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Background. Motor skill learning and performance are optimized when individuals direct their attention externally towards the desired effect. Improvements include increased force production and improved coordination, determinants that also significantly influence rowing performance. However, no consensus surrounding an “ideal” rowing technique and these determinants exists. Attentional focus cues may not only improve rowing performance, but also enhance understanding of factors affecting force production. Aims. Two studies evaluated the efficacy of attentional focus on 1) distance rowed by novice participants; 2) power and peak force generated by novice participants; 3) distance rowed by novice & expert participants 4) force production measures of power, peak force, peak force max, and joules, as well as force signature measures of stroke length, peak force position, mean to peak force ratio, and variability in novice and expert participants; 5) rowing outcomes while controlling for participant stature; and 6) coordination of the legs and trunk during dynamic indoor rowing. Methods. Thirty novice and nineteen experts completed three 45 second long trials on a dynamic indoor rower (RP3), with the goal of rowing as fast as possible between 24 and 26 strokes per minute. Prior to each trial, participants were given attentional focus cues: internal - “As you row, focus on pushing with your legs”; external - “As you row, focus on creating pressure on the handle”; and a baseline condition, where no cue was provided. All three cues were counter-balanced. Results. There were no effects of attentional focus on outcomes, with the exception of increased stroke length for expert participants while rowing with an external focus. Significant effects were found for gender, expertise, and stature. Variability distinguished novices from experts. Participants reported difficulty managing their ability to row as fast as possible, maintain a stroke rate of 24 to 26, and focus on the cue. Conclusion. As the first study to evaluate the efficacy of attentional focus on force production in rowing, results indicated limited support for an external focus of attention. Individual, task, and environmental factors may have influenced rowing outcomes. Further investigation evaluating attentional focus and rowing that accounts for these factors is suggested.

Use of load-bearing materials whose functionality arises from architectured microstructures, so called architectured materials, has been hindered by the challenge of connecting them. A solution in nature is found at the tendon enthesis, a tissue that connects tendon and bone, two vastly different natural architectured materials. The tendon enthesis provides stability and allows for mobility of a joint though effective transfer of muscle forces from tendon to bone, while exhibiting toughness across a wide range of loadings. Unfortunately, many painful and physically debilitating conditions occur at or near this interface when the enthesis architecture is compromised due to injury or degeneration. Surgical and natural repairs do not reconstitute the natural toughening mechanisms of the enthesis and often fail. Hence, understanding the architectural mechanisms by which healthy and pathologic tendon entheses achieve strength and toughness would inform the development of both biological and engineered attachments.Integrating biomechanical analyses, failure characterizations, numerical simulations, and novel imaging, this thesis presents architectural mechanisms of enthesis toughening in a mouse model. Imaging uncovered fibrous architecture within the enthesis, which controlled trade-offs between strength and toughness. Ex vivo enthesis failure modes exhibited nanoscale differences in damage, milliscale differences in fiber load-sharing, and macroscale differences in energy absorption that depended on structure, composition, and the nature of loading. The elastic and failure responses of the tendon enthesis also varied with the direction of loading. This variation was due to the fibrous nature of the tendon enthesis, with a clear role for bony anatomy and fiber recruitment in enthesis toughening behavior. In vivo, , the loss of toughening mechanisms at the enthesis due to pathologic loading was evaluated by either increased (i.e., overuse) loading via downhill treadmill running or decreased (i.e., underuse) loading via botulinum toxin A induced paralysis. These loading environments led to changes in the mineralization and architecture at the tendon enthesis. These micro-architectural adaptations compromised the trade-offs between strength and toughness; overuse loading prompted active reinforcement and stiffening of the underlying trabeculae, leading a maintenance of strength and a compromise in overall toughness, whereas underloading prompted active resorption of the underlying trabecular architecture, leading to a compromise in both strength and toughness. The mouse models of the tendon enthesis failure revealed a correlation between tendon enthesis architecture and injury prevention (i.e., toughening) mechanisms. To test this concept in a clinical setting, an injury classification system was developed for patellar tendinopathy and partial patellar tendon tears. This classification system identified the stages of tear progression and prognosis by tracking changes to patellar tendon architecture. Results revealed a relationship between patellar tendon thickness and likelihood of improvement with nonoperative treatment. Taken together, this dissertation revealed how fibrous architecture can be tailored to toughen attachments between vastly different materials. This understanding can have prognostic value: tracking changes to enthesis architecture can be used as a tool for identifying candidates for various treatment options, as we showed for the patellar tendon clinical example. Furthermore, the toughening mechanisms identified here provide guidance for enhancing enthesis surgical repair and designing enthesis tissue engineered scaffolds, as well as motivating biomimetic approaches for attachment of architectured engineering material systems.

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Lower extremity muscle activity during balance can be affected by footwear characteristics. A dearth in literature remains regarding minimalist footwear in combination with a military-type workload on muscle activation during balance. The purpose of the study was to assess lower extremity muscular activity during balance tasks before and after a military workload, in two military footwear [standard tactical (STD), minimalist (MIN)]. Twentyour trained males (18-35 years) participated, following a repeated measures counter balanced footwear assignment. Participants performed maximal voluntary contractions (MVC) and balance assessments before and after a military treadmill workload. Muscle activity was collected on tibialis anterior, medial gastrocnemius, tibialis posterior, and peroneus-longus. A repeated measures 2x2 [2(Boot #1 x Boot #2) x 2(Pre-test x Post-test)] RM ANOVA with alpha set at 0.05. Significant differences occurred in mean, root-mean square, and peak muscle activities and in %MVC and co-contraction index, that were attributed to footwear design and physiological workload.

The proposed research investigates the unique structure of the rostrum of the paddlefish (Polyodon spathula) for use in bio-inspiration. The rostrum comprises three different materials: midline cartilage, a network cartilage structure, and matrix tissue. The structure-property relationships of these materials were studied with various mechanical testing and imaging techniques. The mechanical properties and stress-strain behavior were applied to a material model that characterizes each material. A three-dimensional model was constructed from computed tomography images, and a mesh was exported for use in finite element simulations. Different boundary conditions were applied to show how the rostrum responds under deformation giving a stress distribution arising from different loadings. Finally, a new robust design paradigm is introduced with bio-inspiration introducing constraints and is explained through using the paddlefish rostrum as an example of a cell tower or antenna.

Each year, 6.4 million automobile accidents account for approximately 40,000 deaths in the United States. With increasing requirements for automobile safety, computational models capable of simulating organ deformation/ injury during high impact scenarios would be extremely valuable for optimizing safety measures. Accurate experimental data is essential for the accuracy of the models; however, there has been a sparse investigation into high-strain biomechanics which is necessary to address organ/tissue response in high impact scenarios. Damage threshold criterion and damage evolution are other areas that have not been well studied. In vehicular accidents, damage to the liver is the most common cause of death after abdominal injury. High fidelity computational modeling with damage predictor is thus capable of describing liver tissue that is subjected to blunt impact. In this study, we address high strain biomechanics and damage evolution of liver tissue in an effort to generate valuable meaningful FE models.

Fractures occur commonly in veterinary medicine and are usually the result of vehicular trauma. Traditionally, comminuted mid-diaphyseal fractures are repaired with an interlocking nail, dynamic compression plate, or combination of a bone plate with an intramedullary pin. In recent years, the locking compression plate has gained popularity in human orthopedics due to its biomechanical characteristics and stability in osteoporotic or periprosthetic bone. In addition, the plate may be applied in a percutaneous manner, thereby allowing for biological osteosynthesis. This study evaluates the combination of a locking compression plate and an intramedullary pin in a Delrin rod gap model. Modalities tested include axial load to failure, torsion, and cyclic loading.