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Richard N. Hinrichs

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 contributions of the arms to the total-body angular momentum about three orthogonal axes passing through the body center of mass. The results showed that while the body possessed varying amounts of angular momentum about all three coordinate axes, the arms made a meaningful contribution to only the vertical component (Hz). The arms were found to generate an alternating positive and negative Hz pattern during the running cycle. This tended to cancel out an opposite Hz pattern of the legs. The trunk was found to be an active participant in this balance of angular momentum, the upper trunk rotating back and forth with the arms and, to a lesser extent, the lower trunk with the legs. The result was a relatively small total-body Hz throughout the running cycle. The inverse relationship between upper- and lower-body angular momentum suggests that the arms and upper trunk provide the majority of the angular impulse about the z axis needed to put the legs through their alternating strides in running.

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Richard N. Hinrichs

Ten male recreational runners ranging in age from 20 to 32 years were filmed using 3-D cinematography while running on a treadmill at 3.8 m/s, 4.5 m/ s, and 5.4 m/s. The 3-D segment endpoint data were entered into a computer program that computed the segmental contributions to the upward and forward propulsive impulses on the body (lift and drive, respectively) and to the vertical component of angular momentum (Hz). The results of two subjects who demonstrated asymmetrical arm action are discussed in detail and compared with the mean results computed over all subjects. The results revealed that the arms possess the potential to compensate for each other and for asymmetries elsewhere in the body.

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Mostafa Afifi and Richard N. Hinrichs

It is common practice to study jump landing mechanics by having subjects step off a box set at a certain height instead of landing from a jump. This practice assumes that the landing mechanics are similar between stepping off a box and a countermovement jump as long as the heights can be matched. The mechanics of the two methods had never been compared when landing from identical heights. Thus, the purpose of this study was to compare the mechanics of landing from a countermovement jump to landing from a step-off. Participants performed three maximal countermovement jumps. The mechanics of one countermovement jump was compared with a center of mass fall height matched step-off landing. The step-off landing showed a more rapid time to peak ground reaction force (GRF) in both genders and greater GRF peak and loading rate in males only. No difference was observed between joint angles at initial contact; however, the countermovement jump showed significantly greater joint flexion angles at peak GRF for both genders. EMG showed greater muscle activity during the countermovement jump condition in all subjects. It was concluded that countermovement jump landings are different from step-off landings; thus, results from analyses involving step-off landings should be taken with caution if the aim is to relate them to landing from a jump.

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Richard N. Hinrichs and Scott P. McLean

Swimmers may be placed at a disadvantage when water in a pool is actively circulated during competition. This circulation may produce currents in specific lanes which add to a swimmer’s speed in one direction and subtract from it in the other direction. This article presents a mathematical model of swimming in a lane with a current. It predicts that even small currents can add significantly to a swimmer’s race time. The effects of the current will not equal out over an even number of lengths swum because the swimmer always loses more time swimming against the current than he or she gains from swimming with the current. Mathematical simulations of races of various distances show that the losses in time can range from 100ths of a second in a 100-m sprint to several seconds in the longer distances. Since circulating water may create currents only in specific lanes, some swimmers may be placed at a disadvantage compared to others. A simple solution to the problem of currents is suggested.

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Scott P. McLean and Richard N. Hinrichs

This study investigated the relationship of gender and buoyancy to sprint swimming performance. The center of buoyancy (CB) and center of mass (CM) were measured using reaction board principles. Performance was evaluated as the time needed to complete the middle 13.7 m of a 22.9-m sprint for kicking and swimming trials. Nineteen female swimmers (mean ± SD, 21.9 ± 3.2 years) had significantly more body fat (24.1 ± 4.5%) than 13 male swimmers (21.7 ± 4.2 years, 14.8 ± 5.0%). Males swam and kicked significantly faster (p < .01) than females. Percent body fat, upper body strength, the distance between the CB and CM (d), and the buoyant force measured in 3 body positions all met the criteria for entrance into a regression equation. When gender was not controlled in the analysis, these variables accounted for 70% of the variance in swim time (p < .008). When gender was controlled in the analysis, these variables accounted for 45% of the variance in swim time (p = .06). Percent body fat accounted for the largest amount variance in both regression analyses (39%, p < .001; 18%, p = 0.02, respectively). Upper body strength accounted for 14% of the variance in swim time (p = .006) when gender was not controlled but only 4% when gender was controlled (p = .27). The distance d as measured in a body position with both arms raised above the head was the buoyancy factor that accounted for the greatest amount of variance in swim time (6% when gender was not controlled, p = .06, 10%; when gender was controlled, p = .07). Percent body fat, d, and the buoyant force accounted for no significant amount of variance in kick time. These data suggested that a swimmer’s buoyancy characteristics did have a small but important influence on sprint swimming performance.

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Peter F. Vint and Richard N. Hinrichs

Isometric knee extension force and average integrated EMG of the vastus lateralis muscle were obtained from 27 healthy subjects using a maximum effort, ramp and hold protocol. In each of the 125 total trials mat were included in the analysis, a 2-s plateau region was extracted and divided into two adjacent 1000-ms bins. Variability and reliability of bin-to-bin measurements of force and EMG were then evaluated across 14 different integration intervals ranging from 10 to 1000 ms. Statistical analyses of bin-to-bin variability measures demonstrated that integration intervals of 250 ms and longer significantly reduced variability and improved reliability of average integrated EMG values during maximum effort isometric exertions. Bin-to-bin EMG reliability increased from .728 at 10 ms to .991 at 1000 ms. Force parameters appeared less sensitive to changes in length of the integration interval. It was suggested that longer intervals might also improve the validity of the EMG-force relationship during maximum effort isometric exertions by reducing problems associated with electromechanical delay.

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Peter F. Vint and Richard N. Hinrichs

The purpose of this investigation was to quantify the differences between one- and two-foot vertical jumping performances. Fourteen subjects performed both jump styles with a four-step, self-paced approach. While overall jump and reach heights were similar between one-foot and two-foot jumps, the strategies employed to achieve these results were notably different. One-foot jumps benefited from an increased takeoff height that was largely attributable to the elevation of the free swinging leg. Further, it was suggested that the actions of this limb may have helped slow the rate of extension of the support leg during the propulsion phase. Greater flight heights were achieved during two-foot jumps, as expected, but the magnitude of this difference was only about 9 cm. It was suggested that factors associated with the development of muscular tension, vertical velocity at touchdown, and horizontal approach speed may have all contributed to the unexpectedly small differences in flight height between one-foot and two-foot jumping performances.

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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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Jin H. Yan, Richard N. Hinrichs, V. Gregory Payne and Jerry R. Thomas

This study was designed to examine Ihe developmental differences in the speed and smoothness of arm movement during overarm throwing. The second purpose of this investigation was to evaluate whether jerk is a useful measure in understanding children's overarm throwing. Fifty-one girls, aged 3 to 6 years, voluntarily participated in the study. Each subject threw tennis balls as hard as she could toward a large target on the wall. A 2-camera video system was used to obtain 3-D coordinates of the hand and ball using the DLT algorithm. The variables of velocity and jerk (for the hand and ball) served as the movement outcome measures. The age-associated differences in velocity and normalized jerk (absolute jerk standardized relative to movement time and distance) were examined by ANOVAs. The results supported the hypothesis that the older subjects demonstrated faster and smoother hand movements than their younger counterparts during the forward acceleration phase (from the beginning of forward motion to ball release). In addition, the correlation results indicated thai increased hand movement speed was associated with decreased movement jerk in older subjects, whereas increased hand speed was associated with increased jerk in younger subjects. The findings suggest that examining the jerk parameter (normalized or absolute jerk) is a useful and alternative approach to capture the variance of hand movement execution for children's overarm throwing.

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Scott P. McLean, Michael J. Holthe, Peter F. Vint, Keith D. Beckett and Richard N. Hinrichs

Ten male collegiate swimmers (age = 20.2 ± 1.4 years, height = 184.6 ± 5.8 cm, mass = 82.9 ± 9.3 kg) performed 3 swimming relay step starts, which incorporated a one or two-step approach, and a no-step relay start. Time to 10 m was not significantly shorter between step and no-step starts. A double-step start increased horizontal takeoff velocity by 0.2 m/s. A single-step together start decreased vertical takeoff velocity by 0.2 m/s but increased takeoff height by 0.16 m. Subjects were more upright at takeoff by 4°, 2°, and 5° in the double-step, single-step apart, and single-step together starts, respectively, than in the no-step start. Entry angle was steeper by 2°, entry orientation was steeper by 3°, and entry vertical velocity was faster by 0.3 m/s in the single-step together start. Restricting step length by 50% had little effect on step starts with the exceptions that horizontal velocity was significantly reduced by 0.1 m/s in the double-step start and vertical takeoff velocity was increased by 0.2 m/s in the single-step together start. These data suggested that step starts offered some performance improvements over the no-step start, but these improvements were not widespread and, in the case of the double-step start, were dependent on the ability to take longer steps.