Golf shots off uneven terrain often require modifications in address position to complete the swing successfully. This study aimed to determine how golf players coordinate the legs to regulate linear and angular impulse (about an axis passing vertically through the center of mass) while modifying the lower-extremity address position during the swing. Nine highly skilled golf players performed swings with a 6-iron under the Normal, Rear Leg Up, and Target Leg Up conditions. Components of linear and angular impulse generated by the rear and target legs (resultant horizontal reaction force, resultant horizontal reaction force angle, and moment arm) were quantified and compared across the group and within a player (α = .05). Net angular impulse did not change between conditions. Target leg angular impulse was greater in the Target Leg Up condition than Rear Leg Up condition. Regulation of linear and angular impulse generation occurred while increasing stance width and redirecting resultant horizontal reaction forces to be more parallel to the target line under modified address positions. Net linear impulse perpendicular to the target was near 0 or slightly posterior. Net linear impulse parallel to the target was less toward the target in the Target Leg Up condition compared with Normal and Rear Leg Up conditions. These results indicate individuals utilized player-specific mechanisms to coordinate the legs and regulate impulse generation during the golf swing under modified address positions.
Travis J. Peterson and Jill L. McNitt-Gray
Travis J. Peterson, Rand R. Wilcox, and Jill L. McNitt-Gray
Our aim was to determine how skilled players regulate linear and angular impulse while maintaining balance during the golf swing. Eleven highly-skilled golf players performed swings with a 6-iron and driver. Components contributing to linear and angular impulse generated by the rear and target legs (resultant horizontal reaction force [RFh], RFh-angle, and moment arm) were quantified and compared across the group and within a player (α = .05). Net angular impulse generated by both the rear and target legs was greater for the driver than the 6-iron. Mechanisms used to regulate angular impulse generation between clubs varied across players and required coordination between the legs. Increases in net angular impulse with a driver involved increases in target leg RFh. Rear leg RFh-angle was maintained between clubs whereas target leg RFh became more aligned with the target line. Net linear impulse perpendicular to the target line remained near zero, preserving balance, while net linear impulse along the target line decreased in magnitude. These results indicate that the net angular impulse was regulated between clubs by coordinating force generation of the rear and target legs while sustaining balance throughout the task.
Rand Wilcox, Travis J. Peterson, and Jill L. McNitt-Gray
The paper reviews advances and insights relevant to comparing groups when the sample sizes are small. There are conditions under which conventional, routinely used techniques are satisfactory. But major insights regarding outliers, skewed distributions, and unequal variances (heteroscedasticity) make it clear that under general conditions they provide poor control over the type I error probability and can have relatively poor power. In practical terms, important differences among groups can be missed and poorly characterized. Many new and improved methods have been derived that are aimed at dealing with the shortcomings of classic methods. To provide a conceptual basis for understanding the practical importance of modern methods, the paper reviews some modern insights related to why methods based on means can perform poorly. Then some strategies for dealing with nonnormal distributions and unequal variances are described. For brevity, the focus is on comparing 2 independent groups or 2 dependent groups based on the usual difference scores. The paper concludes with comments on issues to consider when choosing from among the methods reviewed in the paper.