Reflexes In Leg Muscles Research Articles

The Importance of Being in Touch.

This paper describes a series of studies resulting from the finding that when free floating in weightless conditions with eyes closed, all sense of one's spatial orientation with respect to the aircraft can be lost. But, a touch of the hand to the enclosure restores the sense of spatial anchoring within the environment. This observation led to the exploration of how light touch of the hand can stabilize postural control on Earth even in individuals lacking vestibular function, and can override the effect of otherwise destabilizing tonic vibration reflexes in leg muscles. Such haptic stabilization appears to represent a long loop cortical reflex with contact cues at the hand phase leading EMG activity in leg muscles, which change the center of pressure at the feet to counteract body sway. Experiments on dynamic control of balance in a device programmed to exhibit inverted pendulum behavior about different axes and planes of rotation revealed that the direction of gravity not the direction of balance influences the perceived upright. Active control does not improve the accuracy of indicating the upright vs. passive exposure. In the absence of position dependent gravity shear forces on the otolith organs and body surface, drifting and loss of control soon result and subjects are unaware of their ongoing spatial position. There is a failure of dynamic path integration of the semicircular canal signals, such as occurs in weightless conditions.

Predicting rapid progression of Parkinson's Disease at baseline patients evaluation.

The rate of Parkinson's Disease (PD) progression in the initial post-diagnosis years can vary significantly. In this work, a methodology for the extraction of the most informative features for predicting rapid progression of the disease is proposed, using public data from the Parkinson's Progression Markers Initiative (PPMI) and machine learning techniques. The aim is to determine if a patient is at risk of expressing rapid progression of PD symptoms from the baseline evaluation and as close to diagnosis as possible. By examining the records of 409 patients from the PPMI dataset, the features with the best predictive value at baseline patient evaluation are found to be sleep problems, daytime sleepiness and fatigue, motor symptoms at legs, cognition impairment, early axial and facial symptoms and in the most rapidly advanced cases speech issues, loss of smell and affected leg muscle reflexes.

Muscle Sympathetic Nerve Activity Responses To Plantar Flexion In Humans

Previous studies examining muscle sympathetic nerve activity (MSNA) responses to exercise have focused on arm exercise with only limited data examining responses to leg exercise. PURPOSE: To examine MSNA responses to plantar flexion from one leg. The uniqueness of this experimental paradigm is that plantar flexion engages the gastrocnemius and soleus muscles, which are the major muscles that are activated during running. We hypothesized that MSNA would increase during fatiguing exercise. METHODS: Eleven healthy subjects (27 ± 1 yr) performed a graded bout of plantar flexion to fatigue followed by postexercise muscle ischemia (PEMI). Because time to fatigue varied between subjects, data were expressed as a percent of time to fatigue. MSNA, heart rate, and arterial blood pressure were measured continuously throughout the protocol. RESULTS: Heart rate and arterial blood pressure increased as a function of work rate. Maximal heart rate and mean arterial blood pressure changes were Δ25 ± 2 beats/min and Δ17 ± 3 mmHg, respectively (P<0.001). MSNA was significantly increased only after 50% time to fatigue. MSNA increased from 9 ± 2 bursts/min at rest to 14 ± 2 and 18 ± 2 bursts/min at 75% of fatigue and fatigue, respectively (P<0.001). During PEMI heart rate returned back to baseline, but was still significantly increased above baseline (Δ8 ± 1 beats/min). Mean arterial blood pressure was significantly reduced from pressures at fatigue, but remained elevated from baseline (Δ9 ± 2 mmHg). MSNA remained elevated during PEMI (18 ± 2 bursts/min). CONCLUSION: Plantar flexion elicits significant neurocardiovascular responses that appear to be primarily mediated by the muscle metaboreflex. The current experimental paradigm provides an effective exercise model to examine leg muscle reflexes in humans. Supported by the National Institutes of Health P01-HL-077670.

Soleus h-reflex modulation during stance phase of walking with altered arm swing patterns.

The purpose of this study was to test the effect of arm swing on modulation of soleus H-reflexes amplitudes during walking. Fifteen subjects walked (1.07 m/s) on a treadmill in 4 arm swing conditions: 1-natural arm swing (control), 2-active restraint, 3-passive restraint, and 4-passive-assisted. Tibial nerve was electrically stimulated and soleus EMG was recorded. H-reflex amplitude was significantly greater during active than during passive restraint (p = .013). Remaining arm swing conditions were not significantly different. We detected a subtle effect of arm swing on soleus H-reflex amplitude. Descending regulation may serve as a gating mechanism to control the effect of arm movements on reflex pathways for leg muscles. This gating mechanism may be impaired postneural injury, potentially enhancing the modulation of peripheral sensory inputs on reflexes in leg muscles during walking. Future experiments to test additional conditions and evoking reflexes in more phases of walking are recommended.

Suppression of soleus H-reflex amplitude is graded with frequency of rhythmic arm cycling

In humans, rhythmic arm cycling has been shown to significantly suppress the soleus H-reflex amplitude in stationary legs. The specific nature of the relationship between frequency of arm cycling and H-reflex modulation in the legs has not been explored. We speculated that the effect of arm cycling on reflexes in leg muscles is related to the neural control of arm movement; therefore, we hypothesized that a graded increase in arm cycling frequency would produce a graded suppression of the soleus H-reflex amplitude. We also hypothesized that a threshold frequency of arm cycling would be identified at which the H-reflex amplitude significantly differed from static control trials (i.e., the arms were stationary). Soleus H-reflexes were evoked in stationary legs with tibial nerve stimulation during both control and rhythmic arm cycling (0.03-2.0 Hz) trials. The results show a significant inverse linear relation between arm cycling frequency and soleus H-reflex amplitude (P<0.05). Soleus H-reflex amplitude significantly differed from control at an average threshold cycling frequency of 0.8 Hz. The results demonstrate that increased frequency of upper limb movement increases the intensity of interlimb influences on the neural activity in stationary legs. Further, a minimum threshold frequency of arm cycling is required to produce a significant effect. This suggests that achieving a threshold frequency of rhythmic arm movement may be important to incorporate in rehabilitation strategies to engage the appropriate interlimb neural pathways.

Changes in soleus H-reflex modulation after treadmill training in children with cerebral palsy

In healthy children, short latency leg muscle reflexes are profoundly modulated throughout the step cycle in a functionally meaningful way and contribute to the electromyographic (EMG) pattern observed during gait. With maturation of the corticospinal tract, the reflex amplitudes are depressed via supraspinal inhibitory mechanisms. In the soleus muscle the rhythmic part of the modulation pattern is present in children with cerebral palsy (CP), but the development of tonic depression with increasing age, as seen in healthy children, is disturbed. Treadmill training clinically improves the walking pattern in children with CP. Presuming that short latency reflexes contribute significantly to the walking pattern, a change in the modulation may occur after training. The aim of this study was to assess whether treadmill training also improves the soleus reflex modulation during gait in children with CP. Seven children with CP underwent brief treadmill training for 10 min a day over 10 consecutive days; all of them were functional walkers. Soleus Hoffmann (H-) reflexes were investigated during walking on a treadmill before the first, and one day after the last, training session. Treadmill training led to a considerable clinical improvement in gait velocity. After 10 days of training, soleus H-reflexes during gait were almost completely depressed during the swing phase. The complete suppression of the soleus H-reflex during the swing phase, which is also exhibited by healthy subjects, could reflect an improvement towards a functionally more useful pattern. In conclusion, treadmill training can induce changes in the modulation of short latency reflexes during gait.

Rhythmic arm cycling suppresses hyperactive soleus H-reflex amplitude after stroke

Objective Rhythmic arm cycling movement suppresses the amplitude of soleus H-reflexes in neurologically intact participants. This suppression is greater when the movement frequency is increased. If rhythmic arm movement can still suppress the amplitude of H-reflexes in the legs after stroke, it could potentially be used as a rehabilitation technique to reduce exaggerated reflexes such as those occurring in spasticity. The purpose of this study was to test for maintenance of this suppressive effect after stroke. Since a portion of the effect of arm cycling had previously been ascribed to subcortical and spinal mechanisms, we hypothesized that the suppressive effect of arm cycling would be partially maintained after stroke. Methods Participants with history of single chronic (>6 months) stroke performed rhythmic arm cycling at ∼1 Hz and also at the highest frequency possible (∼1.5 Hz). Soleus H-reflexes were evoked in the more and less affected legs simultaneously and full recruitment curves obtained. Results H-reflex amplitudes in both the more and less affected legs of stroke participants were significantly suppressed during arm cycling. However, the extent of the suppression is weaker compared to neurologically intact and age-matched subjects. Conclusions Neural activity related to arm cycling can still access interlimb pathways after stroke and activate spinal control mechanisms leading to suppression of H-reflex amplitudes. Significance The suppressive effect of arm cycling could be exploited in the modification of exaggerated muscle afferent reflexes in leg muscles after stroke. Whether this has a significant effect on modulation of spasticity requires further substantiation.

Obstacle stepping involves spinal anticipatory activity associated with quadrupedal limb coordination

Obstacle avoidance steps are associated with a facilitation of spinal reflexes in leg muscles. Here we have examined the involvement of both leg and arm muscles. Subjects walking with reduced vision on a treadmill were acoustically informed about an approaching obstacle and received feedback about task performance. Reflex responses evoked by tibial nerve stimulation were observed in all arm and leg muscles examined in this study. They were enhanced before the execution of obstacle avoidance compared with normal steps and showed an exponential adaptation in contralateral arm flexor muscles corresponding to the improvement of task performance. This enhancement was absent when the body was partially supported during the task. During the execution of obstacle steps, electromyographic activity in the arm muscles mimicked the preceding reflex behaviour with respect to enhancement and adaptation. Our results demonstrate an anticipatory quadrupedal limb coordination with an involvement of proximal arm muscles in the acquisition and performance of this precision locomotor task. This is presumably achieved by an up-regulated activity of coupled cervico-thoracal interneuronal circuits.

Neural Coupling Between the Arms and Legs During Rhythmic Locomotor-Like Cycling Movement

Neuronal coupling between the arms and legs allowing coordinated rhythmic movement during locomotion is poorly understood. We used the modulation of cutaneous reflexes to probe this neuronal coupling between the arms and legs using a cycling paradigm. Participants performed rhythmic cycling with arms, legs, or arms and legs together. We hypothesized that any contributions from the arms would be functionally linked to locomotion and would thus be phase-dependent. Reflexes were evoked by electrical stimulation of the superficial peroneal nerve at the ankle, and electromyography (EMG) was recorded from muscles in the arms and legs. The main finding was that the relative contribution from the arms and legs was linked to the functional state of the legs. For example, in tibialis anterior, the largest contribution from arm movement [57% variance accounted for (VAF), P < 0.05] was during the leg power phase, whereas the largest from leg movement (71% VAF, P < 0.05) was during leg cycling recovery. Thus the contribution from the arms was functionally gated throughout the locomotor cycle in a manner that appears to support the action of the legs. Additionally, the effect of arm cycling on reflexes in leg muscles when the legs were not moving was relatively minor; full expression of the effect of rhythmic arm movement was only observed when both the arms and legs were moving. Our findings provide experimental support for the interaction of rhythmic arm and leg movement during human locomotion.

Comparison of tap-evoked and tone-evoked postural reflexes in humans

To find an easy clinical test of postural reflexes, we compared tone and tap stimuli for eliciting postural reactions in leg muscles in 13 healthy subjects during upright stance. Tones (1000 Hz, 90 dB nHl) were presented monaurally via headphones; taps were applied with a reflex hammer to the forehead. Surface EMG was recorded from the medial gastrocnemius and the sternocleidomastoid muscles, and rectified and averaged. Tapping the forehead of a standing subject evoked leg muscle reflexes that began 50 ms after the stimulus in all subjects. Tone-evoked leg muscle reflexes behaved differently, i.e., they had smaller amplitudes and could be recorded in only 5 of 13 subjects. However, this same acoustic stimulus elicited reflex activity in the neck muscles of all subjects. There were also other differences (amplitudes, dependence on pre-activation) between these two reflexes. Tone-evoked leg muscle responses and tone-evoked neck muscle responses seem to be mediated by different structures, i.e., the latter by an oligosynaptic pathway and the former by polysynaptic neural circuits. We conclude that tap-evoked leg muscle responses are not or not solely mediated by saccular receptors but other receptors (i.e., proprioceptors, semicircular canals) are probably also involved.

Réévaluation des mécanismes physiologiques qui génèrent le réflexe dˈétirement : de nouvelles hypothèses sur la physiopathologie de la spasticité

Introduction: Spasticity has been defined as tendon reflex exaggeration and increased muscle reflex contraction in response to its stretch (Lance, 1980). It has been generally admitted that stretch reflex exaggeration was due to myotatic reflex hyperexcitability (Ia fibre-motoneurone synapses). This interpretation has been recently revisited taking into account neurophysiological data obtained in cat and recent data obtained in spastic patients. Problematics: Myotatic reflex has been described in decerebrate cat in 1924 by Liddel and Sherrington. In 1943, Lloyd demonstrated that myotatic reflex was due to monosynaptic Ia fibre motoneurone α synapses. Almost all the following studies of stretch reflexes were devoted to monosynaptic reflexes both in animal and humans. In fact, the existence of group II fibres coming also from spindles and some restricted experiments performed in man have led to discuss the role of group II fibres in the static component of the stretch reflexes. Results: Recent studies performed in humans have shown that group II fibres play an important role in the development of stretch reflexes in leg muscles and that in spastic hemiplegic patients group II fibres facilitatory effects was deeply increased. Discussion: Results obtained both in humans and animals suggest that group II fibres play also a role in a stretch reflex and led to consider that the pathophysiological modifications of group II effects could contribute to spasticity. Conclusion: Modifications of network fed by group II fibres and modifications of muscular fibres intrinsic properties are likely to play a role in the developments of spasticity in humans.

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Leg muscle reflexes mediated by cutaneous A-β fibres are normal during gait in reflex sympathetic dystrophy

Objectives: Reflex sympathetic dystrophy (RSD) is, from the onset, characterized by various neurological deficits such as an alteration of sensation and a decrease in muscle strength. We investigated if afferent A-β fibre-mediated reflexes are changed in lower extremities affected by acute RSD. Methods: The involvement of these fibres was determined by analyzing reflex responses from the tibialis anterior (TA) and biceps femoris (BF) muscles after electrical stimulation of the sural nerve. The reflexes were studied during walking on a treadmill to investigate whether the abnormalities in gait of the patients were related either to abnormal amplitudes or deficient phase-dependent modulation of reflexes. In 5 patients with acute RSD of the leg and 5 healthy volunteers these reflex responses were determined during the early and late swing phase of the step cycle. Results: No significant difference was found between the RSD and the volunteers. During early swing the mean amplitude of the facilitatory P2 responses in BF and TA increased as a function of stimulus intensity (1.5, 2 and 2.5 times the perception threshold) in both groups. At end swing the same stimuli induced suppressive responses in TA. This phase-dependent reflex reversal from facilitation in early swing to suppression in late swing occurred equally in both groups. Conclusions: In the acute phase of RSD of the lower extremity there is no evidence for abnormal A-β fibre-mediated reflexes or for defective regulation of such reflexes. This finding has implications for both the theory on RSD pathophysiology and RSD models, which are based on abnormal functioning of A-β fibres.

The Midcoxal Prong in Flies (Diptera: Brachycera)

The midcoxal prong [MCP] is a fine outgrowth from the distal sclerite of the coxa into the space between the coxa and the trochanter. It is present in members of all but a few families of 'higher flies'. The morphology of MCP was investigated in SEM preparations. Walking in Eristalis and tethered flight in Calliphora were videorecorded in intact flies and after removal of one or both MCPs. Muscle potentials were recorded in tethered Lucilia. MCP morphology is the same in males and females. It lacks any sensilla. No reflexes in leg muscles were recorded after touching MCP. It presumably performs some mechanical function. During walking as well as grooming, start, landing reflex etc the prong glides freely over the trochanter. During flight, the leg is placed in its peculiar flight position by supination of the trochanter, and the prong is clumped between the coxa and the trochanter. The trochanter presses the anterior hairy face of MCP against a hairy field on the anterior coxal sclerite. The morphology and biomechanical properties of the middle coxa suggest that MCP acts as a sort of a Velcro fastener, locking the middle leg in its flight position. However, excision of MCP did not impair either walking or the ability to place the middle leg in a proper flight position and to hold it against a strong airstream. So the function of this strange organ is still unknown.

Vestibulocollic reflexes evoked by short-duration galvanic stimulation in man.

1. Vestibular-dependent responses in leg muscles following transmastoid galvanic stimulation have been well characterized. Here we describe the properties of vestibulocollic responses evoked by transmastoid galvanic stimulation. 2. In twelve healthy human subjects we examined the averaged responses in unrectified sternocleidomastoid (SCM) EMG evoked by transmastoid stimulation using current pulses of 4 mA intensity and 2 ms duration. In ten subjects we also examined the effects of unilateral vestibular stimulation with the indifferent electrode at the vertex. In further experiments we studied the effects of different levels of background muscle activation, head position, current intensity and current duration. We compared these responses with click-evoked vestibulocollic responses in SCM. 3. A clearly defined biphasic response, beginning with a surface positivity, was recorded in the SCM ipsilateral to the side of cathode placement in all subjects. We refer to this as the p13/n23 [g] (galvanic) response, given the close similarity, in terms of waveform and latencies, to the previously described click-evoked p13/n23 vestibulocollic response. The amplitude of this response was linearly related to background muscle activation, current intensity and current duration, but independent of head position. Unilateral galvanic stimulation revealed the p13/n23 [g] response to be solely generated by the cathode. 4. A biphasic response beginning with a surface negativity (n12/p20 [g]) contralateral to the cathode was seen in all subjects and was generated by both the cathode contralaterally and the anode ipsilaterally. 5. Both the p13/n23 [g] and n12/p20 [g] potentials were abolished by selective vestibular nerve section and unaffected by severe sensorineural deafness. 6. We conclude that galvanic stimulation evokes short-latency vestibulocollic reflexes. These vestibulocollic reflexes have properties that are distinct from those described for galvanic-evoked vestibular reflexes in leg muscles, and which may be related to their differing physiological roles.

Cortical facilitation of cutaneous reflexes in leg muscles during human gait

During human gait, cortical convergence on sural nerve reflex pathways was investigated by means of transcranial magnetic stimulation (TMS) of the cortex in five phases of the step cycle during human walking on a treadmill. Muscular responses to paired electrical and magnetic stimulation were compared with the linear summation of the individual stimuli. For both the tibialis anterior (TA) and biceps femoris (BF) muscles, the averaged data of four subjects showed a significant facilitation mainly in the swing phase of the step cycle. It is suggested that facilitation of corticospinal input onto cutaneous reflex pathways is enhanced specifically in these periods of the step cycle.

Postural reflexes in Parkinson's disease during ‘resist’ and ‘yield’ tasks

Postural reflexes in leg muscles appear to be set at a fixed gain in Parkinson's disease. To further investigate gain adaptation, we instructed 16 patients with idiopathic Parkinson's disease (studied during the ‘off’ phase) and 21 healthy controls to either ‘resist’ or ‘yield’ in response to 20 serial 4 ° toe-up perturbations of a supporting platform on which they were standing. We bilaterally recorded destabilizing medium latency (ML) reflexes from stretched gastrocnemius muscles and corrective long latency (LL) reflexes from shortened tibialis anterior muscles. We also assessed changes in center of foot pressure (CFP) and center of gravity (COG). During the ‘resist’ condition, patients had increased destabilizing ML reflexes, decreased corrective LL reflexes, increased backward displacement of the COG and increased forward (destabilizing) displacement of the CFP. In addition, the backward (corrective) displacement of CFP between 150 and 250 ms was delayed. During the ‘yield’ condition, reflex gains were modified in controls: LL reflexes were markedly attenuated, whereas ML reflexes were markedly increased. Although this reflex pattern resembled the ‘resist’ condition in patients, it was not associated with an increased forward displacement of the CFP, but only with a strongly delayed backward displacement of CFP which started after 150 ms. In patients, ML reflex amplitudes remained unchanged during the ‘yield’ condition, suggesting a fixed reflex gain. LL reflex amplitudes were reduced in patients but significantly less compared to controls, which again suggests a fixed reflex gain. This ‘inflexibility’ of postural reflexes was reflected by the CFP which showed much smaller changes between 0 and 250 ms in patients than controls. These results could not be ascribed to a different ability to yield because posterior displacement of the COG was identical in patients and controls during the ‘yield’ condition. We conclude that (1) patients with Parkinson's disease have abnormal and ‘inflexible’ postural reflexes, associated with delayed corrective movements about the ankle joint and increased body sway; and (2) the increased forward displacement of the CFP in patients likely reflects high stiffness in ankle muscles because reflex changes in controls only affected the CFP more than 150 ms after the perturbation. The increased muscle stiffness and inflexibility of postural reflexes in Parkinson's disease may contribute to balance impairment in daily life.

Altered postural reflexes in Parkinson's disease: A reverse hypothesis

In subjects standing on a movable platform, sudden dorsiflexion of the ankle joint elicits a set of reflexes in leg muscles. These responses include a short latency (SL) and medium latency (ML) stretch reflex in the gastrocnemius muscle and a distal to proximal innervation sequence of long latency (LL) reflexes in the shortened tibialis anterior and vastus lateralis muscles. Because of their role in maintaining upright stance these responses have been termed postural reflexes. In patients with Parkinson's disease (PD), the following abnormalities have been described: 1) enhanced ML-amplitudes; 2) a reversed LL innervation sequence; and 3) delayed onset latencies. These abnormalities are thought to be due to defective motor programming and disturbed control of spinal and supraspinal reflex centers by basal ganglia circuits. The altered reflexes have been held responsible for some of the clinical features of PD, including balance impairment and rigidity. In this paper, we argue the reverse hypothesis that postural reflexes are essentially normal in PD, and that the observed alterations are at least in part consequence rather than cause of balance impairment, the stooped parkinsonian posture and rigidity of PD patients.

Applications and uses of static and dynamic measurement of posture (posturography)

Posturography is a very useful clinical instrument to quantify, analyze, and document postural sway and to differentiate patterns of instability that are typical for the different types of lesions encountered within the cerebellum and to differentiate cerebellar ataxia from spinal ataxia. An objective method of measurement like this is most valuable for follow-up studies and the surveillance of therapeutic efficacy. The method of recording short, medium, and long latency reflexes in leg muscles after a sudden tilt of a movable platform toe-up is not only totally atraumatic and fast, but more importantly it gives significant hints towards the possible site of a central lesion in the sensory-motor system.

Long loop reflexes: concepts and consequences.

New experimental results on long latency reflexes in human limb muscles were presented by neurophysiologists and clinicians with great experience in this field. The scope of presentations reached from the pattern of long latency reflexes in leg muscles during stance and the modifications in various motor disorders to the firing behavior of single motor units during torque perturbations of the elbow and to the role of habituation in long latency reflexes. Finally, the effect of stereoencephalotomy on long latency reflexes in normals and patients with parkinsonian tremor was reviewed.