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David M. Andrews and James J. Dowling

A fourth order mass/spring/damper (MSD) mechanical model with linear coefficients was used to estimate axial tibial accelerations following impulsive heel impacts. A generic heel pad with constant stiffness was modeled to improve the temporal characteristics of the model. Subjects (n = 14) dropped (~5 cm) onto a force platform (3 trials), landing on the right heel pad with leg fully extended at the knee. A uni-axial accelerometer was mounted over the skin on the anterior aspect of the medial tibial condyle inferior to the tibial plateau using a Velcro™ strap (normal preload ~45 N). Model coefficients for stiffness (k1, k2) and damping (c1, c2) were varied systematically until the minimum difference in peak tibial acceleration (%PTAmin) plus maximum rate of tibial acceleration (%RTAmax) between the estimated and measured curves was achieved for each trial. Model responses to mean subject and mean group model coefficients were also determined. Subject PTA and RTA magnitudes were reproduced well by the model (%PTAmin = 1.4 ± 1.0 %, %RTAmin = 2.2 ± 2.7%). Model estimates of PTA were fairly repeatable for a given subject despite generally high variability in the model coefficients, for subjects and for the group (coefficients of variation: CVk1 = 57; CVk2 = 59; CVc1 = 48; CVc2 = 85). Differences in estimated parameters increased progressively when subject and group mean coefficients (%PTAsub = 8.4 ± 6.3%, %RTAsub = 18.9 ± 18.6%, and %PTAgrp = 19.9 ± 15.2 %, %RTAgrp = 30.2 ± 30.2%, respectively) were utilized, suggesting that trial specific calibration of coefficients for each subject is required. Additional model refinement seems warranted in order to account for the large intra-subject variability in coefficients.

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Adriana M. Duquette and David M. Andrews

Considerable variability in tibial acceleration slope (AS) values, and different interpretations of injury risk based on these values, have been reported. Acceleration slope variability may be due in part to variations in the quantification methods used. Therefore, the purpose of this study was to quantify differences in tibial AS values determined using end points at various percentage ranges between impact and peak tibial acceleration, as a function of either amplitude or time. Tibial accelerations were recorded from 20 participants (21.8 ± 2.9 years, 1.7 m ± 0.1 m, 75.1 kg ± 17.0 kg) during 24 unshod heel impacts using a human pendulum apparatus. Nine ranges were tested from 5–95% (widest range) to 45–55% (narrowest range) at 5% increments. ASAmplitude values increased consistently from the widest to narrowest ranges, whereas the ASTime values remained essentially the same. The magnitudes of ASAmplitude values were significantly higher and more sensitive to changes in percentage range than ASTime values derived from the same impact data. This study shows that tibial AS magnitudes are highly dependent on the method used to calculate them. Researchers are encouraged to carefully consider the method they use to calculate AS so that equivalent comparisons and assessments of injury risk across studies can be made.

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Bart Van Gheluwe, Philip Roosen and Kaat Desloovere

As the spatial position and orientation of the subtalar ankle axis documented in biomechanical literature has mainly been estimated in unloaded conditions, it was hypothesized that high loads on the subtalar joint during very dynamic movements may force the respective axis away from its normal anatomical location. Therefore, high jump takeoffs of two elite athletes were selected to estimate and analyze the kinematic behavior of the subtalar axis during initial takeoff. The subtalar motion of the calcaneus was reconstructed using 3-D high-speed cinematography and a three-segment ankle model expressing subtalar pronation as the movement of the calcaneus around the talus. Results revealed that the subtalar axis moved away from its initial orientation and position at first heel impact, respectively more horizontally and laterally. The pronational angular displacement and velocity were calculated for all jumps and reached maximal values close to 30°, respectively 2000°/s. They compared surprisingly well with values obtained from frontal plane projections as used in a conventional cinematographical approach. But values corresponding to a subtalar axis fitting conventional anatomical descriptions showed consistently larger discrepancies, up to 10° for pronational displacement and close to 600°/s for pronational velocity. Finally, a comparison with results obtained from helical or screw axes produced nearly identical findings, suggesting good validity of the analytical techniques applied in this study for the 3-D reconstruction of the subtalar axis.

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Alison Schinkel-Ivy, Timothy A. Burkhart and David M. Andrews

To date, there has not been a direct examination of the effect that tissue composition (lean mass/muscle, fat mass, bone mineral content) differences between males and females has on how the tibia responds to impacts similar to those seen during running. To evaluate this, controlled heel impacts were imparted to 36 participants (6 M and 6 F in each of low, medium and high percent body fat [BF] groups) using a human pendulum. A skin-mounted accelerometer medial to the tibial tuberosity was used to determine the tibial response parameters (peak acceleration, acceleration slope and time to peak acceleration). There were no consistent effects of BF or specific tissue masses on the un-normalized tibial response parameters. However, females experienced 25% greater peak acceleration than males. When normalized to lean mass, wobbling mass, and bone mineral content, females experienced 50%, 62% and 70% greater peak acceleration, respectively, per gram of tissue than males. Higher magnitudes of lean mass and bone mass significantly contributed to decreased acceleration responses in general.

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Darren J. Stefanyshyn, Benno M. Nigg, Veronica Fisher, Barry O'Flynn and Wen Liu

The purpose of this investigation was to determine whether a graded response in gait kinematics, kinetics, and EMG occurs as shoe heel height increases. Four different shoes, including one flat shoe and three shoes with high heels, were tested in this investigation. The average heel heights of the four shoes were 1.4 cm, 3.7 cm, 5.4 cm, and 8.5 cm. Kinematics, kinetics, and muscle EMG were measured during the stance phase of gait on 13 healthy female subjects while wearing each of these 4 shoes. Systematic increases in the active vertical, propulsive, and braking forces were found as shoe height increased. Ankle and knee flexion and soleus and rectus femoris activity showed a graded response as heel height increased. One surprising result was the behavior of the maximal vertical impact force peak and the maximal loading rate during heel impact. The vertical impact force peaks and the maximal vertical loading rates were highest for the shoe with 3.7 cm heel height and lowest for the flat shoe and the shoe with heel height of 8.5 cm.

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Youlian Hong, Shao Jun Wang, Wing Kai Lam and Jason Tak-Man Cheung

The lunge is the most fundamental skill in badminton competitions. Fifteen university-level male badminton players performed lunge maneuvers in four directions, namely, right-forward, left-forward, right-backward, and left-backward, while wearing two different brands of badminton shoes. The test compared the kinetics of badminton shoes in performing typical lunge maneuvers. A force plate and an insole measurement system measured the ground reaction forces and plantar pressures. These measurements were compared across all lunge maneuvers. The left-forward lunge generated significantly higher first vertical impact force (2.34 ± 0.52 BW) than that of the right-backward (2.06 ± 0.60 BW) and left-backward lunges (1.78 ± 0.44 BW); higher second vertical impact force (2.44 ± 0.51 BW) than that of the left-backward lunge (2.07 ± 0.38 BW); and higher maximum anterior-posterior shear force (1.48 ± 0.36 BW) than that of the left-backward lunge (1.18 ± 0.38 BW). Compared with other lunge directions, the left-forward lunge showed higher mean maximum vertical impact anterior-posterior shear forces and their respective maximum loading rates, and the plantar pressure at the total foot and heel regions. Therefore, the left-forward lunge is a critical maneuver for badminton biomechanics and related footwear research because of the high loading magnitude generated during heel impact.

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Adriana M. Holmes and David M. Andrews

The purpose of this research was to examine the effects of voluntarily manipulating muscle activation and localized muscle fatigue on tibial response parameters, including peak tibial acceleration, time to peak tibial acceleration, and the acceleration slope, measured at the knee during unshod heel impacts. A human pendulum delivered consistent impacts to 15 female and 15 male subjects. The tibialis anterior and lateral gastrocnemius were examined using electromyography, thus allowing voluntary contraction to various activation states (baseline, 15%, 30%, 45%, and 60% of the maximum activation state) and assessing localized muscle fatigue. A skin-mounted uniaxial accelerometer, preloaded medial to the tibial tuberosity, allowed tibial response parameter determination. There were significant decreases in peak acceleration during tibialis anterior fatigue, compared to baseline and all other activation states. In females, increased time to peak acceleration and decreased acceleration slope occurred during fatigue compared to 30% and 45%, and compared to 15% through 60% of the maximum activation state, respectively. Slight peak acceleration and acceleration slope increases, and decreased time to peak acceleration as activation state increased during tibialis anterior testing, were noted. When examining the lateral gastrocnemius, the time to peak acceleration was significantly higher across gender in the middle activation states than at the baseline and fatigue states. The acceleration slope decreased at all activation states above baseline in females, and decreased at 60% of the maximum activation state in males compared to the baseline and fatigue states. Findings agree with localized muscle fatigue literature, suggesting that with fatigue there is decreased impact transmission, which may protect the leg. The relative effects of leg stiffness and ankle angle on tibial response need to be verified.

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.1123/jab.16.3.248 Stretch-Shortening Cycle in Roller Ski Skating: Effects of Speed Stéphane Perrey * Guillaume Millet * Robin Candau * Jean-Denis Rouillon * 8 2000 16 3 264 275 10.1123/jab.16.3.264 Mechanical Modeling of Tibial Axial Accelerations Following Impulsive Heel Impact David M. Andrews

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Bastiaan Breine, Philippe Malcolm, Veerle Segers, Joeri Gerlo, Rud Derie, Todd Pataky, Edward C. Frederick and Dirk De Clercq

.0000183477.75808.92 10.1249/01.mss.0000183477.75808.92 16531902 6. Shorten M , Mientjes MIV . The “heel impact” force peak during running is neither “heel” nor “impact” and does not quantify shoe cushioning effects . Footwear Sci . 2011 ; 3 ( 1 ): 41 – 58 . doi:10

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Nicole C. George, Charles Kahelin, Timothy A. Burkhart and David M. Andrews

, Burkhart TA , Altenhof WJ , Andrews DM . Leg soft tissue position and velocity from skin markers can be obtained with good to acceptable reliability following heel impacts . J Sports Sci . 2015 ; 33 ( 15 ): 1606 – 1613 . PubMed doi:10.1080/02640414.2014.1003583 25626597 10