Background: Youth sports participation has numerous positive mental and physical health benefits. In young athletes, injuries result in millions of emergency room visits and millions of dollars spent every year offsetting many of the positive benefits gained by participation in sports. An increase in traumatic injury rates has been found to occur during the year of peak height growth (PHV), with a subsequent increase in risk of overuse injury in the years immediately following. This may be the result of changes to movement coordination around the time of adolescent growth spurts, a phenomenon called adolescent motor awkwardness (AMA). Though this phenomenon is well known to parents and coaches of young athletes, scientific research into its causes, symptoms, and timeline remains sparse. Minimal scientific evidence exists to quantify the impact of AMA on specific areas of movement coordination (ex. gait) and muscle performance, as well as its relation to growth spurts. Equally as poorly understood are the potential causes of motor disruptions during this period. As adolescents experience a wide variety of alterations to body size, proportions, and composition during puberty, there are many factors which could lead to disruptions to movement coordination. Additionally, there are substantial differences which arise in body proportions and composition between the sexes during puberty, yet any between-sex-group differences in the timeline, causes, or specific changes to movement coordination have not yet been explored. Purpose: The purpose of this dissertation was threefold: 1) To understand how gait stability changes with age and height during adolescence, and how these changes differ between the sexes (aim 1; chapter 2); 2) To understand the immediate effects of physical growth on gait smoothness during adolescence (aim 2; chapter 3); 3) To understand how peripheral fatigue affects gait smoothness during adolescence, and to understand how physical growth impacts muscular fatigability (aim 3; chapter 4). Participants: Sixty-Seven individuals (n=34 female, n=33 male) participated in the first study session to obtain Harmonic Ratio (HR), age, height, and fatigue data for aims 1 and 3. A subset of 46 participants (n=20 female, n=26 male) returned to participate in a second study session to obtain growth rate, HR, and fatigue data for aims 2 and 3. Methods: The testing protocol used in both sessions was identical. Trigno sensors were adhered to the participants skin at four locations determined by manual palpation: C7, L5, and the right and left rectus femoris. Once sensors were secured, participants completed a 15-minute treadmill warm-up in which their self-reported preferred walking speed was obtained. Following the warm-up, participants completed two 9-minute treadmill walking trials at three set speeds: 70% (slow walking speed; SWS), 100% (preferred walking speed; PWS), and 130% (Fast Walking Speed; FWS) of preferred walking speed. The walking trials were separated by a 10-minute leg-focused fatigue protocol. During each walking trial, accelerations of the upper (C7) and lower (L5) trunk were recorded in three planes of motion: Anterior-Posterior (AP), Medio-Lateral (ML), and Vertical (V). Harmonic Ratios were calculated from these acceleration signals. Prior to beginning each walking trial (i.e., pre-fatigue and post-fatigue) surface electromyography (sEMG) of the right and left rectus femoris was obtained during a 10-second sustained maximal contraction. Median frequency (Fmed) of this sEMG signal was used to calculate muscular fatigue level before and after the fatiguing protocol. Descriptive statistics were calculated for both the first session group and the second session subgroup. To accomplish aim 1, relationships between age, height, and HRs were assessed using multiple linear regression models with Holm-Bonferroni correction. Gait and anthropometric characteristics were compared by sex using independent sample t-tests. To accomplish aim 2, associations between growth rate and HRs were assessed through multiple linear regression adjusted for age and height. To accomplish aim 3, pre- and post- fatigue HRs were compared within subjects using paired t-tests. The association between muscular fatigability and growth rate was assessed using linear regression. Results: In aim 1, male and female groups differed significantly in height, age, and gait speeds. HRs improved with age for females at C7AP at all speeds pre-fatigue and at C7V in SWS and PWS post-fatigue. Males’ HRs increased with age during FWS pre-fatigue at C7V, C7AP , and L5ML . Females had a significant negative association between height and HR post-fatigue at C7V during both SWS and PWS, and at C7AP during FWS. In aim 2, male and female groups differed significantly in height, but not in age, growth rate (GR), walking speeds, or average HRs. When accounting for age and height, GR over a four-month period was a significant linear predictor of smoothness of trunk motion only for females during fast walking at L5AP. In aim 3, Females showed a significant effect of fatigue at SWS and at PWS on smoothness of motion of the lower trunk. Males showed a significant effect of fatigue during FWS at C7 in all planes of motion. Conclusions: These findings overall suggest substantial sex differences in changes to smoothness of trunk motion during gait in adolescents and in the effects of fatigue on trunk smoothness. In aim 1, several HRs improved with age in both sexes, but benefits were eliminated with fatigue in males. Aim 2 suggests that physical growth does not have immediate impacts on HR in adolescence. The results of aim 3 show substantial differences between the sexes in how muscular fatigue impacts gait stability. Males were most affected by fatigue at the upper trunk, particularly at FWS, while females were most affected by fatigue at the lower trunk at PWS. / Physical Therapy

Gait assessments can help identify individuals at an elevated risk of falling. Gait variability and local dynamic stability (LDS) are considered the most valid measures to assess gait stability and predict gait-related falls. Specifically, LDS of the trunk is most often used to assess gait stability given its important contribution to the centre of mass and the ability to discriminate between fallers and non-fallers using its kinematics. Reliable wearable sensors can be implemented in real-world gait assessments to actively screen for fall risk. Instrumented insoles are an example of unobtrusive wearable technology that can perform accurate gait assessments in real-world settings; however, they have not been validated for gait stability assessments, and cannot directly measure trunk LDS. The purpose of this thesis was to develop a framework to estimate gait stability using instrumented insoles. Fifteen participants were recruited to walk on a treadmill for seven minutes at their preferred walking speed while wearing instrumented insoles and a full-body inertial measurement unit suit. The reliability of foot LDS calculated from instrumented insole data was evaluated against the inertial measurement unit suit using intraclass correlation coefficients. Trunk LDS, measured via the IMU suit, was then predicted by applying linear regressions to the insole-derived metrics. A simple linear regression was used to establish the base amount of variance in trunk LDS that could be explained by foot LDS. Subsequently, a multiple linear regression model consisting of the standard deviation of stride time, standard deviation of double support time, mean single support time, mean yaw variability, and median absolute deviation of yaw variability was used to estimate trunk LDS. Results show that instrumented insoles can reliably measure foot LDS (ICC₃,₁ = 0.860). Moreover, the multiple linear regression explained 47.7% more variance than the simple linear regression (adjusted R² of 0.845 versus 0.368). This thesis demonstrates that instrumented insoles are an appropriate measurement tool for foot stability and that they can be used to predict trunk LDS with good accuracy during gait.

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Decreased gait symmetry has been correlated with an increased fall risk, abnormal joint loading and decreased functional outcomes. Therefore, symmetry is focused on in the rehabilitation of many patient populations. Currently, load based symmetry is collected using expensive and immobile devices that are not clinically accessible, but there is a clinical need for an objective measure of loading symmetry during daily tasks like walking. Therefore, the purpose of this dissertation was to 1) assess the validity and reliability of the loadsol® to capture ground reaction force data, 2) use the loadsol® to determine the differences in symmetry between adults with a TKA and their healthy peers and 3) explore the potential of a commercially available biofeedback system to acutely improve gait symmetry in adults. The results of this work indicate that the loadsol® is a valid and reliable method of collecting loading measures during walking in both young and older adults. TKA patients who are 12-24 months post-TKA have lower symmetry in the weight acceptance peak force, propulsive peak force and impulse when compared to their healthy peers. Finally, a case study with four asymmetric adults demonstrated that a 10-minute biofeedback intervention with the loadsol® resulted in an acute improvement in symmetry. Future work is needed to determine the potential of this intervention to improve symmetry in patient populations and to determine whether the acute response is retained following the completion of the intervention. / Doctor of Philosophy / Symmetry during walking is a valuable attribute as asymmetry has been correlated with an increased fall risk and decreased mobility. Currently, load based symmetry is collected using expensive and immobile devices that are not clinically accessible. As a result, there is a critical need for a system that can objectively measure load and loading symmetry during rehabilitation and everyday tasks in a variety of settings. A new device has been developed (loadsol®) that could potentially fill this need. Before it can be used to assess and treat patients, the loadsol® needed to be assessed for accuracy and reliability in both older and younger adults and at various speeds. Then we needed to determine if the loadsol® can be used to look at the levels of symmetry in patients who have had a knee replacement compared to their healthy peers. Finally, we tested a visual biofeedback intervention with the loadsol® to see if this intervention was able to improve symmetry. We found that the loadsol® is accurate and reliable. Patients with a knee replacement were less symmetric than their age matched peers. Finally, in a small study, the visual biofeedback intervention improved symmetry during walking in a group of people with less than 90% symmetry. Future work is needed to explore the potential of this biofeedback intervention to improve symmetry in various patient populations and to determine the extent to which patients are able to retain these improvements.

Yes / Descending kerbs during locomotion involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to the new level. Previous research has shown that vision is used in such adaptive gait tasks for feedforward planning, with vision from the lower visual field (lvf) used for online updating. The present study determined when lvf information is used to control/update locomotion when stepping from a kerb. Methodology/Principal Findings: 12 young adults stepped down a kerb during ongoing gait. Force sensitive resistors (attached to participants' feet) interfaced with an high-speed PDLC 'smart glass' sheet, allowed the lvf to be unpredictably occluded at either heel-contact of the penultimate or final step before the kerb-edge up to contact with the lower level. Analysis focussed on determining changes in foot placement distance before the kerb-edge, clearance over it, and in kinematic measures of the step down. Lvf occlusion from the instant of final step contact had no significant effect on any dependant variable (p>0.09). Occlusion of the lvf from the instant of penultimate step contact had a significant effect on foot clearance and on several kinematic measures, with findings consistent with participants becoming uncertain regarding relative horizontal location of the kerb-edge. Conclusion/Significance: These findings suggest concurrent feedback of the lower limb, kerb-edge, and/or floor area immediately in front/below the kerb is not used when stepping from a kerb during ongoing gait. Instead heel-clearance and pre-landing-kinematic parameters are determined/planned using lvf information acquired in the penultimate step during the approach to the kerb-edge, with information related to foot placement before the kerb-edge being the most salient.

Maintaining dynamic balance during walking is a major challenge in many patient populations including older adults and post-stroke hemiparetic subjects. To maintain dynamic balance, whole-body angular-momentum has to be regulated through proper foot placement and generation of the ground-reaction-forces. Thus, the overall goal of this research was to understand the mechanisms and adaptations used to maintain dynamic balance during walking by analyzing whole-body angular-momentum, foot placement and ground-reaction-forces in older adults and post-stroke subjects. The analysis of healthy older adults showed that they regulated their frontal-plane angular-momentum poorly compared to the younger adults. This was mainly related to the increased step width, which when combined with the dominant vertical ground-reaction-force, created a higher destabilizing external moment during single-leg stance. The results also suggested that exercise programs targeting appropriate foot placement and lower extremity muscle strengthening, particularly of the ankle plantarflexors and hip abductors, may enhance balance control in older adults. During post-stroke hemiparetic walking, ankle-foot-orthosis and locomotor therapy are used in an effort to improve the overall mobility. However, the analyses of healthy subjects walking with and without a solid ankle-foot-orthosis showed that they can restrict ankle plantarflexor output and limit the successful regulation of angular-momentum and generation of forward propulsion. Thus, the prescription of solid ankle-foot-orthosis should be carefully considered. The analysis of hemiparetic subjects walking pre- and post-therapy showed that locomotor training did not improve dynamic balance. However, for those subjects who achieved a clinically meaningful improvement in their self-selected walking speed, their change in speed was correlated with improved dynamic balance. Also, improved balance was associated with narrower mediolateral paretic foot placement, longer anterior nonparetic steps, higher braking ground-reaction-force peaks and impulses, higher (lower) propulsive ground-reaction-force peaks and impulses from the paretic (nonparetic) leg, and higher vertical ground-reaction-force impulses from both legs during the late stance. Further, simulation analyses of hemiparetic walking highlighted the importance of ankle plantarflexors, knee extensors and hip abductors in maintaining balance and revealed the existence of compensatory mechanisms due to the paretic leg muscle weakness. Collectively, these studies showed the importance of ankle plantarflexors and hip abductors in maintaining dynamic balance. / text

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