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Bing Yu and James G. Hay

The purposes of this study were (a) to determine the magnitude of the angular momentum elite triple jumpers possess during each of the three phases of a triple jump, and (b) to identify those components of the angular momentum that are closely related to the actual distance of the triple jump. Angular momentum about each of three orthogonal axes at the takeoff of each of the last stride, hop, step, and jump was computed from the smoothed 3-D coordinate data of 21 body landmarks and joint centers and normalized to body mass (mb) and standing height (hb). Linear and nonlinear regression analyses were conducted to examine the relationships between angular momenta and actual distance. The results suggested that the estimated optimum magnitude of this side-somersaulting angular momentum is 0.0069 mb hb 2 kg · m2 · s-1 toward the side of the free leg, that the side-somersaulting angular momentum needed at the takeoff of the step should be obtained during the support phase of the hop; and that the change in the side-somersaulting angular momentum during the support phase of the step should be minimized.

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Bing Yu and James G. Andrews

The purpose of this study was to investigate relationships between free limb motions and triple jump performance. The subjects were 13 elite male triple jumpers. Three-dimensional videographic data were collected using a direct linear transformation technique with panning cameras. Changes in the velocity of the whole body center of gravity (G), changes in the whole body angular momentum about G, changes in the velocity of G due to free limb motions, and changes in the whole body angular momentum about G due to free limb motions were determined for each of the three support phases. Free limb motions were associated with decreases in the forward horizontal velocity of G and increases in the vertical velocity of G and significantly influenced changes of the corresponding velocity components of G when the changes were large. The free limb motions also created some angular momentum components about G during each support phase but did not significantly influence the changes of the corresponding angular momentum components of the whole body. Neither the changes in the three velocity components of G nor the changes in the three angular momentum components of the whole body about G due to free limb motions were significantly related to the actual distance of the triple jump.

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Cheng-Feng Lin, Hui Liu, William E. Garrett and Bing Yu

Small knee flexion angle during landing has been proposed as a potential risk factor for sustaining noncontact ACL injury. A brace that promotes increased knee flexion and decreased posterior ground reaction force during landing may prove to be advantageous for developing prevention strategies. Forty male and forty female recreational athletes were recruited. Three-dimensional videographic and ground reaction force data in a stop-jump task were collected in three conditions. Knee flexion angle at peak posterior ground reaction force, peak posterior ground reaction force, the horizontal velocity of approach run, the vertical velocity at takeoff, and the knee flexion angle at takeoff were compared among conditions: knee extension constraint brace, nonconstraint brace, and no brace. The knee extension constraint brace significantly increased knee flexion angle at peak posterior ground reaction force. Both knee extension constraint brace and nonconstraint brace significantly decreased peak posterior ground reaction force during landing. The brace and knee extension constraint did not significantly affect the horizontal velocity of approach run, the vertical velocity at takeoff, and the knee flexion angle at takeoff. A knee extension constraint brace exhibits the ability to modify the knee flexion angle at peak posterior ground reaction force and peak posterior ground reaction force during landing.

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Scott Ross, Kevin Guskiewicz, William Prentice, Robert Schneider and Bing Yu

Objective:

T o determine differences between contralateral limbs’ strength, proprio-ception, and kinetic and knee-kinematic variables during single-limb landing.

Setting:

Laboratory.

Subjects:

30.

Measurements:

Hip, knee, and foot isokinetic peak torques; anterior/posterior (AP) and medial/lateral (ML) sway displacements during a balance task; and stabilization times, vertical ground-reaction force (VGRF), time to peak VGRF, and knee-flexion range of motion (ROM) from initial foot contact to peak VGRF during single-limb landing.

Results:

The kicking limb had significantly greater values for knee-extension (P = .008) and -flexion (P = .047) peak torques, AP sway displacement (P = .010), knee-flexion ROM from initial foot contact to peak VGRF (P < .001), and time to peak VGRF (P = .004). No other dependent measures were significantly different between limbs (P > .05).

Conclusion:

The kicking limb had superior thigh strength, better proprioception, and greater knee-flexion ROM than the stance limb.

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Bing Yu, David Gabriel, Larry Noble and Kai-Nan An

The purposes of this study were (a) to develop a procedure for objectively determining the optimum cutoff frequency for the Butterworth low-pass digital filler, and (b) to evaluate the cutoff frequencies derived from the residual analysis. A set of knee flexion-extension angle data in normal gait was used as the standard data set. The standard data were sampled at different sampling frequencies. Random errors with different magnitudes were added to the standard data to create different sets of raw data with a given sampling frequency. Each raw data set was filtered through a Butterworth low-pass digital filter at different cutoff frequencies. The cutoff frequency corresponding to the minimum error in the second time derivatives for a given set of raw data was considered as the optimum for that set of raw data. A procedure for estimating the optimum cutoff frequency from the sampling frequency and estimated relative mean error in the raw data set was developed. The estimated optimum cutoff frequency significantly correlated to the true optimum cutoff frequency with a correlation determinant value of 0.96. This procedure was applied to estimate the optimum cutoff frequency for another set of kinematic data. The calculated accelerations of the filtered data essentially matched the measured acceleration curve. There is no correlation between the cutoff frequency derived from the residual analysis and the true optimum cutoff frequency. The cutoff frequencies derived from the residual analysis were significantly lower than the optimum, especially when the sampling frequency is high.

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Amber Collins, Troy Blackburn, Chris Olcott, Joanne M. Jordan, Bing Yu and Paul Weinhold

Extended use of knee sleeves in populations at risk for knee osteoarthritis progression has shown functional and quality of life benefits; however, additional comprehensive kinematic and kinetic analyses are needed to determine possible physical mechanisms of these benefits which may be due to the sleeve’s ability to enhance knee proprioception. A novel means of extending these enhancements may be through stochastic resonance stimulation. Our goal was to determine whether the use of a knee sleeve alone or combined with stochastic resonance electrical stimulation improves knee mechanics in knee osteoarthritis. Gait kinetics and kinematics were assessed in subjects with medial knee osteoarthritis when presented with four conditions: control1, no electrical stimulation/sleeve, 75% threshold stimulation/sleeve, and control2. An increase in knee flexion angle throughout stance and a decrease in flexion moment occurring immediately after initial contact were seen in the stimulation/sleeve and sleeve alone conditions; however, these treatment conditions did not affect the knee adduction angle and internal knee abduction moment during weight acceptance. No differences were found between the sleeve alone and the stochastic resonance with sleeve conditions. A knee sleeve can improve sagittal-plane knee kinematics and kinetics, although adding the current configuration of stochastic resonance did not enhance these effects.