Stroboscopic Study of Motion Changes That Accompany Modifications and Improvements in a Throwing Performance

This study identifies and analyzes the effects of practice on the movement changes of an upper limb while engaged in a novel ball throwing task for accuracy. Eight male university students served as subjects and participated in a training program consisting of 50 throws per day at a target for 20 consecutive days. Information taken from stroboscopic photographs of the first and last days of the practice sessions served as the data for the study. Accounts made each day of the average deviation of the ball about the target center indicated a considerable reduction in throwing error. The motor modifications that accompanied this performance improvement included changes in rate (velocity magnitude) and changes in position (wrist angle). Posttest limb velocity scores were reduced in value from their pretest counterparts. These posttest velocities were also considerably more consistent. Initial posttest limb accelerations were much lower than similar measurements made of the pretest throws. Subsequent posttest deceleration for the ball release was more gradual and controlled than the pretest measurements. Posttest acceleration rates were again more consistent than pretest accelerations. Finally, measurements of the degrees of ulnar flexion for the posttest far exceeded the pretest values. This was similarly accompanied by an increase in the consistency of occurrence.