Context: Knee pain is experienced by many people. Because of this, authors have started researching the effects of pain on lower extremity mechanics and also on static and dynamic postural control. However, the effects of pain are difficult to study due to associated confounding variables. Objective: We asked: (1) Will experimentally-induced anterior knee pain alter perceived pain using the visual analogue scale? ; (2) will perceived pain affect postural control as measured by center-of-pressure during static and dynamic movement? Design: Crossover. Setting: Biomechanics laboratory. Participants: Fifteen healthy subjects. Intervention: Each subject participated in single leg quiet stance, landing, and walking trials under three conditions (pain, sham, control), at three different times for each condition (pre-injection, injection, and post-injection). Main Outcome Measures: The dependent variables were measured at pre-injection, injection, and post-injection. Pain was measured using the visual analogue scale across all three times during each condition. Center-of-pressure sway was measured during single leg quiet stance to calculate the average center-of-pressure velocity in the anterior-posterior and medial-lateral directions. The center-of-pressure time to stabilization was measured in anterior-posterior, medial-lateral, and vertical directions, and center-of-pressure trajectory excursion was measured in the medial-lateral direction during walking. Results: Perceived pain was significant (P < 0.05) but did not affect postural control as measured by center-of-pressure medial-lateral and anterior-posterior sway during single leg quiet stance, in time to stabilization during landing, and in medial-lateral excursion during walking. Conclusions: Injection of hypertonic saline resulted in statistically significant perceived pain but did not affect postural control as measured by center-of-pressure medial-lateral and anterior-posterior sway during single leg quiet stance, in time to stabilization during landing, and medial-lateral excursion during walking.

Yes / Normal ankle function provides a key contribution to everyday activities, particularly step/stair ascent and descent, where many falls occur. The rising to up-on-the-toes (UTT) 30 second test (UTT-30) is used in the clinical assessment of ankle muscle strength/function and endurance and is typically assessed by an observer counting the UTT movement completed. The aims of this study are: (i) to determine whether inertial measurement units (IMUs) provide valid assessment of the UTT-30 by comparing IMU-derived metrics with those from a force-platform (FP), and (ii) to de-scribe how IMUs can be used to provide valid assessment of the movement dynamics/stability when performing a single UTT movement that is held for 5 s (UTT-stand). Twenty adults (26.2 ± 7.7 years) performed a UTT-30 and a UTT-stand on a force-platform with IMUs attached to each foot and the lumbar spine. We evaluate the agreement/association between IMU measures and measures de-termined from the FP. For UTT-30, IMU analysis of peaks in plantarflexion velocity and in FP’s centre of pressure (CoP) velocity was used to identify each repeated UTT movement and provided an objective means to discount any UTT movements that were not completed ‘fully’. UTT movements that were deemed to have not been completed ‘fully’ were those that yielded peak plantarflexion and CoP velocity values during the period of rising to up-on-the-toes that were below 1 SD of each participant’s mean peak rising velocity across their repeated UTT. The number of UTT movements detected by the IMU approach (23.5) agreed with the number determined by the FP (23.6), and each approach determined the same number of ‘fully’ completed movements (IMU, 19.9; FP, 19.7). For UTT-stand, IMU-derived movement dynamics/postural stability were moderately-to-strongly correlated with measures derived from the FP. Our findings highlight that the use of IMUs can provide valid assessment of UTT test(s).

This dissertation aims to understand how attention can be used to improve sensory integration for postural control. Decades of research have been done using visual manipulations to study how healthy and clinical populations resolve multisensory (vision, vestibular, and somatosensory) mismatches to maintain postural stability. Postural control is a complex motor skill that requires accurate integration of multiple senses to maintain body alignment and orientation with respect to the environment. Age-related decline in visual, vestibular, and somatosensory acuity increases the risk for falls, and these sensory declines can be identified by assessing sensory reweighting. Sensory reweighting is the process in which the nervous redistributes the reliance, or "weight," on the sensory inputs to achieve postural stability. While the literature on sensory manipulation on postural control and fall risk has uncovered a wealth of knowledge on sensory reweighting for balance, it has neglected to identify how sensory reweighting can be improved. At the same time, motor learning literature has demonstrated the importance of focus attention during balance training to improve postural control. However, rudimentary analyses such as duration of balance and sway variability in this literature have limited deeper examination of the underlying neural mechanisms affected by focus of attention. This dissertation aims to bridge the gap between the two works of literature by implementing sensory manipulation techniques on posture using the latest technologies in virtual reality (VR) head-mount display (HMD) with motion capture and electroencephalography (EEG) recordings to study how different focuses of attention help resolve multisensory conflicts. In aim one, forty-two healthy adults participated in the study that used VR manipulation to induce a multisensory conflict. Participants were tasked to maintain upright stability on a rocker board while given different instructions on where to focus their attention. Instructions included focusing on keeping the rocker board leveled (external focus), focusing on keeping feet leveled to each other (internal focus), and focusing on staying as still as possible (control). This study revealed an immediate improvement in postural stability when instructed with external focus compared to control. This improvement was also associated with a significant decrease in visual weighting. Additionally, this aim revealed an immediate change in cortical activity within the frontal and occipital regions of the brain as identified by EEG recordings when participants are instructed to use external focus and internal focus. In aim two, twenty-eight healthy adults participated in the crossover study that demonstrated order effects when multiple instructions of attentional focus were given to the same participant for postural stability and visual reweighting. This study showed that the effects of external focus on postural stability and visual reweighting are greater when external focus is used before internal focus. However, the effects of external focus were nullified when used after using internal focus. Furthermore, the order of the instructions may have corresponded with a recency bias regarding how the participant perceived the effectiveness depending on when they received the attentional focus instruction. Guided by the findings from aims one and two, aim three recruited twenty-seven older adults to participate in a single-session balance training using repeated exposure to VR manipulation that challenged their balance on a rocker board. The older adults were randomized into one of the three groups: external focus, internal focus, and control group. The external focus group did not demonstrate an immediate reduction in visual weighting as found in aim 1. However, the external focus group did demonstrate better immediate postural stability when compared to the internal focus groups. Both external and internal focus groups revealed a significant improvement in visual weighting and postural stability across training blocks, suggesting a potential role of attentional focus on postural control adaption to repeated VR exposure. This dissertation was one of the first studies to investigate how the attentional focus impacts sensory reweighting and postural control in young and older adults using VR HMD. This project also established a VR experimental paradigm that can be used to study the focus of attention and the resolution of multisensory mismatch. With the increased use of VR for balance training and rehabilitation, this project is at the forefront of utilizing VR HMD technology to expose underlying sensory mechanisms for postural control. Results from this study can guide future rehabilitation and balance training interventions by identifying how attention should be directed during training. / Public Health

While it has been established that postural control is affected by executive function, research is lacking in identifying if specific executive function components are most responsible or if certain aspects of postural control are more affected than others (e.g., proprioception, vestibular, visual). The current study examined the role of inhibition, processing speed, and visuospatial ability in postural control under conditions affecting visual, proprioceptive, and vestibular sensory input. Cognitive assessments consisted of the Flanker Inhibitory Control and Attention Test, Digit Symbol Substitution Test, Clock Drawing Test, Trail Making Test – Part B, and simple reaction time. Standing Balance was used to assess postural sway. Analyses revealed that average balance was significantly associated with simple reaction time (r(88) = -0.31, p < .01) and the clock drawing test (r(88) = -0.25, p< .05). Further analyses revealed a significantly stronger relationship between pose #1 (eyes opened, firm) and average balance (r(88) = -0.845, p< 0.1) when compared to pose #2 (eyes closed, firm), and pose #3 (eyes opened, foam) and average balance r(88) = -0.8015, p< 0.1) when compared to pose #4 (eyes closed, foam). The significantly stronger relationship between these two measures demonstrates that visual input in both conditions #1 and #3 was associated with better postural control. The findings of this study demonstrate that reaction time and visuospatial abilities are associated with overall postural control in healthy older adults. Results suggest that reaction time should be more thoroughly researched to determine the extent of its influence on EF and physical function.

No description available.

No description available.

No description available.

<p>Maintaining upright posture is seemingly an automatic task in younger adults, but it may require additional resources in late adulthood due to decreases in sensorimotor and cognitive functions. The thesis used a dual-task paradigm to investigate age-related changes in relation to the secondary task and context-dependent factors attributes to postural control. The postural task involved visuomotor tracking. Successfully performing the visuomotor task necessitated proper sensory feedback, motor response, and sensorimotor integration. Moreover, we used silent counting as a cognitive task to investigate attentional demands on postural control and age-related difference in cognitive processing.</p> <p>We first investigated the relative contributions of visual feedback delay and cognitive task load on postural dynamics as well as age-related difference in this effect. Our results supported distinct timescale mechanisms for postural control. Moment-to-moment center of pressure fluctuations are dependent on cognitive performance during delayed visual feedback postural control. Also, we demonstrated the increased role of vision with age in postural control. Next, we investigated whether postural control improved when performing a cognitive task with an internal focus of attention. We found that devoting less attention internally by performing a cognitive dual-task enhanced postural control in young adults. Yet, the age-related declines diminish the attentional allocation ability. Lastly, we investigated how older and younger adults differ in employing sensorimotor strategies in a dual-task situation. Our results suggested that age-related changes in postural control may degrade the flexible coordination of the sensory feedback and motor execution. Furthermore, diminished cognitive and attentional capacities may alter postural performance in dual-task conditions.</p> <p>This thesis adds to the current understanding of the role of sensorimotor processing, attentional influence and age in the control of posture. Our data provide convergent evidence that deterioration of peripheral sensorimotor systems and reduced flexibility in central information processing are responsible for the age-related differences in postural control. <strong></strong></p> / Doctor of Philosophy (PhD)

Our human balance system is critical for preventing falls. The system consists of a complex set of sensorimotor controls that includes integration of sensory inputs including sight, touch and vestibular to produce motor output. Tactile afferents from the plantar surface contribute to the human balance and movement control system. Loss of sensory information could lead to impaired balance primarily because of impaired detection of changes in upright position, delayed postural reflexes, or failure to realize how far one's center of mass has been displaced thus increasing the probability of falls. Somatosensory and visual information must be integrated to interpret complex sensory environment. Sensory pathways that are simultaneously feeding inputs into the system exhibit non-linear behavior and it is unlikely that the role of a single pathway can be characterized in a static environment. As the sensory environment changes, the need to re-weight the relative dependence on each senses is essential for maintaining stability. Thus, attention also plays an important role in postural control. Attention can be defined as the individual's capacity for information processing. Performing two or more tasks at the same time may require more than an individual's attention capacity and thereby may weaken performance in the other task. Stochastic resonance phenomena has been shown to enhance sensory information processing and perception. This series of studies sought to analyze the effects of vibrotactile noise on human postural responses using a sub-threshold vibration (SV) and above-threshold vibration (AV). The vibrotactile noise was applied at the soles of both feet with six DC vibrator disks embedded in open-type footwear. Twenty one healthy adults wearing the vibrating footwear stood quietly on a compliant surface for 90 seconds inside a three-wall virtual environment. The visual conditions were either eyes closed, eyes open or a continuous visual flow field in a pitch-up direction at constant velocity of 30°/sec. A dual task paradigm was presented as a computation task, the Fibonacci sequence. The first 30 seconds of the 90 seconds trial had no vibration followed by 30 seconds of either sub-threshold or above-threshold vibration. Vibration was removed for the final 30 seconds. Root mean squares (RMS) and approximate entropy (ApEn) of center of mass (COM) and center of pressure (COP) excursions were calculated in the anterior-posterior (AP) and medio-lateral (ML) directions for each 30 second time period and normalized to each subject's initial position. Approximate entropy (ApEn) was used to detect movement variability in a time series to determine the unpredictability of the postural responses. COP and COM data were tested for statistical significance using repeated measures analysis of variance (ANOVA) with within-subject factors of vision (3 levels: eyes closed, eyes open and pitch-up), task (2 levels: single task and dual task), and vibration level (2 levels: sub-threshold vibration and above-threshold vibration) at a 95% confidence level (p&lt;0.05). Results supported the hypothesis that the application of SV and AV affected COP regularity and variability differently when subjected to different visual conditions (eyes closed, eyes open and pitch-up). COM randomness increased (higher ApEn) when attention was diverted from postural control which is in agreement with previous studies. The decrease in COM AP randomness (lower ApEn) with vibration suggested that the application of vibration increased the amount of attention invested in postural control or balance when performing an attention demanding cognitive task. The SV increased the COP-AP regularity (lower ApEn) during eyes-closed and eyes-open conditions while AV increased COP-AP variability (increased RMS) during the pitch-up visual condition. In conclusion, posture and balance were affected by the application of vibration noise. The vibration noise enhanced the amount of attention invested in postural control while performing an attention demanding cognitive task and sensory-motor learning was achieved by increasing COM sway structure regularity (lower ApEn) but not the sway magnitude. These results suggest that the interaction between vibration noise and an attention demanding task resulted in the temporal re-structuring of the postural control system without affecting the equilibrium region for the COM sway excursion. Vibration noise appears to facilitate postural control by altering postural response regularity (lower ApEn). For COM, only postural response regularity but not sway variability was affected by vibration noise in relation to vision regardless of the vibration level (SV or AV). For COP postural responses, the effect of SV and AV differs. Due to the perception of self-motion from the pitch-up visual condition, COP postural response most likely arise from cortical level. Since AV only affected COP responses during pitch-up visual condition and not SV, this study suggests that AV applied affected the cortical level of postural control. Effects of SV on postural responses between the eyes-open and eyes-closed vision conditions suggests that SV may affect a subcortical level of postural control. Understanding the effects and mechanism of vibratory noise may help in the design of effective interventions to prevent falls and rehabilitation. These results provide the scientific basis for development of a SR-based rehabilitation device for people with sensory information and processing deficiency as occurs with aging or stroke. The finding of after effects of vibratory noise can be used to determine dosage of vibrotactile stimulation in the design of vibrating footwear. / Bioengineering

Human postural control is a complex process, but that is critical to understand in order to reduce the prevalence of occupational falls. Localized muscle fatigue (LMF), altered sensory input, and inter-individual differences (e.g. age and gender) have been shown to influence postural control, and numerous methods have been developed in order to quantify such effects. Recently, methods based on statistical mechanics have become popular, and when applied to center of pressure (COP) data, appear to provide new information regarding the postural control system. This study addresses in particular the stabilogram diffusion and Hurst exponent methods. An existing dataset was employed, in which sway during quiet stance was measured under different visual and surface compliance conditions, among both genders and different age groups, as well as before and after induction of localized muscle fatigue at the ankle, knee, torso, and shoulder. The stabilogram diffusion method determines both short-term and long-term diffusion coefficients, which correspond to open- and closed-loop control of posture, respectively. To do so, a "critical point" (or critical time interval) needs to be determined to distinguish between the two diffusion regions. Several limitations are inherent in existing methods to determine this critical point. To address this, a new algorithm was developed, based on a wavelet transform of COP data. The new algorithm is able to detect local maxima over specified frequency bands within COP data; therefore it can identify postural control mechanisms correspondent to those frequency bands. Results showed that older adults had smaller critical time intervals, and indicating that sway control of older adults was essentially different from young adults. Diffusion coefficients show that among young adults, torso LMF significantly compromised sway stability. In contrast, older adults appeared more resistance to LMF. Similar to earlier work, vision was found to play a crucial role in maintaining sway stability, and that stability was worse under eyes-closed (EC) than eyes-opened (EO) conditions. It was also found that the short-term Hurst exponent was not successful at detecting the effects of LMF on sway stability, likely because of a small sample size. The new critical point identification algorithm was verified to have better sensitivity and reliability than the traditional approach. The new algorithm can be used in future work to aid in the assessment of postural control and the mechanisms underlying this control. / Master of Science