H-reflex changes under spinal loading and unloading conditions in normal subjects

Differences in soleus H-reflex to M-wave ratio between obese and non-obese individuals

BACKGROUND

The aim of this cross-sectional comparative study was to investigate potential differences in soleus H-reflex to M-wave ratio between obese and non-obese individuals under different postural constraints.

METHODS

A total of 23 obese individuals and 23 matched non-obese controls took part in the study. The maximal soleus H-reflex to M-wave ratio (peak-to-peak amplitude) was quantified in three different conditions: seated at rest, seated with a light contraction of the plantar flexors and during bipedal quiet standing.

FINDINGS

Soleus H-reflex to M-wave ratio was significantly higher in obese than in non-obese individuals in all the experimental conditions (p < 0.01).

INTERPRETATION

Obese individuals showed larger normalized soleus H-reflex responses than their non-obese counterparts, probably as a reflect of long-term neurophysiological adaptations to excessive body weight and postural demands.

Reliability of the Soleus H-Reflex in Different Sitting Postures

The Soleus (SOL) Hoffmann reflex (H-reflex) is commonly recorded in sitting position. However, the reliability of recording is unknown. We assessed the reliability of SOL H-reflex amplitude measurements across multiple traces and sessions during erect, slumped, and slouched sitting postures using the generalizability theory. Five traces of the SOL H-reflex maximum amplitude (H_max) were recorded from 10 healthy participants during erect, slumped, and slouched sitting postures in two sessions. A decision study analysis was then conducted to calculate the reliability coefficients of the H_max for five traces and two sessions and to mathematically calculate the coefficients for seven and ten traces, and one and three sessions in the three sitting postures. For five traces and two sessions, the results showed reliability coefficients between 0.970 and 0.971, 0.980 and 0.979, and equal to 0.943 for erect, slumped, and slouched sitting, respectively. Averaging five traces of the H_max in a single recording session was sufficient to obtain acceptable reliability in the three sitting postures (reliability range, 0.892–0.988). It was concluded that the SOL H_max can be recorded during erect, slumped, and slouched sitting postures with adequate reliability.

Stumbling Reactions in Partial Gravity - Neuromechanics of Compensatory Postural Responses and Inter-Limb Coordination During Perturbation of Human Stance

Spontaneous changes in gravity play a significant role in interplanetary space missions. To preserve the astronauts’ capability to execute mission-critical tasks and reduce the risk of injury in transit and on planetary surfaces, a comprehensive understanding of the neuromuscular control of postural responses after balance deterioration in hypo- or hyper-gravity conditions is essential. Therefore, this study aimed to evaluate the effect of acute gravitational variation on postural adjustments in response to perturbations. Gravitational changes were induced using parabolic flight. Postural set was manipulated by randomly providing unilateral left, bilateral or split perturbations which require balance corrections to restore postural stability. In six subjects, postural reactions were recorded after anterior and posterior surface perturbations for progressively increased gravitational conditions spanning from 0.25 to 1.75 g. Ankle and knee joint kinematics and electromyograms (EMG) of eight leg muscles were recorded prior (PRE) and after perturbation onset. Muscle activation onset latencies and amplitudes in the short-, medium-, and long-latency responses (SLR, MLR, LLR) were assessed. Results demonstrate an increased muscle activity (p < 0.05) and co-contraction in the lower extremities (p < 0.05) prior to perturbation in hypo- and hyper-gravity. After perturbation, reduced muscle onset latencies (p < 0.05) and increased muscle activations in the MLR and LLR (p < 0.05), concomitant with an increased co-contraction in the SLR, were manifested with a progressive rise in gravity. Ankle and knee joint deflections remained unaffected, whereas angular velocities increased (p < 0.05) with increasing gravitation. Effects were more pronounced in bi- compared to unilateral or split perturbations (p < 0.05). Neuro-mechanical adaptations to gravity were more distinct and muscle onset latencies were shorter in the displaced compared to the non-displaced leg. In conclusion, the timing and magnitude of postural reflexes involved in stabilization of bipedal stance are gravity-dependent. The approximately linear relationship between gravity and impulse-directed EMG amplitudes or muscle onset latencies after perturbation indicates that the central nervous system correctly predicts the level of gravity. Moreover, it accurately governs contractions in the antigravity musculature to counterbalance the gravitational pull and to regain upright posture after its disturbance. Importantly, unilateral perturbations evoked fast reflex responses in the synergistic muscles of the non-displaced contralateral leg suggesting a synchronized inter-limb coordination mediated by spinal circuitries.

Significance of EMG and ENMG in the Diagnosis and Treatment of Degenerative-Dystrophic Diseases of the Spine (Literature Review)

The article presents the review of domestic and foreign literature on the use of neurophysiological diagnostic methods – electroneuromyography (ENMG) and electromyography (EMG) in degenerative-dystrophic diseases of the spine. The ENMG method is of great importance for theoretical neurology, obtaining new data on the structural and functional organization of the central and peripheral nervous system in the process of individual development. Electromyography as a diagnostic method studies the electrical activity of the peripheral apparatus of the nervous system. With these methods we directly evaluate both voluntary bioelectric activity of muscles at rest and during their activation (EMG), and caused by stimulation (ENMG). Most authors believe that modifications of stimulation electromyography are objective diagnostic methods that allow to assess the functional state of the peripheral nervous system. Interesting is the fact that changes in EMG and ENMG parameters for osteochondrosis of the spine are recorded even in the absence of external manifestations of the disease. At the same time, for patients with myofascial syndrome in lumbar osteochondrosis, a bilateral decrease in the direct and reflex excitability of motoneurons is characteristic, a slowing down of the pulse along the arc of the H-reflex on the side of the pain and a two-sided local acceleration of the pulse on the distal part of the efferent part of the H-reflex arc from the popliteal pits to soleus muscle. Noteworthy is the fact that the pathological process in the nervous tissue according to ENMG in patients with osteochondrosis of the spine with unilateral radicular syndromes is bilateral. The work of our clinic has shown that diagnostic electroneuromyography can be considered as a medical procedure – electropuncture, according to its results, tactics of both surgical and conservative treatment can be determined. Data of EMG and EMG, carried out after the end of any of the listed types of treatment, serve as an objective control of their effectiveness.

Electrodiagnosis-based management of patients with radiculopathy: The concept and application involving a patient with a large lumbosacral disc herniation

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Postural H-reflex evaluates the degree/direction of neural compression/decompression.

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Direction sensitive exercise protocol based on H-reflex rehabilitates disc hernia.

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In this case report, 19 mm disc hernia reduced to 4 mm by the end of the treatment.

Objectives

The evaluation of patients with lower back pain (LBP) is based mainly on clinical examinations and imaging procedures that are subjective or anatomic in nature. The treatments, either physical therapy or osteopathy, lack evidence-based protocol and may be disruptive to the spine. Therefore, a neurophysiologic-based approach to managing such patients is necessary.

Methods

A 40-year-old female complained of LBP and radiculopathy for more than 12 years, a condition that was accompanied by numbness, tingling and weakness in the left leg. This study examined the effectiveness of using an innovative concept and method on a patient with a 19-mm disc herniation. An electro diagnosis-based evaluation and treatment approach testing tool, Soleus H-reflexes, was applied during unloading (with the patient lying down), loading (with the patient standing or sitting), and various trunk position protocols. A structured treatment was based on the results of H-reflex, including direction-sensitive exercises and manipulation, progressing from unloading to full loading. A custom-based home program was developed for sleeping and sitting positions, with all being directed at non-invasively decompressing the compromised nerve root. Data was analyzed using descriptive statistics.

Intervention and results

Stepwise application of the developed procedures resulted in complete resolution of the radicular and spinal symptoms, with a reduction in the size of the herniated disc from 19 mm to 4 mm and recovery of the H-amplitude by the end of the treatment. Functional recovery was also complete by the end of the program. A follow-up after 12 months showed maintained results.

Conclusions

The discussed concept and method exhibited their effectiveness in this case study, and the results obtained are due to the consistency and maintenance of the neural decompression using a direction sensitive therapy protocol.

Significance

Direction sensitive exercise therapy based on H-reflex testing is effective in treating large herniated lumbar discs.

Virtual Balancing for Studying and Training Postural Control

Postural control during free stance has been frequently interpreted in terms of balancing an inverted pendulum. This even holds, if subjects do not balance their own, but an external body weight. We introduce here a virtual balancing apparatus, which produces torque in the ankle joint as a function of ankle angle resembling the gravity and inertial effects of free standing. As a first aim of this study, we systematically modified gravity, damping, and inertia to examine its effect on postural control beyond the physical constraints given in the real world. As a second aim, we compared virtual balancing to free stance to test its suitability for balance training in patients who are not able to balance their full body weight due to certain medical conditions. In a feasibility study, we analyzed postural control during free stance and virtual balancing in 15 healthy subjects. Postural control was characterized by spontaneous sway measures and measures of perturbed stance. During free stance, perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. In the virtual balancing task, we systematically varied the anterior-posterior position of the foot plate where the balancing forces are zero following a similar pseudorandom stimulus profile. We found that subjects' behavior during virtual balancing resembles free stance on a tilting platform. This specifically holds for the profile of body excursions as a function of stimulus frequencies. Moreover, non-linearity between stimulus and response amplitude is similar in free and virtual balancing. The overall larger stimulus induced body excursions together with an altered phase behavior between stimulus and response could be in part explained by the limited use of vestibular and visual feedback in our experimental setting. Varying gravity or damping significantly affected postural behavior. Inertia as an isolated factor had a mild effect on the response functions. We conclude that virtual balancing may be well suited to simulate conditions which could otherwise only be realized in space experiments or during parabolic flights. Further studies are needed to examine patients' potential benefit of virtual balance training.

H-reflex changes in adolescents with idiopathic scoliosis: a randomized clinical trial

[Purpose] To detect H-reflex asymmetry and investigate the effect of direction sensitive exercise therapy protocol among patients with thoracolumbar and/or lumbar scoliosis. [Subjects and Methods] Fifty patients (10-17 years), Cobb's angle 10-20 degrees with thoracolumbar and lumbar scoliosis participated in the study. Soleus H-reflex was tested on both sides during prone lying position and standing position. Patients were randomly assigned into two groups. Group I received direction sensitive exercise therapy while the participants in group II received traditional exercise. Exercises were applied three times per week for twelve successive weeks. [Results] There were significant differences indicating asymmetry in the H-reflex amplitude on concave side. Cobb's angle significantly decreased and the H-reflex amplitude on concave side as well as H concave/convex ratios in both lying and standing significantly increased in both groups. Direction sensitive exercise therapy showed a more significant increase in the measured outcomes than traditional exercises therapy protocol. [Conclusion] H-reflex test was effective in discovering the asymmetry between concave and convex sides. Based on H-reflex test, direction-sensitive exercise therapy was more effective than traditional exercises in decreasing Cobb's angle and increasing H-reflex values as well as H/H percent in concave side in patients with adolescent idiopathic scoliosis.

Influence of Menstrual Cycle and Oral Contraceptive Phase on Spinal Excitability

BACKGROUND

Rates of musculoskeletal injury differ substantially between the genders, with females more likely to experience conditions such as anterior cruciate ligament (ACL) injuries than males in the same sports. Emerging evidence suggests a significant hormonal contribution. Most research has focused solely on how hormonal fluctuations affect connective tissue, but a direct link between hormonal shifts, ligamentous laxity, and ACL injury has not been borne out. There is also evidence to suggest that sex hormones can modulate the central nervous system, but how this affects neuromuscular control is not well understood.

OBJECTIVE

To determine whether changes in sex hormone concentrations would alter spinal excitability, measured across the menstrual and oral contraceptive pill cycle. We hypothesized that spinal excitability would fluctuate across the menstrual cycle (with increased excitability during the periovulatory phase due to peak estradiol concentration), but that there would be no fluctuation in oral contraceptive users.

DESIGN

This was a prospective cohort study.

SETTING

The study took place at a biomechanics laboratory at a rehabilitation hospital.

PARTICIPANTS

A total of 30 healthy women aged 18-35 who were similar in age, body composition, and exercise-training status were included. Fifteen of the women were eumenorrheic and nonusers of oral contraceptives (nonusers), and 15 of the women were taking oral contraceptives (users).

MAIN OUTCOME MEASURES

H-reflex (Hmax/Mmax ratio), serum estradiol, and progesterone concentrations were measured at 3 time points during the menstrual and contraceptive pill cycle.

RESULTS

The H-reflex (Hmax/Mmax ratio) remained stable across the menstrual and contraceptive pill cycle. Spinal excitability was lower in the users compared with the nonusers across all testing sessions, but this was not statistically significant.

CONCLUSIONS

Our results suggest that acute fluctuations of endogenous estradiol and progesterone do not modulate spinal excitability. However, long-term exposure to exogenous estrogen and progesterone (oral contraceptives) might have an impact on spinal excitability and neuromuscular control. Further research is necessary to better understand the potential differential effect of endogenous and exogenous sex hormones on spinal excitability.

Impaired H-Reflex Gain during Postural Loaded Locomotion in Individuals Post-Stroke

Objective

Successful execution of upright locomotion requires coordinated interaction between controllers for locomotion and posture. Our earlier research supported this model in the non-impaired and found impaired interaction in the post-stroke nervous system during locomotion. In this study, we sought to examine the role of the Ia afferent spinal loop, via the H-reflex response, under postural influence during a locomotor task. We tested the hypothesis that the ability to increase stretch reflex gain in response to postural loads during locomotion would be reduced post-stroke.

Methods

Fifteen individuals with chronic post-stroke hemiparesis and 13 non-impaired controls pedaled on a motorized cycle ergometer with specialized backboard support system under (1) seated supported, and (2) non-seated postural-loaded conditions, generating matched pedal force outputs of two levels. H-reflexes were elicited at 90°crank angle.

Results

We observed increased H-reflex gain with postural influence in non-impaired individuals, but a lack of increase in individuals post-stroke. Furthermore, we observed decreased H-reflex gain at higher postural loads in the stroke-impaired group.

Conclusion

These findings suggest an impaired Ia afferent pathway potentially underlies the defects in the interaction between postural and locomotor control post-stroke and may explain reduced ability of paretic limb support during locomotor weight-bearing in individuals post-stroke.

Significance

These results support the judicious use of bodyweight support training when first helping individuals post-stroke to regain locomotor pattern generation and weight-bearing capability.

Load Dependency of Postural Control--Kinematic and Neuromuscular Changes in Response to over and under Load Conditions

Introduction

Load variation is associated with changes in joint torque and compensatory reflex activation and thus, has a considerable impact on balance control. Previous studies dealing with over (OL) and under loading (UL) used water buoyancy or additional weight with the side effects of increased friction and inertia, resulting in substantially modified test paradigms. The purpose of this study was to identify gravity-induced load dependency of postural control in comparable experimental conditions and to determine the underlying neuromuscular mechanisms.

Methods

Balance performance was recorded under normal loading (NL, 1g), UL (0.16g; 0.38g) and OL (1.8g) in monopedal stance. Center of pressure (COP) displacement and frequency distribution (low 0.15-0.5Hz (LF), medium 0.5-2Hz (MF), high 2-6Hz (HF)) as well as ankle, knee and hip joint kinematics were assessed. Soleus spinal excitability was determined by H/M-recruitment curves (H/M-ratios).

Results

Compared to NL, OL caused an increase in ankle joint excursion, COP HF domain and H/M-ratio. Concomitantly, hip joint excursion and COP LF decreased. Compared to NL, UL caused modulations in the opposite direction: UL decreased ankle joint excursions, COP HF and H/M-ratio. Collaterally, hip joint excursion and COP LF increased. COP was augmented both in UL and in OL compared to NL.

Conclusion

Subjects achieved postural stability in OL and UL with greater difficulty compared to NL. Reduced postural control was accompanied by modified balance strategies and compensatory reflex activation. With increasing load, a shift from hip to ankle strategy was observed. Accompanying, COP frequency distribution shifted from LF to HF and spinal excitability was enhanced. It is suggested that in OL, augmented ankle joint torques are compensated by quick reflex-induced postural reactions in distal muscles. Contrarily, UL is associated with diminished joint torques and thus, postural equilibrium may be controlled by the proximal segments to adjust the center of gravity above the base of support.

Evaluating the differential electrophysiological effects of the focal vibrator on the tendon and muscle belly in healthy people

Objective

To investigate the electrophysiological effects of focal vibration on the tendon and muscle belly in healthy people.

Methods

The miniaturized focal vibrator consisted of an unbalanced mass rotating offset and wireless controller. The parameters of vibratory stimulation were adjusted on a flat rigid surface as 65 µm at 70 Hz. Two consecutive tests on the different vibration sites were conducted in 10 healthy volunteers (test 1, the Achilles tendon; test 2, the muscle belly on the medial head of the gastrocnemius). The Hoffman (H)-reflex was measured 7 times during each test. The minimal H-reflex latency, maximal amplitude of H-reflex (H_max), and maximal amplitude of the M-response (M_max) were acquired. The ratio of H_max and M_max (HMR) and the vibratory inhibition index (VII: the ratio of the H_max after vibration and H_max before vibration) were calculated. The changes in parameters according to the time and site of stimulation were analyzed using the generalized estimating equation methods.

Results

All subjects completed the two tests without serious adverse effects. The minimal H-reflex latency did not show significant changes over time (Wald test: χ²=11.62, p=0.07), and between the two sites (χ²=0.42, p=0.52). The changes in H_max (χ²=53.74, p<0.01), HMR (χ²=20.49, p<0.01), and VII (χ²=13.16, p=0.02) were significant over time with the adjustment of sites. These parameters were reduced at all time points compared to the baseline, but the decrements reverted instantly after the cessation of stimulation. When adjusted over time, a 1.99-mV decrease in the H_max (χ²=4.02, p=0.04) and a 9.02% decrease in the VII (χ²=4.54, p=0.03) were observed when the muscle belly was vibrated compared to the tendon.

Conclusion

The differential electrophysiological effects of focal vibration were verified. The muscle belly may be the more effective site for reducing the H-reflex compared to the tendon. This study provides the neurophysiological basis for a selective and safe rehabilitation program for spasticity management with focal vibration.

Does acute passive stretching increase muscle length in children with cerebral palsy?

BACKGROUND

Children with spastic cerebral palsy experience increased muscle stiffness and reduced muscle length, which may prevent elongation of the muscle during stretch. Stretching performed either by the clinician, or children themselves is used as a treatment modality to increase/maintain joint range of motion. It is not clear whether the associated increases in muscle-tendon unit length are due to increases in muscle or tendon length. The purpose was to determine whether alterations in ankle range of motion in response to acute stretching were accompanied by increases in muscle length, and whether any effects would be dependent upon stretch technique.

METHODS

Eight children (6-14 y) with cerebral palsy received a passive dorsiflexion stretch for 5 × 20 s to each leg, which was applied by a physiotherapist or the children themselves. Maximum dorsiflexion angle, medial gastrocnemius muscle and fascicle lengths, and Achilles tendon length were calculated at a reference angle of 10 ° plantarflexion, and at maximum dorsiflexion in the pre- and post-stretch trials.

FINDINGS

All variables were significantly greater during pre- and post-stretch trials compared to the resting angle, and were independent of stretch technique. There was an approximate 10 ° increase in maximum dorsiflexion post-stretch, and this was accounted for by elongation of both muscle (0.8 cm) and tendon (1.0 cm). Muscle fascicle length increased significantly (0.6 cm) from pre- to post-stretch.

INTERPRETATION

The results provide evidence that commonly used stretching techniques can increase overall muscle, and fascicle lengths immediately post-stretch in children with cerebral palsy.

What triggers the continuous muscle activity during upright standing?

The ankle extensors play a dominant role in controlling the equilibrium during bipedal quiet standing. Their primary role is to resist the gravity toppling torque that pulls the body forward. The purpose of this study was to investigate whether the continuous muscle activity of the anti-gravity muscles during standing is triggered by the joint torque requirement for opposing the gravity toppling torque, rather than by the vertical load on the lower limbs. Healthy adults subjects stood on a force plate. The ankle torque, ankle angle, and electromyograms from the right lower leg muscles were measured. A ground-fixed support device was used to support the subject at his/her knees, without changing the posture from the free standing one. During the supported condition, which eliminates the ankle torque requirement while maintaining both the vertical load on the lower limbs and the natural upright standing posture, the plantarflexor activity was attenuated to the resting level. Also, this attenuated plantarflexor activity was found only in one side when the ipsilateral leg was supported. Our results suggest that the vertical load on the lower limb is not determinant for inducing the continuous muscle activity in the anti-gravity muscles, but that it depends on the required joint torque to oppose the gravity toppling torque.

Limb segment load inhibits post activation depression of soleus H-reflex in humans

OBJECTIVE

We investigated the effect of various doses of limb segment load on soleus H-reflex amplitude and post activation depression in healthy individuals. We also explored the influence of limb segment load on spinal circuitry in one individual with chronic SCI.

METHODS

Twenty-eight healthy adults and one SCI subject received compressive loads applied to the top of their knee at varied doses of load (10%, 25%, and 50% of the body weight). Soleus H-reflexes were measured before (baseline) and during the loading phase.

RESULTS

There were no significant differences in H-reflex amplitudes during the 50% BW load-on phase as compared to either baseline session or the load-off phase. However, the post activation depression was decreased over 9% (p<0.05) during the load-on phase compared to the load-off phase and scaled according to load (50%>25%>10%). The post activation depression ratio also appears less responsive to varying loads after chronic SCI.

CONCLUSIONS

Limb segment load decreases post-activation depression in humans. These findings suggest that the mechanism associated with post activation depression is modulated by limb segment load, and may be influenced by spinal reorganization after SCI.

SIGNIFICANCE

Future studies will determine if various levels of spasticity modulate the response of limb segment load on post activation depression in those with acute and chronic SCI.

Similarities and differences of the soleus and gastrocnemius H-reflexes during varied body postures, foot positions, and muscle function: multifactor designs for repeated measures

Background

Although the soleus (Sol), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles differ in function, composition, and innervations, it is a common practice is to investigate them as single H-reflex recording. The purpose of this study was to compare H-reflex recordings between these three sections of the triceps surae muscle group of healthy participants while lying and standing during three different ankle positions.

Methods

The Sol, MG and LG muscles' H-reflexes were recorded from ten participants during prone lying and standing with the ankle in neutral, maximum dorsiflexion, and maximum plantarflexion positions. Four traces were averaged for each combination of conditions. Three-way ANOVAs (posture X ankle position X muscle) with planned comparisons were used for statistical comparisons.

Results

Although the H-reflex in the three muscle sections differed in latency and amplitude, its dependency on posture and ankle position was similar. The H-reflex amplitudes and maximum H-reflex to M-response (H/M) ratios were significantly 1) lower during standing compared to lying with the ankle in neutral, 2) greater during standing with the ankle in plantarflexion compared to neutral, and 3) less with the ankle in dorsiflexion compared to neutral during lying and standing for all muscles (p ≤ .05).

Conclusion

Varying demands are required for muscles activated during distinctly different postures and ankle movement tasks.

Penetration and spread of interferential current in cutaneous, subcutaneous and muscle tissues

OBJECTIVES

To investigate the penetration depth of interferential current (IFC) through soft tissue and the area over which it spreads during clinical application.

DESIGN

A laboratory-based study of healthy participants.

SETTING

A university research laboratory.

PARTICIPANTS

Twelve healthy subjects.

INTERVENTIONS

Premodulated IFC at 90 Hz and 'true' IFC at frequencies of 4, 40 and 90 Hz were applied via four electrodes, in a quadrant setting, to the distal medial thigh of each participant on separate occasions.

MAIN OUTCOME MEASURE

Voltage induced by tested currents was measured at three locations (middle of the four electrodes, in line with one circuit and outside the four electrodes) and three depths (skin, subcutaneous and muscle tissues) using three Teflon-coated needle electrodes connected to a Cambridge Electronic Design data acquisition system.

RESULTS

All voltages were greater at all depths and locations compared with baseline (P<0.001): premodulated IFC [mean difference 0.112, 95% confidence interval (CI) 0.065 to 0.160], 4 Hz (mean difference 0.168, 95% CI 0.106 to 0.229), 40 Hz (mean difference 0.165, 95% CI 0.107 to 0.223) and 90 Hz (mean difference 0.162, 95% CI 0.102 to 0.221). Voltages decreased with depth. Lower voltages of all currents were recorded in the middle of the four electrodes, with the highest voltage for 'true' IFC being recorded outside the four electrodes (mean difference 0.04, 95% CI 0.01 to 0.029; P=0.011). The premodulated IFC had the highest voltage in line with one circuit.

CONCLUSIONS

IFC passed through soft tissues, with the highest voltages recorded in superficial tissue and the lowest voltages recorded in muscle. For 'true' IFC, the current spread outside the electrodes at higher voltages compared with the intersection of the four electrodes. The premodulated IFC had the highest voltage in line with one circuit. In terms of higher recorded voltages, 'true' IFCs were more efficient than the premodulated IFC when targeting deeper tissues. However, further studies with larger samples are required to confirm the results of this study.

H-reflex amplitude asymmetry is an earlier sign of nerve root involvement than latency in patients with S1 radiculopathy

Background

Based on our clinical experience, the H-reflex amplitude asymmetry might be an earlier sign of nerve root involvement than latency in patients with S1 radiculopathy. However, no data to support this assumption are available. The purpose of this study was to review and report the electrophysiological changes in H-reflex amplitude and latency in patients with radiculopathy in order to determine if there is any evidence to support the assumption that H-reflex amplitude is an earlier sign of nerve root involvement than latency.

Results

Patients with radiculopathy showed significant amplitude asymmetry when compared with healthy controls. However, latency was not always significantly different between patients and healthy controls. These findings suggest nerve root axonal compromise that reduced reflex amplitude earlier than the latency parameter (demyelination) during the pathologic processes.

Conclusion

Contrary to current clinical thought, H-reflex amplitude asymmetry is an earlier sign/parameter of nerve root involvement in patients with radiculopathy compared with latency.

Flexor carpi radialis H-reflex modulation during spinal loading and unloading with varied forearm postures

Flexor carpi radialis (FCR) H-reflex is usually recorded with the patient in lying or sitting postures while the forearm is positioned in supination or pronation to detect C7 radiculopathy. Its amplitude is smaller during forearm supination compared with pronation for unclear reasons and its recordings during postural loading conditions (i.e., sitting or lying) have not been previously reported. The purpose of this study was to examine FCR H-reflex recordings during varied cervical spine loadings and forearm positions. The FCR maximum H-reflex amplitude was recorded from 15 healthy participants during lying, free-sitting and sitting-with-load while the forearm was positioned in either supination or pronation. Four traces were averaged for each combination of conditions. Two-way repeated-measure analysis of variances (2 x 3) was used to examine the statistical differences. The average FCR H-reflex amplitude was significantly greater during free-sitting and sitting-with-load compared with the lying body position. The average FCR H-reflex amplitude was significantly greater when the forearm was positioned in pronation compared with supination. The increase in FCR H-reflex amplitude (augmentation) during forearm pronation and sitting postures compared with supination and lying may have been the result of combined neural and mechanical effects. These results encourage FCR H-reflex recordings during sitting with the forearm in pronation.

Soleus H-reflex modulation and paired reflex depression from prone to standing and from standing to walking

Patterns of soleus H-reflex modulation as a function of posture, task, and reflex activation history were assessed with three experimental paradigms: lying prone compared with standing unsupported; standing compared with the initiation of walking; and standing compared with the mid stance phase of walking. Paired H-reflexes, 80 ms apart, were evoked under each condition. The paired reflex depression (PRD), the percentage depression of the second H-reflex relative to the first H-reflex, was modulated independently of the first H-reflex across the postures and tasks. These results reveal divergent patterns of segmental reflex modulation and support the idea that segmental reflexes are controlled by multiple mechanisms.

Soleus H-reflex modulation in response to change in percentage of leg loading in standing after incomplete spinal cord injury

Body weight support (BWS) is frequently used to retrain standing and walking in persons post spinal cord injury (SCI), but the effects of leg unloading using BWS on H-reflex excitability in this population are unknown. The purpose of the study was to assess the effect of two different loading conditions on soleus H-reflex while standing in persons with motor incomplete SCI (i-SCI) and non-injured persons. Eight persons with motor i-SCI (mean age 50.25 years) and five non-injured persons (mean age 48.6 years) participated in the study. Specific control of the loading conditions was achieved using a BWS system. To compare reflex modulation at 40% versus 0% BWS, soleus H-reflexes were evoked during standing and normalized to the maximum M wave amplitude. These studies revealed that (1) H-reflex excitability is significantly greater after SCI and is exhibited even during quiet standing; and (2) no significant modulation in reflex excitability was observed by change in loading conditions in either the non-injured or the i-SCI subjects. These findings suggest that non-injured persons and persons with i-SCI respond similarly to bilateral limb unloading during standing with no change in H-reflex amplitude. Our results suggest that BWS of up to 40% does not produce detectable changes in the excitability of the soleus H-reflex in persons with i-SCI.

Vastus Medialis H-Reflex Reliability During Standing

Vastus medialis H-reflex is a valid measure to examine quadriceps muscle voluntary activation and inhibition after knee injury. Its reliability during repeated sessions has not been established. The purpose of this study was to establish the intrasession and intersession reliability of vastus medialis H-reflex amplitude recordings during standing with varied knee flexion angles (0, 30, 45, and 60 degrees). Electromyography unit was used to elicit and record the vastus medialis H-reflex from the right leg of five healthy subjects. The femoral nerve was stimulated using 0.5-millisecond pulses at 0.2 pps of H-maximum. Four recordings of the vastus medialis H-reflex amplitude were recorded in three trials for each knee flexion angle within each session for two consecutive days. Reliability was calculated using intraclass correlation coefficients (ICC). Intrasession reliability during standing with varied knee angles was high (ICC [2, 4] range from 0.76 to 0.98), and intersession reliability during standing with varied knee angles was moderate to high (ICC [2, 1] range from 0.51 to 0.84). Recording four traces of vastus medialis H-reflex amplitude per trial was reliable. Vastus medialis H-reflex amplitude recordings while standing during varied knee flexion are reliable within and between sessions.

Reflexes in prior polio and their relation to weakness and anterior horn cell loss

The aim of this study was to evaluate the reflex pattern in patients with prior polio and to relate these findings to the degree of anterior horn cell (AHC) involvement and loss of muscle force. Twenty-five prior polio subjects were investigated with electromyography (EMG), force testing and reflex studies, which included the patellar and Achilles reflex, H-reflex, T-response and interlimb reflex (ILR). The clinical reflexes, H/M-ratio and T-response amplitude at rest were positively correlated with force and negatively correlated with the degree of AHC loss. The H/M-ratio was decreased compared with age matched controls. ILR was present in 68% of the prior polio patients but did not exist in controls. The presence of the ILR was not correlated with the degree of AHC loss or force. The reflex studies gave two main findings. The first is reduced excitability of monosynaptic connections in the motor neuron pool, which is related to weakness. The other is the presence of ILR as an indicator of interneuronal hyper-excitability, which is not related to weakness.

Soleus and vastus medialis H-reflexes: Similarities and differences while standing or lying during varied knee flexion angles

The H-reflex may be a useful measure to examine the lower extremity muscles activation and inhibition following an injury. Recording the vastus medialis H-reflex amplitudes in healthy subjects while standing or lying during varied knee flexion angles may establish a reference for comparison for patients with ACL injury. Vastus medialis and soleus H-reflexes were recorded from 14 healthy subjects while lying and standing during 0, 30, 45, and 60 degrees knee flexion. EMG unit was used to electrically stimulate the tibial and femoral nerves (using 0.5 ms pulses at 0.2 pps of H-maximum amplitude) and to record four traces of the soleus and vastus medialis H-wave and one trace of the M-wave peak-to-peak amplitudes. Repeated measures three-way ANOVAs were calculated with the global alpha=0.05. Results showed that (1) the average soleus H-reflex amplitude was significantly less during standing than lying across all knee flexion conditions, (2) the average vastus medialis H-reflex amplitudes showed no measurable significant differences between neutral standing compared with lying, (3) the average vastus medialis H-reflex amplitudes were significantly greater during standing knee flexion conditions (30, 45, and 60 degrees ) than lying or neutral standing, and (4) there were no differences between soleus and vastus medialis H-reflex amplitudes during lying across all knee flexion conditions. Data from H/M ratio follow the same pattern of H-amplitude. Recording the vastus medialis H-reflex amplitude during standing and knee flexion may be a reflective of the knee function. It is more specific than the soleus H-reflex because it reflects the changes in the excitability of the quadriceps motoneurons acting directly around the knee joint.

Responsiveness of the H reflex to loading and posture in patients following stroke

The objective of the research was to examine the effects of loading and posture on motoneuronal excitability of the triceps surae (TS) for patients with hemiplegia. Twelve healthy subjects and 12 patient subjects with post-stroke hemiparesis (onset period: 3-60 months) were enrolled in this study. The subjects were instructed to remain in quiet sitting with the test knee straight and three standing conditions of different superincumbent loads by shifting body weight to the test leg (10%, 50%, and 90% of body weight), while the H reflexes and M waves of the TS were measured. The results clearly indicated that H reflex amplitudes were not affected by different loading conditions in standing for both healthy subjects and patients who had a previous stroke. In addition, the H reflex amplitude in quiet standing for healthy subjects was significantly downward modulated relative to that in relaxed sitting with the test knee straight, but this posturally driven modulation was impaired in patients following stroke. Current electrophysiological findings imply that body weight as a means for rehabilitation facilitation had little immediate effect on paretic TS, and absence in postural gating of reflex excitability appeared to be an incentive for postural instability resulting from post-stroke hemiparesis.

H-reflex latency and nerve root tension sign correlation in fluoroscopically guided, contrast-confirmed, translaminar lumbar epidural steroid-bupivacaine injections11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

OBJECTIVES

To examine the correlation between physical examination parameters, commonly referred to as "nerve root tension signs," and H-reflex latency measurements both pre- and postepidural steroid-bupivacaine (Marcaine) injection, and to propose mechanisms of pain alleviation.

DESIGN

Prospective observational, with H-reflex latency measurement and physical examination at baseline and at 10 minutes postinjection.

SETTING

Physical medicine and rehabilitation practice, outpatient surgical center, and community setting.

PARTICIPANTS

Ten consecutively recruited patients (6 women, 4 men; age range, 40-71 y) with clinical radiculopathy and compatible magnetic resonance imaging findings, who were unaware of the outcome measures.

INTERVENTIONS

Patients received a fluoroscopically guided, contrast-confirmed, paramedian translaminar lumbar epidural injection of 120 mg of methylprednisolone acetate (80 mg/mL) and 2.0 mL of .25% preservative-free Marcaine.

MAIN OUTCOME MEASURES

Seated slump testing (SST), straight-leg raising (SLR), and H-reflex latency were measured bilaterally both pre- and postinjection. Differences were measured by using the paired t test in an A-B design.

RESULTS

All SST of the affected (injected) side improved from pre- to postinjection, with 3 patients reporting discordant hamstring pain and 7 reporting no pain. SLR ability increased by an average of 29 degrees +/-12 degrees, corresponding to an average relative increase of 54% on the affected side. A statistically significant difference was found (Student t test, P=.02) between pre and post H-reflex latency on the affected side but not when comparing changes between affected and unaffected sides (Student t test, P=0.6).

CONCLUSIONS

Significant improvements in SST and SLR result from low volume epidural injection of Marcaine, with questionable prolongation of the H-reflex to the gastrocnemius-soleus complex on the affected side.

Influence of long-term spaceflight on neuromechanical properties of muscles in humans

Reflex and elastic properties of the triceps surae (TS) were measured on 12 male cosmonauts 28-40 days before a 3- to 6-mo spaceflight, 2 or 3 days after return (R+2/+3) and a few days later (R+5/+6). H reflexes to electrical stimulations and T reflexes to tendon taps gave the reflex excitability at rest. Under voluntary contractions, reflex excitability was assessed by the stretch reflex, elicited by sinusoidal length perturbations. Stiffness measurements concerned the musculoarticular system in passive conditions and the musculotendinous complex in active conditions. Results indicated 1) no changes (P > 0.05) in H reflexes, whatever the day of test, and 2) increase in T reflexes (P < 0.05) by 57%, despite a decrease (P < 0.05) in musculoarticular stiffness (11%) on R+2/+3. T reflexes decreased (P < 0.05) between R+2/+3 and R+5/+6 (-21%); 3) increase in stretch reflexes (P < 0.05) on R+2/+3 by 31%, whereas it decreased (P < 0.05) between R+2/+3 and R+5/+6 (-29%). Musculotendinous stiffness was increased (P < 0.05) whatever the day of test (25%). Links between changes in reflex and stiffness were also studied by considering individual data. At R+2/+3, correlated changes between T reflexes and musculoarticular stiffness suggested that, besides central adaptive phenomena, musculoarticular structures took part in the reflex adaptation. This mechanical contribution was confirmed when data collected at R+2/+3 and R+5/+6 were used because correlations between changes in stretch reflexes and musculotendinous stiffness were improved. In conclusion, the present study shows that peripheral influences take part in reflex changes in gravitational unloaded muscles, but can only be revealed when central influences are reduced.