Physical activity is a powerful modifiable lifestyle factor that reduces the risk of cardiovascular disease (CVD) in adults through favorable changes in conventional risk factors including serum lipids, blood pressure and glycemia. Recent evidence suggests that the cardioprotective effects of physical activity may also be mediated through beneficial effects on vascular function, in particular arterial stiffness. While the beneficial effects of physical activity in CVD risk in adults are irrefutable, data in youth are limited, especially for arterial stiffness. Purpose: The purpose of this project is to explore the continuous association between physical activity and arterial stiffness in youth. Hypothesis: We hypothesized that physical activity is negatively associated with arterial stiffness, whereby highly active youth would display lesser degrees of arterial stiffness than their less active (sedentary) peers. Methods: 485 youth (12-13 yrs) were recruited from the 1995 Manitoba birth cohort involved in the GreatICE asthma and allergy study. Youth were stratified into tertiles (high, medium, low) of self-reported physical activity. Global cardiometabolic risk was determined from a composite score of conventional risk factors including, LDL, SBP, Insulin, Glucose and Triglycerides. Arterial stiffness was assessed non-invasively using conventional pulse wave analysis and velocity. Results: Of the 485 youth who participated in this wave of the study, measures of PWV and PWA were available on 357 and 335 youth respectively. Cardiometabolic risk decreased with increasing levels of vigorous physical activity. Neither measure of arterial stiffness was associated with physical activity. Conclusion: Increased vigorous physical activity is associated with reduced cardiometabolic risk in youth independent of arterial stiffness.

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Objective: The objective of this study was to investigate active shoulder stiffness and strength in recurrent shoulder instability. Additionally, this study sought to investigate the relationship between active stiffness, and quality of life, functional outcome, and perceived instability. The relationship between strength and quality of life, functional outcome and perceived instability was also investigated. Study Design: A cross sectional study of a cohort of subjects with unilateral recurrent anterior shoulder instability was undertaken. Background: Recurrent shoulder instability affects up to 94% of young athletes following a dislocation (Rowe & Skallerides, 1961; Rowe & Zairns, 1956). Active stiffness is possibly an important factor in protecting the joint from episodes of instability (Myers, 2001; Riemann & Lephart, 2002). While studies have examined passive stiffness at the shoulder, there is little that has examined active stiffness. Method: Maximal Voluntary Strength (MVS) of the muscles involved in horizontal flexion and their active stiffness at 30%, 50% and 70% MVS was tested in 16 male subjects, with unilateral traumatic anterior shoulder instability. Additionally, quality of life, function and perceived instability were measured using the Western Ontario Stability Index (WOSI), American Shoulder and Elbow Surgeons Questionnaire (ASES) and the Single Alpha Numeric Evaluation score (SANE) respectively. Results: There was a significant decrease in horizontal flexion strength in the recurrently unstable shoulder. Stiffness was also decreased significantly at 30% and 50% MVS. No statistical difference was demonstrated in stiffness values between limbs at 70% MVS. No significant correlation was shown between active stiffness controlling for strength, and quality of life, function or perceived instability. Additionally, no significant association was shown between strength and quality of life, function or perceived instability. Conclusion: The observed reduction in stiffness in the unstable shoulder warrants the inclusion of exercises in the rehabilitation program to enhance this parameter in an effort to protect the joint from perturbations that might lead to dislocation. Deficits in strength in horizontal flexion indicate that strengthening exercises may also be valuable to enhance performance in activities that incorporate horizontal flexion. The lack of an association between active stiffness and quality of life and overall function may indicate that stiffness investigated in one plane of motion does not adequately reflect tissue stiffness during functional activities. Further examination into stiffness in the unstable shoulder is necessary, utilising methodology that examines stiffness in all three dimensions simultaneously.

Objective: The objective of this study was to investigate active shoulder stiffness and strength in recurrent shoulder instability. Additionally, this study sought to investigate the relationship between active stiffness, and quality of life, functional outcome, and perceived instability. The relationship between strength and quality of life, functional outcome and perceived instability was also investigated. Study Design: A cross sectional study of a cohort of subjects with unilateral recurrent anterior shoulder instability was undertaken. Background: Recurrent shoulder instability affects up to 94% of young athletes following a dislocation (Rowe & Skallerides, 1961; Rowe & Zairns, 1956). Active stiffness is possibly an important factor in protecting the joint from episodes of instability (Myers, 2001; Riemann & Lephart, 2002). While studies have examined passive stiffness at the shoulder, there is little that has examined active stiffness. Method: Maximal Voluntary Strength (MVS) of the muscles involved in horizontal flexion and their active stiffness at 30%, 50% and 70% MVS was tested in 16 male subjects, with unilateral traumatic anterior shoulder instability. Additionally, quality of life, function and perceived instability were measured using the Western Ontario Stability Index (WOSI), American Shoulder and Elbow Surgeons Questionnaire (ASES) and the Single Alpha Numeric Evaluation score (SANE) respectively. Results: There was a significant decrease in horizontal flexion strength in the recurrently unstable shoulder. Stiffness was also decreased significantly at 30% and 50% MVS. No statistical difference was demonstrated in stiffness values between limbs at 70% MVS. No significant correlation was shown between active stiffness controlling for strength, and quality of life, function or perceived instability. Additionally, no significant association was shown between strength and quality of life, function or perceived instability. Conclusion: The observed reduction in stiffness in the unstable shoulder warrants the inclusion of exercises in the rehabilitation program to enhance this parameter in an effort to protect the joint from perturbations that might lead to dislocation. Deficits in strength in horizontal flexion indicate that strengthening exercises may also be valuable to enhance performance in activities that incorporate horizontal flexion. The lack of an association between active stiffness and quality of life and overall function may indicate that stiffness investigated in one plane of motion does not adequately reflect tissue stiffness during functional activities. Further examination into stiffness in the unstable shoulder is necessary, utilising methodology that examines stiffness in all three dimensions simultaneously.

This study investigated effects of fabric and foam elastic properties on the behavior of load-deformation properties of upholstered furniture cushions. A 3×3×3×2 experiment design experiment was designed to study effects of fabric cover type (less stiff, stiff, and stiffer), foam thicknesses (5 inch, 5.5 inch, and 6 inch), human weight level (105 lb., 140 lb., and 190 lb.), and seat foundation type (panel and spring) on cushion stiffness. Experimental results indicated that the increase of cushion stiffness was significant as fabric cover stiffness, foam thickness, and human weight level increased. There was no significant difference between two types of seat foundation on cushion stiffness.

Southern pine (SP) lumber is the primary softwood material in the United States. The main procedure during lumber grading process is the identification of the strength reducing characteristics that impacts the modulus of rupture (MOR). Non-destructive evaluation technology can be used to identify higher-stiffness material. This study investigated the use of vibration methods to evaluate the mechanical properties of southern pine lumber. Significant correlations between the properties determined by non-destructive techniques and the static MOE were found. No strong correlations were found for MOR because it is related to the ultimate strength of material, often associated with the existence of localized defects, such as a knot. Non-destructive measurements, visual characteristics, and lumber density were used as independent variables. Linear models were constructed to indirectly estimate the MOE and MOR. The variables selected was dynamic modulus of elasticity (dMOE) to predict MOE. Adding density and knot diameter ratio to the model it was possible to develop a prediction model for MOR. It was possible to improve predictability of strength (MOR) with a combination of non-destructive and knot evaluation.

Human locomotion is a topic that has been studied for many years in biomechanics. To perform athletic tasks or everyday tasks, balance and symmetry is needed. Symmetry is the perfect balance and correspondence of the body or parts of the body. This concept has often been used to evaluate the normality of movements. Limb symmetry, specifically, is the equal actions of the lower limbs during movement. This is needed to perform tasks safely and efficiently without injury. Gait and movement symmetry has been used to predict lower limb injury risk for many populations and improve performance for athletes. It has also been used in assessment for rehabilitation processes and return to sport processes following injury or surgery. For many years, healthy gait was considered to be symmetrical for simplification purposes. However, many studies have contradicted that conclusion showing that even for has asymmetrical patterns. Deficits in symmetry can reduce quality of life for some individuals and can have detrimental health effects. Many measures have been used to assess symmetry in various tasks that have important implications on gait patterns. Another component of gait and movement that affects performance and injury risk is limb stiffness. Limb stiffness is the body's resistance to deformation when moments and forces are applied to it. The body has been shown to be modeled as a spring mass system that can restore and reuse energy. This is associated with the stretch shortening cycle during cyclic movements, such as running and walking. Limb stiffness is also associated with musculoskeletal loading that impacts performance and injury. Therefore, optimizing limb stiffness is important to improve utilization of elastic energy for athletic performance and reduce injuries associated with high and low limb stiffness values. Imbalances in limb stiffness have been shown to increase injury risk during walking and other tasks. Studying these imbalances using symmetry indices could give insight into the injury risk associated with this metric. In addition, limb stiffness in humans has been shown to change with the type of contact surface. This is associated with compensation methods used by humans when contacting different surfaces. Studying the relationship between limb stiffness symmetry and different surfaces during walking is important to observe how humans adjust and how it impacts injury risk. The purpose of this research was to assess the impact that surface stiffness has on limb stiffness symmetry during walking in healthy adults. To assess limb stiffness differences when transitioning to different surface stiffnesses anteriorly and posteriorly, the Normalized Symmetry Index (NSI) was determined for the two transition conditions and the control. The results showed that limb stiffness NSI was significant between the conditions (p=0.012). More specifically, a difference was seen between the stiff to compliant transition and the control (p=0.020) and the compliant to stiff transition and the control (p=0.032). These results show that humans do compensate when transitioning onto different surfaces. This is essential for understanding how humans adjust during real world walking and what patterns are used to maintain stability. To assess limb stiffness symmetry, when surface stiffness is different between limbs, the limb stiffness NSI was compared between two conditions. This included the side-to-side stiffness difference condition and the control condition. The results revealed that surface stiffness was not significant between conditions (p=0.244). Based on these results, limb stiffness symmetry is not significantly impacted when the surface stiffness is different between limbs. This contradicts prior studies that observed changes limb stiffness and symmetry depending on the surface stiffness. This may be due to overcompensation or the ability of the healthy adult population to quickly adjust to the surface stiffness changes before the measurements were taken. Simulating uneven surfaces is important to understand how humans compensate to maintain stability on surfaces in real world walking and for imbalances due to disorders. Further research is needed to study the changes in limb stiffness symmetry on different surfaces during walking to improve injury prevention methods. / Master of Science / Humans perform many daily tasks and athletic tasks that have been observed in human movement analysis. To perform these tasks safely and efficiently, many factors must be considered. One of the important factors in performing tasks is symmetry. Symmetry is the perfect balance between parts of the body, such as the lower limbs during walking or gait. Gait in healthy adults was considered to be symmetrical for simplification purposes. However, studies have revealed that gait asymmetry is present in the healthy adult population during walking and other movements. Gait symmetry has been used to assess normality of gait patterns in healthy individuals and in clinical populations. Asymmetrical gait patterns can lead to injury and have detrimental effects on health. Therefore, limb symmetry has been an important metric to assess lower limb injury risk and improving injury prevention methods to correct asymmetrical patterns in healthy adults and other populations. Another aspect of human movement that impacts injury is limb stiffness. Limb stiffness is the body's resistance to deformation under applied forces. High limb stiffness values have been associated with bony injuries due to increased loading. However, low stiffness values have been associated with soft tissue injuries. Therefore, regulating limb stiffness is important to reduce injuries in the long term. The type of contact surface during walking and other tasks has been shown to change limb stiffness values. Humans often encounter changes to surfaces when walking. For example, hikers who encounter uneven terrain or everyday walking on uneven pavement. Uneven surfaces have been shown to require more energy and work to move forwards during walking. Therefore, simulating uneven surfaces in the real world is important to understand how humans compensate on different surfaces. This could be important for understanding how limb stiffness imbalances on different surfaces affect injury. To quantify these imbalances, the metric of limb stiffness symmetry will be used. Limb stiffness imbalances due to surface stiffness are essential to assess how humans adapt to instability during real world walking. Therefore, this study aims to determine how humans adjust when transitioning to different surface stiffnesses and when surface stiffness is different between limbs. To determine how humans adjust when transitioning to different surfaces of different stiffnesses, the limb stiffness symmetry was calculated using the Normalized Symmetry Index (NSI). This was calculated for three different surface stiffness conditions, consisting of a stiff to compliant transition, a compliant to stiff transition, and the control condition. The results showed that there was a significant difference between the NSI values of the three conditions. However, there was no difference between the two transition conditions. This indicated that there was no difference between the transition order. Based on the results, limb stiffness symmetry does change when transitioning to different surface stiffness conditions. This agrees with previous literature that suggests that surface stiffness has an impact on limb stiffness. This information is beneficial to understand the patterns humans use to compensate to maintain stability. To determine how limb stiffness symmetry is impacted when surface stiffness is different between limbs, the limb stiffness NSI was calculated for two surface conditions. This included the side-to-side condition and the control condition. The results showed that there was no statistical difference between the limb stiffness NSI values of the two conditions. This shows that limb stiffness symmetry doesn't change when the surface stiffness is different between limbs, which disagrees with previous literature. Overall, this information is important to understand how humans compensate when transitioning on different surfaces or walking on uneven surfaces. This is important to understand how stability is maintained despite imbalances for improvement of injury prevention methods.

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