The Sit-to-Stand (STS) transition is a voluntary daily activity that consists of rising from a sitting position to a standing position, an activity that is typically performed by a person several times a day. To undertake the activity successfully requires the coordination of the body limbs in order to transfer the body weight between the sitting and standing positions, maintaining the balance, in order to avoid a fall. A biomechanical analysis of the STS transition provides useful information about the motor ability and control strategy of a person and as such, it is commonly employed to assess functional performance, and as an indicator of lower limb strength in the elderly and in people with disabling diseases. The aim of the work described in this thesis was to investigate and analyse the STS transition in two groups of healthy subjects, a cohort (n=10) of younger adult participants (age range 28±2 years) and a cohort (n=10) of older adult participants (age range 56±8 years), in order to identify the differences in the performances within and between the two groups when the STS transition was undertaken at different speeds. The two groups of participants performed STS transition trials at three, different, self-selected speeds (normal, slow and fast) during which data was recorded from a caption systems, consisting of a set of six infrared-cameras and two force plates. The in-vivo data obtained was applied to a link segment biomechanical model enabling the kinematic contribution of the major body segments to the STS activity to be determined for each participant. A principal component analysis (PCA) was undertaken to identify any aggregate and segmental differences in the STS transition performance between speeds. In addition, a kinetic analysis was performed to determine the torque and power contributions of the lower limb joints during the STS transition. The results from the analysis showed that younger and older participants performed the STS transition with a similar pattern, but they used different strategies to ascend according to the speed at which the activity was being performed. The younger participants used the same strategy at slow speed than the older participants used at slow and normal speeds. Likewise, the younger participants used the same strategy at normal and fast speeds as the older participants used at fast speed. From the segmental analysis it was found that the upper-body and pelvis segments presented the larger variability than the other segments. From the joint analysis, the knee and hip joints were identified as the joints that provide the greatest contribution to the STS transition as they generated most of the power and torque required for the activity. The results obtained and the methodology developed could help clinicians with the diagnosis, planning and selection of treatment for patients with a lack of mobility. This type of analysis may also find application in fields such as robotics, ergonomics and sports training.

The sit-to-stand (STS) is a multi-articular movement of daily living that requires significantly higher knee extensor (KE) efforts compared to ankle and hip musculature, which approach near maximal levels in older adults populations. As well, fatigue may develop more readily with repetitive actions. Consequently, it is understandable how KE strength reserves have been previously correlated with both functional independence and STS strategy characteristics in older persons, and why STS capacity is a significant predictor of disability. However, it is still unclear why compensatory movement strategies manifest when rising from a seated position, and how this may be influenced by aging. The purpose of this thesis compilation was to evaluate alterations in muscular contributions at the ankle, knee, and hip, in relation to STS performance strategies in young and older adults either: a) with repetitive multi-joint STS exercise or b) before and after isolated fatigue of KE musculature. Results showed that aging caused a redistribution of joint torques when ascending from a seated position, and was associated with significantly higher quadriceps muscular efforts in older persons in comparison to their younger counterparts. In contrast, young and older adults exhibited similar compensatory movement and loading strategies during repetitive STS exercise, which appeared to be limited by the ability to sustain KE force output. In turn, lower KE strength reserves of older persons were responsible for their disproportionately higher quadriceps efforts and reduced STS capacities. Young and older persons also appeared to employ motor strategies to compensate for reduced KE force output via increased contribution of the biarticular rectus femoris within the quadriceps KE synergy, as well as through increases in the initially less active ankle plantar flexor and hip extensor musculature. Older adults may benefit from strengthening of thigh extensor musculature to maintain or improve their strength reserves to promote independent living.

Background: Sit-to-stand is a challenging task as it requires the transition from a large 3-point base of support to a small 2-point base of support while simultaneously controlling anteroposterior and vertical body acceleration. Age-related morphological changes in both the visual and vestibular system could impair the ability to extract and interpret sensory information necessary for motor control in older adults, which can increase instability and the risk of falls. The purpose of this study is to understand the effects of aging on visual-vestibular interaction for maintaining stability during sit-to-stand. Methods: Fifteen younger (age=22.5±1.1) and fifteen older (age=73.9±5.3) healthy adults were asked to stand from a sitting position as quickly as possible. Vestibular input was manipulated using percutaneous bipolar galvanic vestibular stimulation where threshold intensity was individually calculated for each participant during quiet stance with eyes closed. Galvanic vestibular stimulation was applied at both threshold (1xGVS) and 2-times the participant’s threshold intensity (2xGVS). Visual conditions included eyes opened, wearing custom-made vision blurring goggles, or eyes closed. Outcome measures included a global measure of performance (transition phase duration), mediolateral stability (peak-to-peak trunk roll angle, mediolateral center of mass displacement, mediolateral center of pressure displacement) and anteroposterior stability (peak braking force, peak-to-peak trunk pitch angle, and peak anteroposterior center of mass velocity). Results: When vision was suboptimal (blurring goggles), older adults had significantly longer transition phase duration than younger adults (p<0.05). Older adults demonstrated greater mediolateral instability than younger adults. When vision was absent, trunk roll angle was significantly greater with 1xGVS than 2xGVS (p<0.05). Mediolateral center of mass displacement was greater when vision was absent than when vision was available, irrespective of age (p<0.05). No effects of age, vision or galvanic vestibular stimulation were seen in peak braking force, trunk pitch angle, and peak anteroposterior center of mass velocity (p>0.05). Conclusion: Regardless of age, visual inputs were more critical to maintain stability during sit-to-stand than vestibular inputs. Differences between younger adults and older adults were only seen in the mediolateral direction. Despite having greater mediolateral instability, older adults utilized similar strategies as younger adults to overcome sensory perturbations during sit-to-stand. / Thesis (Master, Rehabilitation Science) -- Queen's University, 2013-09-20 23:22:16.695

During pregnancy the female body must accommodate the enlarging gravid uterus and increased mass. Therefore the maternal musculoskeletal system is required to adapt in both morphology and functional workload. After childbirth there is a rapid change in both mass and dimensions, requiring further adaptations. The objectives of the study were to investigate seated and standing upper body posture, the kinematics of seated and standing trunk motion, and the three dimensional kinematics and kinetics during rising to stand from a chair, as pregnancy progressed and in the early post-birth period. Nine maternal subjects (aged 28 to 40 years) were tested at less than 16 weeks, 24 weeks, 30 weeks, 38 weeks gestation and at 8 weeks postbirth. The subjects, fitted with 37 retroreflective markers, were filmed during upright sitting, quiet standing, and four trials each of maximum seated and standing trunk forward flexion, side to side flexion and during maximum seated axial rotation. Three trials each of constrained and free rising to stand from a height adjustable stool and with each foot placed on a forceplate were also recorded. An eight-camera motion analysis system was used to record movements of the body segments and synchronised force plate variables in three dimensions. Motion of the ankle, knee and hip joints, pelvic, thoracic and head segments and the thoracolumbar and cervicothoracic spines and shoulder joints were investigated. Twelve nulliparous subjects (aged 21 to 35 years) were used as controls to provide standard descriptive data and to investigate the consistency of the selected biomechanical variables with repeated testing. A repeated measures ANOVA was used to investigate the possibility of linear and quadratic trends showing systematic changes within the maternal group, over the four test sessions during pregnancy for each variable. Two tailed Student t-tests were used to compare the maternal postbirth variable results with the control group. There was no significant effect of pregnancy on the upper body posture during upright sitting and quiet standing. Postbirth, the pelvic segment had a smaller anterior orientation and the thoracolumbar spine was less extended, indicating a flatter spinal curve. The maternal subjects were similar to the control subjects in early pregnancy and postbirth for trunk segment motions during seated and standing forward flexion and side to side flexion and seated axial rotation. Strategies, such as increasing the width of the base of support and reducing obstruction to movements from other body parts, were used in late pregnancy in attempts to minimise the effects of increased trunk mass and circumference. For seated and standing side to side flexion, the strategies were successful and no significant decreases in range of motion were seen. For seated and standing forward flexion and seated axial rotation, motion of the thoracic segment and the thoracolumbar spine were significantly reduced, although movement of the pelvis was less affected. In early pregnancy and postbirth the kinematics and kinetics of the lower limbs and upper body segment kinematics during constrained and free rising were generally similar to the control subjects. As pregnancy progressed there were increases in mass and dimensions of body segments. The effect of increased mass was seen in increased ground reaction forces and sagittal plane lower limb joint external moments. An increased base of support width was found in association with an increased lateral ground reaction force and ankle inversion moment from each foot, which would move the body centre of mass medially. There was little change in the three dimensional kinematics of the thoracolumbar and cervicothoracic spine, although the contribution of the upper body segments differed for each rise condition. There were also few significant changes in the displacement of the ankle, knee and hip, and the angular velocity of ankle and knee joints. The maternal subjects were thus able to flex the upper body forward, raise the body and maintain stability as pregnancy progressed, regardless of whether the rise to stand was performed in a natural manner or under constrained conditions. The overall results show that, contrary to expectations as pregnancy progressed, maternal subjects minimised propulsion rather than increasing it to overcome the increased mass and possibly limited trunk flexion. A fear of postural instability may have made the subjects more cautious and as they were able to adequately flex the trunk forward, propulsion was minimised in favour of maintaining upright terminal balance.

Grab-bars and transfer poles are common sit-to-stand aids for older adults with mobility limitations. This study investigates differences in kinematics and kinetics in the lower limbs across different transfer pole configurations and positions. Configurations tested are a single pole, two poles and a pole with a horizontal grab-bar at near and far positions. Three-dimensional biomechanics were used to calculate kinetics and kinematics of the lower extremities. Forces were also recorded from the pole. This study found horizontal pole forces were an effective replacement for trunk generated horizontal momentum. Reduced vertical pole forces were applied by participants using the `far' poles which resulted in increases in non-dominant hip moments when using the single and double pole configurations. Horizontal pole use introduced non-dominant directed lateral COM trajectory throughout the movement. This coincided with increased horizontal forces in the dominant foot to balance moments about COM in the transverse plane as a motor control strategy.

Grab-bars and transfer poles are common sit-to-stand aids for older adults with mobility limitations. This study investigates differences in kinematics and kinetics in the lower limbs across different transfer pole configurations and positions. Configurations tested are a single pole, two poles and a pole with a horizontal grab-bar at near and far positions. Three-dimensional biomechanics were used to calculate kinetics and kinematics of the lower extremities. Forces were also recorded from the pole. This study found horizontal pole forces were an effective replacement for trunk generated horizontal momentum. Reduced vertical pole forces were applied by participants using the `far' poles which resulted in increases in non-dominant hip moments when using the single and double pole configurations. Horizontal pole use introduced non-dominant directed lateral COM trajectory throughout the movement. This coincided with increased horizontal forces in the dominant foot to balance moments about COM in the transverse plane as a motor control strategy.

During pregnancy the female body must accommodate the enlarging gravid uterus and increased mass. Therefore the maternal musculoskeletal system is required to adapt in both morphology and functional workload. After childbirth there is a rapid change in both mass and dimensions, requiring further adaptations. The objectives of the study were to investigate seated and standing upper body posture, the kinematics of seated and standing trunk motion, and the three dimensional kinematics and kinetics during rising to stand from a chair, as pregnancy progressed and in the early post-birth period. Nine maternal subjects (aged 28 to 40 years) were tested at less than 16 weeks, 24 weeks, 30 weeks, 38 weeks gestation and at 8 weeks postbirth. The subjects, fitted with 37 retroreflective markers, were filmed during upright sitting, quiet standing, and four trials each of maximum seated and standing trunk forward flexion, side to side flexion and during maximum seated axial rotation. Three trials each of constrained and free rising to stand from a height adjustable stool and with each foot placed on a forceplate were also recorded. An eight-camera motion analysis system was used to record movements of the body segments and synchronised force plate variables in three dimensions. Motion of the ankle, knee and hip joints, pelvic, thoracic and head segments and the thoracolumbar and cervicothoracic spines and shoulder joints were investigated. Twelve nulliparous subjects (aged 21 to 35 years) were used as controls to provide standard descriptive data and to investigate the consistency of the selected biomechanical variables with repeated testing. A repeated measures ANOVA was used to investigate the possibility of linear and quadratic trends showing systematic changes within the maternal group, over the four test sessions during pregnancy for each variable. Two tailed Student t-tests were used to compare the maternal postbirth variable results with the control group. There was no significant effect of pregnancy on the upper body posture during upright sitting and quiet standing. Postbirth, the pelvic segment had a smaller anterior orientation and the thoracolumbar spine was less extended, indicating a flatter spinal curve. The maternal subjects were similar to the control subjects in early pregnancy and postbirth for trunk segment motions during seated and standing forward flexion and side to side flexion and seated axial rotation. Strategies, such as increasing the width of the base of support and reducing obstruction to movements from other body parts, were used in late pregnancy in attempts to minimise the effects of increased trunk mass and circumference. For seated and standing side to side flexion, the strategies were successful and no significant decreases in range of motion were seen. For seated and standing forward flexion and seated axial rotation, motion of the thoracic segment and the thoracolumbar spine were significantly reduced, although movement of the pelvis was less affected. In early pregnancy and postbirth the kinematics and kinetics of the lower limbs and upper body segment kinematics during constrained and free rising were generally similar to the control subjects. As pregnancy progressed there were increases in mass and dimensions of body segments. The effect of increased mass was seen in increased ground reaction forces and sagittal plane lower limb joint external moments. An increased base of support width was found in association with an increased lateral ground reaction force and ankle inversion moment from each foot, which would move the body centre of mass medially. There was little change in the three dimensional kinematics of the thoracolumbar and cervicothoracic spine, although the contribution of the upper body segments differed for each rise condition. There were also few significant changes in the displacement of the ankle, knee and hip, and the angular velocity of ankle and knee joints. The maternal subjects were thus able to flex the upper body forward, raise the body and maintain stability as pregnancy progressed, regardless of whether the rise to stand was performed in a natural manner or under constrained conditions. The overall results show that, contrary to expectations as pregnancy progressed, maternal subjects minimised propulsion rather than increasing it to overcome the increased mass and possibly limited trunk flexion. A fear of postural instability may have made the subjects more cautious and as they were able to adequately flex the trunk forward, propulsion was minimised in favour of maintaining upright terminal balance.

Il est connu que le mouvement volontaire entraîne une perturbation de la posture, qui nécessite d'être compensée par des mouvement contre-perturbateurs définis comme " ajustements posturaux ". Ce processus dynamique, qui se produit avant, pendant et après le mouvement focal, nécessite la mobilité de la chaîne posturale, avec un patron spécifique pour chaque tâche.L'objectif de cette thèse de doctorat a été d'explorer l'influence de la mobilité du rachis sur les composantes focale et posturale du transfert assis- debout, ou sit-to-stand (STS), qui est une tâche indispensable à l'autonomie fonctionnelle. Trois séries expérimentales ont évalué l'effet d'une restriction de mobilité de la colonne vertébrale sur les ajustements posturaux anticipateurs (APAs) et le mouvement focal de la tâche de STS réalisée à vitesse maximale. Des paramètres biomécaniques ont été calculés à partir des données fournies par un plateau de forces et un capteur de pression. La première série a évalué l'effet de la mobilité lombo-pelvienne au moyen de trois types de contentions lombaires, et a montré qu'une réduction du jeu articulaire de cette région était associée des APAs plus longs et plus amples, ainsi qu'à une augmentation de la durée du mouvement focal. La seconde série a mis en évidence les mêmes variations en explorant l'influence de la mobilité de la colonne cervicale au moyen de trois contentions cervicales. La dernière série s'est focalisée sur le rôle de l'augmentation de la tension musculaire le long du tronc, en utilisant un protocole spécifique de compression bimanuelle. Les résultats ont montré qu'une tension musculaire plus élevée induisait une augmentation de la durée des APAs mais sans variation de la durée du mouvement focal. L'ensemble de ces résultats suggèrent que la colonne cervicale et la colonne lombaire sont à la fois impliquées dans les composantes focale et posturale du STS, et que le maintien de leur mobilité peut favoriser l'autonomie fonctionnelle. En revanche, l'augmentation de la tension musculaire le long du tronc nécessite uniquement une réorganisation des ajustements posturaux pour maintenir le même niveau de performance. / It is well known that voluntary movements induce internal disturbances to posture, which need to be balanced by counter-pertubing movements defined as " postural adjustments ". This dynamic process, which occurs before, during, and after the focal movement, requires the mobility of the postural chain, with a specific pattern for each task. The aim of this PhD thesis was to explore the influence of spine mobility on the focal and postural components of the sit-to-stand (STS) task, which is instrumental for functional autonomy. Three series of experiments assessed the effect of spine mobility restriction on anticipatory postural adjustments (APAs) and focal movement (FM) of the STS task peformed at maximum velocity. Biomechanical parameters were calculated from force plate, and pressure sensor data. The first series assessed the effect of lumbo-pelvic mobility using three different lumbar contentions, and showed that restricted articular free play in this area was associated with longer and larger APAs, along with a higher duration of the focal movement. The second series of experiment showed the same variations when exploring the effect of cervical spine mobility using three different cervical contentions. The last series focused on the effect of increased muscular tension along the trunk, using a specific bimanual compressive load paradigm.The results showed that higher tension lead to longer APAs with no variation of FM duration. Taken together, these findings suggest that the lumbar and cervical spine are involved in both the focal and postural components of the STS task, and that preserving their articular free play might be useful to favour functionnal autonomy. In contrast, increased muscular tension along the trunk only require a reorganization of the APAs to keep the same level of task performance.

Powered orthotic devices can be used to restore mobility to the impaired user, and may thereby assist them in daily living tasks. An investigation is performed herein to examine the feasibility of a powered lower-limb orthotic in assisting the sit-to-stand task by 50% of the required torque. Feasibility is considered via simulation. A three-link sit-to-stand model, which is driven by kinematic data, is developed. Models of a Pneumatic Muscle Actuator and a DC motor are used to determine which of the two technologies can make a more appropriate contribution to the sit-to-stand task. Simulation revealed that both the Pneumatic Muscle Actuator and the DC motor are reasonable actuator choices, and neither limited the ability to achieve 50% torque assistance. The ability to assist the task was, however, limited by the ability to derive a control signal for the actuator from the user-orthotic interface. It was concluded that the user-orthotic interface requires further investigation. It was also found that while both actuator technologies are suitable for contributing 50% of the required torque, the Pneumatic Muscle Actuator is preferable due to its ability to scale to greater torques.

Powered orthotic devices can be used to restore mobility to the impaired user, and may thereby assist them in daily living tasks. An investigation is performed herein to examine the feasibility of a powered lower-limb orthotic in assisting the sit-to-stand task by 50% of the required torque. Feasibility is considered via simulation. A three-link sit-to-stand model, which is driven by kinematic data, is developed. Models of a Pneumatic Muscle Actuator and a DC motor are used to determine which of the two technologies can make a more appropriate contribution to the sit-to-stand task. Simulation revealed that both the Pneumatic Muscle Actuator and the DC motor are reasonable actuator choices, and neither limited the ability to achieve 50% torque assistance. The ability to assist the task was, however, limited by the ability to derive a control signal for the actuator from the user-orthotic interface. It was concluded that the user-orthotic interface requires further investigation. It was also found that while both actuator technologies are suitable for contributing 50% of the required torque, the Pneumatic Muscle Actuator is preferable due to its ability to scale to greater torques.