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Nataphoom Benjanuvatra, Brian A. Blanksby, and Bruce C. Elliott

Six 9-, 11-, and 13-year-old, anthropometrically matched males and females were towed on the water surface via a mechanical winch at 1.3 to 2.5 ms−1 in increments of 0.3 ms−1 during a prone streamlined glide. Passive drag force of the 13-year age group was significantly larger than that of the 9-year age group at 1.9, 2.2, and 2.5 ms−1, but not at 1.3-1.6 ms−1. While anthropometry did not feature in any regression equation at any age for passive drag at velocities of 1.3 and 1.6 ms−1, body mass was the best predictor of drag at 1.9 and 2.5 ms−1.

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Bruce C. Elliott, Kevin G. Baxter, and Thor F. Besier

This research examined the influence on performance of no-pause and mean delays of 0.97 s and 1.5 s between the eccentric and concentric phases of the stretch-shorten cycle movement of internal rotation (IR) of me upper arm. Videography and surface electromyography were used in the assessment of 19 athletes throwing a baseball in a manner that constrained all degrees of freedom other than upper-arm IR. Results demonstrated that the pectoralis major, latissimus dorsi, and anterior deltoid muscles were all active at above 100% maximum voluntary contraction (MVC) during IR. The maximum velocity of the wrist decreased with increasing pause time between me eccentric and concentric phases of the IR movement. A mean 21.9% augmentation to the maximum wrist velocity was recorded when the no-pause delay and a mean delay of 1.5 s were compared. There were no electromyographically discernible differences recorded either prior to or after release for any of the monitored muscles during IR across the pause conditions. It is evident therefore that the benefits of a prestretch during external rotation (ER) have a significant influence on the subsequent velocity of IR.

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Joanne E. Richards, Timothy R. Ackland, and Bruce C. Elliott

Thirty-seven females, aged initially between 10 and 13.5 years, completed a mixed longitudinal study over 3.3 years to investigate the effect of training volume and growth upon gymnastic performance. Gymnasts undergoing high volume training (mean = 30 hrs/week: Group 1) and moderate volume training (mean = 15 hrs/week: Group 2) were tested at 4-month intervals on growth measures including height, mass, skinfolds, and segment lengths, as well as the strength of lower limb, upper limb, and trunk musculature. Functional gymnastic development was observed through the assessment of generic, whole body rotation tasks, a vertical jump, and a v-sit action. The high training volume gymnasts were significantly smaller but markedly stronger than those gymnasts in Group 2 despite the size disadvantage. Consequently, Group 1 gymnasts were able to produce higher velocities for front and backward rotations and a faster v-sit action. These training group differences remained significant after initial size differences were taken into account via an analysis of covariance.

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Bruce C. Elliott, Robert N. Marshall, and Guillermo J. Noffal

In the high-velocity tennis serve, the contributions that the upper limb segments' anatomical rotations make to racket head speed at impact depend on both their angular velocity and the instantaneous position of the racket with respect to the segments' axes of rotation. Eleven high-performance tennis players were filmed at a nominal rate of 200 Hz by three Photosonics cameras while hitting a high-velocity serve. The three-dimensional (3-D) displacement histories of 11 selected landmarks were then calculated using the direct linear transformation approach, and 3-D individual segment rotations for the upper limb were calculated using vector equations (Sprigings, Marshall, Elliott, & Jennings, 1994). The major contributors to the mean linear velocity of the center of the racket head of 31.0 m · s-1 at impact were internal rotation of the upper arm (54.2%), flexion of the hand (31.0%), horizontal flexion and abduction of the upper arm (12.9%), and racket shoulder linear velocity (9.7%). Forearm extension at the elbow joint played a negative role (-14.4%) and reduced the forward velocity of the center of the racket at impact.

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Gregory J. Wilson, Bruce C. Elliott, and Graham K. Kerr

The bar movement characteristics of 10 elite powerlifters were analyzed while bench pressing a maximum load and a submaximal load in a simulated competition using high-speed cinematography. Significant differences in bar path and alterations to the general force profile of movement were evident as the load was increased. These movement discrepancies resulted in the following conclusions being drawn with reference to the bench press movement: (a) The movement pattern adopted during the performance of an 81 % maximum load was not specific to that which was utilized during the maximal load. (b) Based upon the concepts of specificity of training and testing, the use of the popular one-repetition maximum test to quantify strength changes derived from submaximal training appeared invalid. This occurrence is further accentuated when the testing protocol is conducted on a bench press machine. (c) The design of “isotonic” bench press machines appeared to be load specific. Further, the development of bench press machines that would allow a number of bar paths to be pursued appear to represent a significant improvement over existing models.

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Rochelle Llewelyn Nicholls, Karol Miller, and Bruce C. Elliott

Regulating ball response to impact is one way to control ball exit velocity in baseball. This is necessary to reduce injuries to defensive players and maintain the balance between offense and defense in the game. This paper presents a model for baseball velocity-dependent behavior. Force-displacement data were obtained using quasi-static compression tests to 50% of ball diameter (n = 70 baseballs). The force-displacement curves for a very stiff baseball (Model B) and a softer type (Model C) were characterized by a Mooney-Rivlin model using implicit finite element analysis (ANSYS software, version 6.1). Agreement between experimental and numerical results was excellent for both Model B (C10 = 0, C01 = 3.7e6 Pa) and Model C (C10 = 0, C01 = 2.6e6 Pa). However, this material model was not available in the ANSYS/LSDYNA explicit dynamic software (version 6.1) used to quantify the transient behavior of the ball. Therefore the modeling process was begun again using a linear viscoelastic material. G∞, the long-term shear modulus of the material, was determined by the same implicit FEA procedure. Explicit FEA was used to quantify the time-dependent response of each ball in terms of instantaneous shear modulus (G0) and a decay term (β). The results were evaluated with respect to published experimental data for the ball coefficient of restitution at five velocities (13.4–40.2 ms–1) and were in agreement with the experimental values. The model forms the basis for future research on baseball response to impact with the bat.

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Marc R. Portus, David G. Lloyd, Bruce C. Elliott, and Neil L. Trama

The measurement of lumbar spine motion is an important step for injury prevention research during complex and high impact activities, such as cricket fast bowling or javelin throwing. This study examined the performance of two designs of a lumbar rig, previously used in gait research, during a controlled high impact bench jump task. An 8-camera retro-reflective motion analysis system was used to track the lumbar rig. Eleven athletes completed the task wearing the two different lumbar rig designs. Flexion extension data were analyzed using a fast Fourier transformation to assess the signal power of these data during the impact phase of the jump. The lumbar rig featuring an increased and pliable base of support recorded moderately less signal power through the 0–60 Hz spectrum, with statistically less magnitudes at the 0–5 Hz (p = .039), 5–10 Hz (p = .005) and 10–20 Hz (p = .006) frequency bins. A lumbar rig of this design would seem likely to provide less noisy lumbar motion data during high impact tasks.

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Alasdair R. Dempsey, Bruce C. Elliott, Bridget J. Munro, Julie R. Steele, and David G. Lloyd

Anterior cruciate ligament (ACL) injuries are costly. Sidestep technique training reduces knee moments that load the ACL. This study examined whether landing technique training alters knee moments. Nineteen team sport athletes completed the study. Motion analysis and ground reaction forces were recorded before and after 6 weeks of technique modification. An inverse dynamic model was used to calculate three-dimensional knee loading. Pre- and postintervention scores were compared using paired t tests. Maximal knee flexion angle during landing was increased following training. There was no change in valgus or flexion moments, but an increase in peak internal rotation moment. This increase in internal rotation moment may increase the risk of ACL injury. However, the increased angle at which the peak internal rotation moment occurred at follow up may mitigate any increase in injury risk by reducing load transmission.

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Brian A. Blanksby, Jennifer R. Simpson, Bruce C. Elliott, and Keith McElroy

Because turning can account for one-third of breaststroke race time in 25 m pools, it is possible that enhancing turning techniques can improve performance significantly. Underwater video cameras and a force platform were used to analyze turning techniques of 23 age-group breaststrokers during three 50 m push-start, maximum-effort swims. The criterion measure was the time elapsed between passing the 5 m mark on the approach and departure from the wall (5 m round-trip time [RTT]). Correlations revealed significant commonality of variance (p < .01) between the 5 m RTT and the 2.5 m RTT, 50 m time, average single-stroke velocity, peak reaction force, pivot time, impulse, peak horizontal velocity off the wall, arm and leg split-stroke resumption distances, surfacing distance, surfacing time, and horizontal velocity, height, and mass of the subjects. All swimmers achieved a net gain at the turn in that the mean 5 m RTT (20% of the distance) represented 18.26% of the total swimming time. Following stepwise regression, a successful turn was predicted by the equation 17.113 - 0.322 surfacing distance - 0.036 height - 0.723 surfacing horizontal velocity + 0.723 pivot time - 0.65 peak horizontal velocity.

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Andrew D. Lyttle, Brian A. Blanksby, Bruce C. Elliott, and David G. Lloyd

Thirty experienced male swimmers with body types ± 1 SD of the mean of selected body form parameters reported for elite male swimmers were recruited for the study. During three freestyle flip turns, selected kinetic, hydrodynamic, and kinematic variables of the push-off following a flip turn were recorded. Kinetics were recorded via a 2D vertically mounted forceplate that recorded peak push-off force and total impulse. The acceleration of each swimmer’s center of gravity and wall exit velocity were calculated from underwater videography. Hydrodynamic peak drag force and drag impulse were calculated from the kinetic and kinematic data using a derivative of Newton’s second law. A stepwise regression yielded peak drag force, peak propulsive force, and push-off time in the final regression equation (R = 0.80; R 2 = 0.64). Beta values indicated that the peak drag force carried the highest weighting of the three variables. The results of the stepwise regression indicated that a combination of a low peak drag force high peak propulsive force, and increased wall push-off time produced the fastest final push-off velocity.