Browsing by Subject "Biomechanics"
Now showing 1 - 20 of 30
Results Per Page
Sort Options
Item A biomechanical dynamic model for lifting in the sagittal plane.(Texas Tech University, 1974-08) el-Bassoussi, Moustafa MohamedNot availableItem Adaptability of stride-to-stride control of stepping movements in human walking and running(2014-05) Bohnsack, Nicole Kristen; Dingwell, Jonathan B.Walking and running are essential tasks people take for granted every day. However, these are highly complex tasks that require significant neural control. This is complicated by the inherent redundancy of the nervous system and by physiological noise. Humans may adopt different control strategies to achieve different goals (environmental or task specific). More specifically, walking/running on a treadmill only requires that one not walk off the treadmill. Of the many possible strategies that can achieve this goal, humans attempt to maintain a constant speed from each stride to the next (Dingwell, John et al. 2010). However, how humans alter the stride-to-stride regulation of their gait when the task goals change (e.g., by maintaining stride length and/or time, during running, or during a predicted walk to run transition speed) has not yet been demonstrated. In the first two of three experiments conducted, healthy adults either walked or ran on a motorized treadmill at a comfortable speed under the following conditions: constant speed, constant speed with the stride length goal (targets on the treadmill), constant speed with the stride time goal (metronome), or constant speed with both stride length and stride time goals. In a third experiment, subjects walked and/or ran at a comfortable speed and also at their predicted theoretical walk to run transition speed. Goal functions derived from the task specifications yielded new variables that defined fluctuations either directly relevant to, or irrelevant to, achieving each goal. The magnitude of the variability, as well as the stride-to-stride temporal fluctuations in these variables, were calculated. During walking, subjects exploited different redundancy relationships in different ways to prioritize certain task goals (maintain stride speed) over others (maintain stride length or stride time) in each different context. In general, subjects made rapid corrections of those stride-to-stride deviations that were most directly relevant to the different task goals adopted in each walking condition. Thus, the central nervous system readily adapts to achieve multiple goals simultaneously. During running, subjects exhibited similar adaptations to walking, but over-corrected to prioritize maintaining stride speed even more strongly. This suggests that stepping control strategies adapt to the level of perceived risk. This purposeful adaptability of these stride-to-stride control strategies could be exploited to developing more effective rehabilitation interventions for patients with locomotor impairments. During the predicted walk-to-run speeds, subjects were able to largely exploit the redundancy within task goal, and effectively operated at “uncomfortable” speeds. These results suggest that the stride speed control is robust even with additional novel tasks and uncomfortable, abnormal speeds of locomotion.Item Biomechanics of lever operations(Texas Tech University, 1964-05) Noud, Patrick FrancisNot availableItem Biomechanics of slips and falls in the elderly: Effects of restricted arm motion on recovery strategies(2013-05) Jayadas, Aditya; Smith, James L.; Hsiang, Simon M.; Patterson, Patrick E.; Boros, Rhonda L.; James, Roger C.Slip and fall accidents pose a serious threat to elderly individuals. Several researchers, over the past few decades, have successfully quantified different gait parameters pertaining to the biomechanics of slips and falls to help reduce the incidence of slip and fall accidents in the elderly. However, a comprehensive understanding of mechanisms including strategies used by the elderly for recovery during a slippery perturbation under different arm restriction conditions is still lacking. This research study investigated gait patterns in young and elderly individuals, in terms of proactive and reactive strategies that individuals used to reduce their likelihood of a fall related injury during a slippery perturbation under different arm restriction conditions. In addition to the gait parameters, the strength capabilities of the lower extremities of young and elderly individuals were also explored. Lastly, a logistic regression equation was developed to predict falls and recoveries. The study did help identify successful strategies used for recovery under different arm restriction conditions. In addition, unsuccessful reactive movements that resulted in falls were also pointed out. Proactive strategies identified including reduced step length, walking velocity, heel contact velocity and foot floor angle were used by both younger and older individuals when they knew the floor was slippery. Reduced step length, foot floor angle and walking velocity were also noted when one or two arms of individuals were restricted. In terms of age, more elderly individuals fell when compared to younger individuals. Several other variables including average sliding heel velocity, peak sliding heel deceleration and separation between whole body center of mass and sliding heel also showed differences for age. Significant differences were noted not only between older and younger individuals but also between fallers and non-fallers in terms of the recovery effort. Variables including average sliding heel velocity, maximum and minimum differences between the upper body center of mass (UBCOM) and the lower body center of mass (LBCOM) showed differences between fallers and non-fallers. In terms of arm restriction, both young and older individuals showed significant differences in maximum wrist velocities for the different arm restriction conditions. Differences in maximum velocities between the WBCOM and heel when comparing the no-arm and two-arm restriction, and also the no-arm and one-arm conditions were also found. In terms of strength, knee and ankle torques were found to be significantly higher for younger individuals when compared to elderly individuals. The leg collapse that was observed which resulted in falls was an additional indicator of poor strength in the elderly. The primary contribution to elderly gait literature and the biomechanics of slips and falls through this study was the development of a novel method through the exploration of UBCOM-LBCOM dynamics during recovery effort from a slippery perturbation under different arm restriction conditions. In terms of findings, the study did show that individuals were able to recover better when their arms were not restricted. The study did also show that the elder fallers were unable to ‘catch up’ by moving their trunk (and UBCOM) quickly to keep up with the sliding heel (and the LBCOM. On the other hand, younger non-fallers were able to have a higher difference in velocities between the UBCOM and LBCOM, and still ‘catch up’ successfully. Thus, the study of UBCOM-LBCOM dynamics might be useful in better understanding elderly slips and falls.Item Biomechanics of the lens capsule(Texas A&M University, 2005-11-01) Heistand, Mark RichardKnowledge of the mechanics of the lens capsule is crucial for improving cataract surgery as well as understanding better the physiological role of the lens capsule in the process of accommodation. Previous research on the mechanical properties of the lens capsule contains many gaps and contradictions due to experimental limitations and inappropriate assumptions. Thus, the goal of this work is to quantify fully the regional, multiaxial mechanical behavior of the lens capsule and to calculate the change in stress and strain fields as a result of cataract surgery. Determining in situ the multiaxial mechanical behavior of the lens capsule required the design and construction of an experimental device capable of altering stresses in the capsule while measuring localized surface deformations. Tests performed on this device reveal that the meridional and circumferential strains align with the principal directions and are equivalent through most of the anterior lens capsule, except close to the equator where the meridional strain is greater. Furthermore, preconditioning effects were also found to be significant. Most importantly, however, these tests provide the data necessary for calculating material properties. This experimental system is advantageous in that it allows reconstruction of 3D geometry of the lens capsule and thereby quantification of curvature changes, as well as measurement of surface deformations that result from various surgical interventions. For instance, a continuous circular capsulorhexis (CCC) is commonly used during cataract surgery to create a hole in the anterior lens capsule (typically with a diameter of 5 mm). After the introduction of a CCC, strain was found to redistribute evenly from the meridional direction (retractional strain) to the circumferential direction (extensional strain), where both directional components of strain reached magnitudes up to 20% near the edge of the CCC. Furthermore, the curvature was found to increase at the edge of the CCC and remain the same near the equator, indicating that the mere introduction of a hole in the lens capsule will alter the focal characteristics of the lens and must therefore be considered in the design of an accommodative intraocular lens.Item Compensatory mechanisms in below-knee amputee walking and their effects on knee joint loading, metabolic cost and angular momentum(2010-08) Silverman, Anne Katherine; Neptune, Richard R.; Barr, Ronald E.; Dingwell, Jonathan B.; Fernandez, Benito; Longoria, Raul G.Unilateral, below-knee amputees have altered gait mechanics, which can significantly affect mobility. For example, amputees often have asymmetric leg loading as well as higher metabolic cost and an increased risk of falling compared to non-amputees. Below-knee amputees lose the functional use of the ankle muscles, which are critical in non-amputee walking for providing body support, forward propulsion and leg-swing initiation. The ankle muscles also regulate angular momentum in non-amputees, which is important for providing body stability and preventing falls. Thus, compensatory mechanisms in amputee walking are developed to accomplish the functional tasks normally provided by the ankle muscles. In Chapters 2 and 3, three-dimensional forward dynamics simulations of amputee and non-amputee walking were generated to identify compensatory mechanisms and their effects on joint loading and metabolic cost. Results showed that the prosthesis provided body support, but did not provide sufficient body propulsion or leg-swing initiation. As a result, compensations by the residual leg gluteus maximus, gluteus medius, and hamstrings were needed. The simulations also showed the intact leg tibio-femoral joint contact impulse was greater than the residual leg and that the vasti and hamstrings were the primary contributors to the joint impulse on both the intact and residual legs. The amputee simulation had higher metabolic cost than the non-amputee simulation, which was primarily due to prolonged muscle activity from the residual leg gluteus maximus, gluteus medius, hamstrings, vasti and intact leg vasti and ankle muscles. In Chapter 4, whole-body angular momentum in amputees and non-amputees was analyzed. Reduced residual leg propulsion resulted in a smaller range of sagittal plane angular momentum in the second half of the gait cycle. Thus, to conserve angular momentum, reduced braking was needed in the first half of the gait cycle. Decreased residual leg braking appears to be an important mechanism to regulate sagittal plane angular momentum in amputee walking, but was also associated with a greater range of angular momentum that may contribute to reduced stability in amputees. These studies have provided important insight into compensatory mechanisms in below-knee amputee walking and have the potential to guide rehabilitation methods to improve amputee mobility.Item Computerized dynamic biomechanical simulation of lifting versus inverse dynamics model: effects of task variables(Texas Tech University, 1995-12) Bernard, Tracey MarieAn examination of the kinetics and kinematics produced by the computerized dynamic biomechanical simulation model was performed to demonstrate the model's rehability in predicting stresses imposed on the body as a lifting task is performed. The peak kinetic parameters predicted by the simulation model were shown to be highly correlated, the kinematics less so, with the stresses imposed in actual lifts under different task conditions (range of lift, weight of load, size of box, and gender of lifter), thus its use can be advocated for lifting evaluations. Although highly correlated, the simulation tended to overestimate the values of the parameters. However, simple linear regression models provided in the analyses with R^2 values often m the range of 0.80 -0.95 can be used to correct for the prediction errors. The sensitivity analysis performed on inputs required to run the simulation model showed that the outputs of the model were consistent with the principles of biomechanics. The results provided in this study demonstrate that the simulation model should prove to be an effective alternative for the analysis of lifting tasks. By using the simulation model as a design tool, the tedious, time-consuming and costly data collection step required without use of a simulation tool can be eliminated and the ergonomist's time and effort spent more productively on design and evaluation.Item Determination of efficient methods of lift by comparing trained and untrained male and female lifters(Texas Tech University, 1978-12) Shannon, Richard HaroldNot availableItem Error analysis for randomized uniaxial stretch test on high strain materials and tissues(Texas A&M University, 2006-08-16) Jhun, Choon-SikMany people have readily suggested different types of hyperelastic models for high strain materials and biotissues since the 1940??s without validating them. But, there is no agreement for those models and no model is better than the other because of the ambiguity. The existence of ambiguity is because the error analysis has not been done yet (Criscione, 2003). The error analysis is motivated by the fact that no physical quantity can be measured without having some degree of uncertainties. Inelastic behavior is inevitable for the high strain materials and biotissues, and validity of the model should be justified by understanding the uncertainty due to it. We applied the fundamental statistical theory to the data obtained by randomized uniaxial stretch-controlled tests. The goodness-of-fit test (2R) and test of significance (t-test) were also employed. We initially presumed the factors that give rise to the inelastic deviation are time spent testing, stretch-rate, and stretch history. We found that these factors characterize the inelastic deviation in a systematic way. A huge amount of inelastic deviation was found at the stretch ratio of 1.1 for both specimens. The significance of this fact is that the inelastic uncertainties in the low stretch ranges of the rubber-like materials and biotissues are primarily related to the entropy. This is why the strain energy can hardly be determined by the experimentation at low strain ranges and there has been a deficiency in the understanding of the exclusive nature of the strain energy function at low strain ranges of the rubber-like materials and biotissues (Criscione, 2003). We also found the answers for the significance, effectiveness, and differences of the presumed factors above. Lastly, we checked the predictive capability by comparing the unused deviation data to the predicted deviation. To check if we have missed any variables for the prediction, we newly defined the prediction deviation which is the difference between the observed deviation and the point forecasting deviation. We found that the prediction deviation is off in a random way and what we have missed is random which means we didn??t miss any factors to predict the degree of inelastic deviation in our fitting.Item Experimental analysis and computational simulation of unilateral transtibial amputee walking to evaluate prosthetic device design characteristics and amputee gait mechanics(2010-05) Ventura, Jessica Dawn; Neptune, Richard R.; Barr, Ronald E.; Crawford, Richard H.; Fernandez, Benito R.; Abraham, Lawrence D.Over one million amputees are living in the United States with major lower limb loss (Ziegler-Graham et al. 2008). Lower limb amputation leads to the functional loss of the ankle plantar flexor muscles, which are important contributors to body support, forward propulsion, and leg swing initiation during walking (Neptune et al. 2001; Liu et al. 2006). Effective prosthetic component design is essential for successful rehabilitation of amputees to return to an active lifestyle by partially replacing the functional role of the ankle muscles. The series of experimental and computer simulation studies presented in this research showed that design characteristics of energy storage and return prosthetic ankles, specifically the elastic stiffness, significantly influence residual and intact leg ground reaction forces, knee joint moments, and muscle activity, thus affecting muscle output. These findings highlight the importance of proper prosthetic foot stiffness prescription for amputees to assure effective rehabilitation outcomes. The research also showed that the ankle muscles serve to stabilize the body during turning the center of mass. When amputees turn while supported by their prosthetic components, they rely more on gravity to redirect the center of mass than active muscle generation. This mechanism increases the risks of falling and identifies a need for prosthetic components and rehabilitation focused on increasing amputee stability during turning. A proper understanding of the effects of prosthetic components on amputee walking mechanics is critical to decreasing complications and risks that are prevalent among lower-limb amputees. The presented research is an important step towards reaching this goal.Item The influence of altering wheelchair propulsion technique on upper extremity demand(2010-08) Rankin, Jeffery Wade; Neptune, Richard R.; Barr, Ronald E.; Fernandez, Benito R.; Dingwell, Jonathan B.; Richter, William M.Most manual wheelchair users will experience upper extremity injury and pain during their lifetime, which can be partly attributed to the high load requirements, repetitive motions and extreme joint postures required during wheelchair propulsion. Recent efforts have attempted to determine how different propulsion techniques influence upper extremity demand using broad measures of demand (e.g., metabolic cost). However studies using more specific measures (e.g., muscle stress), have greater potential to determine how altering propulsion technique influences demand. The goal of this research was to use a musculoskeletal model with forward dynamics simulations of wheelchair propulsion to determine how altering propulsion technique influences muscle demand. Three studies were performed to achieve this goal. In the first study, a wheelchair propulsion simulation was used with a segment power analysis to identify muscle functional roles. The analysis showed that muscles contributed to either the push (i.e. delivering handrim power) or recovery (i.e. repositioning the hand) subtasks, with the transition period between the subtasks requiring high muscle co-contraction. The high co-contraction suggests that future studies focused on altering transition period biomechanics may have the greatest potential to reduce upper extremity demand. The second study investigated how changing the fraction effective force (i.e. the ratio of the tangential to total handrim force, FEF) influenced muscle demand. Simulations maximizing and minimizing FEF both had higher muscle work and stress relative to the nominal simulation. Therefore, the optimal FEF value appears to balance increasing FEF with minimizing upper extremity demand and care should be taken when using FEF to reduce demand. In the third study, simulations of biofeedback trials were used to determine the influence of cadence, push angle and peak handrim force on muscle demand. Although minimizing peak force had the lowest total muscle stress, individual stresses of many muscles were >20% and the simulation had the highest cadence, suggesting that this variable may not reduce demand. Instead minimizing cadence may be most effective, which had the lowest total muscle work and slowest cadence. These results have important implications for designing effective rehabilitation strategies that can reduce upper extremity injury and pain among manual wheelchair users.Item The influence of prosthetic foot design and walking speed on below-knee amputee gait mechanics(2011-12) Fey, Nicholas Phillip; Neptune, Richard R.; Abraham, Lawrence D.; Barr, Ronald E.; Crawford, Richard H.; Longoria, Raul G.Unilateral below-knee amputees commonly experience asymmetrical gait patterns and develop comorbidities in their intact (non-amputated) and residual (amputated) legs, with the mechanisms leading to these asymmetries and comorbidities being poorly understood. Prosthetic feet have been designed in an attempt to minimize walking asymmetries by utilizing elastic energy storage and return (ESAR) to help provide body support, forward propulsion and leg swing initiation. However, identifying the influence of walking speed and prosthetic foot stiffness on amputee gait mechanics is needed to develop evidence-based rationale for prosthetic foot selection and treatment of comorbidities. In this research, experimental and modeling studies were performed to identify the influence of walking speed and prosthetic foot stiffness on amputee walking mechanics. The results showed that when asymptomatic and relatively new amputees walk using clinically prescribed prosthetic feet across a wide range of speeds, loading asymmetries exist between the intact and residual knees. However, knee intersegmental joint force and moment quantities in both legs were not higher compared to non-amputees, suggesting that increased knee loads leading to joint disorders may develop in response to prolonged prosthesis usage or the onset of joint pathology over time. In addition, the results showed that decreasing ESAR foot stiffness can increase prosthesis range of motion, mid-stance energy storage, and late-stance energy return. However, the prosthetic foot contributions to forward propulsion and swing initiation were limited due to muscle compensations needed to provide body support and forward propulsion in the absence of residual leg ankle muscles. A study was also performed that integrated design optimization with forward dynamics simulations of amputee walking to identify the optimal prosthetic foot stiffness that minimized metabolic cost and intact knee joint forces. The optimal stiffness profile stiffened the toe and mid-foot while making the ankle less stiff, which decreased the intact knee joint force during mid-stance while reducing the overall metabolic cost of walking. These studies have provided new insight into the relationships between prosthetic foot stiffness and amputee walking mechanics, which provides biomechanics-based rationale for prosthetic foot prescription that can lead to improved amputee mobility and overall quality of life.Item An integrated computational-experimental approach for the in situ estimation of valve interstitial cell biomechanical state(2016-05) Buchanan, Rachel Marie; Sacks, Michael S.; Baker, Aaron B; Stachowiak, Jeanne C; Moon, Tess J; Guilak, FarshidMechanical forces are known to regulate aortic valve interstitial cell (AVIC) functional state by modulating their biosynthetic activity, translating to differences in tissue composition and structure and, potentially, leading to aortic valve (AV) dysfunction. While advances have been made toward the understanding of AVIC behavior ex-situ, the AVIC biomechanical state in its native extracellular matrix (ECM) remains largely unknown. Consequently, changes in AVIC behaviors, such as stiffness and contractility, resulting from pathological cues in-situ remain unidentified. We hypothesize that improved descriptions of AVIC biomechanical state in-situ, obtained using an inverse modeling approach, will provide deeper insight into AVIC interactions with the surrounding ECM, revealing important changes resulting from pathological state, and possibly informing pharmaceutical therapies. To achieve this, a novel integrated numerical-experimental framework to estimate AVIC mechanobiological state in-situ was developed. Flexural deformation of intact AV leaflets was used to quantify the effects of AVIC stiffness and contraction at the tissue level. In addition to being a relevant deformation mode of the cardiac cycle, flexure is highly sensitive to layer-specific changes in AVIC biomechanics. As a first step, a tissue-level bilayer model that accurately captures the bidirectional flexural response of AV intact layers in a passive state was developed. Next, tissue micromorphology was incorporated in a macro-micro scale framework to simulate layer-specific AVIC-ECM interactions. The macro-micro AV model enables the estimation of changes in effective AVIC stiffness and contraction in-situ that are otherwise grossly inaccessible through experimental approaches alone. Finally, microindentation studies examining AVIC activation were run in parallel with in-situ studies to emphasize the necessity of an in-situ approach, and the advantage it affords over existing ex-situ methodology. In conclusion, the developed numerical-experimental methodology can be used to obtain AVIC properties in-situ. Most importantly, it can lead to further understanding of AVIC-ECM mechanical coupling under various pathophysiological conditions and the investigation of possible treatment strategies targeting the myofibroblast phenotype characteristic of early signs of sclerotic valvular disease.Item A low-cost volume adjustable lower limb prosthetic socket : design and evaluation(2014-08) Vaughan, Meagan Renee; Crawford, Richard H.An issue of great concern for amputees continues to be lack of proper fit and comfort in their sockets. This lack can often be attributed to changes in the shape of the residual limb that cannot be compensated for by existing prosthetic socket technology. In regions where cost is a prohibitive factor in the replacement of ill-fitting prosthetic sockets, the need for a volume adjustable, and potentially longer lasting, socket design is abundant. This research focuses on designing a volume adjustable lower limb prosthetic socket that accommodates the needs of amputees in underdeveloped countries using collaborative design techniques. Though advocated as a means of accurately identifying and satisfying their needs, including end-users in the design process often adds an additional layer of complexity because of differences in culture, language, or geography among the participants. This research therefore includes a study in which product design techniques were applied to the same volume adjustable socket design problem with a variety of users – typical users, lead users, and new Empathic Lead Users - from different countries, one developed and one developing. To overcome differences among participants, this research includes an alternative strategy to create Empathic Lead Users (ELU) from non-user product design engineers through the use of simulated lead user experiences. As a result of this study, customer needs analysis with ELU helps to identify 95% of traditional and lead user customer needs and 100% more latent needs, and possibly more avenues for product innovations, than interviewing lead or traditional users alone. The concepts generated by all users were also compared. Based on the resulting concepts’ novelty, variety, quality, and quantity, all users were able to satisfactorily complete the concept generation exercises and produced competitive design solutions. Using the concepts generated during this co-design study, a volume adjustable socket was developed. The final socket design, based on the analogous rotational movement of a camera aperture, is pursued through mechanical and subject testing. Early users of the socket liked the design and it has been demonstrated to provide the necessary volume adjustments, but future design iterations to improve its comfort are necessary.Item Mobility in individuals with traumatic lower-limb injuries : implications for device design, surgical intervention and rehabilitation therapies(2016-05) Ranz, Ellyn Cymbre; Neptune, Richard R.; Barr, Ronald E; Crawford, Richard H; Sulzer, James S; Wilken, Jason MTraumatic injuries to the extremities are commonly observed in emergency room patients and military personnel in combat. Restoring high mobility and functionality is a primary goal post-injury, which may require the use of rehabilitative devices, surgical interventions, and rehabilitation therapies. The research detailed in this dissertation investigates specific elements of these approaches through the use of experimental study and modeling and simulation. In the first study, the influence of passive-dynamic ankle-foot orthosis bending axis on the gait performance of limb salvage subjects was investigated. Bending axis location was altered by fabricating customized orthosis components using additive manufacturing and was tested in a gait laboratory. Altering bending axis location did not result in large or consistent changes in gait measures, however subjects expressed strong preferences for bending axis condition and preference was strongly related to specific gait measures. This suggests that preference and comfort are important factors guiding the prescription of bending axis location. In the second study, musculoskeletal modeling was used to examine the influence of transfemoral amputation surgical techniques on muscle capacity to generate forces and moments about the hip. Muscle reattachment tension and stabilization were shown to be critical parameters for post-amputation capacity, which supports the use of myodesis stabilization (muscle is reattached directly to bone) in amputation procedures. In the third study, a forward dynamics simulation of transfemoral amputee gait was developed and used to examine individual muscle and prosthesis contributions to walking subtasks. The residual hip muscles, and intact ankle, knee, and hip muscles worked synergistically to provide body support, anteroposterior propulsion, mediolateral control, and leg swing. Increased contributions of contralateral muscles to ipsilateral subtasks as well as increased duration of specific muscle contributions were observed in comparison to non-amputee and transtibial amputee walking. These findings can be used to help develop targeted rehabilitation therapies and improve transfemoral amputee locomotion. Through elucidating the influence of PD-AFO bending axis on gait performance as well as the influence of transfemoral amputation surgical techniques on muscle capacity and function, this research provides a foundation for improved rehabilitation outcomes, and thus mobility for individuals who have experienced traumatic lower-limb injuries.Item Quantifying the strain response in the rat tibia during simulated resistance training used as a disuse countermeasure(2009-05-15) Jeffery, Jay MelvinDisuse of weight bearing bones has been shown to cause bone loss. This poses a health concern for people exposed to microgravity, such as astronauts. Animal studies are used to study factors related to bone loss and countermeasures to prevent bone loss. This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages were implanted on the antero-medial aspect of the proximal tibia to measure the mechanical strain during a typical exercise session. In a separate but parallel study, the exercise was shown to be an effective countermeasure to disuse related bone loss. The current study sought to understand the loading of the bone during the exercise. To determine if the strain response changes during a protocol using this countermeasure, strains were measured on a group of weight bearing animals and a group that were hind limb unloaded and received the countermeasure for 21 days. Strain magnitudes and rates were considered and related to torques at the ankle joint. No significant differences in strain magnitudes were noted between the baseline control group and the hindlimb unloaded group that received the countermeasure. The two kinds of contractions used in an exercise session are isometric and eccentric. The isometric contractions are used to adjust the stimulation equipment for the eccentric contractions, which constitute the exercise. Peak strain levels during the isometric contractions ranged from 900 to 2200 microstrain while the eccentric were 38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than the eccentric contractions, which have previously been thought to be the primary part of the countermeasure.Item Redesign of the total wrist prosthesis to address wrist rotation(2013-05) Mehta, Jay Ravi; Crawford, Richard H.The human wrist is a vital joint in daily life, and it is subject to injuries and disease. Currently, severe wrist disease is normally treated with wrist arthrodesis, which is normally reliable but results in a fixed wrist incapable of allowing wrist motion. Another method of treating a nonfunctional or severely painful wrist is wrist arthroplasty where the wrist joint is replaced with an implant that allows wrist movement. As of yet, a suitable wrist implant has not been developed, especially for the case of the post-traumatic, young male wrist, and most current wrist implants fail from failure of the bone-implant interface. Through simulation and literature review, it is concluded that implants that restrict axial rotation are bound to fail overtime. With this conclusion, a new wrist implant prototype is designed that incorporates state of the art materials, fluid film lubrication, proper kinematics, a suitable range of motion, and more. This implant contributes several improvements to the field of wrist arthroplasty.Item The Role of Muscle Fatigue on Movement Timing and Stability during Repetitive Tasks(2009-05) Gates, Deanna H.; Dingwell, Jonathan B.; Barr, Ronald; Griffin, Lisa; Moore, J.; Rylander, H.Repetitive stress injuries are common in the workplace where workers perform repetitive tasks continuously throughout the day. Muscle fatigue may lead to injury either directly through muscle damage or indirectly through changes in coordination, development of muscle imbalances, kinematic and muscle activation variability, and/or movement instability. To better understand the role of muscle fatigue in changes in movement parameters, we studied how muscle fatigue and muscle imbalances affected the control of movement timing, variability, and stability during a repetitive upper extremity sawing task. Since muscle fatigue leads to delayed muscle and cognitive response times, we might expect the ability to maintain movement timing would decline with muscle fatigue. We compared timing errors pre- and post-fatigue as subjects performed this repetitive sawing task synchronized with a metronome using standard techniques and a goal-equivalent manifold (GEM) approach. No differences in basic performance parameters were found. Significant decreases in the temporal correlations of the timing errors and velocities indicated that subjects made more frequent corrections to their movements post-fatigue. Muscle fatigue may lead to movement instability through a variety of mechanisms including delayed muscle response times and muscle imbalances. To measure movement stability, we must first define a state space that describes the movement. We compared a variety of different state space definitions and found that state spaces composed of angles and velocities with little redundant information provide the most consistent results. We then studied the affect of fatigue on the shoulder flexor muscles and general fatigue of the arm on movement stability. Subjects were able to maintain stability in spite of muscle fatigue, shoulder strength imbalance and decreased muscle cocontraction. Little is known about the time course for adaptations in response to fatigue. We studied the effect of muscle fatigue on movement coordination, kinematic variability and movement stability while subjects performed the same sawing task at two work heights. Increasing the height of the task caused subjects to make more adjustments to their movement patterns in response to muscle fatigue. Subjects also exhibited some increases in kinematic variability at the shoulder but no changes in movement stability. These findings suggest that people alter their kinematic patterns in response to fatigue possibly to maintain stability at the expense of increased variability.Item Sequential High-Impact, Free-Fall Loading and Zoledronic Acid as a Novel Pre-Treatment for Disuse-Induced Bone Loss(2014-03-31) Boudreaux, RamonThe purpose of our investigation was to evaluate the efficacy of prophylactic interventions consisting of simulated exercise (high-impact, free-fall loading) and/or a bisphosphonate (zoledronic acid), to counter disuse-induced bone loss of adult male rats (6 months old) subjected to 28 days of hindlimb unloading. Furthermore, we aimed to define the effects of these treatments on mechanical strength properties and bone turnover. We hypothesized that monotherapy would mitigate adverse alterations in bone mass, microarchitecture, and strength, while the combined sequential treatment would completely prevent them. Animals were assigned to one of six groups (n=12 each): baseline control (BC, euthanized on study day 0), cage control (CC), hindlimb unloading (HU), zoledronic acid treatment plus hindlimb unloading (ZA+HU), simulated exercise treatment plus hindlimb unloading (Ex+HU), and simulated exercise and zoledronic acid treatments plus hindlimb unloading (Ex+ZA+HU). Ex animals were dropped 25 times (five drops from 30 cm followed by 20 drops from 60 cm) three times per week for the first five weeks of the study. ZA (60 ?g/kg body weight) was administered on day 36, immediately following Ex and just prior to HU. HU began on day 37 and persisted for four weeks. At the distal femur metaphysis (DFM), proximal tibia metaphysis (PTM), and femoral neck (FN), HU caused declines in cancellous bone volume fraction (BV/TV, -25%) and total volumetric bone mineral density (vBMD, -4.7% and -14%), respectively, compared to CC. Mechanical strength and bone turnover were also impaired due to unloading. Individually, Ex and ZA attenuated HU-induced changes in mass, microarchitecture, and strength, but when given sequentially, Ex+ZA fully rescued them. While HU caused an uncoupling of bone remodeling, ZA treatment successfully reduced bone degradation without affecting bone formation. Treatment with Ex followed by ZA resulted in enhanced DFM BV/TV (+20%) and trabecular thickness (Tb.Th, +5%), and PTM total vBMD (+13%). Also, FN ultimate force was highest with combination treatment. While Ex and ZA alone attenuated the deleterious effects of disuse on bone quality, when the two were administered in sequence adult male rats were fully protected against HU-induced alterations in bone mass, microarchitecture, strength, and turnover.Item Ses-based difference in the morphology, tensile properties and ultrastructure of the human anterior cruciate ligament and patellar tendon(2005-12) Chandrashekar, Naveen Kugwe; Hashemi, Javad; Mansouri, Hossein; Seshaiyer, Padmanabhan; Hardy, Daniel; Barhorst, Alan; Parameswaran, SivaAnterior Cruciate Ligament (ACL) is an important ligament in the knee which stabilizes it during various daily activities. ACL injury is common is sports such as basketball, soccer and football. Torn ACL does not heal and needs to be reconstructed with a graft tissue to restore knee stability. It is well known that female athletes tear their ACL 2-8 times more frequently than their male counterparts. Higher rates of ACL injury in women translate to more ACL replacement surgeries, more revision surgeries, and a higher chance of developing arthritis with aging. However, there exists no sex-based disparity in the tear rate of reconstructed ACL. Therefore, it is reasonable to believe the tissue mechanics of the ACL itself might play a role in the existing sex-based disparity in the ACL injury incidence. Sex-based differences in the size and tensile properties of ACL may be critical from injury point of view. A biomechanical cadaveric study was conducted to study the possible sex-based differences in the size, tensile properties and ultrastructural variables of human anterior cruciate ligaments. Similar study was also carried out in patellar tendons which is a tissue used for ACL reconstruction. The effect of tissue fatigue on the properties and mechanical behavior of both ACL and patellar tendon were investigated. The effect of notch width on the force generated in the ACL during combined valgus and external tibial rotation was also studied. Results show that female ACLs are not only smaller, but do not grow in proportion to the body height and are of lower mechanical quality even after adjustments to the body anthropometry. No such disparity existed in case of patellar tendon. The female ACL had lower percentage area occupied by the collagen fibrils than the male ACL. The mass density of patellar tendon was found to be a good predictor of its mechanical quality. Smaller intercondylar notch was found to increase the in-situ forces in the ACL. The effect of notch impingement on the forces in the ACL could not be verified. Cyclic loading at higher load was found to affect the mechanical behavior of the ACL but not the patellar tendon. The results are significant from basic science point of view as they show fundamental difference between material make-up of the ACL that possibly is a major reason for sex-based difference in ACL injury incidence. It also appears from the results that patellar tendons have similar material make-up irrespective of sex. Further, the results are also significant from clinical point of view as it shows that mass density of patellar tendons can be used to predict the mechanical quality of graft material prior to ACL reconstruction hence minimizing the chances of a graft of lower mechanical quality being used for reconstruction.