Introduction [1] [2] [3] 4 6 7 10 11 12 13 15 16 17 17 18 20 21 22 23 23 24 Methods and materials Design and subjects A randomized controlled trial was performed to assess the effect of 4-weeks Cinderella-based myofeedback training combined with ergonomic counselling (together referred to as Mfb), compared to ergonomic counselling alone (EC), on pain intensity and disability. Measurements were performed prior to intervention but before randomisation (Baseline), immediately after four weeks of intervention (T0), and at three (T3) and six (T6) months after the intervention. 25 26 27 Subjects were excluded when they reported pain in more than 3 body regions, when they suffered from severe arthrosis or joint disorders, when they were using muscle relaxants, or when reporting other complaints in the upper extremity not related to (computer) work. 23 β α Interventions The interventions were provided by three different therapists: One physiotherapist in Sweden and two health scientists in the Netherlands. They were thoroughly trained and practiced together prior to the start of the study to ensure that they would provide as identical interventions as possible. The character of the intervention made blinding of the therapists and the subjects to the intervention impractical. To prevent from information bias, subjects were informed that the aim of the current study was to compare the effects of two interventions and that there was no evidence favouring one of these interventions. Ergonomic counselling (EC) 28 Myofeedback (Mfb) Subjects randomized to the Mfb group received Cinderella-based myofeedback training on top of EC. A two-channel ambulant myofeedback system combined with a harness incorporating dry surface Electromyography (sEMG) electrodes to enable a stable recording of upper trapezius muscle activity was used. The harness was connected to a sEMG processing and storage device (see Picture 1). Picture 1 Myofeedback system: Harness and processing/storage unit  29 30 Immediately after Baseline, subjects assigned to the Mfb group were given the myofeedback device and they were explained the working mechanism and background of the myofeedback training. Subjects wore the system for four weeks, for at least eight hours a week (distributed over two hours a day and two days a week as a minimum) while performing their regular work. During the weekly visits the sEMG-data from last week were scrutinized and discussed to give the subject insight in their relaxation patterns and to identify possible situations of concern. This procedure was facilitated by means of the diary. Assessment of pain intensity and disability 31 32 34 35 36 Analysis Data inspection showed non-normal distributions for all of the variables, and data were therefore log transformed, enabling parametric analyses. Analyses were performed both on the group as well as the individual level. t 37 34 38 Logistic regression analyses providing Odds Ratios were performed to investigate whether the two intervention groups differed in terms of chances for clinically relevant improvements in pain intensity and disability. Three different models were investigated: Model I represents the crude Odds Ratio describing only the relationship between intervention type and odds for improvement without adjustment for confounding factors. The factors study group and baseline pain intensity/baseline disability were assumed potentially confounding factors. To correct for these factors, two additional models were built as extensions of Model I: Model II incorporates study group as confounding factor, and Model III is an extension of Model II incorporating also the factor baseline pain intensity/baseline disability level. For Models II and III interaction effects were additionally included in the analysis, to study effect modification, but these remained only included when significant. −2 Log Likelihood tests were used to select the best model. Odds Ratios including 95% Confidence Intervals were calculated and presented for each of the models. Statistical Package for Social Sciences 11.5 was used for statistical testing and alpha was set at .05 for statistical significance. Results Subjects Diagram 1 Flow chart subject recruitment and randomisation  p 1 p Table 1 Characteristics of subject population   n n Sociodemographics     Body mass index  25.2 (3.9) 25.2 (3.7)  Side dominance % Right-handed 95% 97%  Living situation % Living alone 16.7 10.8  Working hours per week  32.8 (7.8) 32.8 (8.3)  Working hours per week since (in years)  * * Complaints     Trouble in neck last year Yes 92.9 91.9  Trouble shoulders last year Yes, in both shoulders 36.6 32.4  Yes, in the right shoulder 36.6 43.2  Yes, in the left shoulder 12.2 13.5  Trouble in upper back last year Yes 66.7 48.6  Was work performance affected Yes 31.7 18.9 * Analysis at group level Pain intensity Baseline (geometric) mean VAS scores for each region separately were 27 mm (neck), 15 mm (left shoulder), 14 mm (right shoulder), and 13 mm (upper back) in the Mfb group and 24, 14, 19, and 18 mm in the EC group respectively. 1 Fig. 1 Box plot for averaged VAS score of pain intensity in the neck-shoulder region at Baseline, T0, T3, and T6 for both the Mfb and the EC group  F p F p F p F p t p t p t p t p Disability 2 Fig. 2 Box plot for the Pain Disability Index score at Baseline, T0, T3, and T6 for both the Mfb and the EC group  F p F p F p F p t p t p t p t p t p t p Analysis at the individual level Pain intensity 3 Fig. 3 Percentage of subjects showing improvements in averaged VAS score of pain intensity in the neck-shoulder region at T0, T3, and T6 compared to Baseline for the Mfb and EC group [without correcting for confounding factors]  2 p p p p 2 Table 2 (Adjusted) odds ratios (95% confidence interval) for improvement in pain intensity in the neck-shoulder region for the Mfb group compared to the EC group  Model I Model II Model III VAS 1.56 1.59 3.42 Baseline–T0 (.60–4.05) (.71–4.14) (.55–21.11) VAS .78 .78 .40 Baseline–T3 (.29–2.08) (.29–2.09) (.08–1.99) VAS 1.31 1.31 1.04 Baseline–T6 (.47–3.60) (.47–3.64) (.29–3.77) Model I: Odds Ratio Crude. Model II: Odds Ratio Adjusted for factor study group. Model III: Odds Ratio Adjusted for factor study group and VAS at Baseline. Disability 4 Fig. 4 Percentage of subjects showing clinically relevant improvements in Pain Disability Index at T0, T3, and T6 compared to Baseline for the Mfb and EC group [without correcting for confounding factors]  Immediately after the intervention period about twice as many of the subjects in the Mfb group showed clinically relevant improvements in disability compared to the EC group. This share of subjects increased somewhat in both groups after three months and then showed a small decline after six months where about one third of the subjects of the EC group and half of the Mfb group showed clinically relevant improvements in disability. p p p p p 3 Table 3 (Adjusted) odds ratios (95% confidence interval) for improvement in disability the Mfb group compared to the EC group  Model I Model II Model III Pain disability index 2.70 2.72 1.48 Baseline–T0 (.97–7.54)† (.971–7.60)† (.39–5.62) Pain disability index 2.77 2.99 1.64 Baseline–T3 * * (.34–7.97) Pain disability index 2.54 2.61 1.48 Baseline–T6 (.88–6.82)† (.91–7.47) (.37–5.88) Model I: Odds Ratio Crude. Model II: Odds Ratio Adjusted for factor study group. Model III: Odds Ratio Adjusted for factor study group and Pain Disability Index at Baseline. * p † p Discussion This randomised controlled trial investigated the effects of 4-weeks ambulant myofeedback training combined with ergonomic counselling in subjects with work-related neck-shoulder complaints relative to ergonomic counselling alone, on pain intensity and disability. The effects were evaluated immediately after the interventions, and at three and six months follow-up. Mean pain intensity and disability levels significantly reduced after both interventions (i.e. Mfb and EC). The effects were clinically relevant in a large part of the subjects: About 30–50% of the subjects showed clinically relevant improvements in pain intensity and/or disability. No difference was found for the effect of the intervention on outcome and after correction for confounding factors subjects in both intervention groups did not differ with regard to chances for clinically relevant improvements in pain intensity and disability. 21 39 43 22 21 22 42 44 47 23 23 48 8 10 49 50 24 8 10 51 53 43 54 Methodological considerations 55 56 43 46 57 58 23 48 48 60 59 The drop-out rate in the Mfb group was higher than in the EC group (i.e. nine compared to five), which was probably related to the myofeedback system itself. Some subjects found the system inconvenient and disturbing in daily working activities. This may have suppressed the effect of the intervention. Improvement of the current device in terms of usability is therefore required to optimise the myofeedback training. Conclusions Four-weeks of intervention significantly reduced pain intensity and disability, and this effect remained after three and six months follow-up. Myofeedback training combined with ergonomic counselling is thus beneficial for female computer workers over the age of 45, reporting pain and disability in the neck-shoulder region but no evidence was found favouring myofeedback training combined with ergonomic counselling over ergonomic counselling alone. Future research may aim at identifying possible subgroups of patients in which the interventions are especially beneficial. This may enhance the efficiency and the effectiveness of the interventions. Finally, as non-specific effects may have interfered with outcome, future studies could include a placebo control group for more insight in the specific effects of ambulant myofeedback training combined with ergonomic counselling.