Individual Muscle Contributions to the Axial Knee Joint Contact Force During Normal Walking

Muscles are significant contributors to the high joint forces developed in the knee during human walking. Not only do muscles contribute to the knee joint forces by acting to compress the joint, but they also develop joint forces indirectly through their contributions to the ground reaction forces via dynamic coupling. Thus, muscles can have significant contributions to forces at joints they do not span. However, few studies have investigated how the major lower-limb muscles contribute to the knee joint contact forces during walking. The goal of this study was to use a muscle-actuated forward dynamics simulation of walking to identify how individual muscles contribute to the axial tibio-femoral joint force. The simulation results showed that the vastii muscles are the primary contributors to the axial joint force in early stance while the gastrocnemius is the primary contributor in late stance. The tibio-femoral joint force generated by these muscles was at times greater than the muscle forces themselves. Muscles that do not cross the knee joint (e.g., the gluteus maximus and soleus) also have significant contributions to the tibio-femoral joint force through their contributions to the ground reaction forces. Further, small changes in walking kinematics (e.g., knee flexion angle) can have a significant effect on the magnitude of the knee joint forces. Thus, altering walking mechanics and muscle coordination patterns to utilize muscle groups that perform the same biomechanical function, yet contribute less to the knee joint forces may be an effective way to reduce knee joint loading during walking

Selective Laser Sintering of Passive Dynamic Ankle-Foot Orthoses

Passive dynamic ankle-foot orthoses (AFO’s) are used to improve gait performance in those with various neuromuscular disorders. An important design characteristic of passive dynamic AFOs is the storage and release of elastic energy within its structure to help satisfy the energetic demands of walking. Thus, minimizing energy dissipation through internal friction is a fundamental criterion for selecting the appropriate AFO material. This study compared the mechanical damping of a carbon-fiber AFO to three geometrically identical AFO’s fabricated using selective laser sintering with different materials. Mechanical damping characteristics ranked the materials as Nylon 11 (best), followed by DuraformTM PA and DuraformTM GF (worst).Mechanical Engineerin

The Influence of Orthotic Devices and Vastus Medialis Strength and Timing on Patellofemoral Loads During Running

Objective. To use a musculoskeletal model and simulation of running to examine: (1) the influence of two commonly prescribed treatments for patellofemoral pain (vastus medialis oblique strengthening and orthoses) and (2) the functional significance of timing differences between vastus medialis oblique and vastus lateralis on lateral patellofemoral joint loads. Design. A three-dimensional musculoskeletal model of the lower extremity was used to simulate running at 4 m/s. Background. Repetitive and excessive joint loading is often associated with overuse injuries that require clinical treatments to reduce pain and restore function. Affecting one in four runners, patellofemoral pain is one of the most common injuries in running. Although conservative treatments have been reported to successfully treat patellofemoral pain, the effectiveness is often based on subjective or empirical data, which have generated disagreement on the most effective treatment. Methods. Nine subject specific running simulations were generated and experiments were performed by applying the treatments and timing differences to the nominal simulations. Results. Both treatments significantly reduced the average patellofemoral joint load and the vastus medialis strengthening also significantly reduced the peak patellofemoral joint load. In addition, when the vastus medialis oblique timing was delayed and advanced relative to the vastus lateralis timing, a significant increase and decrease in the joint load was observed, respectively, during the loading response. Conclusions. Increasing vastus medialis oblique strength yielded more consistent results across subjects than the orthosis in reducing patellofemoral joint loads during running. The effect of orthoses was highly variable and sensitive to the individual subject\u27s running mechanics. Vastus medialis oblique activation timing is an important determinant of lateral patellofemoral joint loading during the impact phase. Relevance.These findings indicate that a reduction in patellofemoral pain may be achieved through techniques that selectively increase the vastus medialis oblique strength. Therefore, future studies should be directed towards identifying such techniques. Additionally, the functional significance of timing differences between the vastus medialis oblique and vastus lateralis is an important consideration in patellofemoral pain treatment and orthoses may be beneficial for some patients depending on their running mechanics

Muscle Contributions to Frontal and Transverse Plane Whole-Body Angular Momentum

The purpose of this study was to build upon previous work by analyzing how gravity and individual muscles contribute to frontal and traverse plane whole-body angular momentum. Identifying which muscles are responsible for generating angular momentum has important implications for the diagnosis and treatment of movement disorders

A Method of Altering Coronal Plane Prosthetic Foot Stiffness for Studying its Effect on Amputee Gait

In an effort to understand the effects of prosthetic foot stiffness on amputee gait and mobility, it is useful to produce prototype prosthetic feet that differ in stiffness. While many commercial prosthetic feet are made out of carbon fiber, the manufacturing process is ill-suited to design experimentation as it is expensive, time consuming and requires tooling modifications to produce design changes. In order to facilitate a study of the effects of coronal plane prosthetic foot stiffness on amputee maneuvering gait, we are manufacturing custom prosthetic feet using a form of additive manufacturing, selective laser sintering (SLS), that was developed at the University of Texas at Austin. We have previously used SLS technology to create functional transtibial prosthetic sockets, ankle-foot orthoses, and prosthetic foot prototypes. To manufacture prosthetic feet with different stiffnesses, we first measured the stiffness profile of a commercially available carbon fiber prosthetic foot on an Instron 3345 (Norwood, MA) in two configurations where the foot was loaded to 114 kg in foot flat at 0° eversion and toe-only at 5° eversion positions. A computer aided design model of an SLS prosthetic foot was developed and adjusted to match the stiffness profile of the carbon fiber foot. Finite element analysis (SolidWorks Corp.; Waltham, MA) was then used to verify that the desired stiffness level was achieved. This process was repeated to create three prosthetic feet with altered coronal plane stiffness profiles (25% greater, 50% greater, and 25% less) while sagittal stiffness was held constant. The prototype feet were fabricated using selective laser sintering in a Vanguard HiQ/HS SLS Machine (3D Systems Corp.; Rock Hill, SC). Finally, the feet were mechanically tested in the same configurations as the carbon fiber foot to confirm that they had the desired stiffness profiles. Prototype feet closely matched the sagittal stiffness of the chosen prosthetic foot while coronal plane stiffnesses were approximately the same, 30% greater and 30% less than the carbon fiber foot. Future work will be to use these feet to observe the influence of coronal plane stiffness on amputee gait

Fabrication of Ankle-Foot Orthoses using Selective Laser Sintering Technology

Passive dynamic ankle-foot orthoses (AFOs) are often prescribed to improve gait performance for those with various neuromuscular disorders. Designs and materials used for AFOs range from simple polypropylene braces to advanced custom carbon fiber dynamic AFOs that passively store and release mechanical energy during gait. AFO designs vary in the shape and length of the foot component as well as the stiffness and length of the tibial component, depending on the desired functional outcomes. However, the current fabrication technology is not ideally suited for refined customization of AFO characteristics to optimize performance, or for rapid lowcost, high volume manufacturing and global distribution. A promising engineering solution for producing customized dynamic AFOs is the application of Selective Laser Sintering (SLS), which is a versatile manufacturing technology that provides advantages over traditional methods and has already been successfully used to fabricate prosthetic sockets for lower limb amputees (e.g., Faustini et al., 2006). Thus, the primary objective of this study was to explore the feasibility of using an SLSbased design, analysis and manufacturing framework to produce subject-specific passive dynamic AFOs in a cost-effective manner

The Influence of Foot Positioning on Ankle Sprains

The goal of this study was to examine the influence of changes in foot positioning at touch-down on ankle sprain occurrence. Muscle model driven computer simulations of 10 subjects performing the landing phase of a side-shuffle movement were performed. The relative subtalar joint and talocural joint angles at touchdown were varied, and each subject-specific simulation was exposed to a set of perturbed floor conditions. The touchdown subtalar joint angle was not found to have a considerable influence on sprain occurrence, while increased touchdown plantar flexion caused increased ankle sprain occurrences. Increased touchdown plantar flexion may be the mechanism which causes ankles with a history of ankle sprains to have an increased susceptibility to subsequent sprains. This finding may also reveal a mechanism by which taping of a sprained ankle or the application of an ankle brace leads to decreased ankle sprain susceptibility

Relationships between Muscle Contributions to Walking Subtasks and Functional Walking Status in Persons with Post-Stroke Hemiparesis

Walking speed is commonly used to predict stroke severity and assess functional walking status (i.e., household, limited community and community walking status) post-stroke. The underlying mechanisms that limit walking speed (and functional walking status by extension) need to be understood to improve post-stroke rehabilitation. Previous experimental studies have shown correlations between paretic plantarflexor output during the pre-swing phase and walking speed and suggest that the paretic hip flexors can compensate in some hemiparetic subjects. Modeling and simulation studies of healthy walking have shown that the ankle plantarflexors, soleus (SOL) and gastrocnemius (GAS), and uniarticular hip flexors (IL) are essential contributors to the walking subtasks of forward propulsion, swing initiation and/or power generation during pre-swing. However, the relationships between functional walking status and individual muscle contributions to these walking subtasks in hemiparetic walking are unknown. The goal of this study was to use 3D forward dynamics simulations to investigate the relationships between functional walking status in post-stroke hemiparetic walking and muscle contributions to forward propulsion, swing initiation and power generation

Pre-Swing Deficits in Forward Propulsion, Swing Initiation and Power Generation by Individual Muscles in Hemiparetic Walking

Clinical studies of hemiparetic walking have shown pre-swing abnormalities in the paretic leg suggesting that paretic muscle contributions to important biomechanical walking subtasks are different than those of non-disabled individuals. Three-dimensional forward dynamics simulations of two representative hemiparetic subjects with different levels of walking function classified by self-selected walking speed (i.e., limited community=0.4–0.8 m/s and community walkers=\u3e0.8 m/s) and a speed-matched control were generated to quantify individual muscle contributions to forward propulsion, swing initiation and power generation during the pre-swing phase (i.e., double support phase proceeding toe-off). Simulation analyses identified decreased paretic soleus and gastrocnemius contributions to forward propulsion and power generation as the primary impairment in the limited community walker compared to the control subject. The non-paretic leg did not compensate for decreased forward propulsion by paretic muscles during pre-swing in the limited community walker. Paretic muscles had the net effect to absorb energy from the paretic leg during pre-swing in the community walker suggesting that deficits in swing initiation are a primary impairment. Specifically, the paretic gastrocnemius and hip flexors (i.e., iliacus, psoas and sartorius) contributed less to swing initiation and the paretic soleus and gluteus medius absorbed more power from the paretic leg in the community walker compared to the control subject. Rehabilitation strategies aimed at diminishing these deficits have much potential to improve walking function in these hemiparetic subjects and those with similar deficits

Adubacão foliar de mudas de café (Coffea arabica, L., var. Mundo Nôvo) com três fontes de nitrogênio - 15N

This work was carried out with the aim of evaluating the effect of foliar application of nitrogen in young coffee plants (Coffea arabica L., var. Mundo- Novo). Three sources of nitrogen fertilizers were use: NaN0(3), (NH4)2SO4 and (NH2)2CO 0,7, 0,6 and 0,4 atom % N15 in excess, respectively. Three different methods of application for each source were used: 1) total application of the dosis to the soil; 2) total application of the dosis to the leaves; and 3) fractional application of the dosis, one half to the soil and one half by foliar application. The corresponding checks were also included. The experimental design used was complete randomized blocks, including 14 treatments replicated 3 times. Part of these treatments was in factorial arrangement. The 6 months old coffee plants were grown in a greenhouse during a period of 7 months. The plants were then separated in three fractions: root, stem and leaves. These fractions were oven dried, weighed, ground and total nitrogen and the isotopic relation of 14N/15N were determined. The dry matter yield, the amount of total nitrogen uptake, the quantity of this nutrient coming from the soil and fertilizer, for each treatment and fraction and for the whole plant, were the factors utilized to evaluate the effects of foliar application of the tested nitrogen sources. For the foliar application of nitrogen, a special system of spraying was tried. The most outstanding conclusions obtained are as follows : As a general rule, the effect of the three sources was always similar and the application to the soil followed by the application one half to the soil and one half foliar aplication were responsible for the increased dry matter yield. In relation to the total nitrogen uptake, a higher uptake was obtained with the application to the soil compared to foliar application, for the three nitrogen sources under study. In respect to the nitrogen in these young coffee plants coming from the fertilizes, the application to the soil was also superior to the foliar application. For foliar application, the efficiency of the nitrogen was 12.8%, 9.7% and 8.6% for sodium nitrate, urea and ammonium sulphate, respectively. In one half soil and one half forliar application, the efficiency was 33.5%, 23.3% and 22.7% for sodium nitrate, ammonium sulphate and urea, respectivaly. Nitrogen translocation from the top to the roots of the plant was evident when applied through the leaves. In the half to the soil half to the leaves treatment with ammonium sulphate, no similar results were obtained. It is difficult to explain the low absorption of nitrogen applied to the leaves for the three sources, sodium nitrate being superior to urea.O presente trabalho foi conduzido com a finalidade de se avaliar o efeito da aplicação foliar no nitrogênio em mudas de café (Coffea arabica L, var. Mundo Nôvo). Para isso, três fontes de fertilizantes nitrogenados - NaNO3, (NH4)2SO4 e (NH2)2CO - enriquecidos com 0,7, 0,6 e 0,4% de átomos de 15N em excesso, respectivamente, foram utilizados, aplicando-as de vários modos: 1) aplicação da dose total de cada fonte de nitrogênio ao solo; 2) aplicação da dose total de cada fonte exclusivamente foliar e 3) aplicação da metade desta dose total ao solo e da outra metade por via foliar, além das correspondentes testemunhas. O desenho experimental foi de blocos ao acaso, com 14 tratamentos e 3 repetições, com parte dos tratamentos em arranjo fatorial. As mudas de café, de 6 meses de idade foram cultivadas em casa de vegetação, durante um período de 7 meses. A seguir, as palantas foram separadas em frações raiz, caule e folha. Sobre estas frações, secas em estufa, pesadas e moídas, procedeu-se às análises químicas do nitrogênio e à determinação da relação isotópica 14N/15N. A produção de matéria seca, a quantidade de nitrogênio absorvido, aquela proveniente do solo e do fertilizante, por cada tratamento, em cada fração e na planta toda. foram utilizados para avaliar o efeito da adubação foliar ds fontes de nitrogênio. Pra a aplicação foliar do nitrogênio, foi construído um sistema espacial de pulverização. De acordo com os resultados obtidos são apresentadas, a continuação, as seguintes inferências. De maneira geral, a aplicação das três fontes de nitrogênio ao solo, seguida pela aplicação combinada ao solo e à folha, deram maior produção de matéria seca, não havendo diferença entre as fontes. Em relação a absorção do nitrogênio total, foi verificada uma maior absorção com a aplicação ao solo das três fontes de nitrogênio. No que diz respeito ao nitrogênio nas plantulas provenientes do fertilizante, a aplicação ao solo foi superior a aplicação foliar, para as três fontes. A porcentagem da eficiência do nitrogênio foi de 39%. Na aplicação foliar, a eficiência do nitrogênio foi 12,8%, 9,7% e 8,6% para nitrato de sódio, a uréia e o sulfato de amônio respectivamente. Na aplicação combinada, metade solo mais metade folha, a eficiência foi de 33,5%, 23,3% e 22,7% para o nitrato de sódio, o sulfato de amônio e a uréia, respectivamente. É difícil, no presente trabalho, explicar a pouca absorção do nitrogênio aplicada por pulverização foliar, destacando-se o nitrato de sódio em relação Ys outras fontes