On the mechanism of the post-activation depression of the H-reflex in human subjects

It was demonstrated that the soleus H-reflex was depressed for more than 10 s following a preceding passive dorsiflexion of the ankle joint. This depression was caused by activation of large-diameter afferents with receptors located in the leg muscles, as an ischaemic block of large-diameter fibres just below the knee joint abolished the depression, whereas a similar block just proximal to the ankle joint was ineffective. The depression of the H-reflex was not caused by changes in motoneuronal excitability, as motor-evoked potentials by magnetic brain stimulation were not depressed by the same passive dorsiflexion. Therefore it was concluded that the long-lasting depression is due to mechanisms acting at presynaptic level. The transmission of the monosynaptic Ia excitation from the femoral nerve to soleus motoneurones was not depressed by the ankle dorsiflexion. The depression thus seems to be confined to those afferents that were activated by the conditioning dorsiflexion. In parallel experiments on decerebrate cats, more invasive methods have complemented the indirect techniques used in the experiments on human subjects. A similar long-lasting depression of triceps surae monosynaptic reflexes was evoked by a preceding conditioning stimulation of the triceps surae Ia afferents. This depression was accompanied by a reduction of the monosynaptic Ia excitatory postsynaptic potential recorded intracellularly in triceps surae motoneurones, but not by changes in the input resistance or membrane potential in the motoneurones. Stimulation of separate branches within the triceps surae nerve demonstrated that the depression is confined to those afferents that were activated by the conditioning stimulus. This long-lasting depression was not accompanied by a dorsal root potential. It is concluded that the long-lasting depression is probably caused by a presynaptic effect, but different from the classical GABAergic presynaptic inhibition which is widely distributed among afferent fibres and accompanied by dorsal root potentials. It is more probably related to the phenomenon of a reduced transmitter release from previously activated fibres, i.e. a homosynaptic post-activation depression. The consequences of this post-activation depression for the interpretation of results on spinal mechanisms during voluntary movements in man are discussed.     

Influence of posture and stimulus parameters on post-activation depression of the soleus H-reflex in individuals with chronic spinal cord injury

In non-disabled (ND) individuals, reflexes are modulated by influences related to physiologic state (e.g., posture, joint position, load) and activation history. Repeated activation of the H-reflex results in post-activation depression (PAD) of the response amplitude. The modulation associated with physiologic state and activation history is suppressed or abolished in individuals with spinal cord injury (SCI). While posture is known to affect H-reflex amplitude and PAD in non-disabled individuals, the effect of posture on PAD in SCI individuals is not known. Further, while the amount of PAD is also known to be influenced by the stimulus rate and by the amplitude of the evoked reflex, the interaction of posture with stimulus parameters has not been previously investigated in either group. We investigated differences in PAD of the soleus H-reflex between SCI subjects and ND subjects during sitting versus supported standing. Subjects were tested using paired conditioning-test stimulus pulses of 2.5 s and 5 s interpulse intervals (ISI) and with stimulus intensity adjusted to evoke reflex responses of 20% and 40% of the maximum motor response. We found standing posture to be associated with significantly less PAD in SCI subjects compared to ND subjects. In both groups, shorter ISIs and smaller reflex amplitudes were associated with greater PAD of the H-reflex. These results indicate that postural influences on post-activation modulation, while present, are impaired in individuals with chronic incomplete SCI.     

训练轨迹对上肢肌肉协同的影响

目的通过分析康复机器人辅助训练过程中沿不同轨迹运动的上肢肌肉协同特性,探究运动轨迹对上肢肌肉骨骼特性的影响,为康复机器人训练轨迹优化设计提供基础实验数据与指导。方法首先在末端牵引式康复机器人系统中设计3种上肢运动训练轨迹(L1为直线,L2为弧线,L3为半圆),然后采集12名健康志愿者在沿3种训练轨迹上肢运动过程中的表面肌电信号,并使用非负矩阵分解算法进行肌肉协同特性的获取,对不同轨迹组间肌肉协同结构的相似系数、屈肌占比以及募集模式积分系数进行对比分析,探讨康复机器人不同训练轨迹对上肢肌肉骨骼特性的影响。结果同一训练轨迹中各志愿者的肌肉协同结构具有较高相似性(平均SI>0.81)。各轨迹组的肌肉协同结构中的屈肌占比随运动进程逐渐增加。各轨迹组的肌肉协同募集模式均具有时序特性,前期伸肌起主要作用,后期屈肌起主要作用,中期屈肌占比随轨迹曲率增加而增加。轨迹L1与L2、L2与L3协同结构非常相似(SI>0.90),而L1与L3协同结构较为相似(SI>0.75)。结论康复机器人辅助上肢的训练轨迹对上肢肌肉特性有一定影响,不同训练轨迹带来的肌肉协同结构较为相似,但是运动过程中屈肌群占比及协同贡献度会为了协调动作而发生变化。由此可推测不同训练轨迹对不同肌群的训练强度可能会有所不同。康复机器人训练轨迹设计需根据康复需求进行优化设计。     

Post-activation depression of the soleus H-reflex in the elderly

OBJECTIVES: This study examined the effect of age on the spinal mechanism post-activation depression (PD) and its relationship with postural sway. METHODS: Two groups, young (n = 10, 25.2 +/- 5.2 yr) and elderly (n = 10, 74.6 +/- 6.3 yr) participated in this study. Soleus H-reflex amplitude (peak-to-peak EMG) was measured prior to and after a passive dorsiflexion about the ankle (from 120 degrees plantarflexion to 110 degrees plantarflexion at 15 degrees/s). All H-reflex measurements were recorded at an ankle joint angle of 110 degrees. For each group, stimulus intensity was set at 25% of maximal motor response (M-max) and PD measurement intervals were randomly assigned at 0, 1, 2, 3, 4, 5, 10, 15, and 18 seconds post-movement. To ascertain whether PD was related to postural sway, standing sway area (mm2) was also measured. Subjects stood motionless (20 second duration) on a Kistler force platform during two conditions: with and without vision. RESULTS: A split-plot ANOVA (Group x Interval) indicated significant differences (F(1.18) = 14.80, p < 0.05) in PD between young and elderly, as well as a Group x Interval interaction (F(10, 180) = 16.02, p < 0.05). Simple main effects identified significant (p < 0.05) intervals at 0, 1, 2, and 3 seconds. The elderly had on average 16.1% less H-reflex depression during the first three seconds after muscle activation. Additionally, a split-plot ANOVA (Group x Condition) indicated significant differences (F(1, 18) = 10.72, p < 0.05) in sway area between young and elderly, but regression analysis indicated post-activation depression and postural sway were not significantly correlated. CONCLUSIONS: It is concluded that the integrity of the Ia-motoneuron synapse as measured with a PD protocol, is different between young and elderly subjects, but that this difference is not related to postural sway.     

Post-activation depression of the soleus H-reflex in stroke patients

PURPOSE: We examined post-activation depression in 35 stroke patients and 10 healthy subjects, and investigated whether their clinical symptoms were correlated to post-activation depression. METHODS: Post-activation depression of the soleus H-reflex evoked by electrical stimulation of the common peroneal nerve with supramaximal intensity of motor response on the tibialis anterior muscle. RESULTS: Post-activation depression was decreased on the affected side of the stroke patients. There was a significant difference between the affected and unaffected sides of the patients with post-activation depression, but no difference between the unaffected sides of the patients and healthy subjects. The presence of ankle clonus and the decrease in post-activation depression were correlated. CONCLUSION: Decreased post-activation depression in stroke patients suggests that a mechanism other than postsynaptic inhibition, such as reciprocal Ia inhibition and Ib inhibition, and presynaptic inhibition, may contribute to the exaggerated stretch reflexes, in particular, the manifestation of clonus.     

在线调整对到达运动中人体上肢刚性特性的影响

目的研究在线调整与运动中人体上肢刚性值之间的关系,提高人体刚性值测量的精度以及评判在线调整能力。方法设计5类不同类型的上肢平面到达运动,通过施加快速扰动的方法,对运动过程的前期、前中期、中期、中后期和后期共5个位置的刚性值进行测量,探讨刚性值在受到在线调整影响时的变化规律,以及刚性幅值与运动精度之间的关系。结果运动过程中刚性一直变化,而且刚性值的变化影响了最终的运动误差。运动过程中在线调整的发生会引起刚性幅值的改变,尤其是运动后期的刚性幅值,但是目前没有发现这一变化与在线调整发生的时间或者内容存在密切的联系。结论在线调整在到达运动中扮演了重要的角色。考虑到在线调整的发生会引起刚性幅值的变化,在临床上,通过对患者在特定实验中刚性幅值的测量,结合其他医学诊断方法,可以更精确地表明患者当前在线调整功能的状况。     

Temporal depression of the soleus H-reflex during passive stretch

Synaptic efficacy associated with muscle spindle feedback is regulated via depression at the Ia-motoneurone synapse. The inhibitory effects of repetitive Ia afferent discharge on target motoneurones of different sizes were investigated during a passive stretch of ankle extensors in humans. H-reflex recruitment curves were collected from the soleus muscle for two conditions in ten subjects. H-reflexes were elicited during passive stretch at latencies of 50, 100, 300, and 500 ms after a slow (20°/s) dorsiflexion about the right ankle (from 100 to 90°). Control H-reflexes were recorded at corresponding static (without movement) ankle angles of 99, 98, 94, and 90° of flexion. The slope of the H-reflex recruitment curves (Hslp) was then calculated for both conditions. H-reflex values were similar for the static and passive stretch conditions prior to 50–100 ms, not showing the early facilitation typical of increased muscle spindle discharge rates. However, the H-reflex was significantly depressed by 300 ms and persisted through 500 ms. Furthermore, less than 300 ms into the stretch, there was significantly greater H-reflex depression with a lower stimulus intensity (20 % Mmax) versus a higher stimulus intensity (Hmax), though the effects begin to converge at later latencies (>300 ms). This suggests there is a distinct two-stage temporal process in the depression observed in the Ia afferent pathway for all motoneurones during a passive stretch. Additionally, there is not a single mechanism responsible for the depression, but rather both heterosynaptic presynaptic inhibition and homosynaptic post-activation depression are independently influencing the Ia-motoneurone pathway temporally during movement.     

Comparison of electrically and mechanically induced soleus H-reflex depression

OBJECTIVES: The aim of the present investigation was to compare the responses of mechanically-evoked and electrically-evoked conditioning among three different stimulus intensities and provide possible insight in determining whether these two types of inhibitory conditioning demonstrate the same response across the motor pool. METHODS: The soleus H-reflex was tested under three different stimulus intensities (25% Hmax, 50% Hmax, and Hmax), and peak to peak amplitudes were recorded after either mechanical or electrical conditioning. For electrical conditioning, the ankle was held at 90 degrees, whereas mechanical conditioning utilized a 10 degree passive dorsiflexion at 15 degrees/sec back to the 90 degree position. All H-reflex measurements were recorded with the ankle at 90 degrees. RESULTS: A 3 x 2 (stimulus intensity x treatment condition) repeated measures ANOVA indicated significant main effects for stimulus intensity (FGG = 16.23; p = .003) and condition (FGG = 28.48; p < .001), as well as an interaction (F(2,18) = 6.59; p = .008). Simple main effects identified significantly more H-reflex depression for mechanical conditioning (94%, 91%, and 44%) compared to electrical conditioning (65%, 55%, and 19%) at 25% Hmax, 50% Hmax, and Hmax, respectively. CONCLUSIONS: There appears to be more mechanically than electrically stimulated H-reflex depression when testing at 25% Hmax, 50% Hmax, and Hmax. These results demonstrate the influence of Ia discharge properties on H-reflex depression and may suggest differences in the affinity of Ia terminals to intrinsic presynaptic inhibition at different stimulus intensities.     

The organization of upper limb physiological tremor

The objectives of this study are (1) to assess the relationship between tremor displacement of different segments of the upper limb, (2) to assess whether an attempt to voluntarily reduce tremor amplitude affects this relationship. Twenty-five young healthy participants were tested. Tremor of the finger, hand, arm and shoulder was assessed using laser displacement sensors while the upper limb was in a postural position. Results show strong correlations (r > 0.90), high coherence (>0.9) and in-phase movement between tremor displacement oscillations of different segments. The majority of finger tremor amplitude can be predicted by angular movement generated at the shoulder joint (r ² > 0.86). Participants were able to voluntarily reduce tremor amplitude, but no change in the relationship between segments was observed. Tremor of all segments of the upper limb was mechanically driven by the angular movement generated at the shoulder joint. This study provides evidence that there is no compensatory organization of physiological tremor. This lays the groundwork to evaluate whether pathological tremors also lack this organization.     

Methodological implications of the post activation depression of the soleus H-reflex in man

Summary A long lasting inhibition (> 8 s) of the soleus Hoffmann reflex (H-reflex) was evoked by a preceding soleus H-reflex, by a brief voluntary ankle flexor or extensor muscle contraction or by a tap applied to the Achilles tendon. The time course of this long lasting inhibition was similar in all these cases, suggesting that the same spinal mechanism is involved. Furthermore, it was shown that the post-activation depression may interfere with the determination of inhibitory or facilitatory effects on the H-reflex. It is stressed that when the onset of inhibitory or facilitatory effects on the soleus H-reflex is to be determined in relation to start of an ankle movement, either very long stimulus intervals (> 8 s) must be used, or the onset must be determined in relation to a reference value of the soleus H-reflex, which may be influenced by the long lasting inhibitory effect, but not yet by the succeeding muscle contraction.     

Physiological tremor of the upper limb segments

The acceleration signal produced by physiological tremor from four different upper limb segments (the finger, hand, forearm and upper limb) was measured by an acceleration sensor during holding posture and was analyzed by power spectrum analysis. Two prominent peaks appeared in the power spectrum, suggesting that the tremor in the four different limb segments was composed of two frequency components. The frequency of one peak at 8–12 Hz did not change between the different limb segments, while the frequency of the other peak decreased with the increase in the mass of the limb segment. A model with two reflex pathways was developed for the tremor in the four limb segments. The model includes two reflex pathways, a spinal pathway and a supraspinal pathway. The theoretical values of the frequency and the amplitude of the tremor predicted by the model were in good agreement with the experimental results. Analysis of the model revealed that one of the two frequency components of the tremor was of spinal origin and was dependent upon the mass of the limb segment, and the second was of supraspinal origin, corresponding to the frequency at 8–12 Hz. In the normal subject, it is possible that the tremor could be used to evaluate the change in neuromuscular function produced by prolonged work involving just part of a limb segments (e.g., typing). It may also be used to evaluate the neuromuscular function of patients suffering from neurological diseases such as muscular dystrophy and Parkinson's disease. Electronic Publication     

Periarticular diffuse neurofibroma of the upper limb

The diffuse neurofibroma is an uncommon subtype of neurofibroma that has received little attention in the imaging literature. Most common in ages 10-30, in males and females, with a slight predilection for the trunk, then head and neck, then limbs. May become very large, but very rarely undergo malignant transformation. Treatment of diffuse neurofibromas (not associated with NF1) is often surgical resection. Complete resection is often difficult because of the extensive and infiltrative nature of many of these lesions. To our knowledge, the diffuse neurofibroma has been reported extremely rarely within the shoulder girdle. In this report, we presented an adult patient, without NF1 diagnosed, who developed invalidate status of left upper limb due to a giant diffuse neurofibroma involving the left brachial plexus, with a high growth diffuse pattern and plexiform architecture imagistic, grossly and without results at both surgical interventions. The diagnosed was by MRI and sonographic imaging and histopathologic examination. His immediately survival perspective was not affected but the functionality of the left upper limb was severe reduced.     

Task-specific depression of the soleus H-reflex after cocontraction training of antagonistic ankle muscles

Ballet dancers have small soleus (SOL) H-reflex amplitudes, which may be related to frequent use of cocontraction of antagonistic ankle muscles. Indeed, SOL H-reflexes are depressed during cocontraction compared with plantarflexion at matched background EMG level. We investigated the effect of 30-min training of simultaneous activation of ankle dorsi- and plantarflexor muscles (cocontraction task) on the SOL H-reflex in 10 healthy volunteers. Measurements were taken during cocontraction. After training, there was a significant improvement in the ability of the subjects to perform a stable cocontraction. SOL H-reflex recruitment curves and H-max/M-max ratios were decreased after cocontraction training but not after 30 min of static dorsi or plantarflexion. The decreased H-reflex size correlated with improved motor performance. No changes in SOL and tibialis anterior (TA) EMG activity or EMG power were observed, suggesting that increased presynaptic inhibition of Ia afferents is a likely mechanism for H-reflex depression. In different sessions we measured SOL and TA motor-evoked potentials (MEPs) by using transcranial magnetic stimulation (TMS), TMS-elicited suppression of SOL EMG, and coherence between electroencephalographic (EEG) activity (Cz) and TA and SOL EMG. SOL and TA MEPs were depressed, whereas TMS-elicited suppression of SOL EMG and coherence were increased after training. Decreased excitability of corticospinal neurons due to increased intracortical inhibition seems a likely explanation of these observations. Our results indicate that the depression in H-reflex observed during a cocontraction task can be trained and that repeated performance of tasks involving cocontraction may lead to prolonged changes in reflex and corticospinal excitability.     

Comparison of the depression of H-reflexes following previous activation in upper and lower limb muscles in human subjects

 When conditioning-testing (C-T) stimuli are applied to Ia afferents to elicit H-reflexes, the test reflex is abolished immediately following the conditioning reflex. As the C-T interval is increased, the test response slowly begins to recover, taking several hundred milliseconds to attain control values. The time course of this recovery is known as the H-reflex recovery curve. H- reflex recovery curves were compared using surface EMG and single motor unit activities in lower limb soleus and upper limb flexor carpi radialis (FCR) muscles in seven healthy human subjects. Under rest conditions, the recovery of H-reflexes and single motor unit activity was slow for soleus; the recovery was not complete even in 1 s. In comparison, the recovery was very fast for FCR motor units, occurring in 200–300 ms. The effects of rate of stimulation (0.1–10.0 imp/s) were also examined on the magnitude of H-reflex responses. The reflex response declined with increasing rate of stimulation, the decline being slightly greater in soleus than in FCR. When these phenomena were examined with voluntary facilitation of the spinal cord, the time of recovery shortened and the effect of stimulus rate also diminished. Changes with background facilitation were greater in FCR than in soleus. The differences between the two muscles are attributed mainly to differences in presynaptic inhibition in the two spinal segments, and/or to the differences in dynamics of the transmitter release in terminals of Ia afferents synapsing with slow soleus motoneurons and those synapsing with the fast FCR motoneurons. Received: 23 April 1998 / Accepted: 6 November 1998     

Inhibitory effect of pain-eliciting transcutaneous electrical stimulation on vibration-induced finger flexion reflex in the human upper limb

We studied the effects of non-pain transcutaneous electrical stimulation (TES) and pain-eliciting TES on vibration-induced finger flexion reflex (VFR) in 12 healthy volunteers. Tonic finger flexion reflex in the upper limb was induced by the application of vibratory stimulation on the volar side of the middle fingertip in the right hand before and after TES. Non-pain TES or pain-eliciting TES was applied on the skin between the bases of the first and second metacarpals in the right hand dorsal area in a crossover design. Pain-eliciting TES inhibited VFRs significantly (Fisher's PLSD, p <0.01), compared to those of the time-control group during and after TES. VFRs were reduced approximately to 63.8% and 78.6% of prestimulation flexion force during and after pain-eliciting TES, respectively. Nonpain TES did not inhibit VFR. These results suggest that pain-conducting afferent fibers have inhibitory neuronal connection over the ipsilateral reflex circuits of VFR in the upper limb.     

The effects of depression and age on the Horne-Ostberg morningness-eveningness score.

Effects of depression and age on the Horne-Ostberg morningness-eveningness scale in human volunteers were assessed. Thirty-nine healthy outpatients with current DSM-IIIR depression, free of recent substance abuse or confounding medications, were compared to 39 age- and sex-matched controls. Patients reported greater 'eveningness' than controls (P = 0.014, Wilcoxon signed-ranks test). There was multimodality in the distribution of Horne-Ostberg scale scores in the depressed group, but a normal distribution in controls. Pearson's correlation of age vs. Horne-Ostberg score was positive (r = 0.42-0.55). Depression and age influence the Horne-Ostberg score. Potential multimodality of circadian phase in the depressed group deserves further study.     

Multiple arterial variation of the human upper limb

A case report of multiple variations involving the arteries of the upper limb in a single cadaver is presented. In addition to the proximal origin of the arteries unusual arterial patterns on both the right and left sides were present. On the right side, the subscapular artery gave rise to a large posterior circumflex humeral artery in addition to the thoracodorsal and circumflex scapular arteries. On the left side, the radial and ulnar arteries arose from the brachial artery at the level of arm, with their origins being opposite to the usual arrangement. There was an arciform anastomosis between the radial and ulnar arteries, with the radial recurrent artery arising from the concavity of the arch. The course of both the radial and ulnar arteries was normal at the wrist and hand, except for the absence of the first palmar metacarpal artery and an early bifurcation of the second palmar metacarpal artery. The French version of this article is available in the form of electronic supplementary material and can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00276-002-0011.     

MRI anatomy of the nerves of the upper limb

In view of the good anatomic definition of the images obtained by magnetic resonance imaging (MRI), we have defined MRI sections allowing study of the nerves of the upper limb.