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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115617 |
| Date | 30 June 2023 |
| Creators | Wilson, Jorjie Mariah |
| Contributors | Department of Biomedical Engineering and Mechanics, Queen, Robin M., McCullough, Matthew Bonner Aurelius, Socha, John |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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