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ANN ARBOR, MI, United States

Zelik K.E.,University of Michigan | Zelik K.E.,Laboratory of Neuromotor Physiology | Huang T.W.P.,University of Michigan | Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
Journal of Theoretical Biology | Year: 2014

The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active work demands on the plantarflexor muscles in series. However, this does not explain why or when this ankle work, whether by muscle or tendon, needs to be performed during gait. We therefore employ a simple bipedal walking model to investigate how ankle work and series elasticity impact economical locomotion. Our model shows that ankle elasticity can use passive dynamics to aid push-off late in single support, redirecting the body's center-of-mass (COM) motion upward. An appropriately timed, elastic push-off helps to reduce dissipative collision losses at contralateral heelstrike, and therefore the positive work needed to offset those losses and power steady walking. Thus, the model demonstrates how elastic ankle work can reduce the total energetic demands of walking, including work required from more proximal knee and hip muscles. We found that the key requirement for using ankle elasticity to achieve economical gait is the proper ratio of ankle stiffness to foot length. Optimal combination of these parameters ensures proper timing of elastic energy release prior to contralateral heelstrike, and sufficient energy storage to redirect the COM velocity. In fact, there exist parameter combinations that theoretically yield collision-free walking, thus requiring zero active work, albeit with relatively high ankle torques. Ankle elasticity also allows the hip to power economical walking by contributing indirectly to push-off. Whether walking is powered by the ankle or hip, ankle elasticity may aid walking economy by reducing collision losses. © 2013 Elsevier Ltd. Source

Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
IEEE Transactions on Neural Systems and Rehabilitation Engineering | Year: 2015

Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, step time, step length, and joint mechanics. Although these asymmetries result from weak prosthetic-side push-off, there is no proven mechanistic explanation of how that impairment propagates to the rest of the body. We used a simple dynamic walking model to explore possible consequences of a unilateral impairment similar to that of a transtibial amputee. The model compensates for reduced push-off work from one leg by performing more work elsewhere, for example during the middle of stance by either or both legs. The model predicts several gait abnormalities, including slower forward velocity of the body center-of-mass during intact-side stance, greater energy dissipation in the intact side, and more positive work overall. We tested these predictions with data from unilateral transtibial amputees (N = 11) and nonamputee control subjects (N = 10) walking on an instrumented treadmill. We observed several predicted asymmetries, including forward velocity during stance phases and energy dissipation from the two limbs, as well as greater work overall. Secondary adaptations, such as to reduce discomfort, may exacerbate asymmetry, but these simple principles suggest that some asymmetry may be unavoidable in cases of unilateral limb loss. © 2014 IEEE. Source

Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Adamczyk P.G.,University of Michigan | Kuo A.D.,University of Michigan
Journal of Experimental Biology | Year: 2013

During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, p>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM. © 2013. Published by The Company of Biologists Ltd. Source

Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2007

DESCRIPTION (provided by applicant): Convenient and objective assessment of gait is important for health management of older adults. Measuring gait function and mobility objectively can assess adherence and progress in an exercise or rehabilitation program, or track dosage and efficacy of medication. Accurate measurements can be taken in the clinic or laboratory, but field-based measurements would greatly assist health management. Unfortunately, there is little means of accurately performing real-world, long-term assessments in the home and at reasonable cost. Miniature sensors are rapidly improving in accuracy and power economy, offering great potential for field-based activity assessment. Simple accelerometer-based pedometers have proven highly accurate for step counts, and miniaturized, wireless systems such as the Nike+Ipod Sport Kit provide estimates of running speed and distance accurate enough for casual use, while remaining unobtrusive enough to wear conveniently for long durations. The requirements of research or clinical mobility assessments, however, exceed those of current systems. Several convergent technologies make highly accurate, miniature, inertial sensor systems feasible, including multi-axis accelerometer and angular rate sensors in small chip packages, powerful microprocessors with built-in wireless transmission capabilities, and increases in memory density. Most importantly, model-based sensor integration technology makes it possible to fuse data from multiple sensor types and minimize drift error. The aims of this project are to: 1. Develop a Field-Based Gait Assessment System, which will integrate information from miniature inertial sensors attached to the body and limbs, and process these data onboard to quantify walking speed, stride length, step variability, and other gait variables. We will design the sensor packages mounted in shoes to transmit wirelessly to integration and processing unit mounted at the waist. 2. Test and calibrate this system on human subjects, using simultaneous and independent laboratory-based measurements. We will use optical motion capture to assess actual gait variables using standard techniques of known accuracy. This project seeks to evaluate the gait of elderly individuals to assess fall risk, aid fall prevention, promote exercise, diagnose disease progression, and evaluate medication. This project will develop a set of miniature, wearable, wireless sensors that can record gait activity over long periods of time (> 1 day) with minimal interference with daily activity.

Agency: Department of Health and Human Services | Branch: National Institutes of Health | Program: SBIR | Phase: Phase I | Award Amount: 157.47K | Year: 2015

DESCRIPTION provided by applicant The long term goal of this project is to develop prosthetic foot technology that can function differently for different activities Although current prostheses can be very effective for particular tasks e g walking running or standing an amputee must choose a single prosthesis to achieve reasonably good performance across all daily activities This results in a compromise because the biomechanical demands of walking for example are different from those for standing A prosthetic foot that can modulate its mechanical properties to biomechanically accommodate each activity could be very helpful This prosthesis is intended for use by subjects with amputation of both traumatic and non traumatic origin The proposed biomechanical behavior is to modulate foot stiffness differently for many activities most notably walking and standing During walking the prosthesis needs to provide strong weight support to prevent hard landings on the intact leg This behavior is facilitated by high stiffness During standing different users may desire a stable base of support or a compliant foot with large range of motion The ideal stiffness for each task also depends on the differing demands of dynamic and static stability Based on studies of gait mechanics stiffness should be adjusted for each different task The Specific Aims of this project are to To design and construct a prosthetic foot that modulates its mechanical stiffness under automatic computer control based on the userandapos s activity and test its mechanical characteristics such as stiffness adjustability and fast modulation To perform proof of concept testing of the prototype prosthetic footandapos s effect on walking and standing in amputees PUBLIC HEALTH RELEVANCE The most common mobility issues for lower limb amputees are discomfort stability and fatigue Persons wearing prosthetic feet find it uncomfortable to stand for long periods or to walk more than moderate distances These issues are in part due to the fact that walking and standing and other tasks all have different biomechanical demands which must be addressed by a single prosthetic foot We propose to develop a computer controlled prosthetic foot that can automatically change its mechanical stiffness depending on the userandapos s task The prosthetic foot is intended to improve stability and comfort for standing and reduce impact forces on the leg during walking and to automatically vary its characteristics during daily life Such technology may improve comfort and reduce fatigue for amputees It is intended for use by subjects with amputation of both traumatic and non traumatic etiology

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