Dependence of autogenic and heterogenic stretch reflexes on pre-load activity in the human arm. (original) (raw)
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Experimental Neurology, 1987
Reflex electromyographic (EMG) responses of elbow extensor muscles to unexpected elbow flexion were recorded in the absence of initial tonic activity from subjects instructed not to resist the stretch. The monosynaptic component M1 was present only in the anconeus muscle and only for high accelerations. The acceleration value at which the long-latency components M2 and M3 appeared was lower for anconeus than for triceps brachii. Increases in peak acceleration of stretch resulted in decreases in M2 and M3 latencies and increases in M2 and M3 magnitudes in both muscles. However, M2 and M3 latencies for anconeus were shorter than those of triceps brachii, except at high acceleration values. Furthermore, the magnitude of M2 and M3 components of anconeus activity increased faster for low accelerations than for high accelerations, whereas those of triceps brachii increased in proportion to the acceleration. These differences between anconeus and triceps brachii were similar to those described earlier for voluntary movements. It is suggested that the motoneurons of all elbow extensor muscles may be recruited as a single motoneuron pool following Henneman's size principle, irrespective of whether the activity is voluntary or reflex in origin.
2009
34 Stretch reflexes contribute to arm impedance and longer latency stretch reflexes exhibit 35 increased sensitivity during interactions with compliant or unstable environments. This 36 increased sensitivity is consistent with a regulation of arm impedance to compensate for 37 decreased stability of the environment, but the specificity of this modulation has yet to be 38 investigated. Many tasks, such as tool use, compromise arm stability along specific directions 39 and stretch reflexes tuned to those directions could present an efficient mechanism for 40 regulating arm impedance in a task appropriate manner. To be effective, such tuning should 41 adapt not only to the mechanical properties of the environment but to those properties in 42 relation to the arm, which also has directionally-specific mechanical properties. The purpose of 43 this study was to investigate the specificity of stretch reflex modulation during interactions with 44 mechanical environments that challenge arm s...
Operant Conditioning of Human Upper-Limb Stretch Reflexes
2018
Operant conditioning of short-latency reflex (SLR) and H-reflex have been investigated in animals and humans. We modified previously established protocols for conditioning lower limb H-reflexes to up-condition the SLR in brachioradialis muscle and to investigate the effect of such conditioning on the long-latency response (LLR) of synergistic muscles. Our study included 12 healthy participants. Each participant took part in 3 baseline and 27 conditioning sessions in 6 weeks, followed by two additional sessions one month and two months after the last conditioning session. We found an increase in SLR magnitude in 50% of participants (by 15%±2.50). However, there was no significant effect at the population level. We could not find any statistically significant correlation between SLR in the conditioned muscle with SLR and LLR in synergistic muscles. Although our findings in healthy adults were weak, studying patients with spinal cord injury or other motor dysfunctions might show clinically significant results.
Journal of Neurophysiology, 2010
Stretch reflexes contribute to arm impedance and longer-latency stretch reflexes exhibit increased sensitivity during interactions with compliant or unstable environments. This increased sensitivity is consistent with a regulation of arm impedance to compensate for decreased stability of the environment, but the specificity of this modulation has yet to be investigated. Many tasks, such as tool use, compromise arm stability along specific directions, and stretch reflexes tuned to those directions could present an efficient mechanism for regulating arm impedance in a task-appropriate manner. To be effective, such tuning should adapt not only to the mechanical properties of the environment but to those properties in relation to the arm, which also has directionally specific mechanical properties. The purpose of this study was to investigate the specificity of stretch reflex modulation during interactions with mechanical environments that challenge arm stability. The tested environment...
Journal of Electromyography and Kinesiology, 2005
It is known that the short-latency stretch reflex (SLSR) is modulated by the background muscle activity when it is elicited at matched torque levels. This study was designed to examine the effects of muscle contraction types before a stretch perturbation on SLSR in the human soleus muscle (SOL) when SLSR was elicited at the same levels of effort and at matched electromyographic (EMG) activity levels. A mechanical stretch perturbation was applied to the calf muscles when the ankle joint reached a ninety degree tibio-tarsal joint angle after the muscles performed an isometric (pre-ISO), shortening (pre-SHO) and lengthening contraction (pre-LEN). Subjects were seated on an ankle ergometer chair and developed 0%, 10%, 20%, 30%, 40%, 50%, 60% and 70% ankle joint torque (AJT) of maximum voluntary isometric plantar flexion contraction at 80°in pre-SHO, at 90°in pre-ISO and at 100°in pre-LEN. After that, isometric or dynamic contractions started, and the subjects were asked to maintain effort levels as, needed, to maintain the target torque levels until the end of the stretch. They relaxed their muscles fully after the stretch. This chain of processes was consecutively repeated 10 times. EMG signals obtained from SOL were averaged after they were high-pass filtered and full-wave rectified. Some major findings resulted: (1) there were no differences in SLSR area in the active muscle between pre-ISO and pre-SHO, whereas its waveform was steeper in pre-ISO than in pre-SHO. (2) SLSR p-top amplitude and waveform were larger and steeper in the active muscle than in the relaxed one in all conditions, whereas they were independent of the effort levels once the muscle was activated. This led to steady SLSR modulation in response to the background muscle contraction in the active muscle regardless of whether the SLSR was elicited at matched AJT or EMG activity levels. These findings suggest that SLSR is closely related to the muscle spindle sensitivity influenced by the following factors: (1) the background muscle contraction type, and (2) gamma motoneuron activity set by CNS based on the effort level.
Modulation of reflex activity of motor units in response to stretch of a human finger muscle
The Japanese Journal of Physiology, 1983
Changes in stretch reflex responses were examined in two types of motor task, force control and position control, by applying a small quick stretch to the middle finger extensor digitorum communis (EDC) muscle at an unpredicted time and observing activities of single motor units. Subjects were asked to maintain a constant extending isometric force at the metacarpophalangeal (MP) joint for force control, and to maintain a constant middle finger position against an applied force for position control. No significant differences in the tonic activities of EDC motor units were seen between the two types of motor task when the same force was exerted about the MP joint. Tonic activities of the EDC muscle and its antagonists were thus similar for both types of motor task. Ten of the eighteen motor units investigated showed obvious reflex responses (increase in firing rate) with latencies of 30-60 msec after the stretch. This reflex response was greater for position control than for force control, given the same operating conditions of tonic force, finger position, and activities of motor units. Enhancement of the stretch reflex for position control was also observed in surface electromyograms of the same muscle.
2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2001
In neural tension testing, it is critically important establish a method to investigate the relative contribution of different neuromuscular mechanisms to resistance developed during and at the limit of the upper limb tension test 1 (ULTT1). Three males and seven females in the age range 41-72 years (mean 56, SD±10) participated in a within subject repeated measure study. The study consisted of two major testing protocols. The first was an objective passive movement protocol, which utilized a KIN-COM ® dynamometer to measure range of motion (ROM) and evoked resistive torque during elbow extension. The second was an electromyographic (EMG) protocol, which allowed recording of EMG from 10 shoulder and arm muscles during the controlled passive elbow extension as the last component of ULTT1. A battery-operated micro-switch held by the subject, generated digital rectangular pulses to indicate occurrence of pain onset and pain tolerance limit during the experimental task. There was increased level of EMG activity prior to pain onset (P<0.05). There was also clear evidence that elevated perception of pain and elevated levels of resistive torque (P<0.05), were positively correlated with the EMG activity in the muscles responsible for antalgic posture of the upper limb (P<0.05). From these findings, now it is possible to propose that increased detectable resistance during elbow extension at ULTT1 position involves the protective reflex activation of the shoulder and arm muscles which is mediated by nociceptive and mechano-receptors as a result of the preferential mechanical stretching of the median nerve during the test.
Effects of Acute Static Stretching on Electromyography (EMG) and Peak Force Responses
The purpose of the present study was to investigate the possibility of an interaction between the stretching-induced-force-deficit and bilateral-deficit during maximal voluntary isometric hand flexion under the stretch and non-stretch, bilateral, and unilateral conditions through measurement of EMG and force production. Force output and associated EMG were recorded during either unilateral or bilateral 3-second maximal voluntary isometric hand flexion (MVC) against a force transducer. The effect of the stretch on the right hand in a unilateral MVC was decreased in force with a decrease in integrated EMG (IEMG) activity. The left hand bilateral force in the stretch condition was significantly smaller than the left hand unilateral force in the non-stretched condition. It was concluded that a cumulative deficit might indicate activation of multiple inhibitory mechanisms or pathways or possibly a greater activation of a single inhibitory mechanism or pathway. Trends were observed that may prove to be significant with a stronger experimental design and greater subject numbers with less variability between subjects.