Adaptation to sudden unexpected loading of the low back--the effects of repeated trials

The purpose of this study was to investigate short-term changes in reactions to sudden unexpected loading of the low back. The study utilized a set-up where a horizontal force of 58 N pointing forward suddenly was applied to the upper part of the subject's trunk. EMG activity from the erector spinae muscles and trunk movement data were recorded during 10 trials for 19 subjects. The analysis included EMG reaction time, mean rectified EMG amplitude during the period 50-250 ms after the sudden loading, and time elapsed until stopping of the forward movement of the trunk (stopping time). Reaction time means ranged from 66 to 97 ms (79+/-9 ms), and no difference was found between the trials. Conversely, the mean stopping time for the first trial (468 ms) was significantly higher than for trials 3-10 (359- 371 ms), and the average EMG amplitude during the period 50-250 ms after the sudden loading was lower for the first trial. This study showed that some subjects adapted to sudden unexpected loadings of the low back through a reduction in stopping time and a progression in EMG response during the first few trials. This possible adaptation to repeated trials have been overlooked in previous studies.     

Regulation of mental states and biofeedback techniques: Effects on breathing pattern

The purpose of the present study was to examine whether breathing pattern may be used as a reliable index for the effectiveness of techniques applied for the regulation of mental states. Heart rate (HR), breathing pattern, galvanic skin response (GSR), and electromyogram (EMG) of the frontalis muscle were measured in 39 male and female subjects aged 18–25 years during 10-minute treatment with relaxation technique (autogenic training and/or music) followed by 10 minutes of imagery training. In the first 7 sessions biofeedback (BFB) was not included, while during the last 6 sessions BFB was introduced and utilized by the subjects. Relaxation (music or autogenic training) led to a decrease in breathing frequency, attributed to lengthening of expiration time, as well as reduced HR, GSR, and frontalis EMG response. In most instances imagery training was related to an increase in these indices. Specifically, significant tachypnea was observed during imagery of sprint running. In most cases BFB substantially augmented the physiological responses. In conclusion, our data suggest that, compared with HR, GSR, and EMG responses, the breathing pattern is at least as sensitive to the mental techniques employed, and may be useful as a psychophysiological index for diagnosis and testing, especially in sport practice.     

Activity and functions of the human gluteal muscles in walking,running, sprinting,and climbing

It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speeds for the same subjects. Thus, comparing relative EMG amplitudes between these activities has not been possible. We assessed the EMG activity of the gluteal muscles during walking, running, sprinting, and climbing. To gain further insight into the function of the gluteal muscles during locomotion, we measured muscle activity during walking and running with external devices that increased or decreased the need to control either forward or backward trunk pitch. We hypothesized that 1) GMAX EMG activity would be greatest during sprinting and climbing and 2) GMAX EMG activity would be modulated in response to altered forward trunk pitch demands during running. We found that GMAX activity in running was greater than walking and similar to climbing. However, the activity during sprinting was much greater than during running. Further, only the inferior portion of the GMAX had a significant change with altered trunk pitch demands, suggesting that the hip extensors have a limited contribution to the control of trunk pitch movements during running. Overall, our data suggest that the large size of the GMAX reflects its multifaceted role during rapid and powerful movements rather than as a specific adaptation for a single submaximal task such as endurance running. Am J Phys Anthropol 153:124–131, 2014. © 2013 Wiley Periodicals, Inc.     

Assessment of work-related muscle strain by using surface EMG during test contractions interposed between work periods of simulateted mushroom picking

Surface electromyograms(EMG) during test contractions (TCs) were studied to assess the muscle strain in simulated mushroom picking. Additionally, the duration of the TC for the effective assessment was investigated. Nine female subjects performed standardized shoulder abduction and a stooped posture for one minute as TCs. Each experiment consisted of a 60-min rest, three work periods (W1-W3), a 30-min rest, and two work periods (W4 and W5) separated by a 30-min rest period. The duration of each work period was about 20 min. A total of 18 TCs was performed between the work periods and every 10 minutes in the rest periods. EMGs were recorded from the trapezius, infraspinatus, deltoid, and erector spinae muscles. The amplitude of EMG (AEMG) and mean power frequency (MPF) of EMG were calculated. Each TC was divided equally into three parts. Ratings of perceived exertion (RPE) in the neck, shoulder and low-back were reported during TCs. The work increased RPE of all the parts. AEMG and RPE were increased and MPF was decreased by W1, W2 and W3 in the neck and shoulder muscles. MPF of the erector spinae was increased by the work. The results were not affected by the duration of TCs and the parts during the TCs. AEMG and MPF fluctuated before W1 although the changes of RPE were small. Averaging several TCs was recommended to get stable results from TCs. EMG changes and appropriate TC conditions were discussed in relation to the adaptation in fatiguing contractions.     

Psychophysiological responsivity on a laboratory stress task: methodological implications for a stress-muscle hyperactivity pain model

A stress-muscle hyperactivity-pain (SMP) model has been proposed to explain the etiology of certain musculoskeletal pain disorders. According to this model, subjects should show physiological arousal during periods of stress relative to periods of rest. In a test of this prediction, 31 subjects performed a reaction time task that has been used in previous laboratory studies. Multiple psychophysiological variables were monitored during initial and final 10-minute baselines, during performance on nine 2-minute reaction time tasks, and during 36-second rest intervals following each of the 2-minute tasks, Results showed small but statistically significant differences generally supporting the SMP model when masseter EMG was averaged over time periods of 12 seconds to 2 minutes, but not when masseter EMG was averaged over 10- to 18-minute blocks. These results demonstrated the importance of carefully selecting time intervals for analysis. Additional analyses that compared TMD with symptom-free subjects revealed small differences in EMG that supported the SMP model. Analyses of EMG over shorter time intervals also showed, however, that masseter EMG increased during the 36-second rest interval following performance on a 2-minute stress task; this result suggested that a modification of the SMP model may be necessary.     

Frontal electromyographic feedback

This study evaluated the effects of one session of frontal electromyographic (EMG) feedback on (1) frontal EMG, (2) frontal EMG response to stress, (3) cardiovascular variables, and (4) cardiovascular responses to stress. Eighteen male and female undergraduate volunteers received either frontal EMG feedback or a relaxation instructions control procedure and were then exposed to a fear stimulus (visualization of a feared situation) and a post-stress adaptation period while several cardiovascular measures were monitored. In comparison to the control group, frontal EMG feedback significantly reduced resting levels of frontal EMG and frontal EMG response to stress but had no significant effect on cardiovascular measures. The results of this study suggest that one session of frontal EMG feedback may attenuate response to stress but, within the paradigm utilized, may be confined to the specific muscle groups monitored. Additional areas of needed research were noted including individual differences in generalization, the effects of EMG feedback from multiple sites sequentially and concomitantly, and the generalized effects from symptom-specific sites.     

Frontal electromyographic feedback. Stress attenuation and generalization.

This study evaluated the effects of one session of frontal electromyographic (EMG) feedback on (1) frontal EMG, (2) frontal EMG response to stress, (3) cardiovascular variables, and (4) cardiovascular responses to stress. Eighteen male and female undergraduate volunteers received either frontal EMG feedback or a relaxation instructions control procedure and were then exposed to a fear stimulus (visualization of a feared situation) and a post-stress adaptation period while several cardiovascular measures were monitored. In comparison to the control group, frontal EMG feedback significantly reduced resting levels of frontal EMG and frontal EMG response to stress but had no significant effect on cardiovascular measures. The results of this study suggest that one session of frontal EMG feedback may attenuate response to stress but, within the paradigm utilized, may be confined to the specific muscle groups monitored. Additional areas of needed research were noted including individual differences in generalization, the effects of EMG feedback from multiple sites sequentially and concomitantly, and the generalized effects from symptom-specific sites.     

Psychophysiological responsivity on a laboratory stress task: Methodological implications for a stress-muscle hyperactivity pain model

A stress-muscle hyperactivity-pain (SMP) model has been proposed to explain the etiology of certain musculoskeletal pain disorders. According to this model, subjects should show physiological arousal during periods of stress relative to periods of rest. In a test of this prediction, 31 subjects performed a reaction time task that has been used in previous laboratory studies. Multiple psychophysiological variables were monitored during initial and final 10-minute baselines, during performance on nine 2-minute reaction time tasks, and during 36-second rest intervals following each of the 2-minute tasks. Results showed small but statistically significant differences generally supporting the SMP model when masseter EMG was averaged over time periods of 12 seconds to 2 minutes, but not when masseter EMG was averaged over 10- to 18-minute blocks. These results demonstrated the importance of carefully selecting time intervals for analysis. Additional analyses that compared TMD with symptom-free subjects revealed small differences in EMG that supported the SMP model. Analyses of EMG over shorter time intervals also showed, however, that masseter EMG increased during the 36-second rest interval following performance on a 2-minute stress task; this result suggested that a modification of the SMP model may be necessary.This research was supported in part by Grant 2 S06RR08038-17 funded by the National Institutes of Health.     

Experimentally Induced Stress Validated by EMG Activity

Experience of stress may lead to increased electromyography (EMG) activity in specific muscles compared to a non-stressful situation. The main aim of this study was to develop and validate a stress-EMG paradigm in which a single uncontrollable and unpredictable nociceptive stimulus was presented. EMG activity of the trapezius muscles was the response of interest. In addition to linear time effects, non-linear EMG time courses were also examined. Taking into account the hierarchical structure of the dataset, a multilevel random regression model was applied. The stress paradigm, executed in N = 70 subjects, consisted of a 3-minute baseline measurement, a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. Subjects were unaware of the precise moment of stimulus delivery and its intensity level. EMG activity during the entire experiment was conform a priori expectations: the pre-stimulus phase showed a significantly higher mean EMG activity level compared to the other two phases, and an immediate EMG response to the stimulus was demonstrated. In addition, the analyses revealed significant non-linear EMG time courses in all three phases. Linear and quadratic EMG time courses were significantly modified by subjective anticipatory stress level, measured just before the start of the stress task. Linking subjective anticipatory stress to EMG stress reactivity revealed that subjects with a high anticipatory stress level responded with more EMG activity during the pre-stimulus stress phase, whereas subjects with a low stress level showed an inverse effect. Results suggest that the stress paradigm presented here is a valid test to quantify individual differences in stress susceptibility. Further studies with this paradigm are required to demonstrate its potential use in mechanistic clinical studies.     

Generalization of EMG biofeedback training

Five young adults received audio biofeedback training to reduce trapezius EMG levels while they engaged in reading in an office, seated at a table. A multiple-baseline-across subjects design was employed in two separate studies. After training, all subjects demonstrated reduced EMG levels while reading in a home or library setting. The first study suggested that subjects reduced EMG levels by minimizing movements and altering their postures; the second study systematically demonstrated changes in such behavior, which was correlated with EMG levels. The data provide evidence that EMG biofeedback resulted in response generalization across several motoric classes, and in stimulus generalization from the training setting to the natural environment. The importance of assessing generalization is discussed.     

Generalization of EMG biofeedback training

Five young adults received audio biofeedback training to reduce trapezius EMG levels while they engaged in reading in an office, seated at a table. A multiple-baseline-across subjects design was employed in two separate studies. After training, all subjects demonstrated reduced EMG levels while reading in a home or library setting. The first study suggested that subjects reduced EMG levels by minimizing movements and altering their postures; the second study systematically demonstrated changes in such behavior, which was correlated with EMG levels. The data provide evidence that EMG biofeedback resulted in response generalization across several motoric classes, and in stimulus generalization from the training setting to the natural environment. The importance of assessing generalization is discussed.     

Effects of aging on EMG variables during fatiguing isometric contractions

The purpose of this study was to evaluate the neuromuscular adaptation that occurred with aging, by comparing young and aged subjects with respect to changes in surface EMG from the tibialis anterior muscle during fatiguing contractions. EMG variables such as the averaged rectified value (ARV), median frequency (MDF), and muscle fiber conduction velocity (MFCV) were calculated during maximal (MVC, 3 sec) and submaximal (60% MVC, 60 sec) isometric contractions. Muscular force, ARV, MDF, and MFCV during MVC were significantly greater in the young than in the elderly (p < 0.05). EMG amplitude increased and the waveform slowed in all subjects during submaximal contractions, indicating the development of local muscle fatigue. As fatigue progressed, the ARV increased and the MDF and MFCV decreased significantly (p < 0.01). The fatigue-induced changes in the MDF and MFCV were significantly smaller in aged than in young subjects (p < 0.05), a trend also seen in the ARV change, which means that the elderly cannot be fatigued as much as the young with contractions of the same relative intensity. These results as a whole suggest that the aged subjects hold an adaptive motor strategy to cope with age-related neuromuscular deteriorations, due to the decline of motor unit activation and selective atrophy of fast twitch muscle fibers.     

Differential shaping of EEG theta rhythms

Heart rate, EEG, frontal EMG, and forearm EMG were recorded in 20 subjects for 3 baseline, 8 feedback, and 2 postbaseline sessions in order to compare two biofeedback methods of teaching subjects to increase theta EEG activity. Subjects were divided into high- and low-EMG groups. Five high-EMG subjects, and 5 low-EMG subjects then received 8 sessions of strictly theta feedback. The remaining 10 subjects, 5 from the high-EMG group, and 5 from the low-EMG group, received a “graduated” training which involved shaping the target response. This procedure consisted of 4 initial sessions of EMG feedback, followed by a second phase consisting of 4 sessions of theta feedback. Results showed a clear relationship between subjects' baseline frontal EMG levels and the effect of the training methods. Although subjects with high-EMG baseline increased their theta output only with the two-phase training, subjects with low-EMG baseline levels performed better when given theta feedback only. This result shows not only that amounts of theta can be reliably increased, but that training techniques should be adapted to the physiological characteristics of the individual—in this case, baseline levels of frontal EMG levels.     

Restitution of EMG spectrum after muscular fatigue

Restitution of the EMG spectrum was studied in upper limb muscles. The subjects performed isometric and isotonic exercises until they refused because of fatigue. Force levels varied from 15 to 60% MVC. The mean frequency was used as an indicator of the modification of the spectrum. Restitution of the EMG spectrum was studied by recording for 10 min after the end of the fatigue experiment at intervals of 1 to 3 minutes. Recovery was rapid at the beginning, levelling off to a plateau in 2 to 5 min. The change was more regular in isometric experiments than in kinetic ones, although interindividual differences were large in both cases.     

Effects of noncontingent feedback on EMG training,EMG responses,and subjective experience

Various types of noncontingent feedback have been used as control procedures in EMG training; however, their effects on such training have received little attention. Experiment 1 in the present study examined the effects of noncontingent feedback on EMG training, and Experiment 2 assessed the effects of feedback characteristics on EMG responses. In Experiment 1, three noncontingent feedback groups (yoked control, randomly fluctuating tones, and decreasing tones) and one contingent group underwent 20 minutes of training for frontal EMG decreases. Procedures in Experiment 2 were identical to those in Experiment 1 except that subjects were instructed merely to listen to the feedback tones. Results of Experiment 1 indicated that contingent and noncontingent fluctuating feedback groups achieved significantly lower EMG levels than noncontingent decreasing and yoked control groups. In Experiment 2, however, no differences in EMG activity were found among groups. In both experiments, groups did not differ in terms of subjective variables such as frustration, suspiciousness about the tone, or length of time attending to the tone. Results of these two experiments suggest that differences in EMG responses to various types of noncontingent feedback result from interactions between characteristics of the feedback stimulus and instructions to decrease the stimulus.This research was supported by Ohio University Research Grants No. 9147 and No. 9155 to the first author.     

Role of Glutamate in the Mechanisms of Adaptation of the System of Respiratory Control in Rats to Intermittent Hypoxia

In experiments on Wistar rats, we studied the role of changes in the state of glutamatergic transmission in the course of adaptation of the system of respiratory control to intermittent hypoxia. The volume/temporal parameters of respiration were estimated according to characteristics of EMG activity (amplitude, integral intensity of EMG discharges) recorded from the diaphragmatic muscle. Changes in EMG activity of the diaphragm induced by acute hypoxia (breathing a 12% О₂-containing gas mixture) were estimated before and after of a 14-day-long course of intermittent hypoxia trainings and before and after inductions of a blocker of NMDA receptors, МK-801. The results prove that the glutamatergic transmitter system is significantly involved in the reaction of the respiratory system to presentation of a hypoxic stimulus within all stages of formation of the ventilatory response, both before and after the action of intermittent hypoxia. Blocking of NMDA receptors under conditions of adaptation to intermittent hypoxia exerted a more intense influence on the amplitude of respiratory EMG discharges of the diaphragm than on their frequency.     

Should we tell them when their blood pressure is up?

We carried out two studies to determine the effects of feedback on subsequent blood pressure and heart rate readings in subjects without significant cardiovascular abnormalities. In both studies the subjects were randomly assigned to be told that their blood pressure was normal or was high or to receive no feedback at all; 3 minutes later another reading was taken and correct feedback provided. Study 1 was done in 114 patients who attended a family practice teaching unit for an office visit; subjects taking cardioactive medication or with chronically elevated blood pressure (diastolic pressure more than 95 mm Hg) or known low pressure (diastolic pressure less than 60 mm Hg) were excluded. Half of the subjects received feedback from a nurse and the other half from a physician. We found no effect of type of feedback or type of practitioner on subsequent readings. No adaptation of diastolic blood pressure or heart rate took place, whereas a similar rest period in the laboratory consistently triggers cardiovascular adaptation. Given the field nature of the study it was not clear whether the intervention was not powerful or whether the practitioner-patient interactions diffused the effects of an otherwise powerful intervention. Therefore, a second study with the same design was carried out in a controlled laboratory setting with 61 university students who believed they were in the adaptation phase of an experimental stress protocol. The subjects did not interact with the experimenter, who provided only the initial feedback, via intercom. The findings replicated those of study 1: type of feedback had no significant effect on subsequent blood pressure levels, and all types of feedback prevented cardiovascular adaptation. We recommend that patients be allowed to rest alone for at least 10 minutes before blood pressure is measured. Our findings suggest that practitioners need not be concerned about telling normotensive or borderline hypertensive patients that their blood pressure is elevated.     

Effects of noncontingent feedback on EMG training, EMG responses, and subjective experience

Various types of noncontingent feedback have been used as control procedures in EMG training; however, their effects on such training have received little attention. Experiment 1 in the present study examined the effects of noncontingent feedback on EMG training, and Experiment 2 assessed the effects of feedback characteristics on EMG responses. In Experiment 1, three noncontingent feedback groups (yoked control, randomly fluctuating tones, and decreasing tones) and one contingent group underwent 20 minutes of training for frontal EMG decreases. Procedures in Experiment 2 were identical to those in Experiment 1 except that subjects were instructed merely to listen to the feedback tones. Results of Experiment 1 indicated that contingent and noncontingent fluctuating feedback groups achieved significantly lower EMG levels than noncontingent decreasing and yoked control groups. In Experiment 2, however, no differences in EMG activity were found among groups. In both experiments, groups did not differ in terms of subjective variables such as frustration, suspiciousness about the tone, or length of time attending to the tone. Results of these two experiments suggest that differences in EMG responses to various types of noncontingent feedback result from interactions between characteristics of the feedback stimulus and instructions to decrease the stimulus.