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Matthew J. Major, José L. Zavaleta, and Steven A. Gard

impact of prosthetic foot properties on user performance, no studies to date have systematically investigated the effects of modifications in prosthesis longitudinal stiffness. This variable is uniquely relevant to commonly prescribed shock-absorbing pylons (SAPs). The longitudinal stiffness of SAPs can

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Jaclyn Megan Sions, Elisa Sarah Arch, and John Robert Horne

sedentary behavior are independent predictors of morbidity and subsequent mortality. 4 , 5 Nonmodifiable factors, such as sex, 6 , 7 age, 7 time since the amputation, 8 and comorbidities (regardless of the cause of the amputation) 8 – 13 have been found to impact prosthetic use and/or physical activity

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Jeremy D. Smith and Philip E. Martin

Unilateral, transtibial amputees exhibit walking asymmetries and higher metabolic costs of walking than nonamputees walking at similar speeds. Using lightweight prostheses has previously been suggested as a contributing factor to walking asymmetries. The purpose was to investigate the effects of prosthesis mass and mass distribution on metabolic costs and walking asymmetries among six unilateral, transtibial amputees. Kinematic and temporal symmetry did not improve when mass was added at different locations on the limb. Stance and swing time asymmetries increased by 3.4% and 7.2%, respectively, with loads positioned distally on the limb. Maximum knee angular velocity asymmetries increased by 6% with mass added to the thigh, whereas maximum thigh angular velocity asymmetries increased by approximately 10% with mass positioned near the prosthetic ankle. Adding 100% of the estimated mass difference between intact and prosthetic legs to the ankle of the prosthesis increased energy costs of walking by 12%; adding the same mass to the prosthesis center of mass or thigh center of mass increased metabolic cost by approximately 7% and 5%, respectively. Unless other benefits are gained by increasing prosthesis mass, this should not be considered as a possible alternative to current lightweight prosthesis designs currently being prescribed to unilateral amputees.

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W. Lee Childers, Robert S. Kistenberg, and Robert J. Gregor

Cyclists with unilateral transtibial amputation (CTA) provide a unique model to study integration of the neuromuscular and bicycle systems while having the option to modify this integration via the properties of the prosthesis. This study included eight CTA and nine intact cyclists. The cyclists pedaled on a stationary bicycle with instrumented force pedals. The CTA group pedaled with a stiff or flexible prosthetic foot during a simulated time trial and a low difficulty condition. During the time trial condition, pedaling with the flexible foot resulted in force and work asymmetries of 11.4% and 30.5%, the stiff foot displayed 11.1% and 21.7%, and the intact group displayed 4.3% and 4.2%, respectively. Similar trends were shown in the low difficulty condition. These data suggest foot stiffness has an effect on cycling symmetry in amputees.

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Li Jin, Peter G. Adamczyk, Michelle Roland, and Michael E. Hahn

Lower limb amputation has been associated with secondary impairments such as knee osteoarthritis in the uninvolved limb. Greater knee loading in the frontal plane has been related to severity and rate of progression in knee osteoarthritis. Reduced push-off work from the involved limb can increase uninvolved limb knee loading. However, little is known about specific effects that prosthetic foot damping may have on uninvolved limb loading. We hypothesized that uninvolved limb peak knee internal abduction moment (IAM) and loading rates would be greater when using a high-damping foot compared with a low-damping foot, across walking speeds. Eight healthy, young subjects walked in a prosthesis simulator boot using the experimental feet. Greater uninvolved limb first peak IAM (+16% in fast speed, P = .002; +11% in slow speed, P = .001) and loading rates (+11% in fast speed, P = .003) were observed when using the high-damping foot compared with low-damping foot. Within each foot, uninvolved limb first peak IAM and loading rates had a trend to increase with increased walking speed. These findings suggest that damping properties of prosthetic feet are related to uninvolved limb peak knee IAM and loading rates.

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Monique Mokha and Richard Conrey

Column-editor : G. Monique Mokha

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Daniel P. Ferris and Bryan R. Schlink

Robotic exoskeletons and bionic prostheses have moved from science fiction to science reality in the last decade. These robotic devices for assisting human movement are now technically feasible given recent advancements in robotic actuators, sensors, and computer processors. However, despite the ability to build robotic hardware that is wearable by humans, we still do not have optimal controllers to allow humans to move with coordination and grace in synergy with the robotic devices. We consider the history of robotic exoskeletons and bionic limb prostheses to provide a better assessment of the roadblocks that have been overcome and to gauge the roadblocks that still remain. There is a strong need for kinesiologists to work with engineers to better assess the performance of robotic movement assistance devices. In addition, the identification of new performance metrics that can objectively assess multiple dimensions of human performance with robotic exoskeletons and bionic prostheses would aid in moving the field forward. We discuss potential control approaches for these robotic devices, with a preference for incorporating feedforward neural signals from human users to provide a wider repertoire of discrete and adaptive rhythmic movements.

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Paolo Taboga, Alena M. Grabowski, Pietro Enrico di Prampero, and Rodger Kram

In the 2012 Paralympic 100 m and 200 m finals, 86% of athletes with a unilateral amputation placed their unaffected leg on the front starting block. Can this preference be explained biomechanically? We measured the biomechanical effects of starting block configuration for seven nonamputee sprinters and nine athletes with a unilateral amputation. Each subject performed six starts, alternating between their usual and unusual starting block configurations. When sprinters with an amputation placed their unaffected leg on the front block, they developed 6% greater mean resultant combined force compared with the opposite configuration (1.38 ± 0.06 vs 1.30 ± 0.11 BW, P = .015). However, because of a more vertical push angle, horizontal acceleration performance was equivalent between starting block configurations. We then used force data from each sprinter with an amputation to calculate the hypothetical starting mechanics for a virtual nonamputee (two unaffected legs) and a virtual bilateral amputee (two affected legs). Accelerations of virtual bilateral amputees were 15% slower compared with athletes with a unilateral amputation, which in turn were 11% slower than virtual nonamputees. Our biomechanical data do not explain the starting block configuration preference but they do explain the starting performance differences observed between nonamputee athletes and those with leg amputations.

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W. Lee Childers, Tim P. Gallagher, J. Chad Duncan, and Douglas K. Taylor

The individual pursuit is a 4-km cycling time trial performed on a velodrome. Parathletes with transtibial amputation (TTA) have lost physiological systems, but this may be offset by the reduced aerodynamic drag of the prosthesis. This research was performed to understand the effect of a unilateral TTA on Olympic 4-km pursuit performance. A forward-integration model of pursuit performance explored the interplay between power loss and aerodynamic gains in parathletes with TTA. The model is calibrated to a 4-km pursuit time of 4:10.5 (baseline), then adjusted to account for a TTA. Conditions simulated were based on typical pedal asymmetry in TTA (AMP), if foot stiffness were decreased (FLEX), if pedaling asymmetries were minimized (ASYM), if the prosthesis were aerodynamically optimized (AERO), if the prosthesis had a cosmetic cover (CC), and if all variables were optimized (OPT). A random Monte Carlo analysis was performed to understand model precision. Four-kilometer pursuit performances predicted by the model were 4:10.5, 4:20.4, 4:27.7, 4:09.2, 4:19.4, 4:27.9, and 4:08.2 for the baseline, AMP, FLEX, ASYM, AERO, CC, and OPT models, respectively. Model precision was ±3.7 s. While the modeled time decreased for ASYM and OPT modeled conditions, the time reduction fell within model precision and therefore was not significant. Practical application of these results suggests that parathletes with a TTA could improve performance by minimizing pedaling asymmetry and/or optimizing aerodynamic design, but, at best, they will have performance similar to that of intact cyclists. In conclusion, parathletes with TTA do not have a net advantage in the individual pursuit.

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Atsushi Makimoto, Yoko Sano, Satoru Hashizume, Akihiko Murai, Yoshiyuki Kobayashi, Hiroshi Takemura, and Hiroaki Hobara

. 7 Therefore, understanding of GRF during sprinting in amputees wearing running-specific prostheses would be expected to aid in the development of more effective training methods. Buckley 8 reported that unilateral transfemoral amputees had asymmetrical kinematics between prosthetic and