Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REFLEX, TENDON”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,747 records · Page 97Linked to original sources
PubMed1993

Influence of quadriceps conditioning on soleus motoneuron excitability in young and old adults.

In an effort to investigate neuromuscular changes with age, the isometric force-time curve of the Achilles tendon-tap reflex (ATR) was measured in 10 college age (M = 20.9 yr) and 10 healthy active old subjects (M = 74.3 yr). In an effort to investigate spinal interneuronal pathways, the tendon-jerk was also conditioned with a tap to the ipsilateral or contralateral patellar tendon. The conditioning stimulus preceded the ATR by 25, 40, 55, 70, 85, 100, 115, 130, or 145 ms. Three trials were elicited at each conditioning interval plus three unilateral trials, for 30 trials per experimental session. Results indicated that the force production of the unilateral Achilles tendon-tap reflex was significantly reduced and the half-relaxation times were significantly lengthened in the old subjects. Moreover, ipsilateral conditioning produced short-latency facilitation and long-latency inhibition to the triceps surae in young subjects, whereas the same conditioning produced only a delayed long-latency inhibition in the old subjects. Similarly, the contralateral conditioning produced short-latency facilitation in the young subjects, with no changes observed in the old subjects. It is concluded that unilateral Achilles tendon-tap responses are different for the two groups, and that the reflex recovery profiles for the two groups are different. Several neurophysiological mechanisms are proposed to contribute to these differences.

Achilles Tendon↗
PubMed1998

Phasic and tonic reflexes evoked in human antagonistic wrist muscles by tendon vibration.

The electromyographic reflex responses of the voluntarily contracting wrist flexor and extensor muscles to periods of vibration-evoked enhanced, Ia-dominated afferent discharge from flexor carpi radialis (FCR) were studied in normal human subjects. Three main response phases were characterised, namely, (i) phasic 'on' responses elicited at the commencement of stimulation, (ii) tonic response levels occurring during prolonged stimulation and (iii) phasic 'off' responses elicited at the termination of stimulation. The phasic 'on' reflex responses of FCR and extensor carpi radialis (ECR) comprised, respectively, a peak of autogenetic excitation of group mean latency 18.8 ms and a trough of reciprocal inhibition of group mean latency 38.0 ms. Prolonged (2 s) trains of FCR (agonist) vibration evoked a phase of tonic reflex excitation in FCR whose mean level was significantly increased, by 20%, above pre-stimulus activity and which did not change over the 0.5-2.0 s vibration period. Progressive reduction of the duration (from 2000 ms to 100 ms) of vibration trains demonstrated that phasic disfacilitatory 'off' troughs regularly occurred, with a consistent latency (mean 24.2 ms), on withdrawal of each period of enhanced Ia-input. This indicates that the responsible excitatory reflex mechanism was operational for the entire duration of each of the vibration periods tested. The extra latency (on average 5.4 ms) of phasic 'off' relative to 'on' responses may be attributed to factors (e.g. 5-10 ms duration of unitary muscle action potentials and afterdischarge in reflex pathways) which inevitably delay the appearance of overt disfacilitatory reductions in EMG rather than the involvement of different reflex pathways. Thus, short-latency, possibly monosynaptic, reflex excitation contributed throughout the entire tonic excitatory response. Sustained FCR (antagonist) vibration produced a significant tonic reciprocal inhibitory reflex depression, by 7% pre-stimulus EMG, of ECR activity which remained steady during the 0.5-2.0 s vibration period. The absence of well-defined phasic disinhibitory 'off' responses in ECR suggests that the contribution of oligosynaptic reflex inhibitory mechanisms to the tonic suppression of activity occurring during continuing vibration is relatively small.

Adult↗
PubMed1997

Acetazolamide reduces peripheral afferent transmission in humans.

Carbonic anhydrase has been localized in skeletal muscle and nerve, thus, inhibition with acetazolamide (ACZ) may alter nerve and/or muscle function in healthy humans. ACZ (3 oral doses 14, 8, and 2 h prior to testing) reduced isometric force (37%) and peak to peak electromyographic (EMG) amplitude (1.38 mV to 0.83 mV), while increasing EMG latency associated with a unilateral Achilles tendon-tap. Reflex recovery profiles, following a contralateral conditioning tap, were similar in both placebo and ACZ experiments. ACZ led to significant changes in Hmax/Mmax ratio (52.19/14.42 to 45.73/15.65) and H-reflex latency (34.18 +/- 2.54 ms to 35.24 +/- 2.74 ms). Motor nerve conduction velocity and maximal voluntary isometric torque (knee extensors) were unaltered by ACZ. These data suggest that inhibition of the tendon-tap reflex and associated isometric force, following ACZ, is related to impairment of synaptic integrity between la fibers of the muscle spindle and the alpha motor neuron and not impairment of the muscle spindle or force-generating capacity.

Acetazolamide↗
PubMed2006

Adductor T and H reflexes in humans.

In the belief that changes in the adductor reflex (AR) may be helpful in evaluating lumbar root and plexus lesions, expression of the AR was studied in 43 healthy human subjects. ARs elicited with an electronic reflex hammer were recorded from the inner side of the proximal thigh using needle and surface electrodes, and patellar reflexes (PRs) were recorded simultaneously. These reflexes were obtained by tapping the ipsilateral medial aspect of the knee, the contralateral patellar tendon, the ipsilateral and contralateral anterior superior iliac spines, and the Achilles tendon. The H reflex of the obturator nerve was also evaluated in 17 cases. ARs were evoked consistently by tapping the ipsilateral medial aspect of the knee and by contralateral patellar tap, and by tapping ipsilateral and contralateral anterior superior iliac spines when a needle recording electrode was used. Sometimes an Achilles tendon tap also elicited the AR ipsilaterally. By contrast, the PR could only be elicited by a tap to the ipsilateral patellar tendon. ARs have somewhat different features than other well-known tendon reflexes such as the PR and are recorded consistently when a needle electrode is used, being elicited from both distal and proximal areas of the legs by tapping the Achilles tendon or anterior superior iliac spines unilaterally or bilaterally. Their role in evaluating lumbar root disease and monitoring adductor spasticity merits investigation.

Achilles Tendon↗
PubMedDate not supplied

Quadriceps mediated changes in soleus motoneuron excitability.

In an effort to investigate the interactions of the quadriceps and soleus muscles, the isometric force-time curve of the Achilles tendon-tap reflex (ATR) was measured in 10 college age subjects. The tendon-jerk was conditioned with a tap to the ipsilateral or contralateral patellar tendon, or by an electrocutaneous (3x perception) stimulus applied to the belly of the quadriceps. The conditioning stimulus preceded the test ATR by 25, 40, 55, 70, 85, 100, 115, 130 or 145 ms. The results indicated that the ipsilateral conditioning tendon-tap produced a wave of short-latency facilitation (40 ms) and long-latency inhibition (85-130 ms) to the triceps surae muscles. The ipsilateral cutaneous conditioning, however, did not alter reflex excitability. A contralateral conditioning to the patellar tendon again produced short-latency (50-70 ms) facilitation, whereas the electrocutaneous stimulus did not alter motoneuron excitability. Moreover, a barrage of electrocutaneous impulses to either the ipsilateral or contralateral quadriceps (1 minute/60 pps) did not significantly alter motoneuron excitability of the soleus muscle. These results indicate that motoneuron excitability changes are observed in the soleus muscle with mechanical conditioning but not with electrocutaneous conditioning. Several neurophysiological mechanisms are proposed to mediate these changes.

Achilles Tendon↗
PubMed1990

Electromyographic reflexes evoked in human flexor carpi radialis by tendon vibration.

The rectified, electromyographic (EMG) reflexes evoked in the voluntarily contracting flexor carpi radialis (FCR) muscle by vibration of its tendon were studied in healthy human subjects. Responses comprised a prominent, transient, short-latency (SL, 20-25 ms) increase in EMG, attributed to Ia mono- and/or oligo-synaptic action, followed by a series of less pronounced troughs and peaks of activity. Evidence of continuing Ia mono- or oligo-synaptic action was indicated by (i) the presence of small subpeaks, at vibration frequency, superimposed upon the excitatory components and (ii) the occurrence of a separate reduction in EMG, of consistent latency (ca. 30 ms), after cessation of stimulation. Progressively shortening the train of vibration from 29 cycles (at 145 Hz) to a single cycle significantly reduced net, excitatory reflex activity. Gradually increasing the level (10-50% maximum) of pre-existing voluntary contraction on top of which reflexes were elicited, by moderately prolonged (29 cycles) trains of vibration, resulted in small increases, in absolute terms, in SL peaks and in later, excitatory EMG activity. Excitatory reflexes, when normalised for pre-stimulus EMG, however, declined in an approximately hyperbolic manner with increasing background activity over this range. Thus, effective "automatic gain compensation" does not operate for vibration reflexes in FCR.

Adult↗
PubMedDate not supplied

Human root and cord potentials evoked by Achilles tendon tap.

Lumbosacral root potentials and sacral spinal cord segmental responses were recorded epidurally in 24 normal adult subjects by tapping the Achilles Tendon with the electronic hammer (mechanical). The averaged responses were also recorded from the same epidural levels after the electrical stimulation of the Posterior Tibial nerve at the popliteal fossa (electrical). While the dorsal and reflexively evoked ventral root responses were easily obtained by the electrical stimulation; by the mechanical stimulation only a late and small ventral root response with two negative deflections could be evoked at the L4-5 or L5-S1 I.V. (intervertebral) epidural levels. The ventral root responses elicited by mechanical stimulation appeared 4.0 msec later than those elicited by the electrical stimulation. This time interval was exactly the same when the latencies of the Soleus reflexes to both stimuli were compared that for the Achilles tendon reflex being 4.0 msec delayed. When the sums of their afferent and the efferent conduction times (to and from Th12-L1 I.V. levels) were extracted from the total conduction times of the Soleus H and Achilles tendon reflex obtained by the EMG recordings, the sacral cord conduction delay was found 1.8 msec for the H-Reflex and 4.1 msec for the Achilles tendon reflex. It was suggested that the twice longer time delay along the sacral cord to Achilles tendon tap might be due to the oligosynaptic linkage of the Achilles tendon reflex or it may result from highly dispersed afferent volley producing a slowly rising wave or excitation that takes longer to reach threshold for the soleus motoneurone discharges.

Achilles Tendon↗
PubMed1990

Ankle reflex photomotogram in thyroid dysfunctions.

The tap to half relaxation time of tendon achilles reflex was measured in thirty control subjects, forty-five thyrotoxic and sixty hypothyroid patients. The half relaxation time in the control males and females was 279.33 +/- 76.39 msec and 320.00 +/- 52.37 msec. respectively. In thyrotoxic males and females the half relaxation time was 256.67 +/- 31.62 msec (P less than 0.01) and 252.50 +/- 47.68 msec (P less than 0.01) respectively. Amongst the hypothyroid male and female patients the half relaxation time was 405.0 +/- 35.56 msec (P less than 0.01) and 422.5 +/- 115.36 (P less than 0.01) respectively. As all these values were statistically significant, we consider the photomotographic measurement of ankle reflex as an important aid to the diagnosis of thyroid hormone imbalances.

Adult↗
PubMed1999

Reflex and muscular adaptations in rat soleus muscle after hindlimb suspension.

Reflex, mechanical and histochemical adaptations of the soleus muscle following 3 weeks of hindlimb suspension (HS) were measured in the rat. HS transformed the soleus muscle fibre type composition from predominantly slow, type I, to approximately equal proportions of fast, type II and slow fibres. Consistent with this transformation was an increase in the maximum shortening velocity, V(max), and a decrease in the stiffness of the series elastic component. Disuse also produced muscle atrophy and a resultant decrease in twitch and tetanic force. Reflex responses of the ankle extensors were also obtained at 5 and 9 weeks of age for six control rats (C group) and six rats subjected to HS for 3 weeks (HS group). The soleus reflexes to a mechanical tap applied to the Achilles tendon (T reflex) and to an electrical stimulation of the sciatic nerve (H reflex) were measured. The maximal amplitude of these reflexes (T(max) and H(max)) were normalised to the maximal direct motor response (M(max)) and the T(max)/H(max) ratio was also calculated to give an index of the relative adaptations of the peripheral and central components of the reflex pathway. The HS group showed significantly higher H reflex gains than the C group, possibly due to changes in synaptic efficiency after HS. Conversely, the HS group presented strongly inhibited T reflexes and negative gains for the T(max)/H(max) ratios. This result indicated a reduced spindle solicitation after HS, which may reflect changes in the spindle sensitivity itself, but it could also be due to the decrease in stiffness of the musculo-tendinous elements in series with the muscle spindles. Such mechanical changes may play an important part in the decreased T reflex responses.

Adaptation, Physiological↗
PubMed1991

Interactions in human quadriceps-triceps surae motoneuron pathways.

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 college age subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130 or 145 ms. The results demonstrate that a tap to the contralateral patellar tendon produced long-latency excitation of quadriceps motoneurons, but a tap to the contralateral Achilles tendon produced short-latency facilitation and long-latency inhibition of the triceps surae motoneurons. Also, a conditioning tap to the contra- or ipsilateral patellar tendon produced a brief short-latency facilitation that was followed by a distinct, long-latency inhibition of triceps surae motoneurons. These results demonstrate that motoneuron excitability changes can be produced as a result of ispi- and contralateral segmental inputs. Moreover, these excitability changes may be long-lasting and only appear after a relatively long-latency. Several neurophysiological mechanisms are proposed to contribute to these changes.

Achilles Tendon↗
PubMed1992

Segmental reflex organization in endurance-trained athletes and untrained subjects.

In an effort to investigate the effects of training on spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 endurance-trained (ET) athletes and 12 control (C) subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130, or 145 ms. The results demonstrated significant differences in control reflexes and conditioned reflexes between the two groups. A contralateral patellar tendon-tap produced a significantly greater excitatory effect to the contralateral quadriceps motoneurons for the ET group, whereas a contra- or ipsilateral conditioning caused a significantly greater inhibitory effect to the triceps surae motoneurons for the ET athletes. These results demonstrate that motoneuron excitability changes can be produced as a result of ipsi- and contralateral segmental inputs, and raise the possibility that trained athletes demonstrate different reflex recovery profiles. Several neurophysiological mechanisms are proposed to contribute to these changes.

Achilles Tendon↗
PubMed2001

An investigation into mechanisms of reflex reinforcement by the Jendrassik manoeuvre.

Tendon jerk and H-reflexes are both potentiated by the Jendrassik manoeuvre, but the mechanism of potentiation remains uncertain. We investigated several possibilities in human subjects. Evidence for fusimotor activation during the Jendrassik manoeuvre was sought by recording the tendon jerk reflex as surface EMG in triceps surae after the muscles had been conditioned to leave their spindles in a slack, insensitive state. Interposing a Jendrassik manoeuvre between conditioning and the test reflex should have increased reflex amplitude by restoring spindle sensitivity, but this was not the case. In humans, a close synergist of the triceps surae is the quadriceps. A possible presynaptic disinhibitory mechanism was investigated by testing the effect of a Jendrassik manoeuvre on facilitation of the soleus H-reflex produced by a quadriceps afferent volley. The Jendrassik manoeuvre failed to increase facilitation, contrary to what would be expected if it reduced the level of tonic presynaptic inhibition; the assumption being that the inhibition acts on both homonymous and synergist afferent terminals. The Jendrassik manoeuvre did not increase the level of ongoing EMG in the soleus during a weak voluntary contraction, indicating that it does not operate by direct facilitation of motoneurones. There was found to be less potentiation of soleus tendon jerk and H-reflexes by the Jendrassik manoeuvre under conditions when spindles in the soleus were likely to have a high resting discharge rate. A remaining possibility is discussed: that the Jendrassik manoeuvre operates by modulation of oligosynaptic pathways that may contribute to the largely monosynaptic reflex response. These experiments demonstrate, with new, more sensitive methods than previously used, that neither is the fusimotor system involved in reinforcement nor are direct excitatory or presynaptic disinhibitory effects on motoneurones. While this confirms the previously prevailing view, none of the lingering uncertainties associated with the methods used now remains.

Adult↗
PubMed1993

Evidence that alterations in presynaptic inhibition contribute to segmental hypo- and hyperexcitability after spinal cord injury in man.

We examined Hoffmann (H) and tendon (T) reflexes in 3 populations of adult subjects: acute SCI (< 2 weeks post injury), controls, and chronic SCI (> 1 year post injury). We further investigated the effects of continuous tendon vibration and different stimulus rates on the size of evoked H reflexes in these subject populations. All reflex amplitudes were expressed as a function of the maximum direct muscle response (M wave), to allow comparison between subjects. Both H and T reflexes were successfully elicited from all subjects examined, including those in 'spinal shock.' Tendon vibration caused a marked attenuation of H reflexes in acute SCI subjects, intermediate attenuation in controls, and relatively little effect in the chronic SCI group. H reflexes showed greatest attenuation for a given stimulus rate in acute SCI subjects compared to controls (intermediate attenuation) or chronic SCI (limited attenuation) subjects. Both rate sensitivity and vibration influence have been linked to presynaptic inhibitory mechanisms. We suggest that spinal cord injury disrupts the supraspinal influence over segmental interneurons mediating presynaptic inhibition, and that the hyporeflexia associated with 'spinal shock' is due in part to a substantial increase in the efficacy of presynaptic inhibition. Conversely, over time the level of presynaptic inhibition of ankle extensor Ia input in SCI subjects declines to levels less than those of control subjects, contributing to the enhancement of spinal reflexes consistent with the clinical state of 'spasticity' seen in chronic SCI.

Adult↗
PubMed2005

Differentiation of hamstring short latency versus medium latency responses after tibia translation.

After injuries to the anterior cruciate ligament (ACL) a functional instability is frequently observed which has been attributed to a disturbed sensorimotor function. In light of the clinical importance of ACL injuries and the resulting functional instability, it is of enormous clinical interest to elucidate the role of sensorimotor pathways that involve the ACL. In animals and humans a direct reflex pathway between the ACL and the hamstrings has been shown. The onset latencies of responses reported after ventral tibia translation were around 40-50 ms (range 17.9-65) and were regarded as medium latency responses (MLR). However, ventral tibia translation should also induce a stretch of the hamstring muscles and evoke a short latency response (SLR). Before any muscle response after ventral tibia translation can be ascribed to anatomical structures, it is crucial to analyze the obtained muscle responses carefully. The aim of the present study was the development of an algorithm to differentiate SLR and MLR responses after ventral tibia translation. In ten healthy subjects reflex responses of the hamstrings after anterior tibia translation and after tendon taps on the biceps femoris tendon were evaluated. To investigate the influence of skin afferents, control experiments were performed after lidocain injection of the dorsal calf. The mean onset latency of the tendon jerk reflex was 21.9 +/- 3.1 ms (range 17.3 - 28.7 ms). Both SLR responses (mean onset latency: 20.3 +/- 3.5 ms; range 15.4 - 25.8) and MLR responses (mean onset latency: 38.9 +/- 4.2 ms; range 32.9 - 46.7) were obtained in all subjects. Skin afferents from the calf do not play a major role. The development of an evaluation algorithm is presented that allows a safe differentiation between these partly superimposed SLR and MLR components. It is demonstrated that by measuring the first part of the SLR from the onset to the first peak the end of the SLR can be predicted and that the onset latency of the MLR component can be assessed reliably. Possible reasons are discussed why previous studies only reported responses at MLR latencies. The fact that both SLR and MLR components can be observed after anterior tibia translation underlines the necessity to differentiate the responses before they can be ascribed to any anatomical structures. As a basis for future work the algorithm presented may become a useful tool to differentiate which afferent pathways play a role in initiating hamstring activity.

Adult↗