Paraspinal muscle EMG fatigue testing with two methods in healthy volunteers. Reliability in the context of clinical applications

Paraspinal strength and electromyographic fatigue in patients with sub-acute back pain and controls: Reliability, clinical applicability and between-group differences

BACKGROUND

Paraspinal muscle strength and fatigue are considered important in low back pain (LBP) prevention and rehabilitation. High reliability of paraspinal strength and electromyographic (EMG)-fatigue parameters has not been universally reported. Moreover, the discriminative validity of these parameters requires further exploration, under the threat of potentially poor reliability of the methods examined.

AIM

To investigate the reliability and discriminative validity of paraspinal strength and EMG-related fatigue in subjects with recurrent LBP and healthy participants.

METHODS

Test-retest measurements were performed in 26 healthy and 66 LBP volunteers, for reliability. Paraspinal isometric maximal and mean strength were determined with a maximum voluntary isometric contraction (MVIC) protocol, performed in a custom-made device. For the fatigue test, participants performed a 60% MIVC level continuous isometric contraction of the paraspinals, in conjunction with EMG analysis from 4 muscle sites of the lumbar spine. Initial median frequency (IMF), the median frequency slope (MFslope), as well as the root mean square (RMS) slope EMG parameters were used as fatigue measures. Data were analysed with repeated measures ANOVA for test-retest differences. For reliability, the intraclass correlation coefficient (ICC_3,1), standard error of the measurement (SEM) and the smallest detectable difference (SDD) were reported. Group-related differences for fatigue measures were analysed with a Multivariate Analysis of Covariance, with age, weight and strength as covariates.

RESULTS

Isometric strength presented statistically significant between-day differences (P < 0.01), however these did not exceed 10% (healthy: 7.2%/LBP-patients: 9.7%) and ICC reliability values were excellent, yet test-retest error was increased for the patient group (healthy: ICC_3,1: 0.92-0.96, SEM: 5.72-5.94 Hz, SDD: 18.51%-18.57%/LBP-patients: ICC_3,1: 0.91-0.96, SEM: 6.49-6.96, SDD: 30.75%-31.61%). For the frequency data, IMF reliability was excellent (healthy: ICC_3,1: 0.91-0.94, SEM: 3.45-7.27 Hz, SDD: 9.56%-20.14%/patients: ICC_3,1: 0.90-0.94, SEM: 6.41-7.59 Hz, SDD: 17.75%-21.02%) and of MF raw and normalised slopes was good (healthy: ICC_3,1: 0.78-0.82, SEM: 4.93-6.02 Hz, SDD: 13.66-16.67%/LBP-patients: ICC_3,1: 0.83-0.85, SEM: 6.75-7.47 Hz, SDD: 18.69%-20.69%). However, the reliability for RMS data presented unacceptably high SDD values and were not considered further. For discriminative validity, less MVIC and less steep MFslopes were registered for the patient group (P < 0.01).

CONCLUSION

Reliability and discriminative ability of paraspinal strength and EMG-related frequency parameters were demonstrated in healthy participants and patients with LBP.

The influence of Kinesio Taping on muscle fatigue in individuals with low back pain: A randomised controlled trial

OBJECTIVE

To evaluate the effect of different taping techniques on back muscle fatigue in people with low back pain.

METHODS

Sixty women with chronic non-specific low back pain were randomly assigned to four groups of 15 participants each: control (CG), Kinesio Taping (KT) with tension (KTT), KT no tension (KTNT) and Micropore® (MP), which were applied over the erector spinae muscles. The median frequency (MF) fatigue slopes of the longissimus muscle and sustained contraction time during a trunk fatigue test (Ito test), and pain using the numerical pain rating scale (NPRS) were collected at three time points: pre-treatment, three and ten days after intervention at a university laboratory.

RESULTS

Significant differences were seen in the MF slopes between groups (p= 0.01, η2= 0.20), with the KTT showing a mean difference (MD = 0.31, p= 0.04) and KTNT (MD = 0.28, p= 0.04) compared with CG. Significant reductions in NPRS were seen between time points (p< 0.001, η2= 0.28), with a reduction between pre and 3 days (MD = 1.87, p< 0.001), and pre and 10 days (MD = 1.38, p< 0.001), with KTT and KTNT both showing clinically important changes.

CONCLUSION

KT, with or without tension, has a tendency to reduce back muscle fatigue and reduce pain in individuals with chronic non-specific low back pain.

A study on the paraspinal muscle surface electromyography in acute nonspecific lower back pain

Aim of this study was to determine if surface electromyography (sEMG) could provide objective data in monitoring the alteration of signal amplitude of myoelectric activity of the paraspinal muscles in the patients with acute nonspecific lower back pain (ANLBP), and to explore the correlation between sEMG data and symptom relief in the ANLBP patients before and after massage therapy.Forty-five ANLBP patients and 20 healthy subjects were enrolled into this study. Patients were given massage therapy for 1 week. The average electromyography (AEMG), visual analogue scale (VAS), and distance of finger to floor (DFTF) were measured before and after treatment.AEMG at flexion and maintained flexion positions were significantly higher in the ANLBP group compared to that in the control group. At extension position, in contrast, AEMG was significantly lower in the ANLBP patients than that of control group, and there was no significant difference between the 2 groups at upright position. After massage therapy for the ANLBP patients, AEMG was significantly reduced at flexion and maintained flexion positions, but significantly increased at extension position than that before treatment. VAS and DFTF were also significantly reduced after treatment. In addition, AEMG alteration at maintained flexion position was significantly correlated with improvement of VAS or DFTF.Myoelectric activity of the paraspinal muscles in the ANLBP patients was different from that of healthy subjects. Massage therapy not only relived patients' symptoms, but also normalized myoelectric activity of the paraspinal muscles in the ANLBP patients.

Insertion and Presence of Fine-Wire Intramuscular Electrodes to the Lumbar Paraspinal Muscles Do Not Affect Muscle Performance and Activation During High-Exertion Spinal Extension Activities

BACKGROUND

Low back pain (LBP) is commonly associated with paraspinal muscle dysfunctions. A method to study deep lumbar paraspinal (ie, multifidus) muscle function and neuromuscular activation pattern is intramuscular electromyography (EMG). Previous studies have shown that the procedure does not significantly impact muscle function during activities involving low-level muscle contractions. However, it is currently unknown how muscular function and activation are affected during high-exertion contractions.

OBJECTIVE

To examine the effects of insertion and presence of fine-wire EMG electrodes in the lumbar multifidus on muscle strength, endurance, and activation profiles during high-exertion spinal extension muscle contractions.

DESIGN

Single-blinded, repeated measures intervention trial.

SETTING

University clinical research laboratory PARTICIPANTS: Twenty individuals between the ages of 18-40 free of recent and current back pain.

METHODS

Muscle performance was assessed during 3 conditions (with [WI] and without [WO] presence of intramuscular electrodes, and insertion followed by removal [IO]). Isometric spinal extension strength was assessed with a motorized dynamometer. Muscle endurance was assessed using the Sorensen test with neuromuscular activation profiles analyzed during the endurance test.

MAIN OUTCOME MEASUREMENTS

Spinal extensor muscle strength, endurance, and activation.

RESULTS

Our data showed no significant difference in isometric strength (P = .20) between the 3 conditions. A significant difference in muscle endurance was found (P = .03). Post hoc analysis showed that the muscle endurance in the IO condition was significantly higher than the WO condition (161.3 ± 58.3 versus 142.1 ± 48.2 seconds, P = .04), likely due to a learning effect. All 3 conditions elicited minimal pain (range 0-4/10) and comparable muscle activation profiles.

CONCLUSION

Our findings suggested the sonographically guided insertion and presence of fine-wire intramuscular EMG electrodes in the lumbar multifidus muscles had no significant impact on spinal extension muscle function. This study provides evidence that implementing intramuscular EMG does not affect muscle performance during high-exertion contractions in individuals with no current back pain.

LEVEL OF EVIDENCE

II.

Comparison of Thoracic and Lumbar Erector Spinae Muscle Activation Before and After a Golf Practice Session

Lower back pain is commonly associated with golfers. The study aimed: to determine whether thoracic- and lumbar-erector-spinae muscle display signs of muscular fatigue after completing a golf practice session, and to examine the effect of the completed practice session on club head speed, ball speed and absolute carry distance performance variables. Fourteen right-handed male golfers participated in the laboratory-based-study. Surface electromyography (EMG) data was collected from the lead and trail sides of the thoracic- and lumbar-erector-spinae muscle. Normalized root mean squared (RMS) EMG activation levels and performance variables for the golf swings were compared before and after the session. Fatigue was assessed using median frequency (MDF) and RMS during the maximum voluntary contraction (MVC) performed before and after the session. No significant differences were observed in RMS thoracic- and lumbar-erector-spinae muscle activation levels during the five phases of the golf swing and performance variables before and after the session (p > .05). Significant changes were displayed in MDF and RMS when comparing the MVC performed before and after the session (p < .05). Fatigue was evident in the trail side of the erector-spinae muscle after the session.

Evaluating the Training Effects of Two Swallowing Rehabilitation Therapies Using Surface Electromyography--Chin Tuck Against Resistance (CTAR) Exercise and the Shaker Exercise

In this study, the efficacy of two dysphagia interventions, the Chin Tuck against Resistance (CTAR) and Shaker exercises, were evaluated based on two principles in exercise science-muscle-specificity and training intensity. Both exercises were developed to strengthen the suprahyoid muscles, whose contractions facilitate the opening of the upper esophageal sphincter, thereby improving bolus transfer. Thirty-nine healthy adults performed two trials of both exercises in counter-balanced order. Surface electromyography (sEMG) recordings were simultaneously collected from suprahyoid muscle group and sternocleidomastoid muscle during the exercises. Converging results using sEMG amplitude analyses suggested that the CTAR was more specific in targeting the suprahyoid muscles than the Shaker exercise. Fatigue analyses on sEMG signals further indicated that the suprahyoid muscle group were equally or significantly fatigued (depending on metric), when participants carried out CTAR compared to the Shaker exercise. Importantly, unlike during Shaker exercise, the sternocleidomastoid muscles were significantly less activated and fatigued during CTAR. Lowering the chin against resistance is therefore sufficiently specific and intense to fatigue the suprahyoid muscles.

Electromyographic analysis of the vertebral extensor muscles during the Biering-Sorensen Test

The purpose of the study was to analyze the electromyographic signal of the multifidus, longissimus thoracis and the lumbar iliocostalis muscles during the Biering-Sorensen test in subjects without lower back pain. Twenty volunteers performed the test on three separate occasions. An analysis of variance detected a difference between the three test times (p = 0.0026). For the frequency domain, it was observed that there were differences between the multifidus and the lumbar erectors muscles; longissimus and iliocostalis muscles. However, in the time domain analysis, no difference was observed. As the values of the slope coefficients of median frequencies were higher for the multifidus muscle, compared to the longissimus and lumbar iliocostalis muscles, this may indicate a higher tendency toward muscle fatigue. Therefore, considering the applied methodology, the study of electromyographic signals in the frequency domain should be considered as an instrument to assess fatigue of the spinal extensor muscles in clinical situations.

A subject-independent method for automatically grading electromyographic features during a fatiguing contraction

Many studies have attempted to monitor fatigue from electromyogram (EMG) signals. However, fatigue affects EMG in a subject-specific manner. We present here a subject-independent framework for monitoring the changes in EMG features that accompany muscle fatigue based on principal component analysis and factor analysis. The proposed framework is based on several time- and frequency-domain features, unlike most of the existing work, which is based on two to three features. Results show that latent factors obtained from factor analysis on these features provide a robust and unified framework. This framework learns a model from EMG signals of multiple subjects, that form a reference group, and monitors the changes in EMG features during a sustained submaximal contraction on a test subject on a scale from zero to one. The framework was tested on EMG signals collected from 12 muscles of eight healthy subjects. The distribution of factor scores of the test subject, when mapped onto the framework was similar for both the subject-specific and subject-independent cases.

The relationship between psychological factors and performance on the Biering-Sørensen back muscle endurance test

BACKGROUND CONTEXT

Many studies report an association between low back pain (LBP) and reduced back muscle endurance and consider this to indicate muscular dysfunction. However, few have investigated the potentially confounding influence of psychological factors on performance during such endurance tests.

PURPOSE

This study examined whether psychological factors were associated with "underperformance" on the Biering-Sørensen (BS) test (ie, not performing as well as one is physiologically capable of).

STUDY DESIGN/SETTING

Cross-sectional study of the baseline data of patients with chronic (>3 months) nonspecific LBP (cLBP) before participation in a clinical trial of exercise therapy.

PATIENT SAMPLE

One hundred forty-eight patients with cLBP (43% men; age, 45±10 years).

OUTCOME MEASURES

The time for which the modified BS isometric endurance test could be performed to exhaustion minus the time that would have been predicted based on the rate of decline in median frequency of the surface electromyographic (EMG) signal recorded bilaterally from the erector spinae at L3 and L5.

METHODS

Back pain and disability, psychological disturbance, catastrophizing, fear-avoidance beliefs, back beliefs, and exercise self-efficacy were measured using validated questionnaires. Patients performed the BS test to exhaustion while physiological muscle fatigability was measured from continuous surface EMG recordings.

RESULTS

Multivariable regression analysis controlling for gender revealed that greater psychological disturbance (p=.003) and more negative back beliefs (p=.015) were unique predictors of the extent of "underperformance," accounting for 22.3% variance in expected endurance time minus actual time.

CONCLUSIONS

It is important that the underlying nature (psychological or physiological) of performance deficits be identified during such tests because this may influence the interpretation of prospective studies reporting risk factors for LBP and dictate the particular treatment or interventional approach required to remedy the situation in individuals with LBP.

Test-retest reliability of step counts with the ActivPAL™ device in common daily activities

The ActivPAL device is a well-established physical activity monitor for assessment of physical activity.

AIM

To investigate test-retest reliability of step counts and establish minimal detectable changes (MDC) in step count to account for intra device error over time in various physical activities.

METHODS

Healthy participants (n=24, age range, 19-28 years) performed activities on two occasions, 1 week apart, in a laboratory setting; self-paced floor walking, treadmill walking at three different speeds (3.2 km/h, 4.5 km/h and 4.5 km/h with incline), treadmill jogging (8.0 km/h), stair walking and cycling on an exercise bike at three speeds (45 rpm, 60 rpm and 75 rpm). Relative reliability was calculated using intraclass correlation coefficient (ICC) and Spearman correlation. Absolute reliability was assessed using standard error of measurement (SEM) and coefficient of repeatability (CR).

RESULTS

The ActivPAL showed high to very high relative reliability for treadmill walking at all speeds and stair walking, while self-paced normal floor walking showed moderate reliability. The absolute reliability was the best for treadmill walking activities, slightly increased for self-paced walking, followed by stair walking and jogging. The use of activity monitors during cycling has been questioned and our results confirm a low absolute and relative reliability. MDC values varied according to the type of activity e.g. treadmill walking 4.5 km/h (10 steps), walking on the floor (45 steps). Data loss in this study (10-13%) was higher than previously reported.

CONCLUSIONS

The ActivPAL is reliable for treadmill walking, jogging and self-paced walking. MCD varies according to the activity and should be considered when establishing true change over time.

Influence of back muscle fatigue on lumbar reflex adaptation during sudden external force perturbations

There is still conflicting evidence about the influence of fatigue on trunk reflex activity. The aim of this study was to measure response latency and amplitude changes of lumbar and abdominal muscles after heavy external force perturbation applied to the trunk in the sagittal plane before and after back muscle fatigue, in expected and unexpected conditions. Ten healthy subjects in a semi-seated position, torso upright in a specific apparatus performed an intermittent back muscle fatigue protocol. EMG reflex activity of erector spinae (ES) and external oblique muscles were recorded in unexpected and in expected (self pre-activation) conditions. After fatigue, the normalized reflex amplitude of ES increased in expected and unexpected conditions (P<0.05) while ES response latency was slightly decreased. Reflexes latencies for ES were systematically shorter (P<0.05) of 25% in expected compared to unexpected conditions. These findings suggest that a large external force perturbation would elicit higher paraspinal magnitude responses and possible earlier activation in order to compensate the loss of muscular force after fatigue. Because of the seated position the postural adjustments were probably not triggered and thus explain the lack of abdominal activation. The self-anticipated pre-activation in order to counteract perturbations was not affected by fatigue illustrating the natural muscular activation to maintain trunk stability.

The reliability of surface electromyography to assess quadriceps fatigue during multi joint tasks in healthy and painful knees

This study's aim was to determine the between days reliability of surface EMG recordings from the superficial quadriceps during a multi joint sub-maximal fatiguing protocol. Three subject groups (healthy n=29; patellofemoral pain syndrome n=74; knee osteoarthritis n=55) performed the task at 60 maximum voluntary isometric contraction on three separate days. Spectral and amplitude EMG parameters were recorded from vastus medialis oblique, vastus lateralis and rectus femoris and were analysed for between days reliability using intraclass correlation coefficient (ICC((2,1))), the standard errors of measure and smallest detectable differences. For frequency results, initial and final frequency values had 'good' or 'excellent' reliability in all groups for all muscles. ICCs for median frequency slopes for vastus medialis oblique, vastus lateralis, and rectus femoris respectively, in the osteoarthritis group were 0.04, 0.55, and 0.72; in the patellofemoral pain group were 0.41, 0.17, and 0.33; in the healthy group were 0.68, 0.64, and 0.31. The standard errors of measurement and smallest detectable differences for all groups and for all muscles were unacceptably high. For amplitude results, ICC root mean squared initial and final values were 'good' to 'excellent' for all groups and all muscles, albeit with high measurement error. The ICCs for root mean squared slopes in all tests were 'poor' with extremely high measurement error. The poor between days reliability and high measurement error suggests that surface EMG should not be adopted to assess fatigue during multi joint sub-maximal isometric quadriceps testing.

Back and hip extensor muscles fatigue in healthy subjects: task-dependency effect of two variants of the Sorensen test

Paraspinal muscle fatigability during various trunk extension tests has been widely investigated by electromyography (EMG), and its task-dependency is established recently. Hip extensor muscle fatigability during the Sorensen test has been reported. The aim of the present experiments was to evaluate the task-dependency of back and hip extensor muscle fatigue during two variants of the Sorensen test. We hypothesized that the rate of muscular fatigue of the hip and back extensor muscles varies according to the test position. Twenty healthy young males with no history of low back pain volunteered to participate in this cross-sectional study. They were asked to perform two body weight-dependent isometric back extension tests (S1 = Sorensen test; S2 = modified Sorensen on a 45 degrees Roman chair). Surface EMG activity of the paraspinal muscles (T10 and L5 levels) and hip extensor muscles (gluteus maximus; biceps femoris) was recorded, and muscular fatigue was assessed through power spectral analysis of the EMG data by calculating the rate of median power frequency change. We observed hip extensor muscle fatigue simultaneously with paraspinal muscle fatigue during both Sorensen variants. However, only L5 level EMG fatigue indices showed a task-dependency effect between S1 and S2. Hip extensor muscles appear to contribute to load sharing of the upper body mass during both Sorensen variants, but to a different extent because L5 level fatigue differs between the Sorensen variants. Our findings suggest that task-dependency has to be considered when EMG variables are compared between two types of lumbar muscle-fatiguing tasks.

Changes in the flexion relaxation response induced by lumbar muscle fatigue

BACKGROUND

The flexion relaxation phenomenon (FRP) is an interesting model to study the modulation of lumbar stability. Previous investigations have explored the effect of load, angular velocity and posture on this particular response. However, the influence of muscular fatigue on FRP parameters has not been thoroughly examined. The objective of the study is to identify the effect of erector spinae (ES) muscle fatigue and spine loading on myoelectric silence onset and cessation in healthy individuals during a flexion-extension task.

METHODS

Twenty healthy subjects participated in this study and performed blocks of 3 complete trunk flexions under 4 different experimental conditions: no fatigue/no load (1), no fatigue/load (2), fatigue/no load(3), and fatigue/load (4). Fatigue was induced according to the Sorenson protocol, and electromyographic (EMG) power spectral analysis confirmed that muscular fatigue was adequate in each subject. Trunk and pelvis angles and surface EMG of the ES L2 and L5 were recorded during a flexion-extension task. Trunk flexion angle corresponding to the onset and cessation of myoelectric silence was then compared across the different experimental conditions using 2 x 2 repeated-measures ANOVA.

RESULTS

Onset of myoelectric silence during the flexion motion appeared earlier after the fatigue task. Additionally, the cessation of myoelectric silence was observed later during the extension after the fatigue task. Statistical analysis also yielded a main effect of load, indicating a persistence of ES myoelectric activity in flexion during the load condition.

CONCLUSION

The results of this study suggest that the presence of fatigue of the ES muscles modifies the FRP. Superficial back muscle fatigue seems to induce a shift in load-sharing towards passive stabilizing structures. The loss of muscle contribution together with or without laxity in the viscoelastic tissues may have a substantial impact on post fatigue stability.

Task dependency in back muscle fatigue--correlations between two test methods

BACKGROUND

Various test methods which engage the back muscles in different tasks have been used in studies of back muscle fatigue with electromyography. The present objective was to study task dependency in lumbar muscle fatigue by comparing two test methods.

METHODS

In this cross-sectional study, 22 healthy subjects performed a seated (45s) and a prone test (to the limit of endurance) of back muscle fatigue in randomised order. Fatigue of the lumbar muscles was assessed using electromyography spectral variables and ratings of back muscle fatigue (Borg scale). Linear regression of the median frequency during contraction, and conventional statistical tests of group differences and correlations were used.

FINDINGS

Significant differences (P<0.001) between the seated and the prone test were found for the initial median frequency, the slope, the median frequency decrease during the whole contraction, and for the ratings. However, correlation coefficients between the seated and the prone test were low for the median frequency decrease (r=0.42), absent for the slopes of median frequency (r=-0.08), higher for the Borg ratings (r(s)=0.51; P<0.05) and highest for the initial median frequency (r=0.69; P<0.05). Within each test, correlations between the Borg ratings and the electromyography variables were essentially absent (r<0.19).

INTERPRETATION

Electromyography variables assessed in one type of task in a fatiguing test may not be valid for other types of fatiguing tasks, for example in daily life work situations. Thus task dependency has to be considered when using surface electromyography in determining lumbar muscle fatigue. Ratings of fatigue, however, seem to be less task dependent than the electromyography variables.

Spinal muscle evaluation using the Sorensen test: a critical appraisal of the literature

The first test for evaluating the isometric endurance of trunk extensor muscles was described by Hansen in 1964. In 1984, following a study by Biering-Sorensen, this test became known as the "Sorensen test" and gained considerable popularity as a tool reported to predict low back pain within the next year in males. The test consists in measuring the amount of time a person can hold the unsupported upper body in a horizontal prone position with the lower body fixed to the examining table. This test has been used in many studies, either in its original version or as variants. Although its discriminative validity, reproducibility, and safety seem good, debate continues to surround its ability to predict low back pain; in addition, the gender-related difference in position-holding time remains unexplained and the influence of body weight unclear. A contribution of the hip extensor muscles to position holding has been established, but its magnitude remains unknown. The influence of personal factors such as motivation complicates the interpretation of the results. Despite these drawbacks, the Sorensen test has become the tool of reference for evaluating muscle performance in patients with low back pain, most notably before and after rehabilitation programs.

Establishment of a protocol to test fatigue of the trunk muscles

BACKGROUND

Muscle fatigue has high relevance in human performance yet little research has evaluated how it should be assessed.

OBJECTIVE

To perform a pilot study to identify suitable methods of generating and assessing fatigue of the trunk flexor and extensor muscles.

METHODS

Sixteen university rugby players (mean (SEM) age 21.9 (0.2) years) were recruited and subjected to four protocols (A, B, C, D), separated by a week to allow recovery, with peak torque being recorded during each test: A, isokinetic measurements before and after fatigue, with a 10 repetition isokinetic fatigue period; B, isokinetic measurements before and after fatigue with a 45 second isometric fatigue period; C, isometric measurements before and after fatigue with a 10 repetition isokinetic fatigue period; D, isometric measurements before and after fatigue with a 45 second isometric fatigue period. All were conducted during flexion and extension of the trunk on the Cybex Norm Isokinetic Dynamometer trunk flexion-extension unit.

RESULTS

All subjects completed all four protocols. Fatigue induction appeared more effective in flexion than extension. Significant differences in mean peak torque before and after fatigue were seen in protocols A, B, and D in flexion and only in protocol D for extension. In flexion, protocol D produced the greatest fatigue, peak torque being 16.2% less after than before fatigue, suggesting greatest sensitivity.

CONCLUSIONS

Protocol D, which incorporates isometric testing and fatigue protocols, appears to be able to produce fatigue most effectively, and therefore may provide the most valid assessment of fatigue in the trunk flexor and extensor muscles.

Issues in relation to the repeatability of and correlation between EMG and Borg scale assessments of neck muscle fatigue

INTRODUCTION

The repeatability of subjective and objective assessments of neck muscle fatigue is very important with regard to the clinical applicability of these methods.

METHOD

To establish between-days reliability, 33 healthy volunteers performed a 60% maximum voluntary isometric contraction test from a standing position in all neck movements. Cervical muscle fatigue was assessed on three separate occasions from the spectral (median frequency, MF) and amplitude (root mean square, RMS) analysis of the electromyogram (EMG) signal recorded from the cervical paraspinal group, splenius capitis, levator scapulae and sternocleidomastoid. Subjective assessment of fatigue was rated by employing the Borg scale. Intraclass correlation coefficient ICC((1,1)), standard error of measurement (SEM), smallest detectable difference (SDD) indices and Pearson's correlation co-efficient were calculated for the analysis of the results.

RESULTS

Normalised median frequency (MF) slope had low repeatability and large between-day error (ICC((1,1))=0.28-0.61; SEM=0.33-0.60%/s; SDD=132.7-703.2%) for the protagonist muscles of each movement. Initial median frequency (IMF) had moderate to good reliability and small error (ICC((1,1))=0.64-0.81; SEM=2.8-8.8Hz; SDD=19.9-38.5%). The RMS slope yielded also poor repeatability. The Borg assessment was more reliable than the EMG estimate though variability between sessions was still quite high (SDD=29.2-136.5%). No correlation was found between the EMG and Borg assessment of neck muscle fatigue (r=-0.01-0.39).

CONCLUSION

The protocol used for assessing neck muscle fatigue proved to be reliable only for the IMF but the clinical usefulness of this measure remains questionable. The lack of correlation between objective and subjective estimation of neck muscle fatigue was possibly a consequence of the poor measurement repeatability. Further research is needed to identify the factors responsible for these results on neck area.

Back extensor muscle fatigue in patients with lumbar disc herniation. Pre-operative and post-operative analysis of electromyography, endurance time and subjective factors

We investigated back muscle fatigue and endurance in patients with lumbar disc herniation before and after surgery, and established the degree of association between perceived fatigue and objectively measured fatigue. Additionally, the relationships between muscle fatigue and endurance time on the one hand, and activity, participation, self-efficacy and health on the other, were investigated to clarify the grades of association between these factors. Forty-three consecutive patients with lumbar disc herniation were tested before surgery and 4 weeks after surgery. The protocol comprised an isometric endurance test (modified Sørensen's test) with concomitant measures of electromyography, and Borg ratings of pain and fatigue. To measure activity, participation, self-efficacy and health, the patients also filled in questionnaires. Results showed a post-operatively significant improvement in lumbar muscle fatigue expressed as a flatter L5 slope for the men. No significant improvement was found for endurance times or for Borg ratings. Endurance time correlated with questionnaire answers on physical activity, the Roland-Morris, the Oswestry, self-efficacy and some items of the SF-36 with correlation coefficients ranging from 0.52 to 0.91. The L5 slope correlated with the Roland-Morris, the Oswestry and some items of the SF-36 only in women with correlation coefficients between 0.53 and 0.77. We conclude that the effects of surgery reduced muscle fatigue for the men. There is an association between muscle fatigue and endurance with activity limitations, participation restrictions, self-efficacy and health in patients undergoing surgery for lumbar disc herniation.

Supplementation of general endurance exercise with stabilisation training versus general exercise only. Physiological and functional outcomes of a randomised controlled trial of patients with recurrent low back pain

BACKGROUND

Determination of the mode of action of new exercise techniques in different back pain populations is lacking. The effectiveness of supplementing an exercise programme with stabilisation exercises concerning physiological and functional parameters in non-specific back pain patients is unknown.

METHODS

Randomised controlled trial, comparing a general trunk muscle endurance exercise approach enhanced with specific muscle stabilisation exercises (S&G group) with a general exercise approach only (G group). 55 patients with recurrent back pain were randomised in S&G group (n=29) and G group (n=26). Both groups received an 8-week exercise intervention and written advice. Paraspinal muscle strength and electromyographic fatigue of the erector spinae and multifidus were measured. Additionally, 3 functional speed tests were assessed. Outcomes were collected pre- and post-intervention.

FINDINGS

No differences were detected for any of the paraspinal fatigue characteristics either within or between groups, apart from a significant decrease in normalised median frequency slope of the erector spinae for the G group. Paraspinal muscle strength and all functional tests have demonstrated significant within-group improvements for both groups, without any between-group differences.

INTERPRETATION

An 8-week stabilisation exercise-enhanced approach presented equal benefits to a general endurance-based exercise programme for patients with recurrent non-specific back pain. A slightly steeper slope for the erector spinae in the G group was the only electromyographic fatigue alteration noted. Concomitant strength improvement probably reflects neural input changes rather than histochemical muscle changes. Physical exercise alone and not the exercise type was the key determinant for improvement in this patient group.

Back muscle strength and fatigue in healthy and chronic low back pain subjects: A comparative study of 3 assessment protocols

OBJECTIVE

To compare the sensitivity of 3 different back test protocols in measuring differences in strength and fatigue between subjects with and without chronic low back pain (CLBP).

DESIGN

Descriptive study using a repeated-measures design.

SETTING

A research laboratory within a rehabilitation center.

PARTICIPANTS

Eighteen healthy subjects and 13 subjects with CLBP were assessed in a single session to compare the 3 protocols. The protocols were an upright position test (UPP), a semicrouched lifting test (LIF), and the Sorensen fatigue test.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Moments of force and surface electromyography were recorded bilaterally from 4 homologous back muscles while the subjects performed static trunk extension efforts for each protocol. Fatigue was quantified by the slopes of the linear regression of electromyography time-series.

RESULTS

The back muscle fatigue and strength scores did not differ significantly for the 2 subject groups for any of the 3 protocols. The electromyography fatigue indices revealed that the Sorensen fatigue test and UPP produced more fatigue in the back muscles than the LIF.

CONCLUSIONS

It was impossible to specify which protocol is more sensitive to low back status because no between-group difference was observed for any of the 3 tests.

Intra-rater reliability of electromyographic recordings and subjective evaluation of neck muscle fatigue among helicopter pilots

The aim was to evaluate the reliability of a method of measuring neck muscle fatigue among helicopter pilots.

METHOD

Surface EMG from three areas in the neck region, bilaterally, was recorded among 10 male helicopter pilots while they were performing isometric contractions in flexion and extension for 45 s, sustaining a force representing 75% of maximum strength in a seated position. Perceived fatigue was rated using the Borg CR-10 scale. The test was repeated twice the first day and then two additional times with one-week intervals. Variables analyzed were the slope of the median frequency change, the normalized slope, and the ratings after 15, 30 and 45 s; and also the initial median frequency (IMDF). The intra-class correlation (ICC) and the measurement error (S(w)), intra- and inter-day were calculated statistically.

RESULTS

The best reliability for the slope was found for the 45 s intra-day analysis taking all measurements into account (ICC 0.65-0.83). The reliability after 30 s was poorer but still acceptable (ICC 0.52-0.71). For the subjective ratings, the highest reliability was found after 30 s inter-day (ICC 0.86-0.88). IMDF showed generally high reliability for the intra-day analyses (ICC 0.63-0.80).

CONCLUSION

The method is reliable for use in further research. Since performing a contraction of 75% of maximum was quite strenuous, we recommend that the protocol be shortened to 30 s.

Effects of neck extensor muscles fatigue on balance

OBJECTIVE

Measure the effects of cervical extensor muscle isometric contraction on cervical surface electromyographic spectral shift and balance in healthy subjects.

DESIGN

Experimental within-subject design.

BACKGROUND

Postural instability can be induced by mechanically stimulating cervical muscle spindles. Postural changes are also observed in individuals who suffer from chronic neck pain or whiplash injury. Furthermore these subjects appear to experience neck musculature fatigue more quickly, which in turn not only affects the neck function but also seems to affect the balance in a standing posture.

METHODS

Using a force platform, balance was measured, in 10 blindfolded college students before and after isometric voluntary contraction in neck extension at 5% and 25% maximum voluntary isometric contraction for a period of 5, 10 and 15 min. Paired posturographic data were analysed for differences. Control measurements were performed on the same subjects by measuring balance before and after subjects sitting quietly for 5, 10 and 15 min without performing isometric contraction.

RESULTS

The results indicate that a 25% maximal isometric contraction of the neck extensors for 10 and 15 min duration produced significant changes in some posturographic parameters in young healthy males. Furthermore, this contraction also produced a significant cervical muscle electromyography median frequency spectrum shift of the lower frequencies.

CONCLUSIONS

Balance was affected by 15 min of 25% maximal isometric contraction of the extensor cervical muscles. Posturographic parameters affected are similar to parameters observed in subjects that have suffered a whiplash injury.

RELEVANCE

This study contributes to our understanding of functional aspects of cervical muscle fatigue. The similarity of results with other studies performed on subjects suffering from chronic neck pain and from whiplash injuries may suggest a similar cause for loss of postural control. Ultimately, this may help us in developing objective evaluation procedures for subjects suffering from neck complaints.

Postural and trunk muscle response to sudden release during stoop lifting tasks before and after fatigue of the trunk erector muscles

The effect of fatigue on the muscular and postural response to sudden release of different stoop lifting loads was studied. Ten male volunteers performed a series of stoop lifting trials before and after fatigue of the erector spinae. Trials were performed using loads of 20, 40, 60, and 80 N, and sudden release of load was triggered randomly on one of the repetitions using an electromagnetic release. The onset of release was registered by an accelerometer, centre of pressure (COP) motion was recorded via a forceplate, and EMG activities of the latissimus dorsi (LD), erector spinae (ES), rectus abdominus (RA), external oblique (EO) and internal oblique (IO) muscles were recorded. A slightly reduced lifting speed was seen after fatigue, particularly at the higher loads, but this had little effect on the perturbing force at release, which was dominated by the release load. A significant effect of fatigue was seen on the antero-posterior COP motion, with the postural disturbance being decreased after fatigue. Fatigue resulted in a significant increase in ES (p = 0.029) and LD (p = 0.015) relaxation times and, while the response patterns (relaxation, contraction or no response) of the anterior trunk muscles (RA, EO, IO) were not always consistent, the proportion of response by relaxation was greater after fatigue. This resulted in a lower incidence but longer duration of co-contraction of the ES-RA, ES-EO and ES-EO muscle groups following fatigue, such that the mean co-contraction duration of these groups showed no significant differences before and after fatigue. The response to sudden release is a balance between maintaining postural stability and at the same time preventing the trunk musculature from overloading the spine and risking tissue injury. While fatigue of the trunk extensors does not appear to increase either the risk of fall or stumble or the incidence of co-contraction following sudden release of stoop lifting tasks, the duration of co-contraction appears to increase following fatigue. Further study is required to quantify the loading on the spine during sudden release of different lifting tasks before and after more realistic fatigue conditions.

Chronic low back pain-associated paraspinal muscle dysfunction is not the result of a constitutionally determined "adverse" fiber-type composition

STUDY DESIGN

Investigative case control study.

OBJECTIVES

To determine whether excessive paraspinal muscle fatigue in chronic low back pain results from a paucity of muscle type I fiber content.

SUMMARY OF BACKGROUND DATA

Paraspinal muscle function is vital for spinal protection. Prospective studies suggest that excessive paraspinal muscle fatigability may increase risk of first-time low back pain. As contractile performance of the paraspinal muscles is governed by their constitutionally determined fiber composition, the question arises whether a constitutionally determined "adverse" composition could predispose to low back pain through impaired spinal protection.

METHODS

Thirty-five male patients with chronic low back pain were compared with 32 male control patients of similar age and anthropometry. During Sorensen and 60% of maximum voluntary isometric contraction fatigue tests, median frequency declines in the paraspinal muscle surface electromyograph signal were monitored and correlated with muscle histomorphometry.

RESULTS

Patients were weaker than controls during maximum voluntary isometric contractions (84.47 [28.44]vs. 98.74 [18.11] kg, respectively; P = 0.02) and more fatigable during their Sorensen tests (endurance time 105.29 [28.53]vs. 137.50 [40.38] sec, respectively; P < 0.01). There were no between-group differences in median frequency declines during the Sorensen (-0.37 [0.16]vs. -0.36 [0.12]%.sec) or 60% maximum voluntary isometric contraction (-0.42 [0.31]vs. -0.51 [0.29]%.sec) tests, for patients and controls, respectively. There were no between-group differences in the percent number of paraspinal muscle type I fibers (64 [11]vs. 64 [9]%) or the percent area occupied by type I fibers (67 [11]vs. 69 [9]%), for patients and controls, respectively. Type I and II muscle fiber narrow diameters were similar for both groups.

CONCLUSION

In the patients with chronic low back pain tested, their associated paraspinal muscle dysfunction was not the result of a constitutionally determined "adverse" fiber type composition.

Reliability of electromyographic and torque measures during isometric axial rotation exertions of the trunk

OBJECTIVE

The aim of the present study was to investigate the between-days reliability of electromyographic (EMG) measurement of 6 bilateral trunk muscles and also the torque output in 3 planes during isometric right and left axial rotation at different exertion levels.

METHODS

Ten healthy subjects performed isometric right and left axial rotation at 100, 70, 50 and 30% maximum voluntary contractions in two testing sessions at least 7 days apart. EMG amplitude and frequency analyses of the recorded surface EMG signals were performed for rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were measured.

RESULTS

For both EMG amplitude and frequency values, good (intraclass correlation coefficient, ICC=0.75-0.89) to excellent (ICC>/=0.90) reliability was found in the 6 trunk muscles at different exertion levels during axial rotation. The reliability of both maximal isometric axial rotation torque and coupling torques in sagittal and coronal planes were found to be excellent (ICC>/=0.93).

CONCLUSIONS

Good to excellent reliability of EMG measures of trunk muscles and torque measurements during isometric axial rotation was demonstrated. This provides further confidence of using EMG and triaxial torque assessment as outcome measures in rehabilitation and in the evaluation of the human performance in the work place.