Organization of the upper limb movement for piano key-depression differs between expert pianists and novice players

Abstract

The present study investigated the expert-novice difference in the organization of upper-limb movement for the key-depression on the piano. Kinematic and electromyographic recordings were made while experts (N = 7) and novices (N = 7) of classical-piano players performed a right hand octave keystroke to produce four different sound dynamics. The joint torque generated at the key-bottom moment (key-force torque) was also estimated. At all sound dynamics, the experts showed a larger finger attack angle, more flexed shoulder, wrist, and MP joints, more extended elbow joint, and smaller key-force torque at the MP joint than the novices. The level of co-activation in the finger flexor–extensor muscles during the period prior to the key-bottom moment was also lower for the experts. To attain the large attack angle by the experts, as the fingertip depressed the key to the bottom, their shoulder was actively flexed, the forearm was thrust forward, and the hand was rotated forward. The novices, on the other hand, actively extended their shoulder to move the forearm and hand downward to depress the key. These results confirmed a substantial difference in the key-depression movement organization between the experts and novices. These findings also suggest that experts use a synergistically organized multi-joint limb motion that allows them to minimize the biomechanical load and muscular effort to the distal muscles. The novices, on the other hand, tend to rely on a rudimentary synergy of joint motion developed through daily experience.

Appendix

During the finger-key contacting period, torques (“key-force torque”) from key reaction force are generated at the joints of the upper extremity. The key-force torque can be calculated as follows:

$$ \tau = {\mathbf{J}}^{{\text{T}}} \cdot {\mathbf{F}} $$

where τ is the key-force torque, F is the key-force (F = [Fx,Fy]), and J is the Jacobian matrix described as follows:

$$ {\mathbf{J}} = {\left[ {\begin{array}{*{20}c} {{J_{{11}} }} & {{J_{{12}} }} & {{J_{{13}} }} & {{J_{{14}} }} \\ {{J_{{21}} }} & {{J_{{22}} }} & {{J_{{23}} }} & {{J_{{24}} }} \\ \end{array} } \right]} $$

$$ J_{{11}} = - {\left( {A\sin \theta + B\sin {\left( {\theta + \phi } \right)} + C\sin {\left( {\theta + \phi + \psi } \right)} + D\sin {\left( {\theta + \phi + \psi + \varphi } \right)}} \right)} $$

$$ J_{{12}} = - {\left( {B\sin {\left( {\theta + \phi } \right)} + C\sin {\left( {\theta + \phi + \psi } \right)} + D\sin {\left( {\theta + \phi + \psi + \varphi } \right)}} \right)} $$

$$ J_{{13}} = - {\left( {C\sin {\left( {\theta + \phi + \psi } \right)} + D\sin {\left( {\theta + \phi + \psi + \varphi } \right)}} \right)} $$

$$ J_{{14}} = - D\sin {\left( {\theta + \phi + \psi + \varphi } \right)} $$

$$ J_{{21}} = A\cos \theta + B\cos {\left( {\theta + \phi } \right)} + C\cos {\left( {\theta + \phi + \psi } \right)} + D\cos {\left( {\theta + \phi + \psi + \varphi } \right)} $$

$$ J_{{22}} = B\cos {\left( {\theta + \phi } \right)} + C\cos {\left( {\theta + \phi + \psi } \right)} + D\cos {\left( {\theta + \phi + \psi + \varphi } \right)} $$

$$ J_{{23}} = C\cos {\left( {\theta + \phi + \psi } \right)} + D\cos {\left( {\theta + \phi + \psi + \varphi } \right)} $$

$$ J_{{24}} = D\cos {\left( {\theta + \phi + \psi + \varphi } \right)} $$

where constants are described as follows:

A :

length from shoulder to elbow

B :

length from elbow to wrist

C :

length from wrist to MP

D :

length from MP to fingertip

θ :

shoulder angle

ϕ:

elbow angle

ψ:

wrist angle

φ:

MP angle

These constants were computed using the measured position data of each joint center at the moment of the key’s lowest position for each participant. For all participants, the key-force torque was then computed at all loudness levels while a given amount of key reaction force was assumed to be applied to the fingertip at the moments of the key’s lowest position. For this purpose, the key reaction force at the moment of maximum key displacement was measured in a preliminary experiment using three expert and three novice piano players. A small uni-axial force transducer (Tec-gihan co., Kyoto, Japan) was fastened to the surface of the G3 key front using an adhesive strip, and it was struck by the thumb 10 times at the designated sound dynamics in the octave keystroke mode. The mean key reaction force at the p, mp, mf, and f levels were 2.3, 3.8, 6.5, 9.8 N, respectively, for the experts, and 2.3, 3.7, 6.4, and 10.1 N, respectively, for the novices. These values were doubled to approximate the sum of key reaction forces applied at the thumb and little finger, and inputted into the equation for each of the groups. The tangential force (Fx) was set to nil for simplicity of computation. The key-force torques at the MP, wrist, and elbow joints were computed. The shoulder joint torque was not computed because it was independent of the arm and hand postures.