Increase In Electromyogram Research Articles

Influence of muscle fatigue on electromyogram-kinematic correlation during robot-assisted upper limb training.

IntroductionStudies on adaptive robot-assisted upper limb training interactions do not often consider the implications of muscle fatigue sufficiently.MethodsTo explore this, we initially assessed muscle fatigue in 10 healthy subjects using two electromyogram features, namely average power and median power frequency, during an assist-as-needed interaction with HapticMaster robot. Since robotic assistance resulted in a variable fatigue profile across participants, a completely tiring experiment, without a robot in the loop, was also designed to confirm the results.ResultsA significant increase in average power and a decrease in median frequency were observed in the most active muscles. Average power in the frequency band of 0.8–2.5 Hz and median frequency in the band of 20–450 Hz are potential fatigue indicators. Also, comparing the Spearman’s correlation coefficients (between the electromyogram average power and the kinematic force) across trials indicated that correlation was reduced as individual muscles were fatigued.ConclusionsConfirming fatigue indicators, this study concludes that robotic assistance based on user’s performance resulted in lesser muscle fatigue, which caused an increase in electromyogram–force correlation. We now intend to utilise the electromyogram and kinematic features for auto-adaptation of therapeutic human–robot interactions.

Reacting to and recovering from a stressful situation: The negative affectivity-physiological arousal relationship.

Although it is one of the most widely researched personality correlates of psychological reactions, the relationship between negative affectivity (NA) and physiological arousal has received little attention. This study examined the associations between NA and physiological outcomes of heart rate, skin temperature, and muscle tension. The authors hypothesized that when individuals are in a stressful situation, persons high in NA experience more heightened physiological arousal than those low in NA. After personality and demographic data were collected, 230 individuals participated in a stressful intervention. Individuals high in NA experienced a significantly greater rate of increase in electromyogram during the stress intervention and a lesser rate of decrease in electromyogram after the stressful event than those low in NA. In regard to skin temperature, those high in NA did not recover from the stress intervention as well as those low in NA. Negative affectivity was not related to heart rate.

Accessory muscle activity contributes to the variation in time to task failure for different arm postures and loads

Time to failure and electromyogram activity were measured during two types of sustained submaximal contractions with the elbow flexors that required each subject to exert the same net muscle torque with the forearm in two different postures. Twenty men performed the tasks, either by maintaining a constant force while pushing against a force transducer (force task), or by supporting an equivalent load while maintaining a constant elbow angle (position task). The time to failure for the position task with the elbow flexed at 1.57 rad and the forearm horizontal was less than that for the force task (5.2 +/- 2.6 and 8.8 +/- 3.6 min, P = 0.003), whereas it was similar when the forearm was vertical (7.9 +/- 4.1 and 7.8 +/- 4.5 min, P = 0.995). The activity of the rotator cuff muscles was greater during the position tasks (25.1 +/- 10.1% maximal voluntary contraction) compared with the force tasks (15.2 +/- 5.4% maximal voluntary contraction, P < 0.001) in both forearm postures. However, the rates of increase in electromyogram of the accessory muscles and mean arterial pressure were greater for the position task only when the forearm was horizontal (P < 0.05), whereas it was similar for the elbow flexors. These findings indicate that forearm posture influences the difference in the time to failure for the two fatiguing contractions. When there was a difference between the two tasks, the task with the briefer time to failure involved greater rates of increase in accessory muscle activity and mean arterial pressure.

Changes in cortical negative potential associated with local anesthetization of apex of tooth root

To determine whether cortical negative potential (hereafter referred to as CNP), which was recorded from the scalp (sites: T3, CZ and T4), preceding the right-side chewing is affected by input from the periodontal membrane, the CNP and pattern of the appearance of masseter electric discharge before the anesthetization of the apex of the tooth root and those after the anesthetization were compared. 1) CNP preceding the right-side chewing appeared at T4 early both before and after the anesthetization and showed a maximum amplitude immediately before masseter electric discharge. CNP duration and amplitude increased after the anesthetization as compared with those before the anesthetization. 2) The initial increase in electromyogram associated with chewing became sharper after the anesthetization than before the anesthetization. From these findings, that the cerebral cortex is in a preparatory state at an early stage when the sensation in the periodontal membrane on the chewing side is blocked, and that, as a consequence, strong chewing is produced.

Transient cardiorespiratory events during NREM sleep: a feline model for human microarousals.

Microarousals (MAs) are brief transient events that occur during normal sleep in humans and with increased frequency in disordered sleep, especially in association with sleep apnoea. In a feline model, we discovered transient cardiorespiratory events during nonrapid eye movement (NREM) sleep that exhibited consistent features with similarities to human MAs. It was observed that MAs have two distinct phases. Phase I (MAI) is characterized by an abrupt increase in electromyogram (EMG) amplitude (> 50%), increased electrooculogram (EOG) activity and accelerated frequency of hippocampal electroencephalographic (EEG) activity. MAI lasts 4.1 +/- 0.3 s. Phase II (MAII), lasting 9.8 +/- 0.8 s, is characterized by high frequency EEG activity, but EMG, EOG and hippocampal activity remain at baseline levels. Mean inspiratory rate begins to increase 15 s before the onset of the MA, followed 10 s later by the increase in mean heart rate. Mean respiratory rate decreases sharply through MAII, and returns to baseline levels 15 s after the MA. During MAII mean heart rate decreases quickly; there is increased respiratory irregularity, followed by a prolonged ventilatory overshoot. The abrupt shift in heart rate is coincident with the change in breath timing seen during MAII. Heart rate returns to baseline levels 10 s following the MA. Integrating our findings with those described previously in humans, we propose that MAs may serve as a homeostatic mechanism which is designed to restore cardiorespiratory function allowing the continuity of sleep.

Dynamic Suppression of REM Sleep by Parenteral Administration of the Serotonin-1 Agonist Eltoprazine

The purpose of this study was to determine the effects of the serotonin-1 agonist eltoprazine on the control of rapid eye movement (REM) sleep. Continuous polygraph recordings were performed for 15-17 days in four adult male cats. During the first 5 control days cats received injections of 0.9% saline intraperitoneally (i.p.) twice per day (b.i.d.). Over the next 5-7 days cats received injections of 0.9% saline intraperitoneally (i.p.) twice per day (b.i.d.). Over the next 5-7 days cats received eltoprazine i.p. (1-2 mg/kg, b.i.d.). For the final 5 recovery days cats received saline alone. During the saline control period, the mean REM sleep percent was 13.8 +/- 0.91%. When eltoprazine was administered for the subsequent 5-7 days, the mean REM percent was reduced to 1.5 +/- 0.59%. During the 5-day recovery period, REM percent increased significantly (p less than 0.0001) above both control and drug injection values to a mean of 24.5 +/- 1.3% with a maximum on recovery day 1 of 28.4 +/- 2.6% (n = 4). In addition to REM suppression, eltoprazine produced other electroencephalographic changes: an increase in slow-wave sleep (S) percent without any change in overall wake (W) percent; an increase in electromyogram (EMG) amplitude; and a decrease in ponto-geniculo-occipital (PGO) wave activity. PGO wave frequency and REM% increased significantly during the recovery period. Thus our findings demonstrate REM and PGO suppression by eltoprazine and document dramatic rebound effects following its withdrawal.

Entrainment of duodenal activity to periodic feeding.

The electrical activity of the antrum and proximal duodenum was recorded simultaneously with bar pressing for food in various feeding conditions. During restricted feeding (RF; food available from 1200 to 1600 hr; lights-on from 0800 to 2000 h), large-amplitude slow potentials of duodenal origin were observed 3-5 hr preceding food access. These potentials occurred in short trains at irregular intervals of approximately 1 min and appeared to be associated with the active phase of the migrating motility complex. At least 8-10 days on RF were required before these irregular contractions (ICs) reliably preceded food access. The distribution of ICs showed a circadian variation during food deprivation, and transients lasting 4-6 days were observed in response to 6- or 8-hr phase delays of food access. These observations suggest that ICs are modulated by a circadian mechanism. On the average, the increase in ICs occurred about 2 hr earlier than bar pressing in anticipation of food, and there was no specific relation between individual ICs and bar pressing. However, bar pressing frequently occurred 0.5 min or longer after an increase in electromyogram (EMG) amplitude. Unreinforced bar pressing was never observed during a quiescent EMG.

Observations on the time course of the electromyographic response reflexly elicited by muscle vibration in man.

Surface electromyography has been used to study the initial reflex response of various muscles to vibration, applied to their tendons, when the subject was already contracting them voluntarily. The response at the onset of vibration was of a latency appropriate for Ia monosynaptic action and was always highly phasic with an initial wave rising far above any maintained increase in electromyogram (e.m.g.) activity; its duration was typically well below 20 ms in the rectified average. Thus, there is nothing peculiar, in this respect, about flexor pollicis longus for which such behaviour has already been described, and used to draw certain wide-ranging conclusions about the stretch reflex. Theoretical considerations, developed in an Appendix, show that quite apart from the operation of any inhibitory mechanisms such a phasic response is to be expected from a population of tonically discharging motoneurones when there is a step increase in the level of their excitatory drive.

Spinal kittens: Effect of clamping of the thoracic aorta on long-term increases in electromyograms due to a conditioning routine

Conditioning and pseudoconditioning routines have different effects on EMG responses recorded from the semitendinosus muscle of spinal kittens pinched on tail (CS) and toe (US) 50 times daily for 5 days. The response to tail pinches habituates during each day. However, conditioning routines cause increases in responses between days 5 and 1. Pseudoconditioning routines in which CS and US are separated by 10 sec have no comparable effect. Clamping thoracic aortas for 30 min severely reduces conditioning routines' effectiveness in producing increased responses. Because thoracic clamping selectively destroys the spinal cord interneurons, we conclude that interneurons are essential to the production by conditioning routines of long-term increases in responsiveness of isolated lumbosacral spinal cord.

Spinal kittens: Long-term increases in electromyograms due to a conditioning routine☆

Abstract The effects of conditioning and pseudo-conditioning routines on the habituation of electromyographic responses of spinal kittens to the pinches of the tail (CS) and toe (US) were compared for 5 days. Habituating animals in a conditioning routine caused daily increases in their responses to tail pinches. Habituating them in a pseudo-conditioning routine had no comparable effect. Hence, a conditioning routine appears to cause long-term increases in the responsiveness of the isolated lumbo-sacral spinal cord.