Participants
Active expert pianists from Madrid Music Academy were recruited. The current study focuses on insidious neck pain as main playing-related musculoskeletal disorder. We included pianists with current insidious neck pain and pianists without neck pain the previous years as control group. Insidious neck pain was defined as generalized neck or shoulder pain of mechanical characteristics provoked by neck postures, neck movement, or palpation of the cervical muscles. Participants were excluded if exhibited any of the following criteria: 1, previous surgery and/or steroid injections in the upper quadrant; 2, whiplash cervical or neck surgery; 3, history of wrist or arm trauma; 4, symptoms in any different place than the neck-shoulder area, for instance, in the hand; or, 5, fibromyalgia syndrome [12].
Self-reported handedness, degree of the course and relative year attended, age at start, the possibility to adjust the chair height, number of hours/day and hours/week spent in individual practice, frequency and duration of the breaks, and frequency and duration of preliminary technical exercises were recorded. Participants were asked to indicate whether they believe that "a certain amount of pain is acceptable when attempting to overcome technical difficulties" ("No pain, no gain" criterion). The study was approved by the Ethics committee at Granada University and informed consent was obtained from all participants.
Self-reported measures
An 11-point numerical pain rate scale (NPRS, 0: no pain; 10: maximum pain) was used to assess the current level of neck pain and shoulder pain. The NPRS has been demonstrated to be a reliable and valid instrument to assess pain intensity [13]. Patients also completed the Neck Disability Index (NDI) to assess self-perceived disability. The NDI consist of 10 questions measured on a 6-point scale (0: no disability; 5: full disability) [14]. The numeric score for each item is summed for a score varying from 0 to 50, where higher scores reflect greater disability. The NDI is a reliable and valid outcome of disability in neck pain [15, 16]. Macdemid et al found that studies investigating reliability of the NDI showed intra-class correlation coefficients ranging from 0.50 to 0.98, suggesting that the NDI has sufficient support and usefulness to be the most commonly used self-report measure for neck pain [17]. Finally, piano players traced the outline of their dominant hand in a rest position (minimal abduction angle) on a graph paper. Hand length, breadth and index were evaluated by drawing lines and classified according to Wagner percentiles. [18].
Pressure Pain Threshold Assessment
An electronic algometer (Somedic AB, Sweden) was used to determine pressure pain thresholds (PPT: minimal amount of pressure where a sensation of pressure first changes to pain) [19]. The pressure was applied approximately at a rate of 30 kPa/sec, with the algometer placed perpendicular to the application point. Participants were instructed to press switch when the sensation changed from pressure to pain. The mean of 3 trials (intra-examiner reliability) was calculated and used for the main analysis. A 30-s resting period was allowed between each measure. The reliability of pressure algometry has been found to be high (ICC: 0.91, 95% CI 0.82-0.97) [20].
All participants had abstained from any kind of general exercise the previous day and were not allowed to take analgesics or muscle relaxant through the 72 h prior to the examination. Participants attended a preliminary session for familiarization with PPT assessment. PPT levels were measured bilaterally over the articular pillar of C5-C6 zygapophyseal joint, the deltoid muscle, the second metacarpal and the tibialis anterior muscle by an assessor blinded to the participant condition. The order of assessment was randomized between participants.
Sample Size Determination
The sample size determination was done with an appropriate software (Tamaño de la Muestra, 1.1©, Spain). The determinations were based on detecting significant differences of 20% on PPT levels over each point between both groups [21] with an alpha level of 0.05, and a desired power of 80%. This generated a sample size of at least 16 participants per group.
Statistical Analysis
Data were analysed with the SPSS statistical package (19.0 Version). Results are expressed as mean ± standard deviation and 95% confidence interval (95% CI). The Kolmogorov-Smirnov test was used to analyse the normal distribution of the variables (P > 0.05). Since quantitative data showed a normal distribution, parametric tests were used. Demographic characteristics of both study groups were compared using unpaired Student t-test for quantitative data and χ2 tests of independence for categorical data. A two-way ANOVA test was used to evaluate the differences in PPT levels assessed over each point (C5-C6 joint, deltoid muscle, second metacarpal, tibialis anterior) with side (dominant/non-dominant) as within-subjects factor and group (neck pain or healthy) as between-subjects factor. Finally, the Pearson correlation test (r) was used to analyse the association between PPT, pain intensity (NPRS), and self-reported disability (NDI) in those pianist with insidious neck pain. The statistical analysis was conducted at a 95% confidence level. A P-value less than 0.05 was considered statistically significant.