Movement variability is a common measure of coordination in biomechanics research, especially in sports (Bartlett et al., 2007) and ergonomics (Preatoni et al., 2013). There are two main types of movement variability: 1) intra-participant movement variability, which is the difference between a single individual’s movements when performing repetitions of the same task (Cowin et al., 2022; Zhao et al., 2021), and 2) inter-participant movement variability, which is the difference between multiple individuals’ movements while performing the same task (Zhao et al., 2021). Biomechanics research can use movement variability to understand musculoskeletal pathomechanisms (Preatoni et al., 2013). When executing tasks, motor variability may distribute mechanical loading across musculoskeletal structures, reducing cumulative loading on soft tissues and thus, decreasing the risk of injury (Hamill et al., 2012; Young et al., 2022). Up to 77% of pianists suffer from an injury at some point in their career (Amaral Corrêa et al., 2018). Analysis of intra-movement variability may potentially inform pianists about movement strategies to actively prevent injury during piano performance. Since pianists cannot avoid repetitive tasks, movement strategies could introduce greater kinematic variability by altering upper-limb kinematics to reduce repetitive loading on musculoskeletal structures. Research in music performance has mainly assessed variability in relation to musical outcomes across repetitions, such as performance accuracy (Loria et al., 2022), rhythm (Repp, 1999), sound intensity (Van Vugt et al., 2013), and tempo (Michaud et al., 2022). The influence of the variability in piano practice sessions on note accuracy, timing, and sound intensity has also been studied (Bangert et al., 2014). However, to our knowledge, movement variability is not discussed in piano pedagogy. There is also minimal research on the analysis of movement variability in piano performance biomechanics (Liu et al., 2022; Séguin & Comeau, 2022; Sforza et al., 2003; Wong et al., 2022).
Although it is unclear which movement strategies at the piano are ideal for injury prevention, greater use of proximal movements could reduce the risk of injury by potentially increasing movement variability. Adding movements at proximal joints might alter loading patterns in distal joints to avoid injury, especially in response to muscular fatigue, as observed in ergonomics (Cowley & Gates, 2017) and sports (Brown et al., 2012) research. Studies have shown that expert pianists use a multi-joint upper-limb movement strategy to produce keystrokes (Furuya et al., 2011; Furuya & Kinoshita, 2008). For example, shoulder movements influence distal joints, such as the wrist and finger joints (Verdugo et al., 2020). This concept has been discussed in piano pedagogy literature (Kochevitsky, 1967; Matthay, 1903). Multi-joint movement strategies at the piano might also include trunk motion, as pelvic and thoracic movements contribute to the production of pianists’ hand and finger velocities (Verdugo et al., 2020) and can initiate upper-limb movements (Verdugo et al., 2022). Trunk motion might also play a crucial role in professional pianists’ movement strategies and differ as a function of musical context (Turner et al., 2022) and musical expression (Thompson & Luck, 2012). Trunk movements might also enable greater range of motion (ROM) at upper-limb joints (Verdugo et al., 2022). Since movements are highly individualized among pianists (Turner, Visentin, Oye, et al., 2021), it seems reasonable that shoulder and trunk proximal movement strategies may provide pianists with various approaches to artistic performance while potentially enhancing movement variability.
Repetitive leaps across the keyboard are a commonly found task in piano repertoire. This is a suitable task to study movement variability due to both their repetitive and cyclic nature and the different movement strategies pianists can use to move their hands along the mediolateral axis. On the one hand, while shoulder movement is required to move the hand along the mediolateral axis (i.e., the keyboard), pianists can use different types of shoulder movement, such as back-and-forth, clockwise and counter-clockwise, to perform whole leap cycles (Fink, 1992). On the other hand, trunk motion might or might not be used depending on each pianist’s movement strategy (Turner et al., 2022). The selection of specific shoulder and trunk movement strategies could influence movement patterns and ROM at upper-limb joints and, thus, movement variability. Movements at proximal and distal joints might however be affected by the speed of the leap (i.e., the score-specific tempo and rhythm). These movement strategies, along with tempo, might also influence endpoint (fingertip) accuracy, which is extremely important as pianists are expected to perform accurately a recital repertoire that can include up to 50,000 tones (Goebl, 2017). In this sense, movement variability might be influenced not only by pianists’ choices in relation to multi-joint movement strategy but also by the spatiotemporal constraint of the musical task performed.
The main goal of this study was to assess the impact of proximal movement strategies on intra-participant joint angle variability in the upper-limbs of expert pianists while performing repetitive leaps with the right hand. To this end, the study had two objectives:
-
determine the effect of proximal motion (shoulder and trunk movements) and performance tempo on intra-participant joint angle variability of upper-limb joints as well as the influence on intra-participant endpoint variability.
-
compare joint angle variability between pianist’s upper-limb joints while performing with and without trunk motion.
We hypothesized that movement strategies with greater proximal movements would increase upper-limb intra-participant joint angle variability and that faster tempi would decrease variability, particularly at more distal joints. However, we predicted that neither proximal movement strategies nor changes in performance tempo would increase intra-participant endpoint variability. Given that distal joints in the upper-limb are more involved in fine motor skills, for the second objective we hypothesized that intra-participant joint angle variability would be lowest in the wrist but would increase with the addition of proximal motion. We also performed two secondary analyses to check the two main objectives. To check if variability increases concomitantly with ROM in piano performance, we also assessed the relationship between intra-participant joint angle variability and ROM. Due to minimal literature on pianists’ movement variability, we also documented inter-participant joint angle variability. For the secondary objectives, we hypothesized that ROM and intra-participant joint angle variability would be correlated and that inter-participant joint angle variability would be high.