Are the forearm muscles excited equally in different, professional piano players?

Abstract

Background and objectives: Professional pianists tend to develop playing-related musculoskeletal disorders mostly in the forearm. These injuries are often due to overuse, suggesting the existence of a common forearm region where muscles are often excited during piano playing across subjects. Here we use a grid of electrodes to test this hypothesis, assessing where EMGs with greatest amplitude are more likely to be detected when expert pianists perform different excerpts.

Methods: Tasks were separated into two groups: classical excerpts and octaves, performed by eight, healthy, professional pianists. Monopolar electromyograms (EMGs) were sampled with a grid of 96 electrodes, covering the forearm region where hand and wrist muscles reside. Regions providing consistently high EMG amplitude across subjects were assessed with a non-parametric permutation test, designed for the statistical analysis of neuroimaging experiments. Spatial consistency across trials was assessed with the Binomial test.

Results: Spatial consistency of muscle excitation was found across subjects but not across tasks, confining at most 20% of the electrodes in the grid. These local groups of electrodes providing high EMG amplitude were found at the ventral forearm region during classical excerpts and at the dorsal region during octaves, when performed both at preferred and at high, playing speeds.

Discussion: Our results revealed that professional pianists consistently load a specific forearm region, depending on whether performing octaves or classical excerpts. This spatial consistency may help furthering our understanding on the incidence of playing-related muscular disorders and provide an anatomical reference for the study of active muscle loading in piano players using surface EMG.

Fig 1. Experimental setup.

A. Schematic representation of the experimental protocol and of the positioning of markers and of the grid of electrodes. The detailed procedure considered for standardizing the position of the grid of electrodes across participants is illustrated in B. The first column of electrodes was placed along the line connecting the lateral epicondyle to the ulnar styloid process, whereas 20% of this line was the reference for placing the first row of electrodes.

Fig 2. Computation of EMG maps for octaves.

Hand trajectories along the lateral and the craniocaudal axes are illustrated respectively in panels A and B for a representative subject during wrist octaves. Raw EMGs detected by all electrodes in columns 2, 7 and 14 during an upward phase of the up-down hand trajectory cycles are shown in panel C (left), together with the Root Mean Square (RMS) amplitude of each monopolar EMG averaged across cycles (right).

Fig 3. Statistical assessment of consistent excitation across subjects.

This figure systematically illustrates the procedures necessary for applying the statistical, permutation test described by Nichols et al. [23] to EMG images. The method is spited into five steps, detailed in the text and summarized in insets. In all images illustrated, higher and lower values are represented with respectively darker and brighter pixels. The example is shown for the improvisation task.

Fig 4. Area and centroids of over-significance-threshold EMGs across subjects.

Pseudo t images obtained for classical excerpts are shown in A. White circles denote the region of excitation, defined by pixels providing an average pseudo t value greater than the statistical threshold, set at 5% (Fig 3, Step 4). Crossed circles indicate the centroid of the excitation region, computed as the weighted average of pseudo t values defining the region of excitation. Panel B shows transverse (up) and longitudinal (middle) coordinates of centroids during octaves, as well as the number of electrodes (bottom) defining the region of excitation.

Fig 5. Number of over-significance-threshold EMGs across trials.

Image showing the counts of pixels, across trials, providing pseudo t values which average was greater than the statistical threshold. Maximal count is eight, considering four classical excerpts and the four octaves performed at preferred speed. Counts are schematically represented with respect to anatomical references. Counts greater than 6 would indicate a significant consistency across trials. The exact same distribution of counts was obtained when considering octaves performed at high speeds. Regions where pairs of bipolar electrodes are recommended to be centered for assessing excitation of extensor (blue crossed circle) and flexor (green crossed circle) muscles are shown.