Temporal stability of paraspinal electromyographic recordings in low back pain and non-pain subjects

Time-varying surface electromyography topography as a prognostic tool for chronic low back pain rehabilitation

BACKGROUND CONTEXT

Nonsurgical rehabilitation therapy is a commonly used strategy to treat chronic low back pain (LBP). The selection of the most appropriate therapeutic options is still a big challenge in clinical practices. Surface electromyography (sEMG) topography has been proposed to be an objective assessment of LBP rehabilitation. The quantitative analysis of dynamic sEMG would provide an objective tool of prognosis for LBP rehabilitation.

PURPOSE

To evaluate the prognostic value of quantitative sEMG topographic analysis and to verify the accuracy of the performance of proposed time-varying topographic parameters for identifying the patients who have better response toward the rehabilitation program.

STUDY DESIGN

A retrospective study of consecutive patients.

PATIENT SAMPLE

Thirty-eight patients with chronic nonspecific LBP and 43 healthy subjects.

OUTCOME MEASURES

The accuracy of the time-varying quantitative sEMG topographic analysis for monitoring LBP rehabilitation progress was determined by calculating the corresponding receiver-operating characteristic (ROC) curves. Physiologic measure was the sEMG during lumbar flexion and extension.

METHODS

Patients who suffered from chronic nonspecific LBP without the history of back surgery and any medical conditions causing acute exacerbation of LBP during the clinical test were enlisted to perform the clinical test during the 12-week physiotherapy (PT) treatment. Low back pain patients were classified into two groups: "responding" and "nonresponding" based on the clinical assessment. The responding group referred to the LBP patients who began to recover after the PT treatment, whereas the nonresponding group referred to some LBP patients who did not recover or got worse after the treatment. The results of the time-varying analysis in the responding group were compared with those in the nonresponding group. In addition, the accuracy of the analysis was analyzed through ROC curves.

RESULTS

The time-varying analysis showed discrepancies in the root-mean-square difference (RMSD) parameters between the responding and nonresponding groups. The relative area (RA) and relative width (RW) of RMSD at flexion and extension in the responding group were significantly lower than those in the nonresponding group (p<.05). The areas under the ROC curve of RA and RW of RMSD at flexion and extension were greater than 0.7 and were statistically significant.

CONCLUSIONS

The quantitative time-varying analysis of sEMG topography showed significant difference between the healthy and LBP groups. The discrepancies in quantitative dynamic sEMG topography of LBP group from normal group, in terms of RA and RW of RMSD at flexion and extension, were able to identify those LBP subjects who would respond to a conservative rehabilitation program focused on functional restoration of lumbar muscle.

Creation of an asymmetrical gradient of back muscle activity and spinal stiffness during asymmetrical hip extension

BACKGROUND

Low back pain is often associated with increased spinal stiffness which thought to arise from increased muscle activity. Unfortunately, the association between paraspinal muscle activity and paraspinal stiffness, as well as the spatial distribution of this relation, is unknown. The purpose of this investigation was to employ new technological developments to determine the relation between spinal muscle contraction and spinal stiffness over a large region of the lumbar spine.

METHODS

Thirty-two male subjects performed graded isometric prone right hip extension at four different exertion levels (0%, 10%, 25% and 50% of the maximum voluntary contraction) to induce asymmetric back muscle activity. The corresponding stiffness and muscle activity over bilateral paraspinal lumbar regions was measured by indentation loading and topography surface electromyography, respectively. Paraspinal stiffness and muscle activity were then plotted and their correlation was determined.

FINDINGS

Data from this study demonstrated the existence of an asymmetrical gradient in muscle activation and paraspinal stiffness in the lumbar spine during isometric prone right hip extension. The magnitude and scale of the gradient increased with the contraction force. A positive correlation between paraspinal stiffness and paraspinal muscle activity existed irrespective of the hip extension effort (Pearson correlation coefficient, range 0.566-0.782 (P<0.001)).

INTERPRETATION

Our results demonstrate the creation of an asymmetrical gradient of muscle activity and paraspinal stiffness during right hip extension. Future studies will determine if alterations in this gradient may possess diagnostic or prognostic value for patients with low back pain.

A Meta-Analytic Review of Surface Electromyography Among Persons With Low Back Pain and Normal, Healthy Controls

Significant differences in surface electromyography (SEMG) have been reported between persons with low back pain (LBP) and normal, healthy controls. This manuscript presents a systematic meta-analytic review of studies examining SEMG differences between these groups. Forty-four articles were identified using MEDLINE and a review of reference lists in articles. For static SEMG, the largest effect size was observed for SEMG while standing, with subjects having LBP demonstrating higher SEMG. The effect size for flexion/relaxation measures was found to be very high (d = -1.71). Studies examining SEMG during isometric exercise or muscle recovery following exercise produced inconsistent findings. Sensitivity and specificity of SEMG for dynamic SEMG measures averaged 88.8% and 81.3%. Most classification schemes were statistically determined and utilized a combination of measures. Only one published study prospectively validated a classification scheme. SEMG measures of flexion-relaxation appear to distinguish LBP subjects from controls with good accuracy, and the sensitivity and specificity of SEMG can be increased by using multiple measures. Further research is needed to determine the combination of measures that are cost-effective, reliable, valid and discriminate with a high degree of accuracy between healthy persons and those with LBP.

PERSPECTIVE

SEMG is a simple and noninvasive measure of muscle activity. SEMG measures hold promise as an objective marker of LBP.

Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group--shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10 degrees/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity--specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.

Spine loading characteristics of patients with low back pain compared with asymptomatic individuals

STUDY DESIGN

Patients with low back pain and asymptomatic individuals were evaluated while performing controlled and free-dynamic lifting tasks in a laboratory setting.

OBJECTIVE

To evaluate how low back pain influences spine loading during lifting tasks.

SUMMARY OF BACKGROUND DATA

An important, yet unresolved, issue associated with low back pain is whether patients with low back pain experience spine loading that differs from that of individuals who are asymptomatic for low back pain. This is important to understand because excessive spine loading is suspected of accelerating disc degeneration in those whose spines are damaged already.

METHODS

In this study, 22 patients with low back pain and 22 asymptomatic individuals performed controlled and free-dynamic exertions. Trunk muscle activity, trunk kinematics, and trunk kinetics were used to evaluate three- dimensional spine loading using an electromyography- assisted model in conjunction with a new electromyographic calibration procedure.

RESULTS

Patients with low back pain experienced 26% greater spine compression and 75% greater lateral shear (normalized to moment) than the asymptomatic group during the controlled exertions. The increased spine loading resulted from muscle coactivation. When permitted to move freely, the patients with low back pain compensated kinematically in an attempt to minimize external moment exposure. Increased muscle coactivation and greater body mass resulted in significantly increased absolute spine loading for the patients with low back pain, especially when lifting from low vertical heights.

CONCLUSIONS

The findings suggest a significant mechanical spine loading cost is associated with low back pain resulting from trunk muscle coactivation. This loading is further exacerbated by the increases in body weight that often accompany low back pain. Patient weight control and proper workplace design can minimize the additional spine loading associated with low back pain.

A non-MVC EMG normalization technique for the trunk musculature: Part 2. Validation and use to predict spinal loads

Estimates of the amount of force exerted by a muscle using electromyography (EMG) rely partially upon the accuracy of the reference point used in the normalization technique. Accurate representations of muscle activities are essential for use in EMG-driven spinal loading models. The expected maximum contraction (EMC) normalization method was evaluated to explore whether it could be used to assess individuals who are not capable of performing a maximum exertion such as a person with a low back injury. Hence, this study evaluated the utility of an EMG normalization method (Marras and Davis, A non-MVC EMG normalization technique, Part 1, method development. Journal of Electromyography and Kinesiology 2000) that draws upon sub-maximal exertions to determine the reference points needed for normalization of the muscle activities. The EMC normalization technique was compared to traditional MVC-based EMG normalization by evaluating the spinal loads for 20 subjects (10 males and 10 females) performing dynamic lifts. The spinal loads (estimated via an EMG-assisted model) for the two normalization techniques were very similar with differences being <8%. The model performance variables indicated that both normalization techniques performed well (r(2)>0.9 and average error below 6%) with only the muscle gain being affected by normalization method as a result in different reference points. Based on these results, the proposed normalization technique was considered to be a viable method for EMG normalization and for use in EMG-assisted models. This technique should permit the quantitative evaluation of muscle activity for subjects unable to produce maximum exertions.

Reliability of psychophysiological responding as a function of trait anxiety

This study examined the temporal stability of three psychophysiological responses (frontal electromyographic activity, hand surface temperature, and heart rate) recorded over four sessions (days 1, 2, 8, and 28) on 34 subjects, 17 with high Spielberger Trait Anxiety Inventory scores and 17 with low scores. Each session consisted of a 20-minute adaptation period, a baseline condition, and two stressors (one cognitive, the other physical). Two forms of reliability coefficients were employed, intraclass correlations and Pearson Product Moment; the two types of reliability coefficients arrived at the same conclusions. Results indicated that reliability coefficients for the two anxiety groups did not differ on frontal EMG or heart rate responses; however, hand surface temperature responding was considerably less reliable for high anxious individuals than low anxious individuals. Reliability coefficients on absolute scores were, for the most part, reliable. Treating the responses as relative measures (percent change from baseline or simple change scores from baseline) produced smaller and less reliable coefficients. Magnitudes of the three physiological responses did not significantly differ as a function of high or low trait anxiety. Findings are discussed in terms of their clinical, as well as basic psychophysiological, importance.

Assessment of lumbar EMG during static and dynamic activity in pain-free normals: implications for muscle scanning protocols

The purpose of this study was to provide a thorough description of lumbar surface integrated electromyography (EMG) in pain-free normals during a standardized assessment protocol of static isometric and unresisted dynamic tasks. It has been proposed that in pain-free normals, symmetrical tasks that bend the trunk forward or extend the trunk backward produce symmetrical paraspinal EMG activity, and asymmetrical tasks that rotate or laterally bend the trunk produce asymmetrical paraspinal EMG activity. In addition, it has been observed that lumbar EMG assessment during static tasks has been more consistent than tasks involving dynamic activities. Twenty-eight pain-free normals were assessed during symmetrical and asymmetrical tasks in both static and dynamic activities in a counterbalanced manner. The assessment of paraspinal EMG patterns was conducted while subjects were secured in a triaxial dynamometer, which provided standardization of body position and concurrent measurement of torque, range of motion, and velocity. The results provided experimental evidence for the above-stated propositions. An implication derived from this research is that clinicians may be better served utilizing local norms when using EMG for classification purposes.

Temporal stability of psychophysiological stress profiles: a re-analysis using intraclass correlation coefficients

This is a re-analysis of data from a previous study which examined the temporal stability of three psychophysiological responses [frontal electromyographic activity (EMG), hand surface temperature, and heart rate]. Each response was recorded on 64 subjects over four sessions, each of which consisted of a 20-min, adaptation period, a baseline condition, and two stressors (one cognitive, the other physical). Rather than using Pearson product-moment correlations, as nearly all psychophysiological test-retest reliability studies have, we have now analyzed the data using intraclass correlation coefficients. This type of correlation allows one to incorporate more than two test-retest values on the same subjects. Analysis indicated that, with the exception of EMG during the physical stressor, the absolute values of the responses had quite significant reliability (.70 or greater). Treating the responses as relative measures (percent change from baseline or simple change scores from baseline) produced smaller and frequently less stable coefficients. It is concluded that statistical estimates of psychophysiological response reliability are functions of the design and particular reliability analysis employed.

Reliability of an ambulatory electromyographic activity device for musculoskeletal pain disorders

A number of investigators in recent years have called for the development of devices that can monitor surface EMG levels in individuals' normal environments for use with patients who suffer from disorders in which the etiology or maintenance of the pathology is presumed to be due at least in part to musculoskeletal dysfunction, such as low back pain, phantom limb pain and tension headache. This study examined the test-retest reliability of just such a device. Twenty-six healthy controls wore a lightweight (24 ounce) device which measured bilateral upper trapezius EMG, as well as peak and integral motion, for 5 consecutive days for up to 18 h each day. ANOVAs on the four measures revealed no difference between any of the four measures over the 5 days. Intra-class correlation coefficients for the two EMG variables across 5 days were both significant with alpha levels set at 0.01. The two EMG measures were highly correlated (r = 0.77); the two motion measures were also highly correlated (r = 0.60), but at a lower magnitude than EMG values; the relationship between EMG and motion was significant, but the magnitude of the between EMG motion correlations (0.26 and 0.35) were lower than the within EMG or motion ones. It was concluded that the test-retest reliability of the ambulatory monitoring device is within acceptable limits. Implications for the use of the device with musculoskeletal pain disorders--particularly headache--are discussed.

Electromyographic recordings of low back pain subjects and non-pain controls in six different positions: effect of pain levels

Surface electromyographic (EMG) activity recordings of bilateral paraspinal muscle tension were measured twice on 20 non-pain controls and on 46 low back pain subjects (21 individuals with intervertebral disk disorders and 25 subjects with unspecified musculoskeletal backache) during 6 positions: standing, bending from the waist, rising, sitting with back unsupported, sitting with back supported, and prone. Back pain subjects were measured during both low pain and high pain states. Results revealed a non-significant trend for all subjects, regardless of diagnosis, to have higher paraspinal muscle tension levels on the second (or high pain) assessment. A significant diagnosis by position interaction was observed which was similar to the interaction in our previous study which employed only a single measurement session. Analysis of simple main effects revealed this to be due to control subjects during the standing position having lower EMG levels than the back pain groups, and intervertebral disk disorder subjects having higher EMG levels than the other groups during the supported sitting position. As in our previous study, diagnosis was found to be a clinically significant factor, in that controls had much fewer clinically abnormal readings than back pain patients. The lack of a significant effect for pain state is congruent with findings in the headache literature. The importance of clearly defined diagnostic categories in low back pain research and the utility of measuring subjects in various positions is discussed, as are possible explanations for lack of significant pain state findings.