The relationship between smoothness and performance during the practice of a lower limb obstacle avoidance task.

The relationship between performance (movement time) and smoothness was examined as subjects (n = 8) practiced a simple lower limb obstacle avoidance task. Smoothness was quantified by endpoint 3D jerk-cost, partitioned into magnitudinal and directional components. Data were collected with two WATSMART cameras at a sampling rate of 200 Hz for three sets of two trial blocks, including trials 1, 2, 13, 14, 25, and 26. Ten practice trials were performed between blocks of recorded trials. A DLT method was used to reconstruct 3D position coordinates of the fifth metatarsal of the subject's right (dominant) foot, considered to be the endpoint. After the data were smoothed with a fourth order, zero lag Butterworth filter, the time period was normalized so that a comparison of jerk-cost could be made between trials. Very rapid decreases in both movement time and jerk-cost measures were followed by gradual decreases, indicating that the movement became smoother as performance improved. Correlation coefficients between movement time and the various components of jerk-cost ranged from 0.70 to 0.78, supporting the hypothesis that moving more smoothly enables a person to move more rapidly during an obstacle avoidance task.