in various major leg muscles during treadmill ambulation with those exhibited during robotic-assisted walking.
Robotic devices are now being integrated into neurorehabilitation programs with promising results. The influence of these devices on altering naturally occurring muscle activation patterns utilized during walking have not been quantified.
Muscle activity measured during 60 s of walking was broken up into individual stride cycles, averaged, and normalized. The stride cycle was then broken up into seven distinct phases and the integrated muscle activity during each phase was compared between treadmill and robotic-assisted walking using a multi-factor ANOVA.
Significant differences in the spatial and temporal muscle activation patterns were observed across various portions of the gait cycle between treadmill and robotic-assisted walking. Activity in the quadriceps and hamstrings was significantly higher during the swing phase of Lokomat walking than treadmill walking, while activity in the ankle flexor and extensor muscles was reduced throughout most of the gait cycle in the Lokomat.
Walking within a robotic orthosis that limits the degrees of freedom of leg and pelvis movement leads to changes in naturally occurring muscle activation patterns.
An understanding of how robotic-assisted walking alters muscle activation patterns is necessary clinically in order to establish baseline patterns against which subject's with neurological disorders can be compared. Furthermore, this information will guide further developments in robotic devices targeting gait training.
Clinical Biomechanics 03/2005; 20(2):184-93. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
IEEE Transactions on Neural Systems and Rehabilitation Engineering 07/2004; 12(2):166-76. · 3.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The mechanical properties and reflex actions of muscles crossing the elbow joint were examined during a 60-deg voluntary elbow extension movement. Brief unexpected torque pulses of identical magnitude and time-course (20-Nm extension switching to 20-Nm flexion within 30 ms) were introduced at various points of a movement in randomly selected trials. Single pulses were injected in different trials, some before movement onset and some either during early, mid, late or ending stages of the movement. Changes in movement trajectory induced by a torque pulse were determined over the first 50 ms by a nearest-neighbor prediction algorithm, and then a modified K-B-I (stiffness-damping-inertia) model was fit to the responses. The stiffness and damping coefficients estimated during voluntary movements were compared to values recorded during trials in which subjects were instructed to strongly co-contract while maintaining a static posture. This latter protocol was designed to help determine the maximum impedance a subject could generate. We determined that co-contraction increased joint stiffness greatly, well beyond that recorded under control conditions. In contrast, the stiffness magnitudes were quite small during routine voluntary movements, or when the subjects relaxed their limb. Furthermore, the damping coefficients were always significant and increased measurably at the end of movement. Reflex activity, as measured by EMG responses in biceps and triceps brachii, showed highly variable responses at latencies of 160 ms or greater. These reflexes tended to activate both elbow flexors and extensors simultaneously. These findings suggest that very low intrinsic muscle stiffness values recorded during point-to-point motion render an equilibrium point or impedance control approach implausible as a means to regulate movement trajectories. In particular, muscle that is shortening against inertial loads seems to exhibit much smaller stiffness than similarly active isometric muscle, although some degree of damping is always present and does not simply co-vary with stiffness. Although the limb muscles can be co-contracted statically or during movement with an observable increase in stiffness and even task performance, this control strategy is rarely utilized, presumably due to the greater energetic cost.
Experimental Brain Research 10/2003; 152(1):17-28. · 2.39 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Frequency response characteristics of the ankle plantar flexors were studied in adults both with and without spinal cord injury (SCI) to determine how the muscle contractile properties change after SCI. and to see if there is a relation between the severity of spasticity and how the properties change. Ten controls and ten complete, chronic spinal cord injured subjects were tested, where the tibial nerve was stimulated electrically in a stochastic manner with the ankle fixed isometrically at various joint angles. A nonparametric linear frequency response function was derived, from which a second-order transfer function was calculated. The contractile dynamics were then characterized by the three classic second-order parameters: gain, damping ratio, and natural frequency. We found that in subjects with low degrees of spasticity (as determined by clinical evaluation), the contractile dynamics presented the largest changes, in which the speed of contraction increased significantly while there were no statistical differences in the gains between the two groups. This similarity emerged even though there was noticeable atrophy in the SCI patient group. Differences between the controls and subjects with high levels of spasticity were markedly different, in that these SCI subjects had slower contractile speeds than the controls, but significantly lower gains. Moderately spastic subjects fell somewhere in between, where the speed of muscle contraction increased modestly yet the gain was significantly smaller than that of the control subjects. These findings indicate that in subjects with chronic spinal cord injury, the severity of spasticity can significantly influence the degree of change in muscle contractile properties. It appears that high degrees of spasticity tend to preserve contractile dynamics, while in less spastic subjects, muscle contractile properties may display faster response characteristics.
Annals of Biomedical Engineering 30(7):969-81. · 2.37 Impact Factor
