Falls and hip fractures are a major public health problem among the elderly. In addition to bone strength, sideways falls and direct hip impact are important determinants for hip fracture. However, few falls actually cause serious injury in both young and older adults. Therefore, understanding how individuals facilitate a safe landing during a fall will help guide appropriate exercise-based training programs. The primary purpose of this thesis was to investigate the effects of secondary tasks on movement strategies during a sideways fall. <br /><br /> To address this aim, I used a tether and electromagnet to suddenly release subjects from a sideways leaning position, causing them to fall onto a gymnasium mat. I instructed subjects to "fall and protect yourself, as if you were landing on a hard surface". I acquired trials in four conditions, presented in a pseudo-random order: falling while holding a box, falling while holding an empty mug, falling while reciting spoken text, and falling with no secondary task. In most trials, regardless of condition, impact occurred to the lateral aspect of the pelvis (no secondary task = 87%, box = 82%, cognitive = 90%, mug = 79%). While the frequency of impact to both hands decreased when carrying an object (box=67%, mug=50% compared to cognitive=90% and no secondary task=85%), 40% of trials in the mug condition involved one hand contacting the ground, indicating hand impact was still common. It appears when protective movements such as impact to the knees and hands did occur, they were not used to avoid direct hip impact. Instead, they were used to help break the fall, and to avoid head impact, which was not seen in this experiment. The results from this study indicate that secondary tasks have minimal effects on fall responses and that the rare occurrence of hip fractures in the young is due to some combination of bone strength and effective use of body segments to break the fall. <br /><br /> In a second study, I examined how a cognitive task affected the ability of young women to rotate forward (FR) or backward (BR) during a sideways fall. Subjects were released from a sideways leaning position and were provided with a visual cue upon tether release instructing them on the desired direction of rotation. The site of impact on the pelvis (as reflected by the hip proximity angle) was closer to the lateral aspect of the hip in cognitive trials than in control trials (43 ?? 18?? versus 51 ?? 19?? in FR and 59 ?? 18?? versus 68 ?? 18?? in BR) (p=0. 0006). This was due to a longer delay in the initiation of rotation in cognitive trials (293 ?? 60 ms versus 232 ?? 71 ms in FR and 278 ?? 87 ms versus 239 ?? 60 ms), as opposed to a change in mean angular velocity. Pelvis impact velocity was similar in the two conditions (2. 6 ?? 0. 3 m/s compared to 2. 7 ?? 0. 3 m/s in FR trials and 2. 8 ?? 0. 2 m/s compared to 2. 9 ?? 0. 2 m/s in BR trials) (p=0. 0514). The results from this study indicate that involvement in a secondary task can impair safe landing responses. Secondary attentional tasks cause a delay in the initiation of fall protective responses, which alters landing configuration. However, the motor programme that governs falling, remaining consistent across condition is robust to changes in task execution at the onset of the fall.

Falls and hip fractures are a major public health problem among the elderly. In addition to bone strength, sideways falls and direct hip impact are important determinants for hip fracture. However, few falls actually cause serious injury in both young and older adults. Therefore, understanding how individuals facilitate a safe landing during a fall will help guide appropriate exercise-based training programs. The primary purpose of this thesis was to investigate the effects of secondary tasks on movement strategies during a sideways fall. <br /><br /> To address this aim, I used a tether and electromagnet to suddenly release subjects from a sideways leaning position, causing them to fall onto a gymnasium mat. I instructed subjects to "fall and protect yourself, as if you were landing on a hard surface". I acquired trials in four conditions, presented in a pseudo-random order: falling while holding a box, falling while holding an empty mug, falling while reciting spoken text, and falling with no secondary task. In most trials, regardless of condition, impact occurred to the lateral aspect of the pelvis (no secondary task = 87%, box = 82%, cognitive = 90%, mug = 79%). While the frequency of impact to both hands decreased when carrying an object (box=67%, mug=50% compared to cognitive=90% and no secondary task=85%), 40% of trials in the mug condition involved one hand contacting the ground, indicating hand impact was still common. It appears when protective movements such as impact to the knees and hands did occur, they were not used to avoid direct hip impact. Instead, they were used to help break the fall, and to avoid head impact, which was not seen in this experiment. The results from this study indicate that secondary tasks have minimal effects on fall responses and that the rare occurrence of hip fractures in the young is due to some combination of bone strength and effective use of body segments to break the fall. <br /><br /> In a second study, I examined how a cognitive task affected the ability of young women to rotate forward (FR) or backward (BR) during a sideways fall. Subjects were released from a sideways leaning position and were provided with a visual cue upon tether release instructing them on the desired direction of rotation. The site of impact on the pelvis (as reflected by the hip proximity angle) was closer to the lateral aspect of the hip in cognitive trials than in control trials (43 ± 18º versus 51 ± 19º in FR and 59 ± 18º versus 68 ± 18º in BR) (p=0. 0006). This was due to a longer delay in the initiation of rotation in cognitive trials (293 ± 60 ms versus 232 ± 71 ms in FR and 278 ± 87 ms versus 239 ± 60 ms), as opposed to a change in mean angular velocity. Pelvis impact velocity was similar in the two conditions (2. 6 ± 0. 3 m/s compared to 2. 7 ± 0. 3 m/s in FR trials and 2. 8 ± 0. 2 m/s compared to 2. 9 ± 0. 2 m/s in BR trials) (p=0. 0514). The results from this study indicate that involvement in a secondary task can impair safe landing responses. Secondary attentional tasks cause a delay in the initiation of fall protective responses, which alters landing configuration. However, the motor programme that governs falling, remaining consistent across condition is robust to changes in task execution at the onset of the fall.

A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability.

Overloading of the back can cause instability such that buttressing the instability is a primary objective of many of the leading edge therapeutic approaches. However, a challenge lies in determining the location of the instability or the least stable vertebral joint. A mathematical analysis, based on a commonly used approach in engineering for determining structural stability, has been developed for the lumbar spine. The purpose of this investigation was to determine the feasibility of a method for mathematically locating potential areas of instability within a computer-based model of the lumbar spine. To validate this method, the eigenvector from the stability analysis was compared to the output from a geometric equation that approximated individual vertebral joint rotational stiffness with the idea that the entry in the eigenvector with the largest absolute value would correspond to the vertebral joint and axis with the lowest stiffness. Validation of the eigenvector was not possible due to computational similarities between the stability analysis and the geometric rotational stiffness method. However, it has been previously demonstrated that the eigenvector can be useful for locating instability, and thus warrants future study. Determining the least stable vertebral joint and axis can be used to guide proper motor pattern training as a clinical intervention. It was also shown in this investigation that an even distribution of fascicle force and stiffness generated stability. This supports the idea that well-coordinated efforts of muscle activation are beneficial for improving stability of the lumbar spine.

A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability.

Overloading of the back can cause instability such that buttressing the instability is a primary objective of many of the leading edge therapeutic approaches. However, a challenge lies in determining the location of the instability or the least stable vertebral joint. A mathematical analysis, based on a commonly used approach in engineering for determining structural stability, has been developed for the lumbar spine. The purpose of this investigation was to determine the feasibility of a method for mathematically locating potential areas of instability within a computer-based model of the lumbar spine. To validate this method, the eigenvector from the stability analysis was compared to the output from a geometric equation that approximated individual vertebral joint rotational stiffness with the idea that the entry in the eigenvector with the largest absolute value would correspond to the vertebral joint and axis with the lowest stiffness. Validation of the eigenvector was not possible due to computational similarities between the stability analysis and the geometric rotational stiffness method. However, it has been previously demonstrated that the eigenvector can be useful for locating instability, and thus warrants future study. Determining the least stable vertebral joint and axis can be used to guide proper motor pattern training as a clinical intervention. It was also shown in this investigation that an even distribution of fascicle force and stiffness generated stability. This supports the idea that well-coordinated efforts of muscle activation are beneficial for improving stability of the lumbar spine.

Social Cognitive Theory (SCT: Bandura, 1997) has been used successfully in understanding exercise adherence. To date, the majority of the exercise research has focused on situations of personal agency (i. e. , self as agent: e. g. , McAuley & Blissmer, 2000). However, there are a number of exercise situations in which people look to others to help them manage their exercise participation by enlisting a <i>proxy-agent</i> (Bandura, 1997). While using assistance from a proxy can promote the development of self-regulatory skills, Bandura (1997) cautions that reliance on a proxy actually reduces mastery experiences which can result in an inability to self-regulate one?s behaviour. Although research examined proxy-agency in exercise (e. g. , Bray et al. , 2001), the issue of reliance on the proxy at the expense of the participant?s ability to adjust to exercise without that agent has not been investigated. This potential dilemma of proxy-agency in exercise was at the core of this dissertation and was investigated in a series of three studies. Study 1 investigated whether those who differed in preferred level of proxy-contact also differed in their social-cognitions both within and outside a proxy-led exercise context. In addition, the relationships between proxy-efficacy, reliance and self-efficacy were examined. Results indicated that participants who preferred regular contact with an exercise proxy had lower self-regulatory efficacy, lower task efficacy, and weaker intentions in a proxy-led exercise context. Further, high-contact participants were shown to be less efficacious in dealing with the behavioural challenge of sudden class elimination. It was also demonstrated that higher reliance on the instructor was associated with lower self-efficacy and higher proxy-efficacy. Study 2 served to extend the findings of Study 1 through the examination of behavioural differences characteristic of differential levels of preferred proxy contact and the reasons for use of proxy-agency. It was found that exercise class participants preferring high contact with a proxy found exercising independently more difficult than did their low contact counterparts. It was also found that when faced with class elimination, those preferring high contact chose a self-managed activity alternative less frequently than did those preferring low contact. High contact participants also reported feeling less confident, less satisfied and perceived their alternative activity as more difficult than did those preferring low contact. In examining the reasons for preferring high proxy-contact, results indicated that a preference for high contact was associated with having had less experience exercising independently and allotting more responsibility for in-class participation to the class instructor as compared to preferring low proxy-contact. Study 3 used Lent and Lopez?s (2002) tripartite model of efficacy beliefs to examine the associations between relational efficacies (i. e. , other-efficacy and relation inferred self-efficacy (RISE) beliefs, proxy-efficacy) and various social cognitions relevant to proxy-agency. Results revealed that relational efficacies were distinct yet related constructs which additively predicted self-regulatory efficacy, satisfaction, intended intensity and reliance. Relational efficacies were also shown to make unique contributions to the predictions of the relevant social-cognitions. It was also demonstrated that RISE beliefs were associated with the attributions participants made. Specifically, higher RISE beliefs was associated with making more internal, personally controllable and stable attributions. These results represent the initial examination of relational efficacy beliefs in the exercise literature and provide additional evidence of the proxy-agency dilemma in exercise. Taken together, the present series of studies both support theorizing by Bandura on the dilemma of proxy-agency and represent an extension of the existing literature of proxy-agency in exercise. Results suggest that seemingly healthy, regularly exercising adults who choose to employ proxy-agency may be at risk for nonadherence in situations of behavioural challenge. The current findings have important implications for exercise leaders and interventionists as they must be aware of the balance between helping and hindering.

The self has been identified as the ?psychological apparatus that allows individuals to think consciously about themselves? (Leary & Price Tangney, 2003, p. 8). Further, the self has been identified as a worthwhile construct of investigation in relation to health behaviour (Contrada & Ashmore, 1999). Two self-related variables that have been useful in the study of health behaviour are <em>identity</em> (e. g. Anderson, Cychosz, & Franke, 1998; Petosa, Suminski & Hortz, 2003; Storer, Cychosz, & Anderson, 1997) and <em>self-efficacy</em> (Maddux, Brawley & Boykin, 1995). Identity Theory posits that individuals regulate their behaviour in a manner that is consistent with their goal identity (Gecas & Burke, 2003). Social Cognitive Theory provides a means of measuring social cognitions that may be important in behavioural regulation relative to identity. Further, self-efficacy beliefs may influence individuals? persistence at aligning their identity and behaviour. Research to date has investigated the link between identity and exercise (e. g. Anderson, Cychosz & Franke, 1998; Petosa, et al. , 2003). Further, researchers are beginning to investigate the link between identity and other health behaviours (e. g. Armitage & Conner, 1999; Kendzierski and Costello, 2004; Storer, Cychosz, & Andersen, 1997). However, research has not utilized the predictive frameworks offered by Identity Theory and Social Cognitive Theory to investigate the relationships between identity, behaviour and behavioural regulation. <br /><br /> Study One investigated the role of identity and self-efficacy beliefs in the maintenance of vigorous physical activity. Results were consistent with both Identity Theory and Social Cognitive Theory. Individuals who strongly identified with the runner identity expressed stronger task and self-regulatory efficacy beliefs. They also exercised more frequently and for longer durations than did those who only moderately identified with running. <br /><br /> Study Two further explored the relationship between exercise identity, exercise behaviour and the self-regulatory processes involved in behavioural regulation. Identity Theory and Social Cognitive Theory were used as guiding frameworks for this investigation. High and moderate exercise identity groups were compared in term of their affective and cognitive reactions to a hypothetical behavioural challenge to exercise identity. Consistent with Identity Theory, results indicated that participants appeared to be regulating their behaviour in a manner that was consistent with their exercise identity. Specifically, in response to the behavioural challenge to identity, high exercise identity participants, in contrast to their moderate counterparts, showed (a) less positive and (b) greater negative affect about the challenge, (c) higher self-regulatory efficacy for future exercise under the same challenging conditions, (d) stronger intentions for this future exercise, as well as for (e) using self-regulatory strategies to manage the challenging conditions and (f) intending to exercise more frequently under those conditions. <br /><br /> Study Three investigated whether identity with <em>healthy eating</em> could also be useful in understanding behaviour and behavioural regulation. Similar to Study Two, extreme healthy-eater identity groups? reactions to a hypothetical behavioural challenge to identity were compared. Results were similar to Study Two. Participants responded in a manner that suggested that they would regulate their future behaviour relative to their healthy-eater identity. In response to the behavioural challenge to identity, individuals who highly identified as healthy-eaters expressed less (a) positive affect, greater (b) negative affect, (c) self-regulatory efficacy for managing their healthy eating in the future challenging weeks, (d) intentions to eat a healthy diet, (e) generated more self-regulatory strategies and had (f) stronger intentions to use those strategies in future weeks under the same challenging conditions than did individuals who moderately identified themselves as healthy-eaters. Further, prospective relationships between healthy-eater identity and social cognitive variables, and healthy eating outcomes were examined. As was found in Study One in the context of exercise, healthy-eater identity and social cognitions predicted healthy eating outcomes. <br /><br /> Taken together, the three studies suggest that identity may be important in understanding health behaviours and the regulation of these behaviours. Also, the present findings support the compatible use of Identity Theory and Social Cognitive Theory in the investigation of identity and health behaviour.

Abstract Background: The process that involves the migration of the nucleus pulposus from the innermost annular layers and culminates with the final extrusion of the nucleus has been limited to a few studies. This investigation was directed towards a better understanding of the herniation process. The architecture of the annulus fibrosus and the mechanism of progressive disc herniation were analyzed, using a controlled porcine model. Microscopic and histochemical techniques were employed. <br /><br /> Methodology: Two studies were performed. In the first stage, the macroscopic and microscopic structures of twelve cervical intervertebral discs were compared with young human disc data from studies reported in the literature. Important structural features were studied such as annulus fibrosus thickness, number of lamellae, lamellae thickness, orientation of the lamellae fibers and blood supply. In the second study, sixteen fresh-frozen functional spine units were submitted to repetitive flexion?extension motions combined with a low compressive load in a servo-hydraulic dynamic testing system. Discograms, dissections and histochemical techniques were applied to characterize the cumulative damage. The experiment produced eight complete herniations, four partial herniations and four specimens without any microscopic detectable annular damage. <br /><br /> Results and Discussion: The structure of the cervical porcine disc resembles the lumbar human disc. Some differences are evident. The size of the annulus is smaller, the thickness of the lamellae is narrower and the number of layers is fewer in the pig. It is hypothesized that the flexion-extension motion combined with a low-level load produced an increased hydraulic pressure in the inner wall of the posterior annulus. This pressure and repetitive motion first produced a small cleft, spreading the collagen bundles inside the first layer. The nuclear material was "pumped" through the small cleft to the first layer filling the layer creating a fluid-filled pocket between the collagen fibers. Once the "pocket" acquired enough pressure a new cleft was produced in the weakest part of the layer allowing the nuclear material to create a new "pocket" in the second layer. This was the first stage of damage and disc herniation production. This mechanism was repeated until the nucleus traveled along the annulus reaching the posterior longitudinal ligament. At this point a complete extrusion herniation was produced. <br /><br /> Conclusion: The porcine model appears to be suitable as a model to understand the mechanism of disc herniation when the spine is subjected to flexion-extension motions combined with a low-level load. The first cumulative injury appears to be a cleft between the lamellae bundles produced by the nuclear hydraulic pressure. A cumulative load/cumulative injury model approach was used to create the damage that was quantified in the study.

Gloved work has been shown to increase the effort required to perform manual tasks. In power grip tasks, these differences have been observed as reductions in strength and increases in muscular effort. Decreases in force output have been attributed to a number of factors, including loss of tactile sensitivity, glove flexibility or suppleness, thickness, changes in hand geometry, and friction at the glove-object interface. Glove research has rarely quantified glove attributes, and often compared gloves of varying material and physical properties. This research had the unique opportunity to control for a number of these properties by using three sets of identical gloves (powerline maintainers? insulating rubber gloves), differing only in thickness. <br /><br /> Administering the Von Frey Hair Test indicated that the gloves did indeed decrease tactile sensitivity. This research showed that increasing glove thickness led to large decreases in maximum power grip force. Small changes in hand geometry, such as increased interdigital space or grip span, affected force output. In the same hand posture, participants increased their grip force with increasing glove thickness for the object lifting task but were able to maintain a fixed submaximal force with visual feedback. The decrease in tactile sensitivity is a likely cause of this difference. <br /><br /> Muscular activity was affected by wearing the gloves while performing manual tasks. Inconsistent responses of muscular activation were seen in gloved maximum grip effort, while overall increases in electromyographic activity were recorded for tasks at submaximal levels when wearing gloves. <br /><br /> Interdigital spacing had different effects on maximal and submaximal tasks. For maximum effort power grip, interdigital spacing decreased force output by as much as 10%, with no significant changes in muscle activation. For submaximal tasks, no significant differences were seen in muscular activity or in force output. The overall force capability of the gloved user is hindered by changes in interdigital spacing at near maximal effort, but does not appear to be for tasks requiring lower grip force, such as the lifting task which required roughly 20%MVC. Overall, the effect of wearing these gloves on the users, the powerline maintainers, is a substantially increased effort to work. This research contributes to a greater understanding of why and how gloves inhibit performance.