H-reflexes are less depressed following muscle stretch in spastic spinal cord injured patients than in healthy subjects (original) (raw)
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Frontiers in Physiology, 2018
During the period when the ankle joint is kept in a dorsiflexed position, the soleus (SOL) H-reflex is inhibited. The nature of this inhibition is not fully understood. One hypothesis is that the decrease in spinal excitability could be attributed to post-activation depression of muscle spindle afferents due to their higher firing rate during the stretchand-hold procedure. As the static stretching position is maintained though, a partial restoration of the neurotransmitter is expected and should mirror a decrease in H-reflex inhibition. In the present study, we explored the time course of spinal excitability during a period of stretching. SOL H-reflex was elicited during a passive dorsiflexion movement, at 3, 6, 9, 12, 18, 21, and 25 s during maximal ankle dorsiflexion, during plantar flexion (PF) and after stretching, in 12 healthy young individuals. Measurements during passive dorsiflexion, PF and after stretching were all performed with the ankle at 100 • angle; measurements during static stretching were performed at individual maximal dorsiflexion. H-reflex was strongly inhibited during the dorsiflexion movement and at maximal dorsiflexion (p < 0.0001) but recovered during PF and after stretching. During stretching H-reflex showed a recovery pattern (r = 0.836, P = 0.019) with two distinct recovery steps at 6 and 21 s into stretching. It is hypothesized that the H-reflex inhibition observed until 18 s into stretching is the result of post-activation depression of Ia afferent caused by the passive dorsiflexion movement needed to move the ankle into testing position. From 21 s into stretching, the lower inhibition could be caused by a weaker post-activation depression, inhibition from secondary afferents or post-synaptic inhibitions.
Post-activation depression of soleus stretch reflexes in healthy and spastic humans
Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale, 2008
Reduced depression of transmitter release from Ia afferents following previous activation (post-activation depression) has been suggested to be involved in the pathophysiology of spasticity. However, the effect of this mechanism on the myotatic reflex and its possible contribution to increased reflex excitability in spastic participants has not been tested. To investigate these effects, we examined post-activation depression in Soleus H-reflex responses and in mechanically evoked Soleus stretch reflex responses. Stretch reflex responses were evoked with consecutive dorsiflexion perturbations delivered at different intervals. The magnitude of the stretch reflex and ankle torque response was assessed as a function of the time between perturbations. Soleus stretch reflexes were evoked with constant velocity (175°/s) and amplitude (6°) plantar flexion perturbations. Soleus H-reflexes were evoked by electrical stimulation of the tibial nerve in the popliteal fossa. The stretch reflex and H-reflex responses of 30 spastic participants (with multiple sclerosis or spinal cord injury) were compared with those of 15 healthy participants. In the healthy participants, the magnitude of the soleus stretch reflex and H-reflex decreased as the interval between the stimulus/perturbation was decreased. Similarly, the stretch-evoked torque decreased. In the spastic participants, the post-activation depression of both reflexes and the stretch-evoked torque was significantly smaller than in healthy participants. These findings demonstrate that post-activation depression is an important factor in the evaluation of stretch reflex excitability and muscle stiffness in spasticity, and they strengthen the hypothesis that reduced post-activation depression plays a role in the pathophysiology of spasticity.
Neuroscience Letters, 2007
Imposed static hip stretches substantially modulate the soleus H-reflex in people with an intact or injured spinal cord while stretch of the hip flexors affect the walking pattern in lower vertebrates and humans. The aim of this study was to assess the effects of dynamic hip stretches on the soleus H-reflex in supine spinal cord injured (SCI) subjects. Sinusoidal movements were imposed on the right hip joint at 0.2 Hz by a Biodex system. H-reflexes from the soleus muscle were recorded as the leg moved in flexion or extension. Stimuli were sent only once in every hip movement cycle that each lasted 5 s. Torque responses were recorded at the hip, knee, and ankle joints. A hip phase-dependent soleus H-reflex modulation was present in all subjects. The reflex was facilitated during hip extension and suppressed during hip flexion. There were no significant differences in pre-or post-stimulus soleus background activity between the two conditions. Oscillatory responses were present as the hip was maximally flexed. Sinusoidal hip stretches modulated the soleus H-reflex in a manner similar to that previously observed following static hip stretches. The amount of reflex facilitation depended on the angle of hip extension. Further research is needed on the afferent control of spinal reflex pathways in health and disease in order to better understand the neural control of movement in humans. This will aid in the development of rehabilitation strategies to restore motor function in these patients.
Spinal Cord, 2016
Study design: Although abnormal cutaneous reflex (CR) activity has been identified during gait after incomplete spinal cord injury (SCI), this activity has not been directly compared in subjects with and without the spasticity syndrome. Objectives: Characterisation of CR activity during controlled rest and 'ramp and hold' phases of controlled plantarflexion in subjects with and without the SCI spasticity syndrome. Design: Transverse descriptive study with non-parametric group analysis. Setting: SCI rehabilitation hospital. Methods: Tibialis Anterior (TA) reflexes were evoked by innocuous cutaneous plantar sole stimulation during rest and ramp and hold phases of plantarflexion torque in non-injured subjects (n = 10) and after SCI with (n = 9) and without (n = 10) hypertonia and/or involuntary spasm activity. Integrated TA reflex responses were analysed as total (50-300 ms) or short (50-200 ms) and long-latency (200-300 ms) activity. Results: Total and long-latency TA activity was inhibited in non-injured subjects and the SCI group without the spasticity syndrome during plantarflexion torque but not in the SCI spasticity group. Furthermore, loss of TA reflex inhibition during plantarflexion correlated with time after SCI (ρ = 0.79, P = 0.009). Moreover, TA reflex activity inversely correlated with maximum plantarflexion torque in the spasticity group (ρ = − 0.75, P = 0.02), despite similar non-reflex TA electromyographic activity during plantarflexion after SCI in subjects with (0.11, 0.08-0.13 mV) or without the spasticity syndrome (0.09, 0.07-0.12 mV). Conclusions: This reflex testing procedure supports previously published evidence for abnormal CR activity after SCI and may characterise the progressive disinhibition of TA reflex activity during controlled plantarflexion in subjects diagnosed with the spasticity syndrome.
Clinical Neurophysiology, 2006
Objective: we investigated the H reflexes and the long latency reflexes (LLRs) of the thenar and hypothenar muscles in fifteen normal subjects and in twenty patients with spasticity. The objective were: 1. to elucidate if the H reflexes could be elicited in the intrinsic hand muscles in patients with spasticity under a relaxed condition; 2. evaluate if the amplitude of the H reflex could be increased with muscle contraction and 3. to determine if the absence of the long latency reflexes was related to the size of the preceding H reflex or to a lack of Artemisa medigraphic en línea Increase of the H reflex amplitude and absence of long latency reflexes
Reflex effects of induced muscle contraction in normal and spinal cord injured subjects
Muscle & Nerve, 2002
The modulation of the soleus H reflex in response to functional electrical stimulation (FES) of the rectus femoris (RF) muscle and its overlying skin was examined in 11 normal adults and 6 patients with a clinically defined complete spinal cord injury (SCI). Stimulation of RF at twice motor threshold (MT) resulted in a long-lasting (>1,000 ms) and significant reduction (50-70% of control) in the size of the soleus H reflex in all normal subjects tested. For five of the SCI subjects, 2MT stimulation of RF induced a 55-60% reduction in the soleus H reflex that was also long-lasting (>160 ms). In the remaining SCI subject, 2MT stimulation resulted in an initial period of significant H-reflex facilitation (0-14 ms) that was followed by a longer-lasting inhibition commencing 60 ms after the cessation of the conditioning stimulation. Decreasing the strength of stimulation to below that required to generate a clear contraction in RF resulted in mixed facilitatory and inhibitory actions that were subject dependent. The changes in H-reflex excitability resulting from FES highlight the potential use of FES in the management of hypertonicity in SCI but also suggest that the central actions of FES need to be considered when FES gait restoration programs are designed.
Objective: we investigated the H reflexes and the long latency reflexes (LLRs) of the thenar and hypothenar muscles in fifteen normal subjects and in twenty patients with spasticity. The objective were: 1. to elucidate if the H reflexes could be elicited in the intrinsic hand muscles in patients with spasticity under a relaxed condition; 2. evaluate if the amplitude of the H reflex could be increased with muscle contraction and 3. to determine if the absence of the long latency reflexes was related to the size of the preceding H reflex or to a lack of Artemisa medigraphic en línea Increase of the H reflex amplitude and absence of long latency reflexes