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At least 217 records · Page 12Linked to original sources
PubMed1999

Quantitative evaluation of the stretch reflex before and after hydro kinesy therapy in patients affected by spastic paresis.

The aim of this study was the quantitative evaluation of the myotatic reflex in a group of 26 patients affected by stationary spastic paresis (6: hemiparesis; 5: paraparesis; 8: tetraparesis; 7: multiple sclerosis) before and after a treatment of hydro-kinesy therapy. The treatment was carried out in an indoor pool containing warm (32 degrees C) sea water and consisted of active and passive motion exercises, coordination exercises and immersion walking. The measured parameters were: (i) the peak input force (FpH) measured by means of an instrumented hammer with which the patellar tendon was hit; and (ii) the peak value of the corresponding reflex force of the quadriceps femoris (FpQ) measured by means of a load cell connected to the subject's ankle. The peak values of the reflex response (FpQ) were found to increase as a function of the intensity of the imposed stimulus and to reach a plateau between 15 and 30 N of FpH. A Student's t test applied to the paired values of FpQ (as measured at plateau conditions) on both the lower limbs, before and after therapy, showed no significant changes due to the treatment in the four groups of subjects. However, if all subjects were grouped regardless the type of illness: 1) the average reflex response of the affected limb (the one characterized before therapy by the higher FpQ values) was found to decrease following the treatment (75.1+/-26.7 N pre therapy and 69.1+/-29.3 N post therapy, p = 0.07, n = 26); and 2) the effect of the treatment was found to be significantly larger (p = 0.04, n = 26) on the affected limb (delta FpQ = 6.07+/-16.5 N) as respect with the contra lateral one (delta FpQ = -0.16+/-12.1 N).

Adult↗
PubMed2000

Stretch reflex distinguished from pre-programmed muscle activations following landing impacts in man.

1. Electromyographic activity and joint rotation were measured whilst human subjects jumped down to land on a solid surface 0.45 m below them and then to a false collapsible surface at the same level. The collapsible surface did not produce ankle joint rotation. Objective evidence from post-take-off EMG onset latencies showed that the subjects were surprised by the false surface. 2. Following landing on the solid surface, the gastrocnemius and soleus muscles showed peak responses at latencies of 53 and 56 ms, respectively, and the antagonist m. tibialis anterior showed an early peak response with a latency of 26 ms. These responses occurred following landing on the solid surface but not following passage through the false surface. 3. The rectus femoris and biceps femoris muscles showed no clear reflex activity with this fall distance but pre-programmed activity was clearly present following impact. 4. It is concluded that the post-landing activity in m. soleus and m. gastrocnemius is a short-latency spinal reflex triggered by ankle joint rotation.

Adult↗
PubMed1986

Stretch reflexes of the normal infant.

Tendon-jerk reflexes were tested in normal, fullterm infants aged one to four days. EMGs were recorded from gastrocnemius-soleus and tibialis anterior muscles. Reflex-like EMGs were evoked when tapping sites which should not excite the muscles from which that activity is recorded--this included the simultaneous activation of antagonistic muscles by a tendon tap. The possible mechanisms which could produce these results are discussed, as are the possible relationships between the proposed pathways and the reciprocally excitatory paths in cerebral palsy.

Electromyography↗
PubMed1984

The contrasting stretch reflex responses of the long and short flexor muscles of the human thumb.

The electromyographic activity of flexors pollicis longus and brevis (with its synergists) has been compared on forcibly extending the thumb at various velocities with the muscles initially contracting. Both muscles gave short- and long-latency responses, but these differed in their relative magnitude with short-latency responses being better developed for the short flexor. With jerk-type stimuli both muscles gave short-latency responses with the expected slight difference in latency due to their different position in the arm. That of the long flexor was sometimes immediately followed by a long-latency response to the same stimulus. With slower displacements the short flexor regularly showed much more short-latency response than did the long flexor. The ensuing long-latency activity of the short flexor was normally appreciably less than that of the long flexor. However, since the short-latency response may be presumed to leave the motoneurones refractory it cannot be definitively concluded from this that acting in isolation long-latency pathways would be less potent for the short flexor, though this seems quite likely to be so. In some cases the first reflex activity occurred nearly synchronously for the two muscles in spite of their different separation from the spinal cord. That for the more distal short flexor was a short-latency response, whereas that for the more proximal long flexor was a long-latency response. The findings conflict with the provisional generalization that for muscles of the primate hand short-latency responses have been regularly supplanted by long-latency responses. They also provide the basis for a teleological argument against the view that the long-latency response is mediated transcortically.

Adult↗
PubMedDate not supplied

Cross-bridge mechanisms underlying the history-dependent properties of muscle spindles and stretch reflexes.

The effects of prior movement on the force responses of skeletal muscle are compared with the effects of movement history on the changes in firing rate of muscle spindle receptors. Prior release results in the linearization of the mechanical properties of skeletal muscles, which can be provisionally explained by cross-bridge models of muscular contraction. The history-dependence of responses of muscle spindle receptors in unanesthetized decerebrate preparations appears to result from the kinetics of cycling and noncycling cross-bridges. The results of this comparison indicate that the integration of mechanical properties of muscle and spindle receptor promotes stiffness regulation.

Animals↗
PubMed1985

Characteristics of the tonic stretch reflex in spastic spinal cord and head-injured patients.

Spasticity is a known sequelae of spinal cord injury and head injury. We sought to examine whether there were any significant differences in the characteristics or underlying mechanisms of spasticity in these two groups in the chronic period which may be related to the level of injury of the neuraxis. The response to vibration applied to the muscle, or the tonic vibratory reflex, has been shown to be related to the degree of spasticity, and was therefore studied along with phasic reflexes and passive movements. These studies were carried out on cooperative, stabilized patients who were otherwise healthy, 5 with head injuries, and 5 with spinal cord injuries. The patients were examined in a supine position while surface EMG recordings were made of quadriceps and triceps surae muscles bilaterally. Tendon jerk responses, passive and volitional movements, and responses to a powerful vibratory stimulator were measured. In both head injury and spinal cord injury patient groups, a large EMG response was elicited by passive maneuvers, and tendon jerks were exaggerated. The tonic vibratory response, previously shown to be dependent upon brain influence, was present in both groups. These observations suggest that similar suprasegmental mechanisms may be responsible for hypertonia in both head-injured and spinal cord-injured patients.

Adolescent↗
PubMed2000

Stretch reflexes in the rectus abdominis muscle in man.

The spinal reflex circuitry of the rectus abdominis (RA) muscle in man was investigated by the application of a mechanical tap to the muscle. Electromyographic recordings were made in ten healthy subjects, performing a series of manoeuvres, using pairs of surface electrodes placed bilaterally. The reflex responses elicited largely depended on the amount of tonic (postural) activity of the trunk. When standing in the upright position, no reflex activity was recorded in response to the tap. Reflex activity due to mechanical tap was readily recorded when the muscle became tonically active. Moderate, backward trunk extension introduced short-latency reflexes at 18.8 +/- 1.9 ms (mean +/- S.D.) ipsilaterally and 20.8 +/- 1.8 ms contralaterally. Excitatory reflex activity of longer latency was also recorded contralaterally in all subjects (latency 45.1 +/- 4.3 ms) and ipsilaterally in five of the ten subjects (latency 47.2 +/- 2.6 ms). Vibration of the tapped muscle produced a reduction in the amplitude of the early reflex responses, whilst increasing the amplitude of the late responses. Moreover, the early reflexes were facilitated by the Jendrassik manoeuvre. Such observations are consistent with the early responses being mediated, at least partly, monosynaptically, and the late responses being of polysynaptic nature. This implies that muscle spindle afferents from rectus abdominis monosynaptically activate motoneurones contralaterally.

Adult↗