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Previous planar models of the downswing in golf have suggested that upper limb segments (left shoulder girdle and left arm) move in a consistent fixed plane and that the clubhead also moves only in this plane. This study sought to examine these assumptions. Three-dimensional kinematic analysis of seven right-handed golfers of various abilities (handicap 0?–?15) was used to define a plane (named the left-arm plane) containing the 7th cervical vertebra, left shoulder and left wrist. We found that the angles of this plane to the reference horizontal z axis and target line axis (parallel to the reference x axis) were not consistent. The angle to the horizontal z axis varied from a mean of 133° (s = 1°) at the start of the downswing to 102° (s = 4°) at impact, suggesting a “steepening” of the left-arm plane. The angle of the plane to the target line changed from ??9° (s = 16°) to 5° (s = 15°) during the same period, showing anticlockwise (from above) rotation, although there was large inter-individual variation. The distance of the clubhead from the left-arm plane was 0.019?m (s = 0.280?m) at the start at the downswing and 0.291?m (s = 0.077?m) at impact, showing that the clubhead did not lie in the same plane as the body segments. We conclude that the left arm and shoulder girdle do not move in a consistent plane throughout the downswing, and that the clubhead does not move in this plane. Previous models of the downswing in golf may therefore be incorrect, and more complex (but realistic) simulations should be performed. 相似文献
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Maternal behaviors within mother-infant games were examined to determine the amount, type, and functional value of maternal helping behaviors. 17 mother-infant pairs were videotaped on monthly visits from 8 to 16 months as they played 5 separate games. 2 of these games, roll the ball and peekaboo, were analyzed in terms of "rounds" of each game. Results show that dyads play more rounds of both games in the first months that infants perform game-relevant behaviors (e.g., returning a ball, performing uncovering or covering-uncovering). Maternal attention-getting and physical "stage-setting" behaviors occur in the early rounds of both games. In roll the ball, maternal hands-out and reinforcement behaviors increase in the months after the child begins to return the ball, while the percentage of rounds in which dyads play nonreturn variants decreases. Infants are more likely to return a ball when mother holds out her hands than when she does not. Infants are also able to perform returning or uncovering in game contexts before they perform similar behaviors in cognitive tests. The general similarity of findings in the peekaboo and roll-the-ball games, in spite of differences in the amounts of scaffolding, attention-getting, stage-setting, and reinforcement behaviors between the 2 games, indicates that the types and functions of maternal helping behaviors may be generalizable to other contexts of mother-infant interactions. 相似文献
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Kalakanis LE Goldfield GS Paluch RA Epstein LH 《Research quarterly for exercise and sport》2001,72(3):202-209
The purposes of this study were to measure the level and pattern of moderate-to-vigorous physical activity (MVPA = > 4.5 METs) and examine predictors of activity in obese children. Fifty-one 8-12-year-old children seeking obesity treatment wore accelerometers for 3 or 4 days. Children averaged 12.2 bouts of MVPA per day that lasted an average of 4.2 min, while parents engaged in 3.9 bouts of MVPA that lasted 4.2 min. Hierarchical regression models showed parent activity improved the prediction of obese children's activity levels and the number of bouts of MVPA but not the duration of MVPA. These results suggest that programs to increase physical activity in obese children should structure the activity in short bouts and attempt to increase parental physical activity. 相似文献
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