Britt Elfving

Reliability of EMG spectral parameters in repeated measurements of back muscle fatigue.

The change in median frequency of the power spectrum of the electromyographic (EMG) signal may be used as a measure of muscle fatigue. The reliability of the median frequency parameters was investigated for EMG-recording sites at L1 and L5 right and left on the erector spinae. The reliability of subjective fatigue ratings of the back muscles (Borg CR-10 scale) and of maximal trunk extension torque (MVC) was also investigated. Eleven subjects with healthy backs performed a 45-s isometric trunk extension at 80% of MVC twice a day, on three different days. Two-factor analysis of variance was made to obtain the different variances from which the standard error of measurement (SEM) and the intra class correlation coefficient (ICC) were calculated. The SEM within-day was somewhat lower than that between-days. Both were about the same at all four electrode sites. The 95% confidence interval for the studied variables was for the initial median frequency +/- 10 Hz, for the slope +/- 0.4-0.5%/s, for the MVC +/- 36 Nm and for the Borg ratings +/- 1.6. We conclude that, with the presently used method, changes or differences within these limits should be regarded as normal variability. The slope may be of limited value because of its large variability. Whether the low intraclass correlation coefficient for the EMG parameters in the presently studied test group implies a low potential in discriminating subjects with back pain can not be decisively concluded.

Lumbar muscle fatigue and recovery in patients with long-term low-back trouble––electromyography and health-related factors

OBJECTIVE The aim was to explore the validity and reliability of EMG for assessing lumbar muscle fatigue. DESIGN Patients with long-term low-back trouble (n=57) were compared to a healthy reference group (n=55). Back muscle fatigue and recovery were studied in relation to health-related factors. BACKGROUND EMG spectral variables are important tools in the assessment of patients with low-back trouble. The influence of disability on these variables needs further investigation. METHODS EMG from the lower back muscles was recorded during a 45 s trunk extension at 80% of maximal voluntary contraction torque and during recovery. Disability was studied using questionnaires. RESULTS The reliability was high for maximal voluntary contraction torque and EMG initial median frequency, lower for the median frequency slope, and insufficient for median frequency recovery half-time. The patients had lower maximal voluntary contraction torque, higher initial median frequency at L5 level, flatter slope, and longer recovery half-time than the healthy subjects did. However, for subjects with significantly negative slope, indicating fatigue, there was no significant difference in slope between patients and healthy subjects, while, for subjects without such fatigue, patients showed significantly flatter slopes at L5. The sensitivity/specificity of the test was 86%/78%. The most significant variables selected with logistic regression were maximal voluntary contraction torque and initial median frequency at L5. Patients without significantly negative slopes during contraction and/or not exponential-like EMG recovery scored worse on several items concerning disability and self-efficacy. CONCLUSIONS EMG spectral variables in combination with torque might be used for classification. For patients with long-term low-back trouble, the ability to fatigue the lumbar muscles sufficiently to obtain a significantly negative slope during an 80% maximal voluntary contraction may be a sign of better functioning. RELEVANCE The ability to fatigue the back muscles during a test requiring a high force output might be achieved with back muscle training focused on increasing strength and self-efficacy.

Between-days reliability of subjective and objective assessments of back extensor muscle fatigue in subjects without lower-back pain

BACKGROUND It is important to evaluate the reliability of common used methods of examining muscle fatigue from the lower back since the methods are used in patient evaluation. METHODS To establish between-days reliability, ten subjects without lower-back pain performed a Sorensen test, a prone test for back extensor muscles against gravity, on three separate days. EMG was recorded from the L1 and L5 of the back extensor muscles. Fatigue was subjectively rated using a Borg CR-10 scale. Intraclass correlation coefficient, standard error of measurement and coefficient of variation were calculated from a one-way ANOVA. Percent agreement was also calculated. RESULTS The study revealed good reliability for the slope for the total time (ICC 0.65-0.90), the initial and end median frequency (ICC 0.75-0.89), median frequencies at Borg ratings of three (ICC 0.63-0.88), five (ICC 0.62-0.84) and seven (ICC 0.67-0. 87), endurance time (ICC 0.89). The Borg ratings of the first minute agreed better than those of the second and the third. The Borg ratings at the second and the third test agreed to 40-80%, indicating a need for a practice session. CONCLUSION The protocol used for assessing fatigue in the back extensor muscles proved to be reliable and is recommended for further use.

Intra-rater reliability in measuring range of motion in infants with congenital muscular torticollis

The aim of this study was to test the intra-rater reliability of measures in rotation and lateral flexion of the head in infants with congenital muscular torticollis (CMT). Twenty-three infants with CMT, aged 1–5 months, were classified into two groups. Group I was measured twice without time interval and Group II was measured with an interval of 1 h. All infants were examined supine. A goniometer was used to measure rotation and a protractor for lateral flexion. Photos were taken simultaneously with the readings of range of motion. Repeated-measures analysis of variance (ANOVA) was used to determine any significant differences between test and retest. The intraclass correlation coefficient and the standard error of measurement were calculated to determine intra-rater reliability. Results show high intra-rater reliability regardless of time intervals between the two measures, measured movement directions and differences in the end-feel of the sternocleidomastoideus muscle. Least agreement was found when comparing measures on infants and on photos taken simultaneously. The high intra-rater reliability found in this study indicates that evaluation of treatment effects over time can be made with adequate reliability when the measures are performed by an experienced physiotherapist. The methods used could form a good basis for performing a larger inter-rater reliability study.

What factors predict full or partial return to work among sickness absentees with spinal pain participating in rehabilitation

Purpose. To identify the factors that predict full or partial return to work among long-term (≥90 days) sickness absentees due to spinal pain who begin a multidisciplinary rehabilitation programme. Method. In a prospective cohort study, 312 patients with neck, thoracic and/or lumbar pain, aged 20–64, participated in a 4-week multidisciplinary rehabilitation programme in Sweden. Questionnaire data at inclusion were used. Factors included in logistic regressions were as follows: age, gender, type of work, pain location, pain intensity (visual analogue scale), activity limitations [Disability Rating Index (DRI)], health-related quality of life (SF-36), pain-related fear of movement (Tampa Scale of Kinesiophobia), motivation (Self Motivation Inventory), sickness absence at baseline and number of sick-leave days during the previous 2 years. Outcome factor was increased versus not increased working time at follow-up 6 months later. Results. Most patients (68%) reported two or three pain locations. At baseline, 56% were full-time sickness absent and 23% at follow-up; 61% had increased their working time. Predictors for increased working time were age below 40 years, low activity limitation (DRI < 50), low SF-36 bodily pain (>30) and high SF-36 social functioning (>60). Number of sick-leave days during the previous 2 years (md 360; range 90–730) had no influence. Conclusions. Even patients with long previous sick leave can increase working time after a multidisciplinary rehabilitation programme, especially if they are younger, have lower levels of activity limitations and pain and better social functioning. To include information on part-time work is useful when evaluating work ability following rehabilitation programmes.

Fear-avoidance beliefs and pain as predictors for low physical activity in patients with leg ulcer

BACKGROUND AND PURPOSE Previous studies have shown that patients with chronic venous insufficiency are deconditioned and physically inactive. The present study aimed to examine the occurrence of fear-avoidance beliefs in patients with chronic venous insufficiency, and to investigate the role of fear-avoidance beliefs and pain severity in predicting the low level of physical activity in these patients. METHOD Data were collected by a postal questionnaire sent to 146 patients with chronic venous insufficiency and current or previous venous leg ulcer. Complete data were collected from 98 patients aged 60-85 years - 63% women - giving a response rate of 67%. Fear-avoidance beliefs were assessed by the Fear-Avoidance Beliefs Questionnaire, physical activity subscale. Pain and physical activity were assessed by the Six-point Verbal Rating Scale of Pain Assessment and the Physical Activity Questionnaire, respectively. RESULTS Fear-avoidance beliefs were present in 81 (83%) of the patients with chronic venous insufficiency (range 0-24, median 12). Forty patients (41%) had strong fear-avoidance beliefs. One-third of the patients with healed ulcers had strong fear-avoidance beliefs. Patients with low physical activity had significantly stronger fear-avoidance beliefs and more severe pain than patients with high physical activity. Multiple logistic regression showed that the odds ratio (OR) for low physical activity were about three times higher for patients with strong fear-avoidance beliefs (OR 3.1, 95% confidence interval 1.1-8.3; p = 0.027) than for patients with weak fear-avoidance beliefs. CONCLUSIONS Fear-avoidance beliefs were present in most patients with chronic venous insufficiency and were associated with low physical activity. Clinical implications ought to include a better recognition of fear-avoidance beliefs, early information about the negative consequences of such beliefs, and the importance of physical activity to counteract poor mobility.

Back muscle fatigue in healthy men and women studied by electromyography spectral parameters and subjective ratings.

To obtain reference data for future studies of patients with low back pain, back muscle fatigue was studied by surface electromyography at L1 and L5 lumbar levels in 55 healthy subjects exerting 80% of maximal voluntary contraction of the back extensors in a sitting position. Reference data were the initial value and rate of decrease (slope) of the median frequency during the contraction. The aim was also to study the effects of contraction time, gender differences, electrode locations and correlations with torque, age and subjective ratings. Initial median frequency was 52 Hz +/- 7.5, with no difference between electrode locations; steeper slopes were found at L5 level (-0.44%/s +/- 0.25) than at L1 (-0.36%/s +/- 0.26). No right-left differences and no gender differences were found for these parameters. A correlation was observed between slope and initial median frequency, higher for men (r approximately -0.7) than for women (r approximately -0.5). Intersubject coefficient of variation for the slope was smallest for the longest (45 seconds) recording time (60-70%), but still much higher than for the initial median frequency (14%). The torque and the subjective ratings of fatigue showed no correlation with the electromyography variables. We conclude that the same reference values can be used for men and women. Owing to the large intersubject range of the slope, the clinical use of this variable may, however, be impeded.

Physical activity in patients with venous leg ulcer – between engagement and avoidance. A patient perspective

Objective: To identify and describe the qualitative variations in how physical activity is perceived and understood by individuals with current or previous venous leg ulcer. Design: A qualitative study using semi-structured interviews. Method: Twenty-two individuals aged 60–85 years were interviewed. The interviews were recorded, transcribed verbatim and analysed by three researchers using a phenomenographic research approach. A set of categories of descriptions and their internal relationships were constructed based on the essential features of the variation in patients’ perceptions of physical activity. Results: Four categories of descriptions were identified: (i) ‘self-management’, (ii) ‘instructions and support’, (iii) ‘fear of injury’ and (iv) ‘a wish to stay normal’. The categories could be interpreted by a two-dimensional construct: (1) perception of venous leg ulcer as a chronic or acute condition and (2) engagement or avoidance behaviour toward physical activity. Chronicity and behaviour combined together formed a 2 × 2 square housing the four qualitatively different categories. Irrespective of category, the participants reported that information given by caregivers regarding leg ulcer and physical activity was insufficient or contradictory. Written information or exercise programmes were not obtained regularly and not at all in primary care. Conclusion: A dichotomous view emerged from participants’ experiences of physical activity based on (1) perception of venous leg ulcer as a chronic or acute condition and (2) engagement or avoidance behaviour toward physical activity.

Influence of interelectrode distance and force level on the spectral parameters of surface electromyographic recordings from the lumbar muscles

In order to study the influence of interelectrode distance and force level on the electromyographic (EMG) spectral parameters and on their reliability, bipolar surface EMG measurements were performed on the lumbar muscles of 15 subjects. Two test contractions (45 s) at 40% of maximal voluntary contraction (MVC) were performed, one with 2 cm interelectrode distance and the other with 4 cm, followed by two contractions at 80% MVC with the same change in interelectrode distance. Increasing the interelectrode distance from 2 to 4 cm caused a significant mean decrease (about 8%) in the initial median frequency. It is shown that this shift is of an order of magnitude that may be expected from the bipolar electrode filter factor, and we further conclude that the observed individual variations in the shift are likely to be connected to fluctuations in the shape of the power spectrum and to variations in conduction velocity. No significant change was found for the median frequency slope when changing the interelectrode distance. Increasing the force (from 40 to 80% MVC) also caused a significant mean decrease (about 10%) in the initial median frequency. The median frequency slope became significantly more negative by more than 200%. We conclude, however, that torque fluctuations during the fatigue contractions should have had only minor influence on the standard error of measurement of the initial median frequency and of the median frequency slope.

Change in kinesiophobia and its relation to activity limitation after multidisciplinary rehabilitation in patients with chronic back pain

Purpose: To explore the change in kinesiophobia in relation to activity limitation after a multidisciplinary rehabilitation programme in patients with chronic back pain. Method: A prospective cohort study was made including 265 patients. Data were collected at baseline, after rehabilitation, and at 6-months follow-up. Outcome measures were the Tampa Scale for kinesiophobia (TSK) and the disability rating index (DRI). The smallest detectable change (SDC) in TSK was set to 8 scores. Relationships between kinesiophobia and activity limitation/physical ability were explored with regard to subgroups with high, medium and low baseline TSK scores, and for those patients who did or did not reach the SDC in TSK. Results: Improvements in TSK showed high effect sizes in the groups with high and medium baseline TSK scores. Improvements in DRI showed medium effect sizes in all three TSK subgroups. One third of the patients reached the SDC in TSK, and this group also improved significantly more in DRI. The correlation between change in TSK and change in DRI was low. Half of the patients with high TSK score at baseline remained having high DRI at follow-up. Conclusions: Improvement in physical ability was not related to the initial degree of kinesiophobia but to the SDC in TSK. To prevent patients with high kinesiophobia from preserving high activity limitations, it might be useful to include targeted treatment of kinesiophobia. Implications for Rehabilitation Intensive multidisciplinary rehabilitation decreases kinesiophobia and activity limitation in patients with chronic back pain. Patients improving >8 scores on the Tampa Scale for kinesiophobia are likely to increase their physical ability. Patients with an initially high degree of kinesiophobia as well as a high level of activity limitation need targeted treatment of kinesiophobia to increase their physical ability.