Browsing by Author "Stefanyshyn, Darren J."

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    Are subject-specific models necessary to predict patellar tendon fatigue life? A finite element modelling study
    (Taylor & Francis, 2021-09-11) Firminger, Colin R.; Haider, Ifaz T.; Bruce, Olivia L.; Wannop, John W.; Stefanyshyn, Darren J.; Edwards, W Brent
    Patellar tendinopathy is an overuse injury that occurs from repetitive loading of the patellar tendon in a scenario resembling that of mechanical fatigue. As such, fatigue-life estimates provide a quantifiable approach to assess tendinopathy risk and may be tabulated using nominal strain (NS) or finite element (FE) models with varied subject-specificity. We compared patellar tendon fatigue-life estimates from NS and FE models of twenty-nine athletes performing countermovement jumps with subject-specific versus generic geometry and material properties. Subject-specific patellar tendon material properties and geometry were obtained using a data collection protocol of dynamometry, ultrasound, and magnetic resonance imaging. Three FE models were created for each subject, with: subject-specific (hyperelastic) material properties and geometry, subject-specific material properties and generic geometry, and generic material properties and subject-specific geometry. Four NS models were created for each subject, with: subject-specific (linear elastic) material properties and moment arm, generic material properties and subject-specific moment arm, subject-specific material properties and generic moment arm, and generic material properties and moment arm. NS- and FE-modelled fatigue-life estimates with generic material properties were poorly correlated with their subject-specific counterparts (r2≤0.073), while all NS models overestimated fatigue life compared to the subject-specific FE model (r2≤0.223). Furthermore, FE models with generic tendon geometry were unable to accurately represent the heterogeneous strain distributions found in the subject-specific FE models or those with generic material properties. These findings illustrate the importance of incorporating subject-specific material properties and FE-modelled strain distributions into fatigue-life estimations.
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    Effect of Relative Marker Movement on the Calculation of the Foot Torsion Axis Using a Combined Cardan Angle and Helical Axis Approach
    (2012-05-14) Graf, Eveline S.; Wright, Ian C.; Stefanyshyn, Darren J.
    The two main movements occurring between the forefoot and rearfoot segment of a human foot are flexion at the metatarsophalangeal joints and torsion in the midfoot. The location of the torsion axis within the foot is currently unknown. The purpose of this study was to develop a method based on Cardan angles and the finite helical axis approach to calculate the torsion axis without the effect of flexion. As the finite helical axis method is susceptible to error due to noise with small helical rotations, a minimal amount of rotation was defined in order to accurately determine the torsion axis location. Using simulation, the location of the axis based on data containing noise was compared to the axis location of data without noise with a one-sample t-test and Fisher's combined probability score. When using only data with helical rotation of seven degrees or more, the location of the torsion axis based on the data with noise was within 0.2 mm of the reference location. Therefore, the proposed method allowed an accurate calculation of the foot torsion axis location.
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    Pushing for Gold On Force Application in Bobsleigh and Cycling
    (2023-07) Onasch, Franziska Maren; Herzog, Walter; Stefanyshyn, Darren J.; Edwards, William Brent; Jordan, Matthew James; Thompson, Robert Ian; McErlain-Naylor, Stuart
    In many sports, performance is governed by an athlete’s ability to produce force paired with a given movement velocity and, thereby, generate power. The 4-man bobsled push start is an event that requires team effort, and its goal is to maximize sled velocity in the shortest possible time. Fractions of a second can decide the outcome of a race, and off-ice tests designed to assess strength and speed are used to identify the athletes that will perform best. However, the actual contributions of the team members during the push start on ice have not been measured. The objective of the first project in this thesis was to better understand the push contributions of the four athletes in a 4-man team by analyzing the components of the push start. A 4-man bobsled was instrumented to record both sled velocity and 2D push forces as applied to the sled by the athletes during the push start. Push force was observed to decrease quickly once the sled picked up speed, and the execution of the loading was discovered to be a crucial component of the push start that can affect overall performance. In project 2, a prowler sled was instrumented to measure sled velocity and push force in an off-ice push force-velocity test to be used as a training and assessment tool in bobsleigh athletes. Greater force results in greater power output – if the force is applied the right way. In project 3 we studied force effectiveness in cycling, where only pedal force directed perpendicular to the crank is effective i.e., results in propulsion, while forces parallel to the crank have been considered wasted. In our study, we aimed to determine the impact of constrained pedal force direction on force output. Constraining static pedal force to be perpendicular to the crank only was counterproductive and resulted in significantly reduced force magnitude. In summary, this thesis work contributes to the applied study of power output in sports, with instrumented devices aiding the study of force and power output in athletes, novel data, and the proposal for a new training method.
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    Towards the Real-time Monitoring of Achilles Tendon Strain
    (2018-07-18) Bruce, Olivia Leigh; Edwards, William Brent; Stefanyshyn, Darren J.; Wiley, James Preston; Bertram, John Edward Arthur
    Achilles tendinopathy is an overuse injury affecting jumping athletes, associated with the accumulation of microdamage due to repetitive tendon strain. Surface and footwear modifications may influence tendon strain magnitude. The purpose of this thesis was to examine the influence of surface and footwear modifications on Achilles tendon strain during vertical countermovement jump landings and to quantify the relationship between tendon strain and accelerometer measures. The parameters were quantified for three shoes (Boost™, 55C, and 70C) and three surfaces (ACS, BC3, and MVP) using motion capture, accelerometry, and dynamometry-ultrasound measures. Surface and footwear influenced Achilles tendon strain; strain was lower in the Boost™ shoe and MVP surface conditions. Differences in strain could be due to stiffness or other material properties of the shoes and surfaces. Only weak correlations were found between tendon strain and accelerometer measures, suggesting that data obtained from accelerometers may not reflect internal loading.