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Janice K. Loudon and Marcie Swift

ground using a rearfoot strike, there is an initial impact load. Impact load can be quantified by using kinetic data from a force plate, typically the vertical ground reaction force (VGRF), impact peak (IP), and the loading rate (LR). As depicted in Figure  1 , the IP is the greatest force during initial

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Yi Wang, Wing K. Lam, Charis K. Wong, Lok Y. Park, Mohammad F. Tan, and Aaron K.L. Leung

-support orthoses are shown to reduce impact 14 , 23 or increase impact loading in previous running studies. 24 It is still questionable whether the use of arch-support orthosis would attenuate impact forces during running. It is also suggested that medial longitudinal arch collapse is accounted for inadequate

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Arnel Aguinaldo and Andrew Mahar

This study evaluated the effects of running shoes—with two types of cushioning column systems—on impact force patterns during running. Kinematic and ground reaction force data were collected from 10 normal participants wearing shoes with the following cushions: 4-column multicellular urethane elastomer (Shoe 1), 4-column thermoplastic polyester elastomer (Shoe 2), and 1-unit EVA foam (Shoe 3). Participants exhibited significantly lower impact force (p = .02) and loading rate (p = .005) with Shoe 2 (1.84 ± 0.24 BW; 45.6 ± 11.6 BW/s) compared to Shoe 1 (1.94 ± 0.18 BW; 57.9 ± 12.1 BW/s). Both cushioning column shoes showed impact force characteristics similar to those of a top-model running shoe (Shoe 3), and improved cushioning performance over shoes previously tested in similar conditions. Alterations in impact force patterns induced by lower limb alignment and running speed were negligible since participants did not differ in ankle position, knee position, or speed during all shod running trials. Ankle plantarflexion, however, was higher for barefoot running, indicating an apparent midfoot strike. Mechanical testing of each shoe during physiologic, cyclic loading demonstrated that Shoe 3 had the greatest stiffness, followed by Shoe 2 and Shoe 1. Shoe 1 was the least stiff of the two shoes with cushioning column systems, yet it displayed a significantly higher impact loading rate during running, possibly due to rearfoot motion alterations induced by the stiffer shoe. This study showed that even in similar shoe types, impact force and loading rate values could vary significantly with midsole cushion constructions. The findings of this study suggest that using these newer running shoes may be effective for runners who want optimal cushioning during running.

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Jeffrey J. Chu and Graham E. Caldwell

Studies on shock attenuation during running have induced alterations in impact loading by imposing kinematic constraints, e.g., stride length changes. The role of shock attenuation mechanisms has been shown using mass-spring-damper (MSD) models, with spring stiffness related to impact shock dissipation. The present study altered the magnitude of impact loading by changing downhill surface grade, thus allowing runners to choose their own preferred kinematic patterns. We hypothesized that increasing downhill grade would cause concomitant increases in both impact shock and shock attenuation, and that MSD model stiffness values would reflect these increases. Ten experienced runners ran at 4.17 m/s on a treadmill at surface grades of 0% (level) to 12% downhill. Accelerometers were placed on the tibia and head, and reflective markers were used to register segmental kinematics. An MSD model was used in conjunction with head and tibial accelerations to determine head/arm/trunk center of mass (HATCOM) stiffness (K1), and lower extremity (LEGCOM) stiffness (K2) and damping (C). Participants responded to increases in downhill grade in one of two ways. Group LowSA had lower peak tibial accelerations but greater peak head accelerations than Group HighSA, and thus had lower shock attenuation. LowSA also showed greater joint extension at heelstrike, higher HATCOM heelstrike velocity, reduced K1 stiffness, and decreased damping than HighSA. The differences between groups were exaggerated at the steeper downhill grades. The separate responses may be due to conflicts between the requirements of controlling HATCOM kinematics and shock attenuation. LowSA needed greater joint extension to resist their higher HATCOM heelstrike velocities, but a consequence of this strategy was the reduced ability to attenuate shock with the lower extremity joints during early stance. With lower HATCOM impact velocities, the HighSA runners were able to adopt a strategy that gave more control of shock attenuation, especially at the steepest grades.

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Felix Capanni, Kirk Hansen, Daniel C. Fitzpatrick, Steven M. Madey, and Michael Bottlang

Impact damping by elastic fixation is a principal engineering strategy to increase the durability of load-bearing structures exposed to prolonged dynamic loading. This biomechanical study evaluated axial impact damping provided by a novel dynamic locking plate. In this design, locking screw holes are elastically suspended within a silicone envelope inside the locking plate. Axial impact damping was assessed for 3 distinct fixation constructs applied to bridge a 10-mm fracture gap of a femoral diaphysis surrogate: a standard locking plate, a dynamic locking plate, and an Ilizarov ring fixator. First, the 3 fixation constructs were characterized by determining their axial stiffness. Subsequently, constructs were subjected to a range of axial impact loads to quantify damping of force transmission. Compared with standard locked plating constructs, dynamic plating constructs were 58% less stiff (P < .01) and Ilizarov constructs were 88% less stiff (P < .01). Impact damping correlated inversely with construct stiffness. Compared with standard plating, dynamic plating constructs and Ilizarov constructs dampened the transmission of impact loads by up to 48% (P < .01) and 74% (P < .01), respectively. In conclusion, lower construct stiffness correlated with superior damping of axial impact loads. Dynamic locking plates provide significantly greater impact damping compared with standard locking plates.

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Anamaria Laudet Silva Mangubat, Janet Hanwen Zhang, Zoe Yau-Shan Chan, Aislinn Joan MacPhail, Ivan Pui-Hung Au, and Roy Tsz-Hei Cheung

transmitted upward, eventually reaching the head. 3 This initial force of impact on the ground may also be referred to as impact loading. 4 Vertical head accelerations when walking or running are controlled by several factors, including head and neck reflexes, trunk and neck muscles, and absorption by the

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Allison H. Gruber, Shuqi Zhang, Jiahao Pan, and Li Li

The introduction of ultracushioning or maximalist running footwear has reignited the debate regarding the influence of cushioning on running mechanics. Running shoe cushioning was designed to protect the runner from potentially hazardous impact loading. However, reports from the running shoe

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Zach Fassett, Adam E. Jagodinsky, David Q. Thomas, and Skip M. Williams

Deteriorations to bone strength and bone mineral density (BMD) typically begin around 40 years of age and directly contribute to heightened risk of bone-related injury and disease ( 17 ). Following early adulthood, physical activities with high rates and magnitudes of loading (impact loading) have

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Sophie E. Heywood, Benjamin F. Mentiplay, Ann E. Rahmann, Jodie A. McClelland, Paula R. Geigle, Kelly J. Bower, and Ross A. Clark

individuals for improving strength 1 , 4 and vertical jump height. 1 , 5 , 6 When prescribing plyometric exercise, common considerations include ensuring an adequate foundation level of strength, endurance, and neuromuscular control, slow progression to higher impact load, appropriate recovery time, and

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Warlindo Carneiro da Silva Neto, Alexandre Dias Lopes, and Ana Paula Ribeiro

retraining with real-time visual feedback on an instrumented treadmill was effective in lowering impact loading in 320 recreational runners. 26 More importantly, the occurrence of injury was 62% lower after 2 weeks of running-gait modification. The results of the present research are in agreement with those