Intraclass correlation - A discussion and demonstration of basic features.

A re-analysis of intraclass correlation (ICC) theory is presented together with Monte Carlo simulations of ICC probability distributions. A partly revised and simplified theory of the single-score ICC is obtained, together with an alternative and simple recipe for its use in reliability studies. Our main, practical conclusion is that in the analysis of a reliability study it is neither necessary nor convenient to start from an initial choice of a specified statistical model. Rather, one may impartially use all three single-score ICC formulas. A near equality of the three ICC values indicates the absence of bias (systematic error), in which case the classical (one-way random) ICC may be used. A consistency ICC larger than absolute agreement ICC indicates the presence of non-negligible bias; if so, classical ICC is invalid and misleading. An F-test may be used to confirm whether biases are present. From the resulting model (without or with bias) variances and confidence intervals may then be calculated. In presence of bias, both absolute agreement ICC and consistency ICC should be reported, since they give different and complementary information about the reliability of the method. A clinical example with data from the literature is given.

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.

Reliability of measurements of endurance time, electromyographic fatigue and recovery, and associations to activity limitations, in patients with lumbar disc herniation.

BACKGROUND: Electromyographic (EMG) spectral parameters and endurance tests for back muscles have long been used to estimate low-back muscle fatigue. PURPOSE: The present purpose was to evaluate the test-retest reliability of a fatigue-testing protocol and to investigate associations between activity limitations and fatigue in patients with lumbar disc herniation. METHODS: To evaluate the reliability, endurance time, EMG spectral parameters and ratings of lumbar muscle fatigue and back pain were measured three times in 15 patients with lumbar disc herniation. The patients performed a modified Sørensen test with concurrent recordings of electromyography from the lumbar muscles at four recording sites. Ratings of their perceived fatigue and pain on a Borg scale were collected simultaneously. Recovery over five minutes was recorded. Questionnaires about activity, participation, self-efficacy and health were also used. RESULTS: Endurance time had an ICC of 0.85 indicating good reliability. Initial, end and median frequency recovery had intraclass correlation coefficients (ICCs) over 0.6 that is acceptable but with large standard errors of measurement. The median frequency slopes for the four recording sites had ICCs of 0.19-0.48. Agreement coefficients for the Borg ratings ranged between 0.78 and 0.97. Moderate correlation was found between activity limitations and endurance time. CONCLUSIONS: Endurance time measurement and Borg ratings may be recommended for evaluating intervention both with groups of patients, i.e. for research purposes, and for individuals. The median frequency parameters may be recommended for groups only. The study shows the importance of establishing the reliability of the patient category if the results are to be used to evaluate intervention.

Exploring activity limitations and sick leave among patients with spinal pain participating in multidisciplinary rehabilitation.

PURPOSE: To describe limitations in 12 activities at baseline, after multidisciplinary rehabilitation and at a 6-month follow-up for patients with spinal pain and, further, to investigate whether low limitation in any of the activities or in the mean score at baseline might predict increased working time at follow-up. METHOD: A prospective cohort study of 302 patients, 22- to 63-years old, who participated in multidisciplinary rehabilitation because of chronic neck, thoracic and/or lumbar pain. Data from the Disability Rating Index questionnaire were obtained at baseline, after the 4-week rehabilitation programme, and at the 6-month follow-up. Two subgroups are described: patients who at baseline (1) worked full-time or (2) were on part- or full-time sick leave. RESULTS: The degree of limitation in the 12 activities (items) showed large variations in median scores (7-91). Both subgroups showed significant improvements in most activities after rehabilitation, which remained at the follow-up. Nevertheless, in the sick-leave group, patients who had increased their working time at follow-up (62%) were still very limited in running, heavy work, and lifting heavy objects. In logistic regressions, low limitation in standing bent over a sink at baseline was the only single activity that predicted increased working time at the follow-up: odds ratio (OR) 1.93 (95% CI 1.1-3.5). OR for the mean score was 1.8 (1.0-3.3). CONCLUSION: A profile of the separate activities demonstrates the large variation in the degree of limitation, which is concealed in a mean score. The single items can be useful when evaluating interventions. However, to predict increased working time after rehabilitation, the mean score, as well as the activity standing bent over a sink, proved useful.

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 (> or =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.

Urinary incontinence in women with low back pain.

Urinary incontinence (UI) is a common female dysfunction, affecting women in all ages. Experienced physiotherapists and experts on low back pain (LBP) have since long observed and discussed the empirical association between LBP and UI. The aim of this study was to describe the occurrence of UI in women with LBP and to compare this group with a reference group of comparable age, language, culture and parity. The authors of this study had previously collected all original data from the reference group. A validated questionnaire concerning UI was answered by 200 consecutive women with LBP visiting specialised physiotherapy clinics in the area of Stockholm. Inclusion criteria were LBP, female, not pregnant, Swedish speaking, age between 17 and 45 years. Seventy-eight percent of the women with LBP reported UI. In comparison with the reference group, the prevalence of UI and signs of dysfunctional pelvic floor muscles (PFM) were greatly increased (p < 0.001) in the LBP group. Logistic regression analysis showed that the condition LBP and PFM dysfunction i.e. inability to interrupt the urine flow (p < 0.001) were risk factors for UI irrespective of parity. Physiotherapists treating patients with LBP should be aware of possible incontinence problems in this patient group.

Tests of walking ability at different speeds in patients with knee osteoarthritis.

BACKGROUND AND PURPOSE: Measurements of walking speeds are commonly used as an objective measure of functional performance in patients with knee osteoarthritis (OA) and are easily performed in a clinical setting. However, the choice in which the walking speed evaluation should be performed is controversial. The aim of this study was to identify the most discriminating walking speed after surgical interventions in patients with knee osteoarthritis, and to compare the responsiveness of the different gait speeds. METHOD: A prospective clinical one-year follow-up study involving 54 patients with knee osteoarthritis (63 (+/-5) years of age) who were operated with either a unicompartmental knee arthroplasty or a high tibial osteotomy was undertaken. Thirty-nine patients had unilateral knee OA and 15 patients had bilateral knee OA or other symptoms from the lower extremities that could influence walking. The patients were examined at a gait laboratory before surgery, and one year after surgery. The patients were instructed to walk at slow, normal and fast walking speed. RESULTS: All patients (n=54) walked.faster one year after the surgical intervention compared to before surgery (p = 0.001) at slow (+15%), normal (+8%) and fast (+7%) walking speed. This increase was similar for the three walking speeds (p = 0.171). Patients with unilateral knee OA (n=39) reached an average change of +0.12 m/s, which was considered clinically important, while patients with bilateral knee OA (n=15) did not increase their walking speed > 0.12 m/s. Effect size was moderate for slow walking speed and small for normal and fast walking speeds, respectively. CONCLUSIONS: The different walking speeds were equally good in detecting changes one year after surgical interventions. In this study, responsiveness favoured slow walking speed, however, the advantages of normal walking speed are discussed.

Low levels of physical activity in back pain patients are associated with high levels of fear-avoidance beliefs and pain catastrophizing.

BACKGROUND AND PURPOSE: Fear-avoidance beliefs are important determinants for disability in patients with non-specific low-back pain (LBP). The association with self-reported level of physical activity is less known. The aim of the present study was to describe the level of physical activity in patients with chronic non-specific LBP and its relation to fear-avoidance beliefs and pain catastrophizing. METHOD: A cross-sectional study on 64 patients with chronic non-specific LBP in primary healthcare. The variables measured and the questionnaires used were: level of physical activity (six-graded scale); activity limitations (Roland Morris Disability Questionnare (RDQ)); fear-avoidance beliefs (Tampa Scale of Kinesiophobia (TSK) 13-item and sub-scales 'activity avoidance' and 'somatic focus'); and pain catastrophizing (Pain Catastrophizing Scale (PCS)). The level of physical activity was dichotomised into low and high physical activity. Individual median scores on the TSKandPCSscales were used to group the patients into different levels offear-avoidance beliefs and pain catastrophizing. Univariate logistic regressions were used to calculate odds ratios for having low physical activity. RESULTS: Patients with low physical activity had significantly higher scores in fear-avoidance beliefs and pain catastrophizing (p < 0.05). Odds ratios for low level of physical activity were between 4 and 8 (p < 0.05) for patients with high fear-avoidance beliefs or medium/high pain catastrophizing. CONCLUSIONS: This study indicates that it seems important for physiotherapists in primary care to measure levels of fear-avoidance beliefs or pain catastrophizing. In particular, the two subscales of the TSK could be of real value for clinicians when making treatment decisions concerning physical exercise therapy for patients with chronic LBP.

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.

EMG recovery and ratings after back extensor fatigue in patients with lumbar disc herniation and healthy subjects.

This prospective study aimed to examine whether patients with lumbar disc herniation, before and after surgery, showed impaired recovery from fatigue measured with EMG and subjective ratings as compared to healthy subjects. Forty-three patients due for, and after, lumbar disc surgery and 60 healthy subjects were fatigued using a modified Sørensen's test. Recovery of back extensor muscles was assessed using electromyography and the Borg scale ratings at 1, 2, 3, and 5 minutes of recovery, and was further analyzed using an exponential time-dependence model. The patients completed four questionnaires: the Oswestry, the Roland-Morris, a self-efficacy scale and the SF-36. The exponential time-dependence model was successful for 14 of the 43 patients and 57 of the 60 healthy subjects. The patients for whom the model succeeded had significantly better scores on the questionnaires than those for whom the model was unsuccessful. Specific items related to standing and lifting were identified. The patients' recovery was impaired compared to the healthy subjects, as determined by use of the exponential time-dependence model. The combination of fatigue and recovery measures was reflected in the questionnaire scores and is therefore important for evaluating patients with lumbar disc herniation.

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.

Recovery of electromyograph median frequency after lumbar muscle fatigue analysed using an exponential time dependence model.

The recovery of the median frequency of the power spectrum of the electromyogram (EMG) after fatigue has been studied to obtain reference data for healthy subjects (n = 55). In a seated position, the subjects performed a 45 s isometric back muscle contraction at 80% of maximal voluntary contraction, followed by 5 s contractions after 1, 2, 3, and 5 min in the recovery phase. In an additional reliability study (n = 11), this was performed six times. Surface EMG was recorded on four sites, namely, bilaterally from the lumbar muscles at the level of the first (L1) and fifth (L5) vertebrae. By non-linear regression, an exponential time dependence model was used to analyse the recovery of median frequency, giving recovery half-time as a resulting measure. Agreement with exponential time dependence was very good (coefficient of determination r(2) = 0.98) in the analysis of mean data (n = 55), with recovery half-times in the range 32-39 s on the four recording sites. Analysis of individual recordings, for which r(2) values in general were lower, revealed further details. Median values of the half-times in general agreed well with the half-times obtained from the analysis of mean data. Recovery half-time and median frequency slope during contraction were not correlated; this is in agreement with what may be expected from an exponential time dependence. Non-significant negative slopes occurred on apparently randomly selected sites, possibly indicating varying muscle coordination in the seated test method. The reliability of the half-time was not sufficient to allow for follow-up measurements on individuals, due to the fluctuations of the recovery data in recordings from individuals.

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.