This study was designed to examine Ihe developmental differences in the speed and smoothness of arm movement during overarm throwing. The second purpose of this investigation was to evaluate whether jerk is a useful measure in understanding children's overarm throwing. Fifty-one girls, aged 3 to 6 years, voluntarily participated in the study. Each subject threw tennis balls as hard as she could toward a large target on the wall. A 2-camera video system was used to obtain 3-D coordinates of the hand and ball using the DLT algorithm. The variables of velocity and jerk (for the hand and ball) served as the movement outcome measures. The age-associated differences in velocity and normalized jerk (absolute jerk standardized relative to movement time and distance) were examined by ANOVAs. The results supported the hypothesis that the older subjects demonstrated faster and smoother hand movements than their younger counterparts during the forward acceleration phase (from the beginning of forward motion to ball release). In addition, the correlation results indicated thai increased hand movement speed was associated with decreased movement jerk in older subjects, whereas increased hand speed was associated with increased jerk in younger subjects. The findings suggest that examining the jerk parameter (normalized or absolute jerk) is a useful and alternative approach to capture the variance of hand movement execution for children's overarm throwing.
J.H. Yan is with the Department of Health and Human Performance, The University of Houston, Houston, TX 77204-6321. R.N. Hinrichs is with the Department of Bxercise Science and Physical Education, Arizona Stale University, Tempe, AZ 85287. V.G. Payne is with the Department of Human Performance, San Jose State University, San Jose, CA 95192. J.R. Thomas is with the Department of Health and Human Performance, Iowa State University, Ames, IA 50011.