Low back pain (LBP) affects many individuals worldwide. The established association between LBP and spine motor control has led to the development of many control assessment techniques. To understand the association between motor control and LBP, it is essential to understand the relationship between separate assessment techniques. Systems identification (SI) and local dynamic stability (LDS) are two methods commonly used to quantify spine control. SI provides a detailed description of control but uses linear assumptions, whereas LDS provides a “black box” non-linear assessment and can be quantified during dynamic movements. Although both SI and LDS techniques aim to measure the control of the spine, each employs different experimental setups and data processing strategies. Therefore, the purpose of this thesis was to compare the motor behaviour outcomes of SI and LDS quantification techniques. To do this, 15 participants completed two tasks (SI and LDS) in a random order. For the SI task, participants were seated and ventrally perturbed at the level of the 10th thoracic vertebrae (T10). They completed this task under instructions to resist the perturbations (resist condition) or relax and remain upright (relax condition). Admittance was represented using frequency response functions, and a validated neuromuscular control model quantified lumbar stiffness, damping and muscle spindle feedback gains. The LDS task involved participants completing three repetitive movement blocks consisting of flexion/extension, axial rotation, and complex movements. In each block, the maximum finite-time Lyapunov exponent (λmax) was estimated. A stepwise linear regression determined that λmax during the rotation task was best predicted by SI outcomes in the relax condition (adjusted R square = 0.65). Many conditions demonstrated no significant relationship between λmax and SI outcomes. These findings outline the importance of a consistent framework for the assessment of spine control. This could improve clinical assessment efficiency as well as the understanding of the association between LBP and motor control.

Inertial measurement units (IMUs) are being recognized as a portable and cost-effective alternative to motion analysis systems and have the potential to be introduced into clinical settings for the assessment of functional movement quality of the spine in patients with low back pain. However, uncertainties regarding sensor accuracy and reliability are limiting the widespread use and acceptance of IMU-based assessments into routine clinical practice. The objective of this work was to assess the performance of inexpensive wearable IMUs (Mbientlab MetaMotionR IMUs; Mbientlab Inc., San Francisco, USA; product specifications available in Appendix C) relative to conventional optical motion capture equipment (Vicon Motion Systems Ltd., Oxford, UK) in: 1) a controlled environment, and 2) an uncontrolled environment. The first study evaluated the performance of 2 IMUs in a controlled environment during simulated repetitive spine motion carried out by means of a motorized gimbal. Root mean square error (RMSE) and mean absolute measurement differences between cycle-to-cycle minimum, maximum, and range of motion values, as well as correlational analyses within IMUs and between IMUs and Vicon, in all movement directions (i.e., simulated flexion-extension (FE), lateral bending (LB), and axial twisting (AT)), were compared. Measurement error was low in all axes during all tests (i.e., ≤ 1.54°); however, low-to-moderate correlational results were found in one non-primary axis, and this axis changed depending on the direction of the movement (i.e., LB during FE-motion (0.244 ≤ R ≤ 0.515), AT during LB-motion (0.594 ≤ R ≤ 0.795), and FE during AT-motion (0.002 ≤ R ≤ 0.255)). The second study was designed to assess the performance of the IMUs in an uncontrolled environment during repetitive spine FE in human participants. Absolute angles and local dynamic stability were compared for individual IMUs (which were placed over T10-T12 spinous processes, and the pelvis) as well as for relative motion between IMUs. Maximum finite-time Lyapunov exponents (λmax) were used to quantify local dynamic stability and were calculated using both FE and the sum of squares (SS) from measured spine kinematics. It was found that the IMUs have acceptable performance in all axes when tracking motion (RMSE ≤ 2.43°); however, low-to-moderate correlational results were found in one non-primary axis (0.987 ≤ RFE ≤ 0.998; 0.746 ≤ RLB ≤ 0.978; 0.343 ≤ RAT ≤ 0.679). In addition, correlations between λmax estimates were high; therefore, local dynamic stability can be accurately estimated using both FE and SS data (0.807 ≤ 〖ICC〗_2,1^FE ≤ 0.919; 0.738 ≤ 〖ICC〗_2,1^SS ≤ 0.868). Correlation between λmax estimates was higher when using FE data for individual sensors/rigid-body marker clusters; however, correlation was higher when using SS data for relative motion. In general, the results of these studies show that the MetaMotionR IMUs have acceptable performance in all axes when considering absolute angle orientation and motion tracking, and measurement of local dynamic stability; however, there is low-to-moderate correlation in one non-primary axis, and that axis changes depending on the direction of motion. Future research will investigate how to optimize performance of the third axis for motion tracking; it will also focus on understanding the significance of the third axis performance when calculating specific outcome measures related to spine movement quality.

Background: The most common injuries in new or novice runners include medial tibial stress syndrome and patellofemoral pain syndrome; both overuse injuries. It is known that novice runners use a rearfoot strike pattern 98% of the time while running in traditional running footwear. Furthermore, footwear that is constructed with less cushioning (minimal shoes) and is said to promote forefoot running has increased in popularity. It is still unknown if novice runners convert their strike pattern in minimal shoes or continue to use a rearfoot strike pattern. Consequences of continuing to use a rearfoot strike pattern with less cushioning underfoot include higher vertical loading rates which are directly related to the types of injuries experienced. Aside from the strike pattern in a given shoe, movement stability is an important feature in healthy locomotion. There is a trade-off between being overly stable and being too unstable while running. It is known that the level of experience in running is related to the amount of stride length variability. It is still unknown if altering midsole stiffness has an effect on local dynamic stability while running. Purpose: The primary purpose of this thesis was to compare landing kinematics and kinetics between trained and novice runners in minimal and traditional shoes. The secondary purpose of this thesis was to examine the effect of running experience and midsole construction on local dynamic stability at the ankle, knee and hip. Methods: Twelve trained runners and twelve novice runners were recruited for participation. Four prototypical shoe conditions were tested with midsole geometry and material stiffness being manipulated. This yielded traditional/soft, traditional/hard, minimal/soft and minimal/hard shoe conditions. Participants ran down a 30m indoor runway which was instrumented with force platforms to measure vertical loading rates and motion capture cameras to capture landing kinematics. Participants also ran on a treadmill in each shoe condition to allow for local dynamic stability to be estimated at the ankle, knee and hip in the sagittal plane. Results: Novice runners landed with increased knee extension compared to trained runners. Increasing midsole thickness of the shoes caused an increase in dorsi-flexion of the ankle at heel strike. Manipulating material stiffness did not influence landing kinematics but did influence kinetics. Furthermore, decreasing material stiffness lowered vertical loading rates. Trained runners exhibited increased local dynamic stability (more stable) at the ankle, knee and hip compared to novice runners. Local dynamic stability was not affected by midsole stiffness. Conclusions: Novice runners did not alter their strike pattern in minimally constructed shoes. For this reason, cushioning properties of the shoe dictated vertical loading rates upon the body. Shoe conditions did not alter landing kinematics above the ankle, which is where the between group differences existed as novice runners landed with a more extended knee. Running experience appears to play a role in knee orientation at landing and is unaffected by shoe condition. Local dynamic stability was affected by running experience and does not appear to be related to the shoe condition being worn. Even when kinematics changed across shoe conditions, the stability of the movement did not.

abstract: Fall accident is a significant problem associated with our society both in terms of economic losses and human suffering [1]. In 2016, more than 800,000 people were hospitalized and over 33,000 deaths resulted from falling. Health costs associated with falling in 2016 yielded at 33% of total medical expenses in the US- mounting to approximately $31 billion per year. As such, it is imperative to find intervention strategies to mitigate deaths and injuries associated with fall accidents. In order for this goal to be realized, it is necessary to understand the mechanisms associated with fall accidents and more specifically, the movement profiles that may represent the cogent behavior of the locomotor system that may be amendable to rehabilitation and intervention strategies. In this light, this Thesis is focused on better understanding the factors influencing dynamic stability measure (as measured by Lyapunov exponents) during over-ground ambulation utilizing wireless Inertial Measurement Unit (IMU). Four pilot studies were conducted: the First study was carried out to verify if IMU system was sophisticated enough to determine different load-carrying conditions. Second, to test the effects of walking inclinations, three incline levels on gait dynamic stability were examined. Third, tested whether different sections from the total gait cycle can be stitched together to assess LDS using the laboratory collected data. Finally, the fourth study examines the effect of “stitching” the data on dynamic stability measure from a longitudinally assessed (3-day continuous data collection) data to assess the effects of free-range data on assessment of dynamic stability. Results indicated that load carrying significantly influenced dynamic stability measure but not for the floor inclination levels – indicating that future use of such measure should further implicate normalization of dynamic stability measures associated with different activities and terrain conditions. Additionally, stitching method was successful in obtaining dynamic stability measure utilizing free-living IMU data. / Dissertation/Thesis / Masters Thesis Biomedical Engineering 2017

The primary goal of human locomotion is to translate the body from point A to point B, but humans must have the variability and stability to adapt and recover from constraints they may encounter. The overarching aim of this dissertation was to investigate how constraints arising from external factors (i.e., military load carriage and speed) and internal factors (i.e., hip pain) affect kinematic variability and local dynamic stability of gait. In study 1, I focus on using traditional biomechanical measures to investigate if females and males use different gait mechanics when carrying military-relevant loads, as females and males are known to use different mechanics when walking with no load. In this study, I found that females and males do use different gait mechanics when walking with military-relevant loads. Females make kinematic adaptations at the ankle and knee while males make kinematic adaptations at the hip. The differences in adaptations between females and males may be related to females’ greater risk of injury when carrying load. In study 2, I used the same cohort to investigate how military-relevant loads affect the kinematic variability and local dynamic stability of gait. I found that kinematic variability and local dynamic stability were similarly affected by load. Participants had greater kinematic variability and decreased local dynamic stability when carrying loads, which may indicate an increased risk of falling while carrying load. I also found that local dynamic stability increased with increased walking speed at all loads in the mediolateral and anteroposterior directions. However, decreased stability was detected in the vertical direction, which may require increased energy expenditure. The results of this study indicate that walking faster with increased loads may be more stable, but less energy efficient. In study 3, I investigated the how kinematic variability and local dynamic stability were affected in individuals with hip pain and a history of developmental dysplasia. I found that kinematic variability and local dynamic stability were not similarly affected in these individuals. I found that kinematic variability was greater in individuals with hip pain compared to healthy controls, but there was no difference in local dynamic stability between groups. The overall finding of this dissertation is that the relationship between kinematic variability and local dynamic stability may be dependent on the factor investigated. / 2020-07-06T00:00:00Z

Millions of people sustain a mild traumatic brain injury (concussion) each year. While most clinical signs and symptoms resolve within 7-10 days for the majority of typical concussions, some gait and balance tasks have shown abnormalities lasting beyond the resolution of clinical symptoms. These abnormalities can persist after athletes have been medically cleared for competition, yet the implications of such changes are unclear. Most prior research has examined straight gait and standard measures of balance, yet there is a lack of knowledge regarding potential persistent effects on non-straight maneuvers or on indicators of motor control variability or complexity. To expand the knowledge of post-concussion locomotor and postural changes, this investigation examined the recovery of recently concussed athletes longitudinally, over the course of one year, in three domains: 1) path selection and body kinematics during turning gait, 2) non-linear local dynamic stability during straight gait, and 3) postural control complexity during quiet standing. Compared to matched health controls, concussed athletes exhibited significant and persistent differences in turning kinematics, local dynamic stability, and postural complexity over the initial six weeks following injury. These motor differences may increase the risk of injury to concussed athletes who are cleared to return to play. Given the persistent nature of these effects, future clinical tests may benefit from incorporating gait assessments before returning athletes to competition. Future research should prospectively and longitudinally monitor locomotor and postural control in conjunction with structural and functional changes within the brain to better understand the pathophysiology of concussions and potential rehabilitation strategies. / Ph. D.