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John H. Challis, Chloe Murdoch, and Samantha L. Winter

The purpose of this study was to compare the heel pad mechanical properties of runners, who repetitively load the heel pad during training, with cyclists who do not load their heel pads during training. Ten competitive long distance runners and 10 competitive cyclists volunteered for this study. The thickness of the unloaded heel pad was measured using realtime B-mode ultrasonography. A heel pad indentation device was used to measure the mechanical properties of the heel pads. To evaluate the differences between the two groups, in heel pad properties, a repeat measures analysis of variance was used (p < .05). Heel pad thickness was not different between groups when normalized with respect to subject height. There was no significant difference between the groups in percentage energy loss during loading and unloading (runners: 61.4% ± 8.6; cyclists: 62.5% ± 4.6). Heel pad stiffness for the runners was statistically significantly less than that of the cyclists (p = .0018; runners: 17.1 N·mm−1 ± 3.0; cyclists: 20.4 N·mm−1 ± 4.0). These results indicate that the nature of the activity undertaken by individuals may influence their heel pad properties. This finding may be important when considering differences in heel pad properties between different populations.

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Enrique Alcántara, Arturo Forner, Elena Ferrús, Ana-Cruz García, and José Ramiro

Impact mechanics of the human heel pad were studied using a ballistic pendulum. Young and elderly men and women took part in the experiment. Twelve parameters were used to describe heel pad properties. Analysis of variance was conducted to assess the influence of age, gender, and obesity. Heel pad properties were correlated with impact force and time to peak force in order to study impact mechanics. Maximal stiffness, peak displacement, and energy absorption were established so as to sufficiently describe impact properties of the heel pad. Age, gender, and obesity introduced significant differences in heel pad properties. Peak displacement and time to peak force increased in the elderly. Women presented a shorter time to peak force together with lower peak displacement, energy absorption, and lower maximal stiffness than men. Obese elderly showed lower impact forces, longer time to peak, and greater peak displacement than non-obese and younger participants. In addition, energy absorption was greater and maximal stiffness was lower for obese than for non-obese participants.

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Matthew T.G. Pain and John H. Challis

Wobbling mass models have been used to gain insight into joint loading during impacts. This study investigated the sensitivity of a wobbling mass model of landing from a drop to the model's parameters. A 2-D wobbling mass model was developed. Three rigid linked segments designed to represent the skeleton each had a second mass attached to them, via two translational nonlinear spring dampers, representing the soft tissue. Model parameters were systematically varied one at a time and the effect this had on the peak vertical ground reaction force and segment kinematics was examined. Model output showed low sensitivity to most model parameters but was sensitive to the timing of joint torque initiation. Varying the heel pad stiffness in the range of stiffness values reported in the literature had the largest influence on peak vertical ground reaction force. The analysis indicated that the more proximal body segments had a lower influence on peak vertical ground reaction force per unit mass than the segments nearer the contact point. Model simulations were relatively insensitive to variations in the properties of the connection between wobbling masses and the skeleton. If the goal is to examine the effects of wobbling mass on the system, this insensitivity is an advantage, with the proviso that estimates for the other model parameters and joint torque activation timings lie in a realistic range. If precise knowledge about the motion of the wobbling mass is of interest, however, this calls for more experimental work to precisely determine these model parameters.

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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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Dorianne Schuitema, Christian Greve, Klaas Postema, Rienk Dekker, and Juha M. Hijmans

Bonanno et al (2004) 54 CO 36 (24/12) 71 (6.9) [65–92] (1) Shoe (2) Shoe + silicon heel cup (3) Shoe + soft foam heel pad (4) Shoe + heel lift (5) Shoe + prefabricated insole Unknown – Single visit Chia et al (2009) 48 CO 30 (16/14) M: 53.31 (6.24) F: 32.43 (7.86) (1) No insole (2) Flat insole (3) Bone

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Kevin Deschamps, Giovanni Matricali, Maarten Eerdekens, Sander Wuite, Alberto Leardini, and Filip Staes

running and sprinting . J Biomech . 1997 ; 30 ( 11–12 ): 1081 – 1085 . doi:10.1016/S0021-9290(97)00081-X 9456374 10.1016/S0021-9290(97)00081-X 32. De Clercq D , Aerts P , Kunnen M . The human heel pad during foot strike in running: an in vivo cineradiographic study . J Biomech . 1994 ; 27

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

, Aerts P , Kunnen M . The mechanical characteristics of the human heel pad during foot strike in running: an in vivo cineradiographic study . J Biomech . 1994 ; 27 ( 10 ): 1213 – 1222 . PubMed doi:10.1016/0021-9290(94)90275-5 10.1016/0021-9290(94)90275-5 11. Breine B

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Paul J. Felton, Maurice R. Yeadon, and Mark A. King

.jbiomech.2010.07.030 10.1016/j.jbiomech.2010.07.030 20709319 20. Pain MTG , Challis JH . The role of the heel pad and shank soft tissue during impacts: a further resolution of a paradox . J Biomech . 2001 ; 34 : 327 – 333 . PubMed ID: 11182123 doi:10.1016/S0021-9290(00)00199-8 11182123 10.1016/S0021

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Oren Tirosh, Guy Orland, Alon Eliakim, Dan Nemet, and Nili Steinberg

this group. Previously, it was suggested that attenuation is probably achieved by a change in the gait pattern. 36 The deficiency in shock attenuation found in overweight children may further relate to passive attenuation caused by anatomical structures (such as heel pad, ligaments, articular

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Akane Yoshimura, Robert Schleip, and Norikazu Hirose

gastrocnemius muscle generally increases linearly with increased DF ROM. 22 In contrast, as there is age-dependent fiber continuity from the plantar fascia via the heel pad and posterior calcaneal periosteum to the Achilles tendon, 25 force transmission between the plantar fascia and the gastrocnemius muscle