One type of optimization, the minimum jerk model (maximum smoothness) proposes that endpoint trajectory is planned in a way to minimize the jerk cost (JC) ...
JERK OPTIMIZATION AS AN INDICATOR OF SKILL IN A COMPLEX DANCE MOVEMENT. Bronner S, Spriggs J. Soar Research, Long Island University, Brooklyn, NY. PURPOSE: Motor learning and control theory propose several alternate models to explain experimental data. Optimization theory suggests skilled movement minimizes various cost functions (energy, force, speed, etc) in order to maximize success and efficiency of the task. What is optimized in movement may depend on the task goal. One type of optimization, the minimum jerk model (maximum smoothness) proposes that endpoint trajectory is planned in a way to minimize the jerk cost (JC) function. [Jerk is the third time derivative of displacement. JC is mean squared jerk integrated over the entire movement.] This study examined jerk cost, a measure of smoothness, of the end segment (toe) in dancers of varying skill levels when performing a complex dance movement (arabesque). It has been suggested that skilled performance is characterized by decreased JC through smoother movement. METHODS: 30 adult subjects (age range 18-36) represented three distinct levels of dance training: Expert, Advanced and Beginner. Data acquisition was conducted with a 5-camera Vicon system, sampled at 120 Hz. A fourth order Butterworth filter with cut off frequencies of 6 and 10 Hz was used to smooth displacement and acceleration data respectively. The arabesque is a complex multi-joint movement consisting of several phases. Following displacement scoring to determine the beginning and end of each phase, JC was time normalized for each phase, as well as limb length. RESULTS: Toe endpoint resultant displacement displayed similar shape across groups. Mean peak tangential velocity of the toe was also similar across groups. However, there was a reduction in mean phase JC from Beginners to Expert, suggesting increased smoothness parallels increased skill. CONCLUSION: As movement becomes more skillful, it appears to become smooth and graceful. JC has been used to examine skill in competitive running, violin bowing, speech, reaching, and throwing. The minimum jerk model appears to be a viable theory when applied to skill acquisition in dancers, the epitome of grace. RELEVANCE: General objectives of movement coordination include efficiency, economy, and accuracy. As we gain insight into the organizing principles used by the CNS to plan and produce movement, we can plan more effective treatment and learning environments for our patients. ACKNOWLEDGEMENTS: This research is supported in part by the Fan Fox and Leslie R Samuels Foundation and NIH MBRS Grant #SO6 GM54650-04. J Orthop Sports Phys Ther 32(1):A-11, 2002. Platform presentation, APTA CSM, Boston, MA, 2002.
