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Clément Theurillat, Ilona Punt, Stéphane Armand, Alice Bonnefoy-Mazure, and Lara Allet

biomechanical models to evaluate active and passive movements. 11 , 12 However, circumduction movement of the ankle has never been studied. From a clinical point of view, identifying deficits in the sagittal and frontal planes during a circumduction movement should provide new insights which might help assess

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Spiros G. Prassas

A biomechanical model of the press handstand was developed to evaluate and predict the shoulder joint torque requirements as well as the motion of a gymnast’s center of mass (CM) from an initial to a final (handstand) position. Five press handstands executed by gymnasts of differing abilities were filmed and analyzed. The results were compared to the predicted parameters of simulated presses. It was found that execution of the skill with fewer fluctuations in trunk and lower extremities angular velocity—a characteristic of skilled performance—required smoother and at times larger shoulder joint torques. Reduction of the hip joint angle by only 5 or 10° did not substantially reduce the shoulder joint torque requirements. Regarding CM motion, it was found that during performance the CM continuously elevated and remained close to a vertical line passing through the center of the wrist joint. All gymnasts, however, were found to be leaning slightly backward during the first part of the movement and slightly forward during the later phases. Modifications in wrist joint angle required to maintain each gymnast’s CM precisely above the center of the wrist joint were investigated.

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Amit Gefen

The extrapolation of biological damage from a biomechanical model requires that a closed-form mathematical damage threshold function (DTF) be included in the model. A DTF typically includes a generic load variable, being the critical load (e.g., pressure, strain, temperature) causing irreversible tissue or cell damage, and a generic time variable, which represents the exposure to the load (e.g., duration, strain rate). Despite the central role that DTFs play in biomechanical studies, there is no coherent literature on how to formulate a DTF, excluding the field of heat-induced damage studies. This technical note describes six mathematical function types (Richards, Boltzmann, Morgan-Mercer-Flodin, Gompertz, Weibull, Bertalanffy) that are suitable for formulating a wide range of DTFs. These functions were adapted from the theory of restricted growth, and were fitted herein to describe biomechanical damage phenomena. Relevant properties of each adapted function type were extracted to allow efficient fitting of its parameters to empirical biomechanical data, and some practical examples are provided.

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Inga Krauss, Thomas Ukelo, Christoph Ziegler, Detlef Axmann, Stefan Grau, Thomas Horstmann, and Alex Stacoff

Results from instrumented gait analysis vary between test situations. Subject characteristics and the biomechanical model can influence the total amount of variability. The purpose of this study was to quantify reliability of gait data in general, and with respect to the applied model, and investigated population group. Reliability was compared between a functional and a predictive gait model in subjects with knee osteoarthritis and healthy controls. Day-to-day consistency for sagittal plane variables was comparable between models and population groups. Transversal plane variables relative to joint excursion showed larger inconsistency for repeated measures, even for a more sophisticated biomechanical approach. In conclusion, the presented reliability data of sagittal plane kinematics should be used for a reasonable interpretation of results derived in clinical gait analysis. Variables of the transversal plane should not be used as long as sources of error are not sufficiently minimized.

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Edited by Thomas S. Buchanan

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Jon Karlsson, Lars Peterson, Gunnar Andreasson, and Christian Högfors

A device to simulate ankle motion associated with inversion ankle injury was constructed. This device consists of a trap door that can be tilted 30° from the horizontal plane. Surface EMG electrodes were placed over the peroneus brevis and peroneus longus muscles. The time measured from the tilting of the plate to the first muscular response on the EMG was defined as the reflex time. Twenty individuals with unilateral ankle joint instability were tested. The mechanical ankle joint stability was measured using standardized radiographic measurements, taking into account anterior talar translation and talar tilt. The mean anterior talar translation was 5.9 mm and the mean talar tilt was 3.2° in the stable ankles, compared to 12.7 mm and 10.5° for the unstable ankles. The mean reflex time was 68.8 ms (peroneus longus) and 69.2 ms (peroneus brevis) in the stable ankles as compared to 84.5 ms (peroneus longus) and 81.6 ms (peroneus brevis) in the unstable ankles. Important factors influencing functional instability are discussed.

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Paul DeVita and Tibor Hortobagyi

Functional knee braces used during rehabilitation from injury and surgery to the anterior cruciate ligament (ACL) have been reported to provide a strain-shielding effect on the ACL in healthy people while standing, reduce quadriceps electromyoraphy in ACL-deficient individuals, and alter joint torque patterns in people with ACL reconstruction during walking. These results led to the hypothesis that functional knee braces protect a reconstructed ACL during dynamic activity by reducing the anterior shear load applied to the knee. This hypothesis was tested by investigating the effects of a functional knee brace on lower extremity muscle forces and the anteroposterior shear force at the knee joint during the stance phase of walking in people with ACL reconstruction. Ground reactions and sagittal plane video were recorded from 9 ACL-reconstructed individuals as they walked with and without a functional knee brace, and from 10 healthy people without the functional knee brace. Inverse dynamics were used to calculate the net joint torques in the lower extremity during the stance phase. Hamstrings, quadriceps, and gastrocnemius muscle and knee anteroposterior shear force were then predicted with a sagittal-plane mathematical model. Compared to healthy individuals, those with ACL reconstruction walked with 78% more hamstrings impulse and 19% less quadriceps impulse (both p < .05). The functional knee brace produced an additional 43% increase in hamstrings impulse and an additional 13% decrease in quadriceps impulse in the ACL group. Peak anterior knee shear force and anterior impulse were 41% lower and 16% lower in ACL vs. healthy individuals, respectively. The functional knee brace further reduced the peak knee shear force and impulse 28% and 19%, respectively, in the ACL group. It was concluded that a functional knee brace protects a reconstructed ACL during walking by altering muscle forces and reducing the anterior shear force applied to the knee joint.

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Brock Laschowski, Naser Mehrabi, and John McPhee

skeletal muscles (ie, dynamometry) is invasive and therefore unpractical in sport environments. 3 With modern advancements in computer science, biomechanical modeling presents a viable method of approximating the dynamics of multibody movements. 3 Considering the emergent interests in determining the

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Geoffrey T. Burns, Kenneth M. Kozloff, and Ronald F. Zernicke

-tendon rupture during a clean-and-jerk lift. By applying a five-segment biomechanical model to the lifting movement and with specific information regarding knee-joint moment arms, they calculated the in vivo force sustained by the patellar tendon at the time of rupture. The estimate, 14.5 kN (17.5 times body

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Benoit R. Lafleur, Alyssa M. Tondat, Steven P. Pretty, Marina Mourtzakis, and Andrew C. Laing

during internal rotation of the hip (hypothesis 2). The secondary objective was to determine the how the differences in TSTT characterized in the first objective would influence biomechanical model estimates of fall-related impact force and hip fracture risk (ie, FOR). We hypothesized that impact force