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Thomas Sinkjær - One of the best experts on this subject based on the ideXlab platform.
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tibialis anterior Stretch Reflex in early stance is suppressed by repetitive transcranial magnetic stimulation
The Journal of Physiology, 2009Co-Authors: Abraham Theodoor Zuur, Thomas Sinkjær, Michael James Grey, Mark Schram Christensen, Jens NielsenAbstract:A rapid plantar flexion perturbation in the early stance phase of walking elicits a large Stretch Reflex in tibialis anterior (TA). In this study we use repetitive transcranial magnetic stimulation (rTMS) to test if this response is mediated through a transcortical pathway. TA Stretch Reflexes were elicited in the early stance phase of the step cycle during treadmill walking. Twenty minutes of 1 Hz rTMS at 115% resting motor threshold (MT(r)) significantly decreased (P < 0.05) the magnitude of the later component of the Reflex at a latency of approximately 100 ms up to 25 min after the rTMS. Control experiments in which Stretch Reflexes were elicited during sitting showed no effect on the spinally mediated short and medium latency Stretch Reflexes (SLR and MLR) while the long latency Stretch Reflex (LLR) and the motor-evoked potential (MEP) showed a significant decrease 10 min after 115% MT(r) rTMS. This study demonstrates that 1 Hz rTMS applied to the leg area of the motor cortex can suppress the long latency TA Stretch Reflex during sitting and in the stance phase of walking. These results are in line with the hypothesis that the later component of the TA Stretch Reflex in the stance phase of walking is mediated by a transcortical pathway. An alternative explanation for the observed results is that the Reflex is mediated by subcortical structures that are affected by the rTMS. This study also shows that rTMS may be used to study the neural control of walking.
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Stretch Reflex regulation in healthy subjects and patients with spasticity.
Neuromodulation : journal of the International Neuromodulation Society, 2005Co-Authors: Jens Nielsen, Nikolaj H.t. Petersen, C. Crone, Thomas SinkjærAbstract:In recent years, part of the muscle resistance in spastic patients has been explained by changes in the elastic properties of muscles. However, the adaptive spinal mechanisms responsible for the exaggeration of Stretch Reflex activity also contribute to muscle stiffness. The available data suggest that no single spinal mechanism is responsible for the development of spasticity but that failure of different spinal inhibitory mechanisms (reciprocal IA inhibition, presynaptic inhibition, IB inhibition, recurrent inhibition) are involved in different patients depending on the site of lesion and the etiology of the spastic symptoms. A recent finding also shows no sign of exaggerated Stretch Reflexes in muscles voluntarily activated by the spastic patient in general. This is easily explained by the control of Stretch Reflex activity in healthy subjects. In healthy subjects, the Stretch Reflex activity is increased during voluntary muscle contraction in part because of depression of the inhibitory mechanisms that are affected in spasticity. In spastic patients, these inhibitory mechanisms are already depressed at rest and cannot be depressed further in connection with a contraction. In relation to most normal movements, antagonist muscles should remain silent and maximally relaxed. This is ensured by increasing transmission in several spinal inhibitory pathways. In spastic patients, this control is inadequate, and therefore Stretch Reflexes in antagonist muscles are easily evoked at the beginning of voluntary movements or in the transition from flexor to extensor muscle activity. This problem is contradicted by the fact that antispastic therapy to improve voluntary movements should be directed.
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guided intrathecal baclofen administration by using soleus Stretch Reflex in moderate severe spastic multiple sclerosis patients with implanted pump
Multiple Sclerosis Journal, 2004Co-Authors: Jorgen Feldbaek Nielsen, Thomas SinkjærAbstract:We tested the hypothesis that changes in soleus Stretch Reflex was correlated to changes in intrathecal baclofen dose in 12 multiple sclerosis patients with moderate-severe spasticity treated with intrathecal baclofen pump. Twice patients were evaluated clinically and biomechanically. The short-latency soleus Stretch Reflex was elicited by rotating the ankle joint 48 with a velocity from 3.1 to 1808/s. There was a strong correlation between changes in intrathecal baclofen dose and amplitude of the short-latency Stretch Reflex (r=- 0.88, PB 50 μV), which indicates an effective antispastic effect of intrathecal baclofen. We suggest that clinical evaluation of spasticity usin...
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No correlation between number of MRI-evident lesions in cerebrum and the soleus Stretch Reflex in multiple sclerosis patients.
European journal of neurology, 2004Co-Authors: Jorgen Feldbaek Nielsen, E. Bech, Paula Gadeberg, Thomas SinkjærAbstract:The aim of the study was to investigate if the Stretch Reflex of the soleus muscle was useful in quantifying upper motor neuron lesions. The soleus Stretch Reflex was recorded in 10 healthy subjects and 20 patients with active relapsing-remitting multiple sclerosis and correlated to the number of MRI lesions in cerebrum and clinical scores (expanded disability status scale and regional functional scoring system). The short latency Stretch Reflex was elicited by rotating the left ankle joint 4 degrees with a rise time in the interval of 40-640 ms. The amplitude of the Stretch was larger in multiple sclerosis patients being 88.5 microV in patients and 12.8 microV in controls, P = 0.007. The sensitivity of the Stretch Reflex expressed as the slope of the best linear fit was increased in MS patients to 2.6 microVs/degree compared with 0.6 microVs/degree (0.1-2.2) in controls, P = 0.009. There was no correlation between amplitude of the Stretch Reflex and number of MRI lesions (r = -0.03). In conclusion, the soleus Stretch Reflex might be useful to quantify spasticity but is not useful in detecting dysfunction of upper motor neurons in MS.
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Quantification of hyperReflexia in amyotrophic lateral sclerosis (ALS) by the soleus Stretch Reflex.
Amyotrophic lateral sclerosis and other motor neuron disorders : official publication of the World Federation of Neurology Research Group on Motor Neu, 2003Co-Authors: P. Christensen, Jorgen Feldbaek Nielsen, Thomas SinkjærAbstract:The aim of this study was to quantify upper motor neuron (UMN) involvement in amyotrophic lateral sclerosis (ALS) by the soleus Stretch Reflex.METHODS: In a group of 24 ALS patients and ten healthy controls the soleus Stretch Reflex was elicited by a four degree rotation at the ankle joint. Amplitude of the short‐latency Stretch Reflex, threshold, and sensitivity were determined. Peripheral excitation/contraction properties were evaluated by supramaximal stimulation of the tibial nerve. Clinical scores of upper motor neuron involvement were applied.RESULTS: A highly significant correlation between threshold and sensitivity of the Stretch Reflex and clinical score of upper motor neuron involvement was found; patients with a low threshold and a high sensitivity in general had a high upper motor neuron score.CONCLUSION: It is suggested that upper motor neuron involvement in ALS can be evaluated by using the soleus Stretch Reflex. This may be useful in monitoring progression of the disease and evaluating new ...
Kimitaka Nakazawa - One of the best experts on this subject based on the ideXlab platform.
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Different modulation pattern of spinal Stretch Reflex excitability in highly trained endurance runners
European journal of applied physiology, 2012Co-Authors: Tetsuya Ogawa, Noritaka Kawashima, Shuji Suzuki, Kimitaka NakazawaAbstract:This study was undertaken to elucidate the impact of long-term physical training on the modulation of Stretch Reflex excitability. To this end, electromyographic activities of the soleus muscle in response to quick toe-up rotation were compared between highly trained endurance runners (n = 8) and non-trained control subjects (n = 9). We specifically focused on the Stretch Reflex modulation under different voluntary activation levels, from rest to pre-activated conditions (5, 10, 20, and 30% of the maximal). While the two groups showed similar modulation patterns of the Stretch Reflex responses, the extent of Reflex modulation in accordance with the muscle pre-activation level was larger in the trained group. The present results therefore suggest a different modulation pattern of the Stretch Reflex responses with changing activation level between individuals with different physical background, and the enhancement of the responses in the trained individuals may particularly be advantageous in exerting high level muscle contraction.
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Aging effects on posture-related modulation of Stretch Reflex excitability in the ankle muscles in humans
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2011Co-Authors: Hiroki Obata, Noritaka Kawashima, Tatsuyuki Ohtsuki, Kimitaka NakazawaAbstract:Abstract The purpose of this study was to examine the effects of aging on posture-related changes of the Stretch Reflex excitability in the ankle extensor, soleus (SOL), and flexor, tibialis anterior (TA) muscles. Fourteen neurologically normal elderly (mean 68±6years) and 12 young (mean 27±3years) subjects participated. Under two postural conditions, upright standing (STD) and sitting (SIT), Stretch Reflex electromyographic (EMG) responses in the SOL/TA muscle were elicited by imposing rapid ankle dorsi-/plantar-flexion. Under the SIT condition, subjects were asked to keep the SOL background EMG level, which is identical to that under the STD condition. In the SOL muscle, both groups showed significant enhancement of the short-latency Stretch Reflex (SLR) response when the posture changed from SIT to STD. In the TA muscle, the young group showed significant enhancement of the middle- (MLR) and long-latency Stretch Reflex (LLR) when the posture changed from SIT to STD; no such modulation was observed in the elderly group. Since the TA Stretch Reflex responses under the STD condition were comparable in the young and elderly groups, the lack of posture-related modulation of the TA muscle in the elderly group might be explained by augmented Stretch Reflex excitability under the SIT condition. The present results suggest that the (1) SOL SLR responses are modulated both in the young and elderly subjects when the posture is changed from SIT to STD, (2) TA MLR and LLR responses are not modulated in the elderly subjects when the posture is changed from SIT to STD, while each response is same between the young and elderly in STD, and (3) the effect of aging on the posture-related Stretch Reflex differs in the SOL and TA muscles.
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Effect of spinal cord injury and its lesion level on Stretch Reflex modulation by cold stimulation in humans
Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 2010Co-Authors: Hisayoshi Ogata, Kiyotaka Kamibayashi, Dimitry G. Sayenko, E. Yamamoto, Taku Kitamura, Shinichirou Yamamoto, Tasuku Miyoshi, Kimitaka NakazawaAbstract:Abstract Objective To determine how short-latency Stretch Reflex amplitude in the soleus muscle is modulated by cold stimulation in able-bodied individuals and individuals with complete spinal cord injury. Methods An initial 100-s baseline period was followed by 50-s cold stimulation periods. Stretch Reflex of the right soleus muscle was elicited for 10-s intervals, while cold stimulation was applied to the left thigh. Results Peak-to-peak amplitude of the Stretch Reflex increased significantly during cold stimulation up to 127 ± 21% of the baseline in the able-bodied group ( n = 9, P n = 4), although this increase was not significant. On the other hand, Stretch Reflex decreased significantly down to 78 ± 20% in a group with injury level at or above thoracic 6 ( n = 8, P Conclusions Effect of afferent inputs induced by cold stimulation on Stretch Reflex modulation is different depending on the extent of central nervous systems participating in the modulation. Significance Our findings provide a better understanding of some basic changes in afferent–efferent spinal Reflex pathways which are probably not monosynaptic in nature.
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Age-related changes of the Stretch Reflex excitability in human ankle muscles.
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2010Co-Authors: Hiroki Obata, Kimitaka Nakazawa, Masami Akai, Noritaka Kawashima, Tatsuyuki OhtsukiAbstract:The purpose of this study was to characterize the effects of aging on the Stretch Reflex in the ankle muscles, and in particular to compare the effects on the ankle dorsi-flexor (tibialis anterior: TA) and the plantar-flexor (soleus: SOL). Stretch Reflex responses were elicited in the TA and SOL at rest and during weak voluntary contractions in 20 elderly and 23 young volunteers. The results indicated that, in the TA muscle, the elderly group had a remarkably larger long-latency Reflex (LLR), whereas no aging effect was found in the short latency Reflex (SLR). These results were very different from those in the SOL muscle, which showed significant aging effects in the SLR and medium latency Reflex (MLR), but not in the LLR. Given the fact that the LLR of the TA Stretch Reflex includes the cortical pathway, it is probable that the effects of aging on the TA Stretch Reflex involve alterations not only at the spinal level but also at the cortical level. The present results indicate that the Stretch Reflexes of each of the ankle antagonistic muscles are affected differently by aging, which might have relevance to the neural properties of each muscle.
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Invariable H-Reflex and sustained facilitation of Stretch Reflex with heightened sympathetic outflow
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2008Co-Authors: Kiyotaka Kamibayashi, Kimitaka Nakazawa, Masami Akai, Hiroki Obata, Hisayoshi Ogata, Minoru ShinoharaAbstract:Abstract Stretch Reflex shows sustained (3-min) increase with heightened sympathetic outflow [Hjortskov N, Skotte J, Hye-Knudsen C, Fallentin N. Sympathetic outflow enhances the Stretch Reflex response in the relaxed soleus muscle in humans. J Appl Physiol 2005;98:1366–70], but it is unknown if it accompanies a sustained increase in H-Reflex. The purpose of the study was to test if there is a sustained facilitation in the H-Reflex in the human soleus muscle during a variety of sustained tasks that are known to elevate sympathetic outflow. Mean arterial blood pressure, heart rate, and H- and Stretch Reflexes in the relaxed soleus muscle were obtained in healthy young adults who performed mental arithmetic, static handgrip exercise, post-handgrip ischemia, and cold stimulation. Each task lasted 3min with a 3-min rest in between tasks. Data were analyzed for the initial 30s and entire 3min of each task. There was a heightened cardiovascular response in all tasks for both durations of analysis. An increase in H-Reflex amplitude was not observed for either the initial or entire duration of the analysis. The tasks increased Stretch Reflex amplitude for both durations of analysis. Invariable H-Reflex and sustained facilitation of Stretch Reflex with heightened sympathetic outflow would imply sympathetic modulation of muscle spindle sensitivity.
Birgit Tine Larsen - One of the best experts on this subject based on the ideXlab platform.
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A task dependent change in the medium latency component of the soleus Stretch Reflex.
Experimental brain research, 2002Co-Authors: Michael James Grey, Birgit Tine Larsen, Thomas SinkjærAbstract:In comparison to the H-Reflex, the task dependency of the human Stretch Reflex during locomotive and postural tasks has not received a great deal of attention in the literature. The few studies on Reflex task dependency that have been performed to date have concentrated on either the group Ia mediated H-Reflex or the short latency Stretch Reflex. In the present study the medium latency component of a mechanically evoked Stretch Reflex is investigated during walking, pedalling, and sitting. Stretch Reflexes were evoked in the soleus muscle using dorsiflexion perturbations generated with a portable Stretching device. Perturbations of equal amplitude and velocity (8 deg, 300 deg/s) were presented to 16 healthy subjects while they walked on a treadmill and pedalled a cycle ergometer. For eight of these subjects, an additional set of data was collected as they sat on the ergometer holding a steady posture. Perturbations were presented in the early to mid stance phase of walking and the downstroke of the pedal cycle. During all three conditions, the background soleus muscle activity was matched. The short (SLR) and medium (MLR) components of the soleus Reflex responses were quantified by calculating the area of each burst in a 15-ms window centred on the peak of the respective burst. In addition, the Stretch velocity-Stretch Reflex input-output curve was examined for the two locomotion tasks over a range of velocities from 100 to 400 deg/s. Peak latencies for the two Reflex responses were observed at 52±5/77±6 ms (SLR/MLR) for walking, 51±3/76±6 ms (SLR/MLR) for pedalling, and 50±3/76±7 ms for sitting. A statistically significant increase in the magnitude of the MLR was observed during walking compared with pedalling and sitting (P=0.007), whereas no difference in magnitude was observed between the three tasks for the SLR (P=0.616). Furthermore, no difference was observed in the Stretch velocity-Stretch Reflex input-output relationship between walking and pedalling. It is suggested that the medium component of the Stretch Reflex response is modulated to provide increased control for the postural demands of walking.
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Soleus Stretch Reflex modulation during gait in humans
Journal of neurophysiology, 1996Co-Authors: Thomas Sinkjær, Jacob Buus Andersen, Birgit Tine LarsenAbstract:1. The modulation of the short-latency Stretch Reflex during walking at different walking speeds was investigated and compared with the Stretch Reflex during standing in healthy human subjects. 2. Ankle joint Stretches were applied by a system able to rotate the human ankle joint during treadmill walking in any phase of the step cycle. The system consisted of a mechanical joint attached to the subject's ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. The weight of the total system attached to the leg of the subject was 900 g. 3. The short-latency soleus Stretch Reflex was modulated during a step. In the stance phase, the amplitude equaled that found during standing at matched soleus background electromyogram (EMG). In the transition from stance to swing, the amplitude was 0 in all subjects. In late swing, the Stretch Reflex amplitude increased to 45 +/- 27% (mean +/- SD) of the maximal amplitude in the stance phase (Stretch amplitude 8 degrees, Stretch velocity 250 degrees/s). 4. The onset (42 +/- 3.2 ms) and peak latencies (59 +/- 2.5 ms) of the Stretch Reflex did not depend on the phase in the step cycle at which the Reflex was elicited. 5. When the ankle joint is rotated, a change in torque can be measured. The torque measured over the first 35 ms after Stretch onset (nonReflex torque) was at a maximum during late stance, when the leg supported a large part of the body's weight, and at a minimum during the swing phase. At heel contact the nonReflex torque was 50% of its maximal value. 6. During the stance phase the maximal EMG Stretch Reflex had a phase lead of approximately 120 ms with respect to the maximal background EMG and a phase lead of approximately 250 ms with respect to the maximal nonReflex torque. 7. The constant latency of the Stretch Reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. 8. The relatively high amplitude of the Stretch Reflex in late swing and at heel contact made it likely that the Stretch Reflex contributed to the activation of the ankle extensor muscles in early stance phase.
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Modulation of the human soleus Stretch Reflex during gait
Proceedings of 16th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1Co-Authors: Jacob Buus Andersen, Birgit Tine Larsen, Thomas SinkjærAbstract:A system able of imposing a fast ankle rotation during gait has been developed. The two-link system consists of a mechanical joint, strapped to the shin and the subjects' foot. The mechanical joint turns around the joint and is, by means of bowden wires, connected to a motor placed next to a treadmill where the subject is walking. It is possible with the attained system to investigate how the Stretch Reflex is modulated during gait and it makes it conceivable to examine to what extend the Stretch Reflex is contributing to the control of locomotion during normal and pathological motor behaviour. Preliminary results show that the modulation of the Stretch Reflex emerged with the same pattern during gait as described in the literature for the H-Reflex. >
Masami Akai - One of the best experts on this subject based on the ideXlab platform.
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Age-related changes of the Stretch Reflex excitability in human ankle muscles.
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2010Co-Authors: Hiroki Obata, Kimitaka Nakazawa, Masami Akai, Noritaka Kawashima, Tatsuyuki OhtsukiAbstract:The purpose of this study was to characterize the effects of aging on the Stretch Reflex in the ankle muscles, and in particular to compare the effects on the ankle dorsi-flexor (tibialis anterior: TA) and the plantar-flexor (soleus: SOL). Stretch Reflex responses were elicited in the TA and SOL at rest and during weak voluntary contractions in 20 elderly and 23 young volunteers. The results indicated that, in the TA muscle, the elderly group had a remarkably larger long-latency Reflex (LLR), whereas no aging effect was found in the short latency Reflex (SLR). These results were very different from those in the SOL muscle, which showed significant aging effects in the SLR and medium latency Reflex (MLR), but not in the LLR. Given the fact that the LLR of the TA Stretch Reflex includes the cortical pathway, it is probable that the effects of aging on the TA Stretch Reflex involve alterations not only at the spinal level but also at the cortical level. The present results indicate that the Stretch Reflexes of each of the ankle antagonistic muscles are affected differently by aging, which might have relevance to the neural properties of each muscle.
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Invariable H-Reflex and sustained facilitation of Stretch Reflex with heightened sympathetic outflow
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2008Co-Authors: Kiyotaka Kamibayashi, Kimitaka Nakazawa, Masami Akai, Hiroki Obata, Hisayoshi Ogata, Minoru ShinoharaAbstract:Abstract Stretch Reflex shows sustained (3-min) increase with heightened sympathetic outflow [Hjortskov N, Skotte J, Hye-Knudsen C, Fallentin N. Sympathetic outflow enhances the Stretch Reflex response in the relaxed soleus muscle in humans. J Appl Physiol 2005;98:1366–70], but it is unknown if it accompanies a sustained increase in H-Reflex. The purpose of the study was to test if there is a sustained facilitation in the H-Reflex in the human soleus muscle during a variety of sustained tasks that are known to elevate sympathetic outflow. Mean arterial blood pressure, heart rate, and H- and Stretch Reflexes in the relaxed soleus muscle were obtained in healthy young adults who performed mental arithmetic, static handgrip exercise, post-handgrip ischemia, and cold stimulation. Each task lasted 3min with a 3-min rest in between tasks. Data were analyzed for the initial 30s and entire 3min of each task. There was a heightened cardiovascular response in all tasks for both durations of analysis. An increase in H-Reflex amplitude was not observed for either the initial or entire duration of the analysis. The tasks increased Stretch Reflex amplitude for both durations of analysis. Invariable H-Reflex and sustained facilitation of Stretch Reflex with heightened sympathetic outflow would imply sympathetic modulation of muscle spindle sensitivity.
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Enhanced Stretch Reflex excitability of the soleus muscle in persons with incomplete rather than complete chronic spinal cord injury.
Archives of physical medicine and rehabilitation, 2006Co-Authors: Kimitaka Nakazawa, Noritaka Kawashima, Masami AkaiAbstract:Abstract Nakazawa K, Kawashima N, Akai M. Enhanced Stretch Reflex excitability of the soleus muscle in persons with incomplete rather than complete chronic spinal cord injury. Objective To compare excitabilities of spinal Stretch Reflex among clinically complete spinal cord injury (SCI), incomplete SCI, elderly healthy, and young healthy subjects. Design Case comparison. Setting Research laboratory. Participants Volunteer sample of 12 complete SCI, 10 incomplete SCI, 10 elderly, and 11 young subjects. Intervention Mechanically induced Stretch Reflex, H-Reflex, and M response in electromyographic activity of the soleus muscle were recorded in all subjects. Main Outcome Measures Absolute peak-to-peak Stretch Reflex amplitude and maximum H-Reflex (Hmax), and those values relative to the maximum M response (Mmax) amplitude (relative peak-to-peak Stretch Reflex amplitude) and H/M ratio. Results Both the absolute and relative peak-to-peak Stretch Reflex amplitudes showed the greatest values in incomplete SCI among the 4 groups. Although absolute and relative peak-to-peak Stretch Reflex amplitudes of the incomplete SCI group were greater than those of the complete SCI group, the H/M ratios of both groups were comparable, and were greater than those of the younger and elderly groups. Conclusions The results suggest that the greater absolute and relative peak-to-peak Stretch Reflex amplitudes of incomplete SCI were mostly due to the greater maximum motor potential (Mmax), while the elevated spinal motoneuronal excitability shown by the increased H/M ratio was maintained in the chronic stage after both complete and incomplete SCIs.
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Gradual increment/decrement of isometric force modulates soleus Stretch Reflex response in humans.
Neuroscience letters, 2003Co-Authors: Toshitaka Kimura, Kimitaka Nakazawa, Daichi Nozaki, Masami Akai, Tatsuyuki OhtsukiAbstract:We investigated how a gradual isometric force-increment and -decrement task modulates the behavior of a soleus Stretch Reflex. Six healthy subjects performed isometric plantar-flexion torque exertion tasks in which they adjusted the torque level to a target changing triangularly (3 s/cycle; the amplitude is 15% of maximal voluntary isometric contraction (MVC)) or to constant targets (3.75, 7.5, and 11.25% of MVC). The magnitude of the short latency Stretch Reflex evoked by dorsi-flexing mechanical perturbation was strongly modulated by the muscle contraction states; it was the largest and the smallest for the torque-increment and -decrement phases, respectively. On the other hand, within each muscle contraction, the magnitude was independent of the torque level. Similar results were observed for the medium latency Stretch Reflex. These results indicate that when the central nervous system increases or decreases the muscular force, it simultaneously regulates the sensitivity of the Stretch Reflex.
Michael James Grey - One of the best experts on this subject based on the ideXlab platform.
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Hamstring Stretch Reflex: could it be a reproducible objective measure of functional knee stability?”
Journal of experimental orthopaedics, 2016Co-Authors: Jawad F. Abulhasan, Cameron M. Anley, Martyn D. Snow, Michael James GreyAbstract:Background The anterior cruciate ligament (ACL) plays an important role in anterior knee stability by preventing anterior translation of the tibia on the femur. Rapid translation of the tibia with respect to the femur produces an ACL-hamstring Stretch Reflex which may provide an object measure of neuromuscular function following ACL injury or reconstruction. The aim of this study was to determine if the ACL-hamstring Stretch Reflex could be reliably and consistently obtained using the KT-2000 arthrometer.
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tibialis anterior Stretch Reflex in early stance is suppressed by repetitive transcranial magnetic stimulation
The Journal of Physiology, 2009Co-Authors: Abraham Theodoor Zuur, Thomas Sinkjær, Michael James Grey, Mark Schram Christensen, Jens NielsenAbstract:A rapid plantar flexion perturbation in the early stance phase of walking elicits a large Stretch Reflex in tibialis anterior (TA). In this study we use repetitive transcranial magnetic stimulation (rTMS) to test if this response is mediated through a transcortical pathway. TA Stretch Reflexes were elicited in the early stance phase of the step cycle during treadmill walking. Twenty minutes of 1 Hz rTMS at 115% resting motor threshold (MT(r)) significantly decreased (P < 0.05) the magnitude of the later component of the Reflex at a latency of approximately 100 ms up to 25 min after the rTMS. Control experiments in which Stretch Reflexes were elicited during sitting showed no effect on the spinally mediated short and medium latency Stretch Reflexes (SLR and MLR) while the long latency Stretch Reflex (LLR) and the motor-evoked potential (MEP) showed a significant decrease 10 min after 115% MT(r) rTMS. This study demonstrates that 1 Hz rTMS applied to the leg area of the motor cortex can suppress the long latency TA Stretch Reflex during sitting and in the stance phase of walking. These results are in line with the hypothesis that the later component of the TA Stretch Reflex in the stance phase of walking is mediated by a transcortical pathway. An alternative explanation for the observed results is that the Reflex is mediated by subcortical structures that are affected by the rTMS. This study also shows that rTMS may be used to study the neural control of walking.
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plantar flexor Stretch Reflex responses to whole body loading unloading during human walking
European Journal of Neuroscience, 2002Co-Authors: Michael James Grey, Johannes Van Doornik, Thomas SinkjærAbstract:Numerous animal and human studies have shown that afferent information from the periphery contributes to the control of walking. In particular, recent studies have consistently shown that load receptor input is an important element of the locomotion control mechanism. The objective of this study was to investigate the contribution of load receptor feedback to the compensatory Stretch Reflex response. We examined the contribution of load receptor feedback to the magnitude of the short and medium latency components of the ankle plantar flexor Stretch Reflex responses following an unexpected dorsiflexion perturbation during human walking. Three body load conditions were investigated: normal body load, a 30% increase in body load, and a 30% decrease in body load. Healthy subjects walked on a treadmill at approximately 3.6 km/h with the left ankle attached to a portable Stretching device. Dorsiflexion perturbations (8 degrees; 350-425 degrees/s) were generated during the late stance phase of gate (approximately 400 ms following heel contact). Electromyographic activity was recorded from the soleus, tibialis anterior, medial gastrocnemius, rectus femoris, and biceps femoris muscles using bipolar surface electrodes. Stretch Reflex responses were observed in the soleus and gastrocnemius muscles for all of the body load conditions; however, increasing or decreasing the body load did not affect the timing and magnitude of the responses. This study provides evidence that load receptor input does not contribute strongly to the corrective response of the Stretch Reflex in the plantar flexor muscles during walking.
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A task dependent change in the medium latency component of the soleus Stretch Reflex.
Experimental brain research, 2002Co-Authors: Michael James Grey, Birgit Tine Larsen, Thomas SinkjærAbstract:In comparison to the H-Reflex, the task dependency of the human Stretch Reflex during locomotive and postural tasks has not received a great deal of attention in the literature. The few studies on Reflex task dependency that have been performed to date have concentrated on either the group Ia mediated H-Reflex or the short latency Stretch Reflex. In the present study the medium latency component of a mechanically evoked Stretch Reflex is investigated during walking, pedalling, and sitting. Stretch Reflexes were evoked in the soleus muscle using dorsiflexion perturbations generated with a portable Stretching device. Perturbations of equal amplitude and velocity (8 deg, 300 deg/s) were presented to 16 healthy subjects while they walked on a treadmill and pedalled a cycle ergometer. For eight of these subjects, an additional set of data was collected as they sat on the ergometer holding a steady posture. Perturbations were presented in the early to mid stance phase of walking and the downstroke of the pedal cycle. During all three conditions, the background soleus muscle activity was matched. The short (SLR) and medium (MLR) components of the soleus Reflex responses were quantified by calculating the area of each burst in a 15-ms window centred on the peak of the respective burst. In addition, the Stretch velocity-Stretch Reflex input-output curve was examined for the two locomotion tasks over a range of velocities from 100 to 400 deg/s. Peak latencies for the two Reflex responses were observed at 52±5/77±6 ms (SLR/MLR) for walking, 51±3/76±6 ms (SLR/MLR) for pedalling, and 50±3/76±7 ms for sitting. A statistically significant increase in the magnitude of the MLR was observed during walking compared with pedalling and sitting (P=0.007), whereas no difference in magnitude was observed between the three tasks for the SLR (P=0.616). Furthermore, no difference was observed in the Stretch velocity-Stretch Reflex input-output relationship between walking and pedalling. It is suggested that the medium component of the Stretch Reflex response is modulated to provide increased control for the postural demands of walking.
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Soleus Stretch Reflex during cycling.
Motor control, 2001Co-Authors: Michael James Grey, Charles W. Pierce, Theodore E. Milner, Thomas SinkjærAbstract:The modulation and strength of the human soleus short latency Stretch Reflex was investigated by mechanically perturbing the ankle during an unconstrained pedaling task. Eight subjects pedaled at 60 rpm against a preload of 10 Nm. A torque pulse was applied to the crank at various positions during the crank cycle, producing ankle dorsiflexion perturbations of similar trajectory. The Stretch Reflex was greatest during the power phase of the crank cycle and was decreased to the level of background EMG during recovery. Matched perturbations were induced under static conditions at the same crank angle and background soleus EMG as recorded during the power phase of active pedaling. The magnitude of the Stretch Reflex was not statistically different from that during the static condition throughout the power phase of the movement. The results of this study indicate that the Stretch Reflex is not depressed during active cycling as has been shown with the H-Reflex. This lack of depression may reflect a decreased susceptibility of the Stretch Reflex to inhibition, possibly originating from presynaptic mechanisms.
