Relative Rest Time Research Articles

Threshold and Standard Error of Measurement for Relative Rest Time of Pericervical Muscles During Prolonged Computer-Typing Tasks in Individuals With Neck Symptoms.

Introduction The most common work-related musculoskeletal disorder worldwide is neck pain, especially among individuals who extensively use computers in a seated position. One biomedical cause of this neck pain is the prolonged activity of the muscles around the neck. Electromyography (EMG) has been used to evaluate the frequency and intensity of muscle activity. "Relative rest time (RRT)" is an index derived indicating the proportion of time below a certain threshold to the total task time. This study aimed to investigate the measurement errors and minimum detectable change (MDC) of RRT of the pericervical muscles during prolonged typing tasks in individuals with neck symptoms and to examine the differences in measurement errors at 3 µV and 6 µV thresholds. Methods This test-retest reliability study was conducted twice with a one-week interval to examine measurement errors of the RRT using surface EMG. The number of participants was set to 30 subjects who had neck symptoms with a Neck Disability Index of 16% or higher. The primary outcome measure was RRT of the following: the pericervical muscles of the right side during a 60-minute typing task; the splenius capitis muscle, upper trapezius (UT) muscle, middle trapezius muscle, sternocleidomastoid muscle, serratus anterior muscle, longissimus muscle, and pectoralis major muscle. RRT was calculated as the percentage of time that muscle activity was below the threshold for more than 0.250 seconds continuously during a 60-minute typing task. The standard error of measurement (SEM) and MDC were calculated with the two thresholds of 3 µV and 6 µV. The SEMs of the two thresholds were compared using a paired method. Results Ultimately, the data of 26 participants were analyzed. The SEM (MDC) values of the RRT at the 3 µV and 6 µV thresholds were 19.22 (53.27) and 9.52 (26.39) for the splenius capitis muscle, 3.24 (8.97) and 0.38 (1.05) for the sternocleidomastoid muscle, 15.47 (42.88) and 18.79 (52.08) for the UT muscle, 21.28 (58.99) and 2.28 (6.32) for the middle trapezius muscle, 13.67 (37.90) and 11.64 (32.27) for the serratus anterior muscle, 16.81 (46.60) and 3.32 (9.20) for the longissimus muscle, and 8.97 (24.87) and 4.24 (11.74) for the pectoralis major muscle, respectively. The SEMs of the RRT with the 6 µV threshold were statistically significantly lower than those with the 3 µV threshold in all pericervical muscles, except for the UT muscle. Conclusion This study identified the SEM and MDC of the RRT for the pericervical muscles during prolonged typing tasks in individuals with neck symptoms. Except for the UT muscle, the SEMs of the RRT with the 6 µV threshold were statistically smaller than those with the 3 µV threshold. Therefore, when using the RRT in intervention studies that aim to reduce muscle activity during typing in those with neck symptoms, the 6 µV threshold measurement would be recommended for the RRT of the pericervical muscles except for the UT muscle.

FEATURES OF ASSESSING THE SEXUAL BEHAVIOR OF MALE RATS IN THE STUDY OF THE EFFECTS OF COMPOUNDS THAT HAVE A STIMULATING EFFECT ON SEXUAL FUNCTION

The paper presents a comparative analysis of information content of methods for assessing the copulatory behavior of male rats with the introduction of compounds that have a stimulating effect on the sexual activity of animals. The social significance of the problem of sexual dysfunctions determines the relevance of the development of various experimental models of sexual behavior that allow assessing the effectiveness and safety of new drug. The probability of detecting the activating effect of pharmacological agents on sexual activity directly depends on the correct choice of the experimental model. The drugs of the central mechanism of action galantamine hydrobromide (1mg/kg) and loxidan (1,7mg/kg), were used as pharmacological agents; drugs of peripheral action were yohimbine hydrochloride (2,6mg/kg) and vardenafil hydrochloride (1,7mg/kg). It has been shown that the determination of the stimulating effects of compounds of the central mechanism of action is possible using methods with different testing duration (from 15 to 180min). Thus, the introduction of galantamine enhances the sexual activity of males in terms of the copulation rate, the number of perfect ejaculations and the duration of the post-ejaculatory refractory period, loxidan in terms of the total number of intromissions and relative rest time in tests of limited duration. In the test showing the completed sexual cycle of males, the stimulating effects of galantamine are shown in terms of the number of completed copulatory series and the number of completed ejaculations. To assess the activating effects of compounds of the peripheral mechanism of action, the expediency of using experimental models with a test duration of 30 minutes or more was shown. The most informative test is the test of paired interaction between a male and a female until the male reaches the state of sexual exhaustion. A method with high information content is presented, which provides a high probability of detecting the activating effect of compounds on the sexual function of male rats.
 Determination of the stimulating effects of compounds of the central mechanism of action is possible using methods with different test duration

The coordination of shoulder girdle muscles during repetitive arm movements at either slow or fast pace among women with or without neck-shoulder pain

Purpose: The aim of this study was to evaluate the coordination of the shoulder girdle muscles among subjects with or without neck-shoulder pain performing repetitive arm movement at either a slow or fast pace. Methods: Thirty female adults were allocated to one of two groups—healthy controls or cases with neck-shoulder pain. Surface electromyography (sEMG) signals from the clavicular, acromial, middle and lower trapezius portions and the serratus anterior muscles were recorded during a task performed for 20min at a slow pace and 20min at a fast pace. The root mean square (RMS), relative rest time (RRT) and normalised mutual information (NMI, an index of functional connectivity between two muscles in a pair) were computed. Results: No significant differences on RMS, RRT and NMI were found between groups. For both groups, the fast movement pace resulted in increased levels of RMS, lower degrees of RRT and higher NMI compared to the slow pace. No interaction between group and movement pace was found. Conclusions: This study highlights the change in sEMG activity of muscles to meet the demands of performing a task at fast movement pace. The fast pace imposed a higher muscle demand evidenced by increased sEMG amplitude, low degree of muscle rest and increased functional connectivity for subjects in both the case and control groups. No indication of impaired sEMG activity was found in individuals with neck-shoulder pain.

Shoulder muscle fatigue development in young and older female adults during a repetitive manual task

Age may modify the association between occupational physical demand and muscle loading, and ultimately increase the risk of musculoskeletal disorders. The goal of this study was to investigate age-related differences in shoulder muscle fatigue development during a repetitive manual task. Twenty participants in two age groups completed an 80-minute simulated low-intensity assembly task. Electromyographic (EMG) manifestation of muscle fatigue was observed in the upper trapezius, deltoid and infraspinatus muscles in both age groups, and coincided with an increase in the subjective ratings of perceived exertions. Compared with the younger group, older group showed a more monotonic decrease in EMG power frequency in the upper trapezius and deltoid muscles. However, the age-related difference in EMG amplitude was less consistent. Relative rest time of the upper trapezius muscle in the older group was less than the young group throughout the task. The observed patterns of EMG measures suggest that older participants may have disadvantages in fatigue resistance in the upper trapezius and posterior deltoid muscles during the simulated repetitive manual task.

Interactive effects of acute experimental pain in trapezius and sored wrist extensor on the electromyography of the forearm muscles during computer work

We investigated the interactive effects of shoulder pain and wrist extensor muscle soreness on surface electromyography (EMG) during computer mouse work. On day one, subjects ( N = 12) performed computer work with/without acute muscle pain induced in the trapezius muscle. Subsequently, eccentric exercise was performed to induce delayed onset muscle soreness (DOMS) in wrist extensor muscles. In presence of DOMS on day two, computer work recordings with/without pain were repeated. EMG signals were recorded from the descending part of trapezius bilaterally, flexor carpi ulnaris and extensor carpi radialis brevis. Experimental muscle pain in trapezius led to a decrease in the muscular activity of the wrist extensor ( P < 0.02) and decreased the relative rest time in the wrist flexor even in presence of DOMS ( P < 0.01). The present result suggests that shoulder pain plays a role in the coordination of wrist flexors and extensors during computer work.

Active biofeedback changes the spatial distribution of upper trapezius muscle activity during computer work

The aim of this study was to investigate the spatio-temporal effects of advanced biofeedback by inducing active and passive pauses on the trapezius activity pattern using high-density surface electromyography (HD-EMG). Thirteen healthy male subjects performed computer work with superimposed feedback either eliciting passive (rest) or active (approximately 30% MVC) pauses based on fuzzy logic design and a control session with no feedback. HD-EMG signals of upper trapezius were recorded using a 5 x 13 multichannel electrode grid. From the HD-EMG recordings, two-dimensional maps of root mean square (RMS), relative rest time (RRT) and permuted sample entropy (PeSaEn) were obtained. The centre of gravity (CoG) and entropy of maps were used to quantify changes in the spatial distribution of muscle activity. PeSaEn as a measure of temporal heterogeneity for each channel, decreased over the whole map in response to active pause (P < 0.05) underlining a more homogenous activation pattern. Concomitantly, the CoG of RRT maps moved in caudal direction and the entropy of RMS maps as a measure of spatial heterogeneity over the whole recording grid, increased in response to active pause session compared with control session (no feedback) (P < 0.05). Active pause compared with control resulted in more heterogeneous coordination of trapezius compared with no feedback implying a more uneven spatial distribution of the biomechanical load. The study introduced new aspects in relation to the potential benefit of superimposed muscle contraction in relation to the spatial organization of muscle activity during computer work.

Short-term effects of implemented high intensity shoulder elevation during computer work

BackgroundWork-site strength training sessions are shown effective to prevent and reduce neck-shoulder pain in computer workers, but difficult to integrate in normal working routines. A solution for avoiding neck-shoulder pain during computer work may be to implement high intensity voluntary contractions during the computer work. However, it is unknown how this may influence productivity, rate of perceived exertion (RPE) as well as activity and rest of neck-shoulder muscles during computer work. The aim of this study was to investigate short-term effects of a high intensity contraction on productivity, RPE and upper trapezius activity and rest during computer work and a subsequent pause from computer work.Methods18 female computer workers performed 2 sessions of 15 min standardized computer mouse work preceded by 1 min pause with and without prior high intensity contraction of shoulder elevation. RPE was reported, productivity (drawings per min) measured, and bipolar surface electromyography (EMG) recorded from the dominant upper trapezius during pauses and sessions of computer work. Repeated measure ANOVA with Bonferroni corrected post-hoc tests was applied for the statistical analyses.ResultsThe main findings were that a high intensity shoulder elevation did not modify RPE, productivity or EMG activity of the upper trapezius during the subsequent pause and computer work. However, the high intensity contraction reduced the relative rest time of the uppermost (clavicular) trapezius part during the subsequent pause from computer work (p < 0.04).ConclusionSince a preceding high intensity shoulder elevation did not impose a negative impact on perceived effort, productivity or upper trapezius activity during computer work, implementation of high intensity contraction during computer work to prevent neck-shoulder pain may be possible without affecting the working routines. However, the unexpected reduction in clavicular trapezius rest during a pause with preceding high intensity contraction requires further investigation before high intensity shoulder elevations can be recommended as an integrated part of computer work.

Effects of eccentric exercise on trapezius electromyography during computer work with active and passive pauses

Background The aim of this laboratory study was to investigate the effects of eccentric exercises on the trapezius muscle spatial electromyographic (EMG) activity during computer work with active and passive pauses. Methods Twelve healthy male subjects performed computer work with passive (relax) and active (30% maximum voluntary contraction of shoulder elevation) pauses given every 40 s over 2 days, before, immediately and 24 h after eccentric exercise. Surface EMG signals were recorded from four parts of the trapezius during computer work. Findings EMG amplitude during computer work decreased immediately after exercise ( P < 0.05). In the clavicular and descending parts of the trapezius, the centroid of exposure variation analysis along the time axis was lower during computer work with active pauses compared with passive ones ( P < 0.05). Further, lower values of relative rest time was observed during active pause ( P < 0.05). Interpretation Eccentric exercises had a short term effect on muscle activation pattern during computer work, and decreased the muscle activity immediately after the exercises. The results of this study showed a more variable trapezius activity pattern and a lower trapezius rest with active pauses compared with passive pauses. Moreover, eccentric exercises resulted in a less variable activation pattern, decreasing the effect of active pauses.

Experimental pain leads to reorganisation of trapezius electromyography during computer work with active and passive pauses

The aim of this laboratory study was to investigate acute effects of experimental muscle pain on spatial electromyographic (EMG) activity of the trapezius muscle during computer work with active and passive pauses. Twelve healthy male subjects performed four sessions of computer work for 2 min in one day, with passive (relax) and active (30% maximum voluntary contraction of shoulder elevation) pauses given every 40 s without and with presence of experimental pain. Surface EMG signals were recorded from four parts of the trapezius. The centroid of exposure variation analysis along the time axis was lower during computer work with active pauses when compared with passive one in all muscle parts (P < 0.05). In presence of experimental pain, EMG amplitude increased in transverse and ascending parts and relative rest time decreased in ascending part. The results of this study showed a more variable trapezius activity pattern and increased activity with active compared with passive pauses, a lowered trapezius rest with presence of experimental pain, and increased activity in the transverse and ascending parts of trapezius due to experimental pain during computer work. Acute pain led to muscle activation pattern during computer work considered to increase the risk of developing work-related musculoskeletal disorders.

Active pauses induce more variable electromyographic pattern of the trapezius muscle activity during computer work

The aim of this laboratory study was to evaluate effects of active and passive pauses and investigate the distribution of the trapezius surface electromyographic (SEMG) activity during computer mouse work. Twelve healthy male subjects performed four sessions of computer work for 10 min in one day, with passive (relax) and active (30% maximum voluntary contraction of shoulder elevation) pauses given every 2 min at two different work paces (low/high). Bipolar SEMG from four parts of the trapezius muscle was recorded. The relative rest time was higher for the lower parts compared with the upper of the trapezius ( p < 0.01). The centroid of exposure variation analysis (EVA) along the time axis was lower during the computer work with active pause compared with passive one ( p < 0.05). The results of this study revealed (i) lower rest time for the upper parts of trapezius compared with the lower parts, in line with previous clinical findings, (ii) active pauses contributed to a more variable muscle activity pattern during computer work that might have functional implications with respect to work-related musculoskeletal disorders.

The influence of biofeedback training on trapezius activity and rest during occupational computer work: a randomized controlled trial

The aim of this study was to investigate effects of biofeedback training on trapezius activity and rest (gaps) during occupational computer work. A randomized controlled trial with 164 computer workers was performed. Two groups working with computer mouse more than 50% (n = 64) and less than 25% (n = 49) of their work time performed five sessions with unilateral electromyographical (EMG) biofeedback from the dominant trapezius during computer work. A third group working with computer mouse more than 50% of their work time (n = 51) served as controls. Bipolar EMG from the bilateral upper trapezius muscles during normal computer work was recorded. Changes in discomfort/pain were not recorded. The biofeedback training reduced activity (P < 0.05), and increased the frequency of short (P < 0.05) and long (P < 0.05) gaps, and the relative rest time (P < 0.05) of the trapezius during computer work. By improving trapezius inactivity during computer work, biofeedback training may have the potential to prevent trapezius myalgia in computer workers.

Upper trapezius muscle activation patterns in neck–shoulder pain patients and healthy controls

This study aimed at investigating whether patients with neck-shoulder complaints from different aetiologies (work-related musculo-skeletal disorders, WMSD; whiplash associated disorders, WAD) show comparable muscle activation patterns, characterised by higher activation and lower relaxation levels of the trapezius muscles compared to healthy controls. Twenty healthy controls, 21 WMSD and 20 WAD patients with non-acute neck-shoulder pain were recruited for this cross-sectional study. Surface electromyography (sEMG) recordings were performed at the upper trapezius muscles during reference contractions, standardised computer tasks (typing and unilateral stress task), and rest measurements. sEMG was continuously recorded during these measurements. Outcome measures were root mean square (RMS) to study muscle activity, and relative rest time (RRT) to study muscle relaxation. Statistical analysis comprised the bootstrap technique and Kruskall-Wallis tests. Results showed no clear evidence for abnormal muscle activation patterns in WMSD and WAD patients compared to healthy controls. However, a tendency was observed for higher RMS levels during the reference contractions and computer tasks in both patient groups compared to healthy controls, and lower RRT levels at the non-dominant side during stress. Both patient groups also showed larger variability in RMS and RRT values. This variability has more often been reported in literature and may suggest the existence of subgroups of pain patients with corresponding different muscle activation patterns not related to aetiology. Future research may focus on identifying these subgroups of patients with neck-shoulder pain.

Trapezius muscle rest time during standardised computer work – A comparison of female computer users with and without self-reported neck/shoulder complaints

Work related musculoskeletal disorders (WMSDs) in the shoulder/neck area are a common and increasing problem among European computer workers, especially women. Long-term low-level workloads with low degree of muscle rest are a potential risk factor for developing WMSDs. The purpose of the present study of female computer users (age 45–65 years) in Denmark and Sweden was to investigate if subjects with self-reported neck/shoulder complaints (cases, N = 35) show less trapezius muscle relative rest time (RRT) than controls ( N = 44) when performing standardised short-term computer work tasks in controlled laboratory conditions. Surface electromyography (EMG) signals were recorded bilaterally from the upper trapezius muscles during a type, edit, precision and colour word stress task. Besides RRT, 10th percentile RMS values were calculated. On the average, 15 of the cases and 18 of the controls showed analysable EMG files per task. For the colour word stress task, the results showed lower RRT values and higher 10th percentile RMS amplitude levels among cases compared to controls. No such signs could be found for the other tasks performed. The present results indicate an increased motor response to a psychological stressor among subjects with self-reported neck/shoulder complaints.

Are changes in pain induced by myofeedback training related to changes in muscle activation patterns in patients with work-related myalgia?

The objective of this explorative study was to investigate to what extent changes in perceived pain, induced by myofeedback training, are correlated to changes in muscle activation patterns. Thirty subjects with work-related myalgia received myofeedback training. Before (T(0)), directly after (T(1)) and 4 weeks or, in a subset of patients, 3 months after (T(2)) this training, surface electromyography (sEMG) measurements of the upper trapezius muscle were performed during standardized computer tasks; a typing and a stress task. Besides this, visual analogue scales (VAS) were filled in to assess the levels of pain in the neck and shoulders. From the sEMG, root mean square (RMS) and relative rest time (RRT, i.e. the percentage of time RMS is below a certain threshold) were used for data analysis. The relationships between RRT, RMS and VAS at T(0) as well as for the changes between T(1)-T(0) and T(2)-T(0) were investigated using Spearman correlation coefficients. The results revealed no significant correlations between VAS and RMS both at baseline (range R = -0.22 to 0.17) and for the observed changes (range R = -0.33 to 0.32). Also, for VAS and RRT, low correlations were found for baseline (range R = -0.27 to 0.21) and for changes between T(1)-T(0) (range R = -0.02 to 0.38). However, for the changes between T(2)-T(0), correlation coefficients for the VAS for the shoulder and the RRT of the right trapezius during both the typing and stress tasks were significant at the P = 0.05 level, whereas the correlation coefficients for the VAS for the neck and both the left and right trapezii during the stress task approached significance (P = 0.05 and P = 0.1, respectively). These results suggest that decreases in pain observed at long term follow up after myofeedback training might occur as a result of an increased ability to relax but not as a result of decreased muscle activation level. However, the largest correlation found was 0.6. This means that the maximal explained variance (R (2)) is low (36%), and that there are also other processes than the changes in muscle activation that contribute to changes in perceived pain.

Effects of electrode dislocation on electromyographic activity and relative rest time: effectiveness of compensation by a normalisation procedure.

Myofeedback seems a promising technique to treat myalgia related to computer work. A garment with embedded electrodes allows independent use by the subject. However, this inevitably results in electrode dislocations that can cause such variability in the electromyogram (EMG) parameters that the treatment fails. The objective was to investigate the variability introduced by electrode displacement on EMG root mean square (RMS) and relative rest time (RRT) and the effect of a normalisation procedure using a reference contraction to compensate for this. Dislocation was simulated using simultaneous recordings of pairs of electrodes situated 15mm apart on the trapezius muscle, surrounding a central electrode pair at the standard position. To assess sensitivity for electrode displacement, intra-subject variability was used. To assess the effects of normalisation, both intra and inter-subject variability were used. Results indicated a large sensitivity of RMS to electrode displacements, with no differences between typing (42%) and the reference task (43%). No systematic changes were found relative to a specific electrode dislocation. Normalisation of RMS resulted in a decrease in the sensitivity for electrode displacement (33%), but did not decrease inter-subject variability (27%). The median value of the intra-subject variability of RRT, using a fixed threshold, was 4.9%, whereas the normalised threshold did not decrease the intra-subject variability (7%). The results suggest that RRT is suitable for individual follow-up measurements and applications such as myofeedback, without the need for a normalisation procedure. The use of RMS requires considerably more care, owing to its large sensitivity to electrode displacement and lack of substantial effects of normalisation.