Comparison of chairs based on HDsEMG of back muscles, biomechanical and comfort indices, for violin and viola players: A short-term study

Accepted Manuscript Comparison of chairs based on HDsEMG of back muscles, biomechanical and comfort indices, for violin and viola players: a short-term study Paolo Cattarello, Silvia Vinelli, Samuel D'Emanuele, Marco Gazzoni, Roberto Merletti PII: DOI: Reference:

S1050-6411(18)30150-0 https://doi.org/10.1016/j.jelekin.2018.06.013 JJEK 2218

To appear in:

Journal of Electromyography and Kinesiology

Received Date: Revised Date: Accepted Date:

28 March 2018 1 June 2018 20 June 2018

Please cite this article as: P. Cattarello, S. Vinelli, S. D'Emanuele, M. Gazzoni, R. Merletti, Comparison of chairs based on HDsEMG of back muscles, biomechanical and comfort indices, for violin and viola players: a short-term study, Journal of Electromyography and Kinesiology (2018), doi: https://doi.org/10.1016/j.jelekin.2018.06.013

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Revised version (R1) of manuscript JEK 2018 131

Comparison of chairs based on HDsEMG of back muscles, biomechanical and comfort indices, for violin and viola players: a short-term study. Paolo Cattarello1, Silvia Vinelli2, Samuel D’Emanuele3, Marco Gazzoni1, Roberto Merletti1, 1

LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Torino, Italy

2

School of Medicine, Department of surgical science, Degree course in physiotherapy, University

of Torino, Torino, Italy 3

School of Exercise and Sport Sciences, University of Torino, Torino, Italy

Corresponding author: Roberto Merletti, LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Italy Tel: +39-3471613643, E-mail: [email protected] Other authors: Paolo Cattarello, Tel: +39-339 764 4543, E-mail: [email protected] Silvia Vinelli, Tel: +39-339013202124, E-mail: [email protected] Samuel D’Emanuele. Tel: +39-348 88 38 001, E-mail: [email protected] Marco Gazzoni, Tel: +39-011-0907756, E-mail: [email protected]

Acknowledgment The authors are grateful to Prof. Angela Colombo, Director of Conservatorio A. Vivaldi, Alessandria, Italy, and to the musicians who participated to this study. The contribution of Dr. Silvia Vinelli was supervised by Prof. Marco Minchillo, School of Medicine, Department of Surgical Science, Degree course in Physiotherapy, University of Torino, Italy. The authors acknowledge a grant from the Lagrange Project–CRT Foundation, ISI Foundation and Varier Furniture Srl, Dormelletto (NO), Italy.

Conflict of interest This work was supported in part by Varier Furniture Srl, Italy. There is no business, financial or potential conflict of interest by any of the authors. 1

Comparison of chairs based on sEMG of back muscle, biomechanical and comfort indices for violin and viola players: a short-term study. Abstract This work investigates the effect of different seats on violin and viola players sitting postures using High-Density-surface-Electromyography techniques (HDsEMG), biomechanical and comfort indices. Five types of chairs were assessed on 18 violin and three viola players by comparing: a) pelvic tilt and kyphosis and lordosis angles, b) subjective comfort indices, and c) EMG amplitude of erector spinae and trapezius. Sitting “as you like” on a standard orchestra chair is the condition with the highest subjective comfort (but not significantly different from other chairs). A saddle chair with low back support is associated to the lowest EMG of the erector spinae (p<0.05) and a saddle stool is associated to the spinal angles closest to those of the standing posture. In 12 out of 21 (57%) musicians, the erector spinae was activated in an intermittent manner, regardless of the chair used. These findings justify further research on the selected chairs, on muscle fatigue and on the intermittent postural control strategy. Keywords: sitting posture; musicians; saddle chair; sEMG; violin; PRMDs; postural control.

1. Introduction Prevalence of Playing Related Musculoskeletal Disorders (PRMD) in string instrument players varies from 73,4% to 87,7% (Zaza, 1998; Lee, 2013). Musicians commonly do not use specific ergonomic chairs and often assume unhealthy postures. A review by Irina et al. (Irina, 2006) investigated the use of appropriate seats to prevent PRMDs. There are no guidelines indicating the most suitable chairs for specific musicians. The sitting posture induces a lumbo-pelvic flexion (causing a posterior pelvic tilt) with respect to the standing position (Claus., 2009; Dunk, 2009; De Carvalho, 2010).

Many authors

(Harrison, 1999; Keegan, 1953; Pynt, 2001; O’Sullivan, 2012) consider advantageous to preserve the physiological lumbar lordosis in sitting position. This can be obtained by reducing seated hip 2

flexion (Keegan, 1953; Saarni, 2007). However, the effect of a reduced hip flexion on the back muscle activity is unclear. Both reduction (Koskelo , 2007) and increase (Lander,1987) of the muscle activity are reported to be associated with a reduced hip flexion. In 1995 Cram claimed that: “static working conditions, coupled with poor or inappropriate body mechanics, may cause prolonged tension in specific muscle groups. This in turn leads to fatigue and eventual muscle strain, and a myogenic etiology of pain. The model of muscle fatigue has been gaining acceptance for explaining the deterioration of human performance over time” (Cram, 1995). Backrest is recommended for office workers (Carcone, 2007) and has been proposed to: a) promote “good” spinal posture, b) reduce trunk muscle activity, c) increase comfort and d) reduce intradiscal pressure (Carcone and Keir, 2007; Jonsson, 1974; Andersson, 1975). A lumbar support may be preferable to a standard backrest for string players who need more freedom of movements. Furthermore, doubts exist on the association between sitting modalities, and the development of low back pain (Vergara, 2000; Claus, 2008). Surface EMG studies of musicians have been limited (Grieco, 1989; Fjellman-Wiklund, 2003a, 2003b; Afsharipour, 2016, Cattarello et al. 2017). The main hypothesis of this study is that ergonomic chairs, with backrest and with adjustable height, providing a trunk-thigh angle > 90 °, are able to lower the activation of the erector spinae and to guarantee a good level of comfort for violin and viola players. The main research questions addressed in this study are: (1) How do violinists and violists habitually sit? (2) What is the effect on the back muscles of a sitting posture with a trunk-thigh angle > 90° ? (3) Is the introduction of a lumbar support desirable for string players? (4) Can the HDsEMG techniques impact on these assessments?

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Figure 1 about here

2. Material and Methods 2.1 Subjects All the procedures used in this study were approved by the Servizio Sanitario Nazionale, Regione Piemonte (National Health Service, Region of Piemonte), and were applied in accordance with the Helsinki Declaration of 1975, as revised in 2000 and 2008. All musicians signed the informed consent form prepared for these tests. A sample of 21 musicians were examined. The sample consisted in both males and females (8/13), students and professionals (14/7), violinists and violists (18/3). Most of the subjects (57%) had a history of minor musculoskeletal disorders not requiring medical attention: 33% of them were suffering from back pain, 9% from disorders at upper limbs and 5% from both. Subjects’ data are presented in table 1. Table 1 about here Exclusion criteria

The subjects were selected after a postural evaluation conducted by a physiotherapist. The exclusion criteria were: 1. Musculoskeletal problems, during the last three months, with pain evaluated as Numerical rating scale (NRS) ≥ 5. 2. Dysmorphic features of the spine such as to alter the head-trunk-pelvis alignment. 3. Thoracic curvature in the sagittal plane < 20° or > 70° and lumbar curvature in the sagittal plane < -71,5° or > -12° (Kuntz , 2008) evaluated with a flexicurve (De Oliveira, 2012). 4. Scoliosis > 5° (As of January 01, 2016, the Italian Soc. for Physical Med. and Rehab. listed on its website http://www.gss.it/index.php/patologie/informazioni/18-la-scoliosi/26-linee-

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guida-simfer) evaluated with an inclinometer during an Adams Forward Bendings Test (Côté, 1998). 5. Pelvic tilt < (-2°) or > 28° (Kuntz IV, 2008) evaluated with an inclinometer with arms (Toppenberg, 1986). 6. Limitations of the range of motion, measured with a standard goniometer and a tape measure, greater than 30% with respect to the normal range (Clarkson, 2002). Out of the 24 subjects initially examined three did not satisfy one or more of the above criteria and 21 were included in the study. None of them reported any pain during the test.

2.2 Protocol Five different seats were evaluated (Figure 1) in random order, during one day, by each musician: 1. The O.D.E.1 chair (Orchestra Design & Ergonomics, http://www.ouneri.fi/en/), specifically designed for musicians, was considered as the reference seat. This chair was evaluated in two conditions: a) the subject was free to seat in his preferred posture (sitting as you like), b) the subject was asked to seat with a trunk-thigh angle (angle between tragus-greater trochanter-lateral femoral epicondyle) of 90° leaning against a backrest reaching up to the lower third of the scapula. 2. The Move chair (Varier Furniture Srl, http://www.varierfurniture.com). 3. The HÅG Capisco Puls chair ( HÅG by Flokk) was evaluated in two conditions: a) without backrest, b) with the subject leaning against a lumbar support. The two configurations of chairs ODE 1 (O and O90 ) and Håg Capisco (H and HB) in Figure 1 were considered in this work as “different chairs” because they change the posture of the subject. Therefore, five sitting modalities are referred to as “chair”.

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The height of the saddle chairs was adjusted to obtain a trunk-thigh angle of 115°, evaluated with a standard goniometer, with a resolution of 1°. This angle preserves the physiological spine lordosis angle of 105o-135o corresponding to a high-perceived comfort (Keegan, 1953; Bendix, 1982). Each subject was asked to play for 5 min two pieces of medium difficulty (Kreutzer studies # 2 and 5), from the lectern, with metronome (88 bpm or adapted according to the ability of the subject) on each seat, in each configuration. The lectern was positioned in front of the player to reduce the asymmetry of his/her posture (Spahn, 2014). Each configuration was assessed by means of: 1. The General Comfort Rating Scale (Shackel, 1969). 2. Postural biomechanical analysis. a) Pelvic tilt was measured on the right side during the task. b) Sagittal spine angles (kyphosis and lordosis angles) were acquired in standing positions and at the end of the measurement session. c) The trunk-thigh angle was measured on the right side during the task on the reference chair (O.D.E.1) while the subject was sitting in his preferred posture (section 2.4). This angle was fixed (115o) on the other chairs. 3. Twenty seconds of monopolar sEMG signal were recorded, after 5 min of playing, while each subject was playing Kreutzer studies #2 (initial part, at 88 bpm). The 5 min delay allowed for initial adaptation to the chair and for completing minor adjustments in the sitting position. Although the disadvantages of monopolar signals are well known, they were investigated because of their higher signal/noise ratio and because they can be detected from a greater detection volume.

2.3 Subjective comfort evaluation General Comfort Rating Scale (GCRS) The General Comfort Rating Scale considers comfort and discomfort as the two ends of the same 6

scale. The subject is asked to indicate the numerical value corresponding to the proposition that best represents his feeling (Shackel, 1969) as shown in Figure 3b.

2.4 Postural biomechanical analysis Pelvic tilt (the angle between the line connecting the anterior superior iliac spine to the posterior superior iliac spine and the vertical axis, perpendicular to the ground) and spine angles in the sagittal plane were evaluated using a palpation meter (PALM) (Azevedo, 2014; Toppenberg, 1986). Lumbar lordosis and thoracic kyphosis spine angles were evaluated with the method of De Oliveira et al. (De Oliveira, 2012) using a flexicurve (Figure 5a). The spine curve was traced with the flexicurve and drawn on a graph paper. The position of C7, T1, T12, L1, L5, S1, of six additional points for the kyphosis curve and six additional points for the lumbar curve were recorded. The resulting 18 points were interpolated with a 3rd order polynomial to reconstruct the lordosis and kyphosis curves. Lordosis and kyphosis angles were calculated as intersection of the lines perpendicular to the tangent lines of the curve at T1 and T12 for the kyphosis and at L1 and L5 for lordosis. Angles measured with this technique show a strong correlation with the Cobb angles obtained using X-rays (De Oliveira, 2012).

2.5 Back muscle activity analysis Monopolar signals were acquired from the trapezius and the lumbar erector spinae muscles on each side of the spine. Longitudinal single differential (SD) signals were obtained off-line by differentiation in the vertical direction. The electrode grids and arrays were fixed to the skin with double adhesive foam layer with holes, corresponding to the electrode positions, filled with conductive paste (Ten20, Weaver and Company). The skin under the electrodes was previously treated with an abrasive paste (Nuprep, Weaver and Company) and rinsed with a wet cloth. A reference electrode was placed over C7.

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Surface EMG acquisition One electrode grid of 32 (8x4) silver plated electrodes (Ø= 3 mm, inter-electrode distance = 10 mm, LISiN, Politecnico di Torino) was placed on each side of the spine, with the first row at the level of the T12 spinous process, on the belly of the lumbar erector spinae muscles. Two arrays of 16 (16x1) silver/silver chloride electrodes (size: 1x5 mm, inter-electrode distance = 10 mm, OT Bioelettronica, Italy) were placed on each side of the spine, consecutively and proximally from the level of T12, in the region halfway between the spine and the medial border of the scapula (Figure 2a). Figure 2 and 3 about here

Surface EMG processing The monopolar signal detected from each electrode was amplified and filtered (10-750 Hz, analog antialiasing filter), sampled at 2048 samples/s and A/D converted at 12 bits (Amplifier: USB128, OT Bioelettronica, Torino). Digital bandpass filtering between 20 and 400 Hz with a 2 nd order Butterworth bidirectional filter was applied to the raw signals. The first and last two seconds of the 20-s recorded signal were discarded to reject possible transients. The first 10 harmonics of the power line were removed and replaced by spectral interpolation (Mewett, 2004). This procedure implies computing the Fourier transform of the signal (epoch= 1 s) and replacing the harmonics at 48 to 52 Hz, 98-102 Hz, etc. (up to 500 Hz) with the value resulting from linear interpolation between the previous and following two harmonics. Inverse Fourier transform provides a signal with reduced power line interference. The ECG signal was visible in all raw EMG signals and was removed using the following algorithm: 1) QRS complexes were automatically identified as 80 ms time windows centred on the R peaks, detected as proposed by Mak et al. (Mak, 2010) based on the envelope of the acquired signal. 2) RMS was then estimated for all epochs between two consecutive QRS windows included

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in the 16 s EMG recording, 3) The mean of the RMS values on the epochs was calculated. This method was chosen, (e.g. Marker, 2014), because of its simple implementation. The monopolar RMS map was obtained for each considered region (TL, TR, LL, LR), for each subject, each side and each chair. The spatial mean of the RMS monopolar map was computed over the entire grid area and for the 16-s observation time (Figure 2b and Figure 7a. This value is indicated as RMS.). These values were used as indices of sEMG activity to compare the chairs, as explained in the following paragraphs. Monopolar signals were analysed to include the activity of deep muscles, as erector spinae muscles, involved in postural activities and to allow easy spatial filtering in the future. In some instances, however, single differential signals were used. Single differential signals were obtained by software subtraction between adjacent monopolar raw signals in the longitudinal direction. Differentiation reduced ECG and power line interference below the noise level so that their removal were no longer required for the analysis of single differential signals.

2.6 Statistical analysis The inferential statistical analysis was conducted with the R software (package: nlme, PMCMR). The General Comfort Rating Scale provided, for each subject, a comfort index for each chair. The non-parametric Friedman test and the Nemenyi post-hoc test were applied to the General Comfort Rating Scale data to compare the comfort indices associated to the tested chairs. Friedman test with Nemenyi post-hoc test were applied to evaluate differences between pelvic tilt data associated to chairs and postures (standing position with and without instrument). After verification of normality of the data distribution (Shapiro-Wilk and Levene test), one way ANOVA followed by Tukey post-hoc test was adopted to assess the effect of the chairs on the spine angles. RMS of EMG was investigated versus the “region” and “chair” as fixed effect factors while 9

“subject” was considered as a random effect factor. The logarithm (base 10) of the mean of the pixels of each monopolar RMS map was considered as dependent variable. The normality (ShapiroWilk test) and the homoscedasticity of the data (Levene test) were verified for the log data. Tukey post-hoc test was performed over “chair” and “region” factors. The interaction plot did not indicate significant interactions between factors

3. Results 3.1 Subjective comfort evaluation and sitting posture General Comfort Rating Scale showed statistically significant differences (Figure 3) between each chair (O, M, H, HB) and the O90. The H chair was considered "quite comfortable" by 13 out of 21 subjects. The M and HB chairs were considered “perfectly comfortable” by 7/21 and by 4/21 subjects respectively (Figure 3). The following three postures were identified by observing the subjects playing while sitting “as you like” on the reference chair O: a) Asymmetric without back support (66%, 14/21). Subjects sit on the edge of the chair, without using the backrest, with the left foot is forward (leg at 90° with respect to the thigh), and the right foot maintained under the seat. The right leg trunk-thigh angle was 105±8° (range 92÷120°). b) Symmetric without back support (24%, 5/21). This posture is similar to a) but the feet are positioned symmetrically, parallel to each other. Four professional violinists out of five use this posture. c) Symmetric with back support (10%, 2/21). This posture is used only by one violin and one viola player.

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When subjects sit “as you like” on the O chair their right trunk-thigh angle is 105±8° (mean ± SD, N= 21)whereas the left angle is generally about 90°. This arrangement partially reduces the lumbar lordosis because of the flexion of one thigh.

3.2 Postural biomechanical analysis Neither the pelvic tilt nor the spinal angles in standing position are influenced by the presence (SV) or absence (S) of the violin/viola (Figure 4 and 5). Only the M and H saddle chairs are associated to pelvic tilts not statistically different with respect to the tilt in standing position. The O90 reference seat induced the maximal deviation of pelvic tilt with respect to the standing position, even inducing an inversion (pelvic tilt < 0). Sitting “as you like” (O) causes a pelvic tilt midway between those measured on the O90 chair and on the saddle chairs, although the differences are not statistically significant. The introduction of a lumbar support in the H chair did not induce a statistically significant change of pelvic tilt (Figure 4). Figure 4 and 5 about here The angle of lumbar lordosis associated to the chair M is not significantly different from the value associated to the standing position (M-S) which makes the M chair biomechanically preferable to the others (Figure 5). The spinal angles associated to chairs that impose the use of a backrest (O 90, HB and O) are not very reliable because the flexicurve is interposed between the subject and the backrest. These comparisons are purely indicative because of the limitations of the measuring instrument and the lack of data about its measurement error.

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3.3

Back muscle EMG analysis

Monopolar signals and surface EMG-based assessment of chairs A sample of monopolar and single differential sEMG signals from the right trapezius and erector spinae muscles is depicted in Figure 6. The large non-propagating components in these signals are likely due to common mode voltages generated by the end-of-fiber effect associated to short muscle fibers of the erector spinae, possibly to crosstalk from other nearby muscles, and to instrumentation noise. These common mode signals are drastically reduced in the single differential derivation at the lumbar level. Figure 7a shows the EMG distributions associated to subject 13 sitting on the O 90 and HB chair. Figure 7b shows the 95% confidence intervals of the EMG differences (both thoracic and lumbar regions) between 10 pairs of chairs (Tukey test after verification of gaussianity of the log distribution). No significant EMG differences were found between the O and O90 chairs or between the H and M chairs. The H and O chairs show marginally different EMG values (p=0.06). All the other pairs show significant differences. The chair that induces the lowest RMS values is the saddle chair with a low lumbar support (HB). Conversely, sitting with a high backrest (adjusted to cover the lower third of the scapula) and sitting with a trunk-thigh angle of 90° (O90) generated the highest RMS values. The RMS values of the examined musicians are generally asymmetric (Figure 2b, Figure 7a). A statistically significant (p << 0.01) higher activity was observed in the TR versus TL region and in the LR versus LL region (Figure 7c). Figure 6 and 7 about here

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Differential signals and burst-like EMG activity This study outlined two main findings that should be further investigated in future works: a) the large non-propagating components in the monopolar detection and the much smaller propagating components in the single differential signals (Figure 6) and b) the intermittent activity observed in the single differential signals detected from the lumbar erector spinae of some subjects. This burstlike pattern is depicted in Figure 8 that shows five bursts in 2.1s. This pattern was observed in 12 subjects out of 21 (57%) regardless of the chair used. In these subjects the burst frequency was 2.4±0.5 bursts/s (mean ± SD) with a burst duration of 167,7 ± 31,9ms for the O chair, and 2.5 ± 0.5 bursts/s with a burst duration of 170.0 ± 30,9ms for the HB chair with greater amplitude on the left side. No correlation was observed between the presence/absence of bursts with the chair used, music played, gender, age, position (standing/sitting) or weekly hours of training. This observation is preliminary and based on visual analysis. It will be further investigated in a subsequent work. Figure 8 about here

4. Discussion More than half of the subjects (12 of 21) habitually practice exclusively in the standing position because this is encouraged by teachers. Some questions arise (which are still open): does practicing in sitting position and on appropriate chairs, lead to benefits (reduction of the occurrence of pain or Playing related musculoskeletal disorders) without reducing the "learning curve" or the performance? Is the school training of the musician affecting the back muscle activity level? A short-term test provided limited information about the effect of using different chairs but was unavoidable, because of time constrains, since many chairs were compared. This work considers, as a first step, the quantitative assessment of five chairs in order to select the best according to criteria based on a) similarity of kyphosis-lordosis angles to those observed in standing and b) EMG amplitude minimization. 13

4.1 Subjective comfort evaluation and postural analysis The pelvic-tilt and the lumbar lordosis vary with chairs and postures in agreement with the work of (Keegan, 1953; Mandal, 1981). The reference seat with a trunk-thigh angle of 90° (O90) induces a pelvic tilt inversion and a reduction of the lumbar angle with respect to the standing position, in agreement with the literature (Keegan, 1953). This chair is also the one associated to the largest EMG amplitude (see 4.4). The saddle chair (M) induces pelvic-tilt and lumbar lordosis closest to those measured in the standing position (Figure 4). These results are in agreement with those of Annetts et al. (Annetts, 2012) who investigated the effects of different office chairs. They observed that, using a saddle chair, the spine angles where closer to those of the standing position, which are considered the most correct (Harrison, 1999; Keegan, 1953; Pynt, Higgs & Mackay, 2001; O’Sullivan, 2012). Lumbar lordosis was found to be a more discriminating parameter than the thoracic kyphosis for comparing different postures and sittings (Figure 5).

4.4 Back muscle activity analysis Comparisons between chairs The EMG RMS value associated to the O90 chair is the highest among the evaluated seats, in disagreement with Corlett at al. (Corlett, 1984) who investigated office chairs. The disagreement may be explained by the different postural needs between office workers and musicians. Consensus is lacking on whether the increase in the trunk-thigh angle influences the activity of the back muscles, likely due to non-identical locations of the electrode pairs used by different investigators. Curran et al. (Curran, 2015) have systematically reviewed the effect of office chair backrests and the effect of reducing seated hip flexion with respect to low back discomfort and trunk muscle activation. They observed no evidence that chairs involving a smaller hip flexion significantly alter the trunk muscle activity. In our study, a statistically significant reduction of 14

EMG RMS value on saddle chairs, with a trunk-thigh angle greater than 90°, has been observed with respect to other chairs (Figure 7b) in agreement with Soderberg et al. (Soderberg,1986). The reduction of EMG activity was considered positive because inappropriate body posture, may cause prolonged tension in specific muscle groups (i.e. erector spinae). This could lead to fatigue, pain and finally to the deterioration of human performance over time (Cram, 1995). As indicated in Figure 7c, thoracic regions have higher EMG RMS values compared to lumbar regions. However, comparison between the T and L regions is questionable, since the thickness of the subcutaneous layer (an important confounding factor) may not be the same in the two locations (Farina, 2002). In this work the thicknesses of the subcutaneous tissue are assumed to be similar in contralateral regions at the same spinal level and, therefore, EMG differences between sides are attributed to differences of muscle activity. The differences between sEMG RMS values due to chairs (Figure 7b) are statistically significant (p < 0.05) for all the pairs indicated in Figure 7b except O-O90 and H-M. The difference between HB and O90 and between HB and O is highly significant. In the case of HB-O the difference is of the order of -0.07 log units corresponding to a relative variation with respect to HB of about 20% on non-transformed data. The results show that HB and M chairs should be preferred with respect to other seats, however, the negative EMG difference between HB and M (Figure 7b) and angle considerations (Figure 5d) suggest that the M chair with lumbar back rest might have further advantages and should be considered in future investigations over longer time intervals.

Differential signals and burst-like EMG activity The intermittent activity of the lumbar erector spinae is evident in the single differential signals of the lumbar erector spine of 12/21 (57%) of the subjects regardless of the chair used. This postural control strategy has been observed in other antigravity muscles (Vieira, 2012). Although its investigation and discussion exceed the purpose of this work, it is underlined that this behavior 15

seems to be related to the subject and not to the type of chair used. Whether this control strategy is desirable or not remains to be investigated.

5. Conclusions This short-term study on violin and viola players leads to the following conclusions: (1) HDsEMG is a useful tool for studying the back muscles of musicians, for the comparison of chairs and for the investigation of posture control strategies (Figure2, 7 and 8). (2) Violinists and violists habitually assume three main postures, evaluated visually on the sample of 21 subjects (section 3.1). A greater number of subjects is necessary to indicate whether any of the three postures should be preferred. (3) Differences between chairs are better reflected by EMG signals detected at the lumbar level than at the thoracic level (Figure 7a). (4) The EMG signal detected near the spine at the lumbar level is not continuous in all subjects. It often shows a burst-like activity (Figure 8) whose effect on Playing related musculoskeletal disorders should be further investigated in future studies. (5) The EMG of back muscles of violin and viola players is generally asymmetric (Figure 7). It is always higher on the right side both at the lumbar (LR) and the thoracic levels (TR). (6) High backrest chairs and sitting with a trunk-thigh angle of 90° (O90) imply: a) a pelvic tilt inversion, b) a reduction of lumbar lordosis and c) an increase of the muscle activity with respect to that detected on saddle chairs (M, H, HB) and to that detected when the subject was sitting in his preferred posture (O). These effects are not considered positive because this posture shows kyphosis-lordosis angles departing from those in orthostatism. (7) The qualitative comfort scale did not prove, in the short term, to be an effective tool to highlight differences between chairs. The repeatability of these scales remains to be demonstrated. Sitting “as you like” (O) is the condition with the highest comfort and lowest 16

discomfort but differences with other chairs are not statistically significative. The mean EMG amplitude and the postural indices (pelvic tilt and spine angles) observed for chair O are in between those of the saddle chairs (M and H) and the 90° seat (O 90) (Figure 5, 7). According to these criteria the M, H and HB chairs should be preferred. (8) In the standing position, the lumbar lordosis and thoracic kyphosis angles and pelvic tilt are not significantly affected by the instrument (viola or violin). (Figure 5). (9) Lumbar lordosis is affected by the chair used but thoracic kyphosis is not (Figure 5). (10) In order to evaluate different chairs, attention should be more focused on the lumbar region since the trapezius activity is directly involved with music production. In summary, the investigated chairs can be ordered according to three criteria of preference: Criterion 1. EMG amplitude of back muscles from low to high: HB; H and M; O and O90 (with chairs HB, H and M to be preferred) Criterion 2. Pelvic tilt/lordosis, in order of increasing difference with respect to standing: M; H; HB and O; O90 (with chairs M, H and HB to be preferred) Criterion 3. Comfort, from high to low (subjective and possibly conditioned by habit): O; M; H; HB; O90 (with O, M and H to be preferred) The use of a saddle chair with a trunk-thigh angle of about 115°, preferably equipped with a lumbar support, can be a good compromise. A second option, based on the EMG signal minimization criterion, is the HB chair. However, these conclusions must be validated and confirmed by tests of longer duration that should include the analysis of fatigue and EMG burst-like activity.

5.1 Limitations of the study and suggestions for future work Only three violist were evaluated in this study. It was decided to consider violin and viola players as a single population since viola requires a posture very similar to that of the violinist and no 17

significant differences in the range of motion were reported between them (Turner-Stokes, 1999). The sample is heterogeneous. Age (as well as dominance and gender) differences are confounding factors. Despite these factors, differences between chairs turn out to be statistically significant. In other words, differences between chairs are not masked by differences of age, gender, dominance and practice hours. Individual habits (sitting in different ways, training in standing or sitting position) might have played a role as confounding factors, as well as the wide ranges of age and experience. Grids of larger size with a greater number of electrodes should be used in future works to cover a larger area and provide a more accurate description of EMG activity. Other features of the HDsEMG maps should be investigated during long term tests (e.g. progressive shift of the map centroid, fatigue indicators based on spectral variables or conduction velocity estimates). Signals from the lumbar region are more sensitive to chair differences. Despite their lower amplitude and information content with respect to monopolar signals, single differential signals should be preferred for analysis because of their lower sensitivity to ECG, power line interference and end-of-fiber effects and because of their capability to bring forward phenomena such as the intermittent posture control revealed by burst activity.

References Afsharipour, B., Petracca, F., Gasparini, M., and Merletti, R., 2016. Spatial distribution of surface EMG on trapezius and lumbar muscles of violin and cello players in single note playing. Journal of Electromyography and Kinesiology, 31, 144-153. doi: 10.1016/j.jelekin.2016.10.003. Andersson, B. J., Jonsson, B., and Ortengren, R., 1974. Myoelectric activity in individual lumbar erector spinae muscles in sitting. A study with surface and wire electrodes. Scandinavian journal of rehabilitation medicine. Supplement 3: 91-108. Andersson, B. J., Ortengren, R., Nachemson, A. L., Elfström, G., and Broman, H., 1975. The sitting posture: an electromyographic and discometric study. The Orthopedic clinics of North America 6 (1): 105-120. 18

Annetts, S., Coales, P., Colville, R., Mistry, D., Moles, K., Thomas, B., and Van Deursen, R., 2012. A pilot investigation into the effects of different office chairs on spinal angles. European Spine Journal 21 (2): 165-170. doi: 10.1007/s00586-012-2189-z. Azevedo, D. C., Santos, H., Carneiro, R. L., & Andrade, G. T., 2014. Reliability of sagittal pelvic position assessments in standing, sitting and during hip flexion using palpation meter. Journal of bodywork and movement therapies, 18(2), 210-214. Bendix, T., and Biering-Sørensen, F., 1982. Posture of the trunk when sitting on forward inclining seats. Scandinavian journal of rehabilitation medicine 15 (4): 197-203. Carcone, S. M., and Keir, P. J., 2007. Effects of backrest design on biomechanics and comfort during seated work. Applied Ergonomics 38 (6): 755-764. doi: 10.1016/j.apergo.2006.11.001. Cattarello, P., Merletti, R. and Petracca F., 2017. Analysis of High-Density surface EMG and finger pressure in the left forearm of violin players: a feasibility study. Medical Problems of Performing Artists, 32 (3): 139-151. doi: 10.21091/mppa.2017.3023. Clarkson, H. M., and Pace, P., 2002. Kinesiological evaluation: Examination of joint mobility and muscle strength (in italian). Milano: Ermes. Claus, A. P., Hides, J. A., Moseley, G. L., and Hodges, P. W., 2009. Is ‘ideal’sitting posture real? Measurement of spinal curves in four sitting postures. Manual Therapy 14 (4): 404-408. doi: 10.1016/j.math.2008.06.001. Claus, A., Hides, J., Moseley, G. L., and Hodges, P., 2008. Sitting versus standing: does the intradiscal pressure cause disc degeneration or low back pain?. Journal of Electromyography and Kinesiology 18 (4): 550-558. doi: 10.1016/j.jelekin.2006.10.011. Corlett, E. N., and Eklund, J. A. E., 1984. How does a backrest work? Applied Ergonomics 15 (2): 111-114. doi: 10.1016/0003-6870(84)90282-5. Côté, P., Kreitz, B. G., Cassidy, J. D., Dzus, A. K., and Martel, J., 1998. A study of the diagnostic accuracy and reliability of the Scoliometer and Adam's forward bend test. Spine 23 (7): 796-802. Cram, J. R., and Vinitzky, I., 1995. Effects of chair design on back muscle fatigue. Journal of Occupational Rehabilitation, 5(2), 101-113. Curran, M., O’Sullivan, L., O’Sullivan, P., Dankaerts, W., and O’Sullivan, K., 2015. Does Using a Chair Backrest or Reducing Seated Hip Flexion Influence Trunk Muscle Activity and Discomfort? A Systematic Review. Human Factors: The Journal of the Human Factors and Ergonomics Society 57 (7): 1115-1148. doi: 10.1177/0018720815591905. De Carvalho, D. E., Soave, D., Ross, K., and Callaghan, J. P., 2010. Lumbar spine and pelvic posture between standing and sitting: a radiologic investigation including reliability and repeatability of the lumbar lordosis measure. Journal of manipulative and physiological therapeutics 33 (1): 48-55. doi: 10.1016/j.jmpt.2009.11.008. De Oliveira, T. S., Candotti, C. T., La Torre, M., Pelinson, P. P. T., Furlanetto, T. S., Kutchak, F. M., and Loss, J. F., 2012. Validity and reproducibility of the measurements obtained using the flexicurve instrument to evaluate the angles of thoracic and lumbar curvatures of the spine in the sagittal plane. Rehabilitation research and practice 2012. doi: 10.1155/2012/186156. Dunk, N. M., Kedgley, A. E., Jenkyn, T. R., and Callaghan, J. P., 2009. Evidence of a pelvis-driven flexion pattern: are the joints of the lower lumbar spine fully flexed in seated postures?. Clinical Biomechanics 24 (2): 164-168. doi: 10.1016/j.clinbiomech.2008.12.003. Farina, D., Cescon, C., and Merletti, R., 2002. Influence of anatomical, physical, and detectionsystem parameters on surface EMG. Biological cybernetics 86 (6): 445-456. doi: 19

10.1007/s00422-002-0309-2. Fjellman-Wiklund, A., Grip, H., Karlsson, J. S., and Sundelin, G., 2004a. EMG trapezius muscle activity pattern in string players: Part I—is there variability in the playing technique? International journal of industrial ergonomics 33 (4): 347-356. doi: 10.1016/j.ergon.2003.10.007. Fjellman-Wiklund, A., Grip, H., Andersson, H., Karlsson, J. S., and Sundelin, G., 2004b. EMG trapezius muscle activity pattern in string players: Part II—Influences of basic body awareness therapy on the violin playing technique. International Journal of Industrial Ergonomics 33 (4): 357-367. doi: 10.1016/j.ergon.2003.10.008. Grieco, A., Occhipinti, E., Colombini, D., Menoni, O., Bulgheroni, M., Frigo, C., and Boccardi, S., 1989. Muscular effort and musculoskeletal disorders in piano students: electromyographic, clinical and preventive aspects. Ergonomics 32 (7): 697-716. doi: 10.1080/00140138908966837. Harrison, D. D., Harrison, S. O., Croft, A. C., Harrison, D. E., and Troyanovich, S. J., 1999. Sitting biomechanics part I: review of the literature. Journal of manipulative and physiological therapeutics 22 (9): 594-609. doi: 10.1016/S0161-4754(99)70020-5. Irina Foxman, M. S., and Burgel, B. J., 2006. Musician health and safety: Preventing playingrelated musculoskeletal disorders. Workplace Health & Safety 54 (7): 309-316. Kaufman-Cohen, Y., and Ratzon, N. Z., 2011. Correlation between risk factors and musculoskeletal disorders among classical musicians. Occupational Medicine 61 (2): 90-95. doi: 10.1093/occmed/kqq196. Keegan, J. J., 1953. Alterations of the lumbar curve related to posture and seating. J Bone Joint Surg Am 35 (3): 589-603. Koskelo, R., Vuorikari, K., and Hänninen, O., 2007. Sitting and standing postures are corrected by adjustable furniture with lowered muscle tension in high-school students. Ergonomics 50 (10): 1643-1656. doi: 10.1080/00140130701587236. Kuntz IV, C., Shaffrey, C. I., Ondra, S. L., Durrani, A. A., Mummaneni, P. V., Levin, L. S., and Pettigrew, D. B., 2008. Spinal deformity: a new classification derived from neutral upright spinal alignment measurements in asymptomatic juvenile, adolescent, adult, and geriatric individuals. Neurosurgery 63 (3): A25-A39. doi: 10.1227/01.NEU.0000313120.81565.D7. Lander, C., Korbon, G. A., Degood, D. E., and Rowlingson, J. C., 1987. The Balans chair and its semi-kneeling position: an ergonomic comparison with the conventional sitting position. Spine 12 (3): 269-272. Lee, H. S., Park, H. Y., Yoon, J. O., Kim, J. S., Chun, J. M., Aminata, I. W., and Jeon, I. H., 2013. Musicians' medicine: musculoskeletal problems in string players. Clinics in orthopedic surgery 5 (3): 155-160. doi: 10.4055/cios.2013.5.3.155. Mak, J. N., Hu, Y., and Luk, K. D., 2010. An automated ECG-artifact removal method for trunk muscle surface EMG recordings. Medical engineering & physics 32 (8): 840-848. doi: 10.1016/j.medengphy.2010.05.007. Mandal, A. C.,1981. The seated man (Homo Sedens) the seated work position. Theory and practice. Applied Ergonomics 12 (1): 19-26. doi: 10.1016/0003-6870(81)90089-2. Marker, R. J., and Maluf, K. S., 2014. Effects of electrocardiography contamination and comparison of ECG removal methods on upper trapezius electromyography recordings. Journal of Electromyography and Kinesiology 24 (6): 902-909. doi: 10.1016/j.jelekin.2014.08.003. Mewett, D. T., Reynolds, K. J., and Nazeran, H., 2004. Reducing power line interference in 20

digitised electromyogram recordings by spectrum interpolation. Medical and Biological Engineering and Computing 42 (4): 524-531. doi: 10.1007/BF02350994. O'Sullivan, K., O'Sullivan, P., O'Sullivan, L., and Dankaerts, W., 2012. What do physiotherapists consider to be the best sitting spinal posture?. Manual therapy 17 (5): 432-437. doi: 10.1016/j.math.2012.04.007. Pynt, J., Higgs, J., and Mackey, M., 2001. Seeking the optimal posture of the seated lumbar spine. Physiotherapy theory and practice 17 (1): 5-21. doi: 10.1080/09593980151143228. Saarni, L., Nygård, C. H., Rimpelä, A., Nummi, T., and Kaukiainen, A., 2007The working postures among schoolchildren—a controlled intervention study on the effects of newly designed workstations. Journal of school Health 77 (5): 240-247. doi: 10.1111/j.1746-1561.2007.00199.x. Shackel, B., Chidsey, K. D., and Shipley, P., 1969. The assessment of chair comfort. Ergonomics 12 (2): 269-306. doi: 10.1080/00140136908931053. Soderberg, G. L., Blanco, M. K., Cosentino, T. L., and Kurdelmeier, K. A., 1986. An EMG analysis of posterior trunk musculature during flat and anteriorly inclined sitting. Human Factors: The Journal of the Human Factors and Ergonomics Society 28 (4): 483-491. Spahn, C., Wasmer, C., Eickhoff, F., and Nusseck, M., 2014. Comparing Violinists' Body Movements While Standing, Sitting, and in Sitting Orientations to the Right or Left of a Music Stand. Medical problems of performing artists 29 (2): 86. Toppenberg, R. M., and Bullock, M. I., 1986. The interrelation of spinal curves, pelvic tilt and muscle lengths in the adolescent female. Australian Journal of Physiotherapy 32 (1): 6-12. doi: 10.1016/S0004-9514(14)60638-3. Turner-Stokes, L., and Reid, K., 1999. Three-dimensional motion analysis of upper limb movement in the bowing arm of string-playing musicians. Clinical Biomechanics 14 (6): 426-433. doi: 10.1016/S0268-0033(98)00110-7. Vergara, M., and Page, Á., 2000. Technique to measure lumbar curvature in the ergonomic evaluation of chairs: description and validation. Clinical Biomechanics 15 (10): 786-789. doi: 10.1016/S0268-0033(00)00042-5. Vieira, T. M., Loram, I. D., Muceli, S., Merletti, R., & Farina, D., 2012. Recruitment of motor units in the medial gastrocnemius muscle during human quiet standing: is recruitment intermittent? What triggers recruitment? Journal of neurophysiology, 107(2), 666-676 Zaza, C., 1998. Playing-related musculoskeletal disorders in musicians: a systematic review of incidence and prevalence. Canadian medical association journal 158 (8): 1019–1025. Zaza, C., and Farewell, V. T., 1997. Musicians' playing‐related musculoskeletal disorders: An examination of risk factors. American journal of industrial medicine 32 (3): 292-300.

FIGURE CAPTIONS Figure 1. Chairs and their codes used in this study. The backrest of the O90 chair is higher than that of the HB chair and reaches the lower third of the scapula.

21

Figure 2. a) Electrode positioning. b) Example of monopolar RMS maps for each of the considered regions (TL, TR, LL, LR). These maps were calculated over a 16s epoch (playing Kreutzer Studies #2 at 88 bpm). Each pixel (channel) value represents the average of the RMS values computed between subsequent QRS complexes of the ECG, over the 16s epoch. The average value and the range of the RMS values of the pixels are shown above each map. The colour scale is the same for the four electrode systems. c) Outlines of the four regions considered. Figure 3. a) Bar histogram of the answers to the General Comfort Rating Scale (GCRS) for the 21 examined subjects. b) General Comfort Rating Scale scores. c) Box plot of the scores for the considered chairs (see Figure 1). d) Results of the Nemenyi post-hoc test after the Friedman test. Statistically significant differences (p < 0.05) are highlighted. Figure 4. a) Example of pelvic tilt measurement in standing position. The instrument consists of an inclinometer and two caliper arms. The inclinometer is a semi-circular arc with 1o gradations for pelvic tilt measurement (Azevedo, 2014). b) Box plot of pelvic tilt values (21 subjects) for several chairs and assumed postures: S = standing; SV = standing with the instrument; for the labels of the chairs, refer to Figure 1. c) Results Nemenyi post-hoc test after Friedman test. The statistically significant differences (p < 0.05) are highlighted. Figure 5. a) Example of the spine contour detection to extract the lordosis and kyphosis angles. Box plot (21 subjects) of the kyphosis (b) and lordosis (c) angles for the different chairs (Fig. 1) and the assumed postures: S = standing; SV = standing with the instrument. d) Results of Tukey post-hoc test to compare the chairs and the standing positions. Differences are statistically significant when their 95% confidence interval does not intersect the zero line. p-values are indicated. Values of p > 0.05 are indicated as NS. For the kyphosis angle (graph not reported) there were no statistically significant differences. Gaussian distribution and the homoscedasticity of the differences was verified with Shapiro-Wilk and Levene tests. Figure 6. Examples of sEMG signals. Monopolar and single differential (SD) signals are reported for thoracic (upper panels) and one column of the grids on the lumbar regions (lower panels). Motor unit action potential (MUAP) showing propagation are marked with dashed lines. Note the different amplitude scales and the large amplitude of non-propagating components. Figure 7. a) Examples of monopolar RMS maps of a subject sitting on chairs O90 and HB (Figure 1). b) Results of the Tukey post-hoc test for factors "chair" (b) and "region" (c). Differences are statistically significant when the 95% confidence interval of the difference between the means does 22

not intersect the zero line. Values of p >> 0.05 are indicated as NS. Considering two factors, A and B, it should be noted that the difference, in b) and c), is between their log values

LogA –LogB = Log(A/B) = x . So for untransformed data we have: A=10x B.

Gaussian distribution and the homoscedasticity of the differences were verified with Shapiro-Wilk and Levene tests.

Figure 8. Example of raw single differential signals from the columns of the lumbar arrays closest to the spine. Five bursts are evident.

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FIGURES WITH CAPTIONS

Figure 1. Chairs and their codes used in this study. The backrest of the O90 chair is higher than that of the HB chair and reaches the lower third of the scapula.

24

Figure 2. a) Electrode positioning. b) Example of monopolar RMS maps for each of the considered regions (TL, TR, LL, LR). These maps were calculated over a 16s epoch (playing Kreutzer Studies #2 at 88 bpm). Each pixel (channel) value represents the average of the RMS values computed between subsequent QRS complexes of the ECG, over the 16s epoch. The average value and the range of the RMS values of the pixels are shown above each map. The colour scale is the same for the four electrode systems. c) Outlines of the four regions considered.

25

Figure 3. a) Bar histogram of the answers to the General Comfort Rating Scale (GCRS) for the 21 examined subjects. b) General Comfort Rating Scale scores. c) Box plot of the scores for the considered chairs (see Figure 1). d) Results of the Nemenyi post-hoc test after the Friedman test. Statistically significant differences (p < 0.05) are highlighted.

26

Figure 4. a) Example of pelvic tilt measurement in standing position. The instrument consists of an inclinometer and two caliper arms. The inclinometer is a semi-circular arc with 1o gradations for pelvic tilt measurement (Azevedo, 2014). b) Box plot of pelvic tilt values (21 subjects) for several chairs and assumed postures: S = standing; SV = standing with the instrument; for the labels of the chairs, refer to Figure 1. c) Results Nemenyi post-hoc test after Friedman test. The statistically significant differences (p < 0.05) are highlighted.

27

Figure 5. a) Example of the spine contour detection to extract the lordosis and kyphosis angles. Box plot (21 subjects) of the kyphosis (b) and lordosis (c) angles for the different chairs (Fig. 1) and the assumed postures: S = standing; SV = standing with the instrument. d) Results of Tukey post-hoc test to compare the chairs and the standing positions. Differences are statistically significant when their 95% confidence interval does not intersect the zero line. p-values are indicated. Values of p > 0.05 are indicated as NS. For the kyphosis angle (graph not reported) there were no statistically significant differences. Gaussian distribution and the homoscedasticity of the differences was verified with Shapiro-Wilk and Levene tests.

28

Figure 6. Examples of sEMG signals. Monopolar and single differential (SD) signals are reported for thoracic (upper panels) and one column of the grids on the lumbar regions (lower panels). Motor unit action potential (MUAP) showing propagation are marked with dashed lines. Note the different amplitude scales and the large amplitude of non-propagating components.

29

Figure 7. a) Examples of monopolar RMS maps of a subject sitting on chairs O90 and HB (Figure 1). b) Results of the Tukey post-hoc test for factors "chair" (b) and "region" (c). Differences are statistically significant when the 95% confidence interval of the difference between the means does not intersect the zero line. Values of p >> 0.05 are indicated as NS. Considering two factors, A and B, it should be noted that the difference, in b) and c), is between their log values

LogA –LogB = Log(A/B) = x . So for untransformed data we have: A=10x B.

Gaussian distribution and the homoscedasticity of the differences were verified with Shapiro-Wilk and Levene tests.

30

Figure 8. Example of raw single differential signals from the columns of the lumbar arrays closest to the spine. Five bursts are evident.

31

Subject number

Student/ Professor

Male/ Female

Age (years)

Height (cm)

Body mass (kg)

Musical career (years)

Training (h/week)

Side domin.

1 2

P S

F F

22 16

165 175

52 72

10 10

45,5 6

R R

3

S

F

19

163

53

12

5

R

4 5 6

S S S

F M M

15 15 19

160 180 176

50 75 90

10 9 14

14 5 10

R R R

7

S

F

15

172

58

8

24,5

R

8

S

M

23

190

82

10

28

L

9

S

M

18

170

58

8

24,5

R

10

S

F

16

164

69

12

17,5

R

11

S

M

25

171

52

8

17,5

R

12

P

F

53

150

53

45

7

R

13

S

F

21

170

57

13

4,5

R

14

S

F

29

165

55

12

35

R

15

P

F

34

163

52

25

2

R

16

P

M

50

185

90

39

8

R

17

P

F

29

167

67

20

10

R

18

P

F

42

165

60

30

3

R

19

S

F

19

160

50

12

12,5

R

20

P

M

25

170

78

20

28

L

21

S

M

17

172

70

9

10

R

Comments and remarks

Viola player. History of back pain with NRS= 2

History of back pain with NRS= 1 Viola player. History of back pain with NRS= 1 History of back pain with NRS= 3 Viola player. History of pain at upper limbs with NRS= 2 History of general pain with NRS= 2 History of back pain with NRS= 3 History of general pain with NRS= 4 History of back pain and pain at upper limbs with NRS= 3 History of back pain with NRS= 2 History of pain at upper limbs with NRS= 1 History of back pain with NRS= 1

8/13

25 169 64 15÷53 150÷190 50÷90

16 8÷45

15 2÷45,5

R/L Domin.

14/7

Training (h/week)

21

Musical career (years)

M/F

Body mass (kg)

S/P

Height (cm)

N

Age (years)

Statistics (mean and range values)

19/2

Most of the subjects (57%) had a history of minor musculoskeletal disorders

32

Table 1 Characteristics of the 21 players involved in the study. NRS = Numerical rating scale. The two left-handed subjects held the instrument like the right-handed colleagues.

33

Biosketches for JEK

Paolo Cattarello graduated in Biomedical Engineering at Politecnico di Torino (Italy) in 2015, with an experimental thesis titled: Study of Electrode-Skin interface and development of wearable elastic matrix for High Density Surface Electromyo-graphy (HDsEMG). In 2016, he obtained a Lagrange fellowship and joined the Laboratory for Engineering of the Neuromuscular System (LISiN) where he conducted his research on the study and the interpretation of sEMG signal detected from musicians.

Dr Samuel D’Emanuele graduated “cum laude” in Sciences and Advanced Techniques of Sport from SUISM (Torino, Italy) with an experimental thesis titled: "An experimental protocol of ergonomics and kinesiology for pianists and violinists" carried out at LISiN.

Silvia Vinelli graduated “cum laude” in Physiotherapy at Università degli studi di Torino with the thesis : “Investigation into

34

ergonomics of the sitting posture based on biomechanical parameters, sEMG and comfort for the prevention of PRMDs in

Marco Gazzoni obtained his PhD Biomedical Engineering at Politecnico di Torino, Italy where he is now associate Professor. Since 1997 he has been associated with Laboratory for Engineering of the Neuromuscular System (LISiN) which he directs since 2015. His main interests are in the development of scientific software and new processing techniques applied to neurophysiology and motor rehabilitation.

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Roberto Merletti obtained his M.Sc. and PhD in Biomedical Engineering from the Ohio State University. He has been Research Associate at the NeuroMuscular Research Center and Associate Professor of Biomedical Engineering at Boston University. He has been Full Professor of Biomedical Engineering at Politecnico di Torino where he established, in 1996, the Laboratory for Engineering of the Neuromuscular System (LISiN) which he directed up to 2015. His activity led to over 150 peer reviewed publications and four textbooks. Prof. Merletti is now retired but active in teaching and research activities . He is Senior Member of IEEE, Fellow of ISEK, and member of the Editorial Board of three international journals. His personal web site www.robertomerletti.it has a strong teaching connotation.

36