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Melvin R. Ramey and Keith R. Williams

Ground reaction forces were obtained for the three phases of the triple jump for four collegiate triple jumpers, two men and two women. A single force platform was used, which thereby required the subjects to execute three separate jumps to produce a single triple jump record. The vertical force records for each phase showed two peaks having magnitudes in the range of 7 to 12 times body weight (BW) and 3.3 to 5 BW, respectively. These magnitudes are substantially higher than has been reported by others for distance running, sprinting, and in some cases other jumps. The maximum horizontal forces act to decrease the velocity of the mass center, but to different degrees for the different subjects. The data show that for any phase of the jump there is considerable variability in the timing and magnitudes of the force records among the different subjects although general patterns are similar. The results suggest that the use of mean force data from a number of subjects may conceal important differences between the way individuals execute the jump.

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Keith R. Williams and Jodi L. Ziff

There is little information on how a change in one feature of an individual’s running mechanics affects other aspects of running style. This study manipulated experimental conditions such that eight subjects ran with three different step lengths, three step widths, and three varying degrees of shoulder rotation. The effect of these changes on rearfoot pronation measures, step length, and step width were examined. Results showed that varying step length over a range of 18 cm and shoulder rotation over a range of 17° caused no significant differences in maximal pronation angle, total amount of pronation, or maximal pronation velocity. Varying step width from landing approximately 5 cm lateral to the midline to crossing over a midline by 2 cm increased the maximum pronation from 12.2 to 18.3°, the amount of pronation from 14.1 to 21.1°, and maximal pronation velocity from. 329°/s to 535°/s. It is suggested that runners with problems due to excessive pronation might try changing step width. Changes in step width and shoulder rotation had no significant effect on step length, and alterations to shoulder rotation did not affect step length or step width significantly. These results suggest that a runner attempts to maintain some aspects of running mechanics despite major alterations to other elements of running style.

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Keith R. Williams, Rebecca Snow, and Chris Agruss

This study investigated changes in kinematics with fatigue during intercollegiate competition, a noncompetitive track run, and a constant speed treadmill run. To account for changes in kinematics resulting from speed differences, regression equations for each individual generated from nonfatigue data were used to predict rested kinematics for speeds matching those of the fatigue conditions. A factor analysis procedure grouped 29 kinematic variables into sets of independent factors, and both factor variables and individual variables were analyzed for changes with fatigue, which were minimal. Only one significant difference was found in the factor variables between nonfatigue and fatigue states. Comparisons of specific kinematic variables showed a significant increase in step length with fatigue, an increased maximal knee flexion angle during swing, and an increased maximal thigh angle during hip flexion. While fatigue did not result in marked changes in kinematics for the group as a whole, changes for individuals were at times large.

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Richard N. Hinrichs, Peter R. Cavanagh, and Keith R. Williams

Ten male recreational runners were filmed using three-dimensional cinematography while running on a treadmill at 3.8 m/s, 4.5 m/s, and 5.4 m/s. A 14-segment mathematical model was used to examine the influence of the arm swing on the three-dimensional motion of the body center of mass (CM), and on the vertical and horizontal propulsive impulses (“lift” and “drive”) on the body over the contact phase of the running cycle. The arms were found to reduce the horizontal excursions of the body CM both front to back and side to side, thus tending to make a runner's horizontal velocity more constant. The vertical range of motion of the body CM was increased by the action of the arms. The arms were found to make a small but important contribution to lift, roughly 5–10% of the total. This contribution increased with running speed. The arms were generally not found to contribute to drive, although considerable variation existed between subjects. Consistent with the CM results, the arms were found to reduce the changes in forward velocity of the runner rather than increasing them. It was concluded that there is no apparent advantage of the “classic” style of swinging the arms directly forward and backward over the style that most distance runners adopt of letting the arms cross over slightly in front. The crossover, in fact, helps reduce side-to-side excursions of the body CM mentioned above, hence promoting a more constant horizontal velocity.

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Sarah Taylor, Bradley Fawver, Joseph L. Thomas, A. Mark Williams, and Keith R. Lohse

Contextual interference is an established phenomenon in learning research; random practice schedules are associated with poorer performance, but superior learning, compared with blocked practice schedules. We present a secondary analysis of N = 84 healthy young adults, replicating the contextual interference effect in a time estimation task. We used the determinant of a correlation matrix to measure the amount of order in participant responses. We calculated this determinant in different phase spaces: trial space, the determinant of the previous five trials (lagged constant error 0–4); and target space, the determinant of the previous five trials of the same target. In trial space, there was no significant difference between groups (p = .98) and no Group × Lag interaction (p = .54), although there was an effect of Lag (p < .01). In target space, there were effects of Group (p = .02), Lag (p < .01), and a Group × Lag interaction (p = .03). Ultimately, randomly scheduled practice was associated with adaptive corrections but positive correlations between errors from trial to trial (e.g., overshoots followed by smaller overshoots). Blocked practice was associated with more adaptive corrections but uncorrelated responses. Our findings suggest that random practice leads to the retrieval and updating of the target from memory, facilitating long-term retention and transfer.

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Irene S. McClay, John R. Robinson, Thomas P. Andriacchi, Edward C Frederick, Ted Gross, Philip Martin, Gordon Valiant, Keith R. Williams, and Peter R. Cavanagh

Basketball is a sport that involves multiple impacts with the ground through a variety of moves such as running Jumping, and cutting. Repetitive impacts have been associated with stress-related injuries in other sports such as running. The purpose of this investigation was to gain an understanding of the typical stresses the body experiences during common basketball moves. To this end, the ground reaction forces from 24 players from five professional basketball teams were studied. In addition, a game analysis was performed to determine the frequency of selected moves. These data indicated that certain common movements, such as jump landings and shuffling, resulted in absolute and relative forces much greater than many of those reported previously in studies of other sports. These movements were also identified in a companion paper as being associated with large angular excursions and velocities. Findings are discussed with respect to injury risks, and suggestions for future study are made.

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Irene S. McClay, John R. Robinson, Thomas P. Andriacchi, Edward C. Frederick, Ted Gross, Philip Martin, Gordon Valiant, Keith R. Williams, and Peter R. Cavanagh

Overuse injuries are common in basketball. To gain insight into their etiology and relationship to mechanics, researchers and clinicians need an understanding of the normal biomechanics of the sport. This study was undertaken with this goal in mind. Lower extremity joint kinematics and structural parameters were collected from 24 players from five professional basketball teams as they performed maneuvers typical of their sport. The results indicated that certain common moves such as the layup landing resulted in knee flexion velocities almost double those seen during the landing phase of running. Lateral movements such as cutting and shuffling placed the foot in extreme positions of supination. Both of these findings have implications for injuries common to basketball such as patellar tendinitis and ankle sprains. It is hoped that this information will initiate a database for normal lower extremity kinematics during basketball and lead to a greater understanding of the relationship of lower extremity movement patterns and injury.