Incident light velocimetry

Individual pathways in the development of forceful throwing

Halverson, Roberton, and Langendorfer (1982) reported the development of children ages 6-13 years filmed longitudinally performing the forceful overarm throw. These authors described the children's progress through developmental sequences for trunk, humerus, and forearm actions; however, they did not study developmental relationships ("profiles") across these components. This paper reports how the profiles changed in the same children across trials within filming sessions and over time. The data revealed both common and individual developmental pathways. The frequencies of some pathways were not chance occurrences (p < or = .01), suggesting that within-person constraints eliminated certain movement relationships while encouraging others. The authors hypothesize that the kinematics of trunk rotation may serve as a control parameter for pattern change.

Predicting children's overarm throw ball velocities from their developmental levels in throwing

This study examined the movement process-product relationship from a developmental perspective. The authors used multiple regression to investigate the changing relationship between qualitative movement descriptions of the overarm throw and the throwing outcome, horizontal ball velocity. Seventeen girls and 22 boys were filmed longitudinally at ages 6, 7, 8, and 13 years. Their movements were assessed using Roberton's (Roberton & Halverson, 1984) developmental sequences for action of the humerus, forearm, trunk, stepping, and stride length. The sequences accounted for 69-85% (adjusted) of the total velocity variance each year. The components that best predicted ball velocity changed over time, although humerus or forearm action always accounted for considerable variance. Gender was a good predictor of ball velocity, but if the developmental descriptions were entered first in a stepwise regression, gender then explained no more than 2% additional variance.

The participant-observer: a source of invalidity in measuring motor skills?

Test validity can be defined as the accuracy of a test score. Artifacts, sources of error that affect validity, have been studied in both research design and written test frameworks but have received little attention in the context of tests of motor behavior in an educational setting. One potential source of invalidity in motor skill testing is the presence of participant-observers. The participant-observer effect is defined as the influence of the presence of other subjects who are waiting to be tested or who have already been tested on subjects who are being tested. This study was designed to measure the test performances of 175 college women with participant-observers present and with participant-observers absent. The test was an overarm throw for speed measured by an incident light velocimeter. The data were analyzed using 2 X 4 fixed-effects analysis of variance. The presence of other participant-observers did not elicit performance scores that were different from those of subjects tested alone. Thus testing subjects in groups where one member of the group is tested while the others observe did not adversely affect performance on the overarm throw compared with that of subjects tested alone.

Comparison of Four Different Methods for Measuring Projectile Velocity

Four techniques for measuring the velocity of a free-falling body (a baseball) were compared for validity and reliability. The baseball, with two steel bolts attached, was made to fall free by releasing it from an electromagnet. The four methods studied were (1) stopwatch ( n = 61), utilizing a 0.1-sec. stopwatch and (2) line-pull ( n = 61), utilizing two lines of different length attached to the baseball. The shorter line when pulled taut triggered a switch to start a clock counter. The longer line when pulled taut stopped the clock. (3) For 16-mm motion picture photography ( n = 11), a Bell & Howell camera with Kodak Tri-X film (ASA 160) at 76 frames/sec. was used and for (4) strobophotography ( n = 10) flash intervals of 20, 40, and 60 msec. were employed to expose sequential images of the free-falling baseball on Polaroid Type 57 film (ASA 3000). Strobophotography gave the best agreement with theoretical velocity ( V0), followed by 16-mm motion photography, line-pull, and stopwatch methods, in that order. Strobophotography was also the most reliable of the four methods, having the lowest standard deviation for Vobs – V0. Next in order of reliability were line-pull, 16-mm motion photography, and stopwatch. Multiple-image strobophotography gave superior validity and reliability in measuring projectile velocity, while line-pull and 16-mm motion picture photography methods seemed adequate for most research applications as well as athletics and instruction. A stopwatch is suitable only when a rough estimate of a projectile's velocity is needed.