This paper describes an experimentally-based analysis of the interaction between musician and instrument in the case of the classical concert harp. The study highlights gestural strategies used by three harpists while performing a short musical excerpt. As a result of years of practicing, a trained musician has developed the ability to deal with a number of trade-offs among simultaneous objectives while playing. She/he has obviously to set the instrument into vibration, but also to convey some musical intention to the audience and to communicate with other musicians, while keeping a safe posture with respect to articular and muscle pain. In order to precisely describe the motion strategies carried out by trained harpists, an experiment has been designed using a motion capture system and corresponding video and audio recordings. This provides accurate three-dimensional positioning of several markers disposed on the harpist and on the harp, within the execution of a musical piece. From the acquired gestural and acoustical signals, a set of kinematic and dynamic descriptors were extracted. The investigation shows that while each musician uses their own specific and repeatable upper-limb movements, the global sound-producing gesture is mostly controlled by the shoulders. Sound-facilitating hand gestures are highlighted for their supporting role to the musician throughout the musical piece.