Desordens motoras são descritas no estágio final da doença de Alzheimer (DA), porém pesquisas recentes têm demonstrado que idosos com comprometimento cognitivo leve (CCL) e em fase inicial da DA apresentam alterações na marcha, especialmente em condições de atenção dividida (tarefa dupla). Esta pesquisa teve como objetivo avaliar o desempenho motor com e sem tarefa de atenção dividida em idosos com CCL e DA; e verificar se esta medida pode ser utilizada para diferenciar idosos cognitivamente saudáveis, com CCL e com DA. Foram avaliados 104 idosos (26 com DA leve, 42 com CCL e 36 cognitivamente saudáveis - controles) por meio do Timed Up and Go teste (TUG), em quatro condições experimentais: (1) tarefa simples (apenas o TUG), (2) TUG com tarefa cognitiva, (3) TUG com tarefa manual, e (4) tarefa tripla (com tarefa cognitiva e manual). Diferenças significativas foram observadas em todas as condições experimentais do TUG entre grupos diagnósticos, especialmente em relação ao tempo (em segundos) e número de passos (TUG 1-4) e paradas (TUG 2-4). Em relação à área sob a curva (AUC), as quatro formas do TUG apresentaram alto grau de discriminação entre os grupos diagnósticos em relação: 1) ao tempo (em segundos): AUC > 0,8 nos TUG 1 ao 4 entre os grupos controle e CCL (p<0,001), AUC > 0,9 nos TUG 1 ao 4 entre os grupos controle e DA (p<0,001), e AUC > 0,7 nos TUG 2 ao 4 entre os grupos CCL e DA (p<0,001); 2) número de passos: AUC >0,7 entre os grupos controle e CCL (p<0,001), AUC > 0,8 entre os grupos controle e DA (p<0,001), e AUC > 0,7 entre os grupos CCL e DA (p<0,02); 3) e número de paradas: AUC > 0,6 nos TUG 2 e 4 entre os grupos controle e CCL (p<0,05), AUC > 0,8 entre os grupos controle e DA nos TUG 2 e 4 (p<0,001) e AUC > 0,7 no TUG 2 entre os grupos CCL e DA (p<0,05). Portanto, o desempenho motor é afetado em idosos com CCL e em fases iniciais da DA em condições de tarefa simples e atenção dividida, sendo todas as condições do TUG boas medidas para diferenciar os grupos diagnósticos / Motor disorders are described in the final stages of Alzheimer\'s disease (AD), but recent research has shown that older adults with mild cognitive impairment (MCI) and early AD exhibit changes in gait, particularly under conditions of divided attention (dual task). This research aimed to evaluate motor performance with and without divided attention task in elderly with MCI and AD and verify that this measure can be used to differentiate elderly cognitively health, MCI and AD. A total of 104 older adults (26 with mild AD, 42 with MCI and 36 cognitively health - controls) were evaluated by the Timed Up and Go test (TUG) under four experimental conditions: (1) TUG simple task (TUG only); (2) TUG in association with a cognitive task; (3) TUG plus a manual task; and (4) TUG triple (plus a cognitive and manual task). Statistically significant differences in TUG were found between diagnostic groups in all experimental conditions, especially with respect to amount of time (in seconds) and number of steps (TUG 1-4) and stops (TUG 2-4). Regarding the area under the curve (AUC), all TUG tasks displayed a high accuracy level in discriminating between diagnostic groups: 1) amount of time (in seconds): AUC> 0.8 in TUG 1-4 between the control and MCI groups(p<0,001), AUC> 0.9 in TUG 1-4 between the control and AD groups(p<0,001), and AUC> 0.7 in TUG 2-4 between the MCI and AD groups(p<0,001); 2) the number of steps: AUC> 0.7 in TUG 1-4 between the control and MCI groups (p<0,001), AUC> 0.8 in TUG 1-4 between the control and AD groups (p<0,001), and AUC> 0.7 between in TUG 1-4 the MCI and AD groups (p<0,02); 3) and in the number of stops: AUC> 0.6 in TUGs 2-4 between the control and MCI groups (p<0,05), AUC> 0.8 in TUGs 2-4 between the control and AD groups (p<0,001) and AUC> 0.7 between the MCI and AD groups (p<0,05). Thus, motor performance is affected in older adults with MCI and early stages of AD, both with and without a divided attention task, and all conditions tested were able to differentiate among diagnostic groups

In everyday life, the ability to perform two tasks simultaneously, dual task, is an omnipresent issue. There are several factors that can limit an individual’s ability to dual task, such as neurological pathologies, or physical disabilities. A reduced ability to perform dual task activities can result in decreased gait performance, higher risk of falls, a high probability of reduced participation, as well as contributing to a number of deterioration processes in the body. There are numerous situations in which dual tasking is used in therapy, however, there is no consensus regarding what kind of dual task to train in order to have the most effective outcomes. The aim of this systematic review is to investigate the relative effect of motor versus cognitive dual task on brain activity patterns and gait performance. Ten studies were identified in a systematic literature review in order to provide insight into the current status concerning the topic. The results showed high variations of analysed parameters and a very small amount of studies examining motor dual tasks. However, results indicated that cognitive dual tasks had a greater impact on brain activity. In regard to gait performance, no definite answer was found. Given the importance of dual tasks in everyday life and the numerous groups of people experiencing difficulties while dual tasking, the possibilities of adapting dual tasks in therapy should be a topic of future research. / Die Fähigkeit, zwei Aufgaben gleichzeitig auszuführen, auch dual tasking genannt, ist im Alltag ein allgegenwärtiges Thema. Es gibt verschiedene Faktoren, die die Fähigkeit eines Menschen, dual tasks auszuführen, einschränken, wie beispielsweise neurologische Pathologien oder körperliche Behinderungen. Die Verminderung dieser Fähigkeit kann zu abnehmender Gangleistung, erhöhtem Fallrisiko und einer hohen Wahrscheinlichkeit für reduzierte Partizipation führen, sowie folglich zu einer Anzahl an Abnützungserscheinungen des Körpers beitragen. Obwohl es zahlreiche Situationen gibt, in denen dual tasking als Intervention in Verwendung kommt, gibt es keinen Konsens bezüglich der Frage welche Art von Doppelaufgabe trainiert werden soll, um möglichst wirksame Resultate zu erzielen. Das Ziel dieser Arbeit ist es, die relativen Effekte von motorischen dual tasks im Vergleich zu kognitiven dual tasks auf die Hirnaktivität und die Gangleistung zu untersuchen. Zehn Studien wurden in der systematischen Übersichtsarbeit ermittelt, um einen Einblick in den aktuellen Stand der Forschung in diesem Thema zu gewährleisten. Die Ergebnisse zeigten eine Vielzahl an verwendeten Analyseparametern und eine kleine Anzahl an Studien zur Untersuchung von motorischen dual tasks. Trotzdem zeigte sich eine größere Auswirkung von kognitiven dual tasks auf die Hirnaktivität. In Bezug auf die Gangleistung konnte keine eindeutige Antwort gefunden werden. Aufgrund der Wichtigkeit von dual tasks im Alltag und der Vielzahl an betroffenen Personengruppen, die Schwierigkeiten bei der Ausführung jener erleben, sollte die Möglichkeiten der Anpassung von dual tasks auf verschiedene Therapieziele und Patientengruppen Thema für zukünftige Forschung sein.

Les chutes chez les personnes âgées ont été attribuées à une baisse de la fonction proprioceptive ainsi qu'à une incapacité à allouer suffisamment d’attention au maintien de l'équilibre dans des conditions multitâches. Cette étude vise à explorer l'interaction entre les demandes proprioceptive et attentionnelle du contrôle postural dynamique de la personne âgée. Des adultes sédentaires âgés et jeunes ont effectué une tâche de limite de la stabilité posturale avec et sans vision ainsi qu’une tâche attentionnelle secondaire de soustraction mathématique (n-3). Ces deux tâches étaient effectuées soit seul (tâche simple) ou simultanément (tâche double). La force de réaction au sol a été collectée à 200 Hz en utilisant une plateforme de force AMTI et les déplacements des centres de pression (COP) ont été analysés. Les limites fonctionnelles de la stabilité ont été quantifiées comme l'excursion maximale du COP pendant l'inclinaison volontaire du corps dans chaque direction. Nous avions émis l'hypothèse que les plus grandes différences liées à l'âge seraient observées dans la condition de tâche double en raison des limitations des ressources attentionnelles pour faire face simultanément à des exigences proprioceptives et cognitives élevées. Nos résultats indiquent que l’addition de la tâche attentionnelle n’a pas influencé les limites de stabilité posturales des participants. Cependant, les personnes âgées ont significativement diminué leur performance dans la tâche attentionnelle lorsqu’ils ont effectué simultanément la tâche posturale, particulièrement en l’absence de vision. Ces résultats supportent l’idée d’une interaction entre les demandes proprioceptives et attentionnelles du contrôle postural dynamique chez la personne âgée. / Falls among seniors have been attributed to declines in proprioceptive function as well as an inability to efficiently allocate attention to balance in multi-task conditions. This study aims to explore the interaction between the proprioceptive and attentional demands for dynamic postural control in seniors. Old and young sedentary adults performed a postural stability limit task with and without vision as well as a secondary attentional subtraction task (n-3). These two tasks were performed either alone (single task) or simultaneously (dual-task). Ground reaction force was collected at 200 Hz using an AMTI force platform and centre of pressure (COP) was analyzed. The functional limits of stability were quantified as the maximum COP excursion during voluntary leaning in each direction. We hypothesized that the greatest age-related differences would be seen under the dual-task condition because of limitations in attentional resources available for concurrently coping with high proprioceptive and cognitive demands. Our findings indicated that the stability limits of both subject groups were not influenced by the addition of the cognitive attentional task. However, seniors markedly decreased their performance in the cognitive task while simultaneously performing the postural task and this trend was accentuated in the absence of vision. These results support the idea of an interaction between the proprioceptive and attentional demands of dynamic postural control in seniors.

No description available.

Bisherige Studien liefern Hinweise für das Auftreten von aktiven Prozessen der Reihenfolgekoordination in Doppelaufgaben. Diese Prozesse sind notwendig für die Regulation der Bearbeitungsreihenfolge von zwei Aufgaben. Bisher ist jedoch wenig über die kognitiven und neuronalen Mechanismen bekannt, die diesen Prozessen zugrunde liegen. Ziel der vorliegenden Dissertation war deshalb die Überprüfung eines Modells aktiver Reihenfolgekoordination in Doppelaufgaben. Das Modell nimmt an, dass diese Prozesse auf Repräsentationen zurückgreifen, die Informationen über die Verarbeitungssequenz zweier Aufgaben enthält. Zusätzlich macht das Modell Annahmen über (1) den Ort der Verarbeitung und (2) den genauen Inhalt dieser Repräsentationen. Weiterhin enthält das Modell die Annahmen, dass (3) der präfrontale Kortex kausal in Reihenfolgekoordination involviert ist und dass (4) diese Prozesse von unterschiedlichen Kriterien beeinflusst werden. In dieser Dissertation wurde das Model in einer Reihe von vier Studien überprüft. Dazu wurde ein Doppelaufgabenparadigma mit zufällig wechselnder Aufgabenreihenfolge verwendet. Ich konnte zeigen, dass die Reihenfolgerepräsentationen im Arbeitsgedächtnis aufrechterhalten und aktiv verarbeitet werden. Ich konnte weiterhin zeigen, dass diese Repräsentationen nur Information über die Sequenz der Aufgaben enthalten. Spezifische Aufgabeninformation wird hingegen separat repräsentiert. Durch den Einsatz transkranieller Magnetstimulation konnte ich zudem nachweisen, dass der präfrontale Kortex eine kausale Rolle für Reihenfolgekoordination spielt. Darüber hinaus konnte ich zeigen, dass Anforderungen an Reihenfolgekoordinationsprozesse in Situationen, in denen Probanden ein von außen vorgegebenes Reihenfolgekriterium befolgen, erhöht sind im Vergleich zu Situationen, in denen Probanden ein auf einer freien Wahl basierendes Kriterium nutzen können. Die Implikationen dieser Ergebnisse werden unter Berücksichtigung des vorgeschlagenen Modells diskutiert. / Evidence from behavioral as well as neurophysiological studies indicates the occurrence of active task-order coordination processes in dual-task situations. These processes are required for planning and regulating the processing sequence of two tasks that overlap in time. So far, however, the cognitive and neural mechanisms underlying active task-order coordination are highly underspecified. To tackle this issue, in the present dissertation I tested a model of task-order coordination in dual-task situations. This model assumes that task-order coordination relies on representations that contain information about the processing sequence of the two component tasks. In addition, the model includes assumptions about the (1) locus of processing as well as (2) the exact content of these order representations. The model further assumes that (3) the lateral prefrontal cortex is causally involved in implementing task-order coordination processes and that (4) these processes are affected by different order criteria. I tested this model in a series of four studies by applying a dual-task paradigm with randomly changing task order. I demonstrated that task-order representations are actively maintained and processed in working memory during dual tasking. Moreover, I found that these order representations only contain information about the processing sequence of tasks, whereas specific component task information is represented separately. By applying transcranial magnetic stimulation, I also provided evidence for the causal role of the lateral prefrontal cortex for task-order coordination. Furthermore, I showed that the demands on task-order coordination are increased when participants have to adhere to an external and mandatory order criterion compared to when they can use an internally generated order criterion that is based on free choice. The implications of these results as well as an outlook for future research will be discussed in the framework of the proposed model.

為了探討注意力與年齡因素對計時行為的影響，本實驗選用事前知道計時派典（prospective paradigm）與不涉及人為時間單位之知識的計時複製方式。針對注意力的因素，本研究採用雙重作業以操弄注意力資源集中或分散，檢測其對計時作業的影響。另針對年齡的因素，本研究比較低年級小學生、高年級小學生、及大學生成人三種不同年齡組的受試。 本研究利用四種計時作業，針對三個不同年齡層的受試進行對兩種不等的時距計時資料收集。計時作業及年齡因子的實驗設計採受試者間設計，而時距因子則採受試者內設計。研究結果發現（1）低年級組的計時準確性較高年級組或成人組差；（2）受試在雙重作業的計時表現的確較單一作業差，這個計時受干擾的結果，在複雜的雙重作業又較在簡單雙重作業明顯，且年紀愈小的受試所受干擾影響愈大；（3）三年齡層受試在雙重作業中皆有低估目標時距的現象，其中以低年級在複雜雙重作業中的低估程度最明顯；（4）低年級組的計時能力之穩定性較高年級或成人組低；（5）在無需對不斷出現之無意義刺激作偵測反應時，三年齡受試的計時準確性未受影響。 這些結果顯示計時的誤差的確隨著注意力需分派於非時間作業的增加，受試所複製的時距也隨之縮短。這項由於注意力分散所致的計時誤差在國小低年級組最明顯，但隨著年齡的成長及腦發展愈臻成熟，這項影響效果愈趨式微，致使計時的表現愈正確。 關鍵詞：時間複製、年齡與發展、雙重作業、注意力、小學生、純量計時 / The purpose of this study was to investigate the effects of the attention and age on time estimation based on the prospective timing paradigm. Four timing tasks, with different degrees of attentional requirement, were utilized to test timing of reproducing the target intervals in three groups of different ages including the lower-grade (M= 7.5 years), higher-grade (M= 11.2 years) elementary school students and adult (M= 20.1 years). The subjects in this work were asked to estimate a stimulus duration lasting for 7 or 14 s, during which they are required to either do or do not perform a concurrent non-temporal task. Thus, the experimental design for the present study was mixed with between-subject factors (age and task) and a within-subject factor (target interval). The results showed (1) the lower-grade children performed less accurate than the higher-grade children; (2) all subjects had worse timing performance in the dual-task condition than the single-task or control condition, which effect was most evident in the lower-grade children; (3) all subjects reproduced shorter interval as compared to the target interval, which effect was most apparently observed from the dual-task for the lower-grade children; (4) the lower-grade children had less reliability in timing; and (5) the effect of age on the single-task and control condition is not significant. Together, these data indicate that concurrent non-temporal task cause temporal reproduction shorter, especially under high attention demand in lower-grade children. In addition to the influence by the task complexity, the accuracy of timing estimation depends on the age. Keywords: time reproduction、age and development、dual task、attention、elementary school student、Scalar expectancy theory(SET)

L’objectif principal de cette thèse était de quantifier et comparer l’effort requis pour reconnaître la parole dans le bruit chez les jeunes adultes et les personnes aînées ayant une audition normale et une acuité visuelle normale (avec ou sans lentille de correction de la vue). L’effort associé à la perception de la parole est lié aux ressources attentionnelles et cognitives requises pour comprendre la parole. La première étude (Expérience 1) avait pour but d’évaluer l’effort associé à la reconnaissance auditive de la parole (entendre un locuteur), tandis que la deuxième étude (Expérience 2) avait comme but d’évaluer l’effort associé à la reconnaissance auditivo-visuelle de la parole (entendre et voir le visage d’un locuteur). L’effort fut mesuré de deux façons différentes. D’abord par une approche comportementale faisant appel à un paradigme expérimental nommé double tâche. Il s’agissait d’une tâche de reconnaissance de mot jumelée à une tâche de reconnaissance de patrons vibro-tactiles. De plus, l’effort fut quantifié à l’aide d’un questionnaire demandant aux participants de coter l’effort associé aux tâches comportementales. Les deux mesures d’effort furent utilisées dans deux conditions expérimentales différentes : 1) niveau équivalent – c'est-à-dire lorsque le niveau du bruit masquant la parole était le même pour tous les participants et, 2) performance équivalente – c'est-à-dire lorsque le niveau du bruit fut ajusté afin que les performances à la tâche de reconnaissance de mots soient identiques pour les deux groupes de participant. Les niveaux de performance obtenus pour la tâche vibro-tactile ont révélé que les personnes aînées fournissent plus d’effort que les jeunes adultes pour les deux conditions expérimentales, et ce, quelle que soit la modalité perceptuelle dans laquelle les stimuli de la parole sont présentés (c.-à.-d., auditive seulement ou auditivo-visuelle). Globalement, le ‘coût’ associé aux performances de la tâche vibro-tactile était au plus élevé pour les personnes aînées lorsque la parole était présentée en modalité auditivo-visuelle. Alors que les indices visuels peuvent améliorer la reconnaissance auditivo-visuelle de la parole, nos résultats suggèrent qu’ils peuvent aussi créer une charge additionnelle sur les ressources utilisées pour traiter l’information. Cette charge additionnelle a des conséquences néfastes sur les performances aux tâches de reconnaissance de mots et de patrons vibro-tactiles lorsque celles-ci sont effectuées sous des conditions de double tâche. Conformément aux études antérieures, les coefficients de corrélations effectuées à partir des données de l’Expérience 1 et de l’Expérience 2 soutiennent la notion que les mesures comportementales de double tâche et les réponses aux questionnaires évaluent différentes dimensions de l’effort associé à la reconnaissance de la parole. Comme l’effort associé à la perception de la parole repose sur des facteurs auditifs et cognitifs, une troisième étude fut complétée afin d’explorer si la mémoire auditive de travail contribue à expliquer la variance dans les données portant sur l’effort associé à la perception de la parole. De plus, ces analyses ont permis de comparer les patrons de réponses obtenues pour ces deux facteurs après des jeunes adultes et des personnes aînées. Pour les jeunes adultes, les résultats d’une analyse de régression séquentielle ont démontré qu’une mesure de la capacité auditive (taille de l’empan) était reliée à l’effort, tandis qu’une mesure du traitement auditif (rappel alphabétique) était reliée à la précision avec laquelle les mots étaient reconnus lorsqu’ils étaient présentés sous les conditions de double tâche. Cependant, ces mêmes relations n’étaient pas présentes dans les données obtenues pour le groupe de personnes aînées ni dans les données obtenues lorsque les tâches de reconnaissance de la parole étaient effectuées en modalité auditivo-visuelle. D’autres études sont nécessaires pour identifier les facteurs cognitifs qui sous-tendent l’effort associé à la perception de la parole, et ce, particulièrement chez les personnes aînées. / The primary objective of the current thesis was to quantify and compare the amount of listening effort that young and older, normal-hearing adults with normal (or corrected normal) vision expend when speech is presented in background noise. Listening effort refers to the attentional and cognitive resources required to understand speech. Study 1 was designed to determine the listening effort associated with auditory speech recognition (hearing a speaker) whereas Study 2 examined the listening effort involved with audiovisual speech recognition (hearing and seeing the face of a speaker). Listening effort was assessed behaviourally, using a dual task paradigm where a word recognition task was paired with a tactile pattern recognition task and, with self-reported ratings. Both measures of listening effort were assessed under two experimental conditions: 1) equated level - where the level of background noise was the same for all participants and, 2) equated performance - where single task word recognition performance did not differ between groups. The tactile task costs revealed that older adults expended more listening effort than young adults for both experimental conditions regardless of the perceptual modality in which the speech stimuli were presented (i.e., audio-only and audiovisual). Overall, the cost involved with tactile task performance was highest for older adults when speech was presented audiovisually. While visual cues can improve audiovisual speech recognition our results suggest they can also place an extra demand on processing resources with performance consequences for the word and tactile tasks under dual task conditions. Consistent with the literature, the correlation findings of Study 1 and Study 2 support the idea that dual task measures and self-reported ratings each assess different aspects of listening effort. As listening effort draws upon auditory and cognitive factors, the purpose of Study 3 was to determine to what extent the separate components of auditory working memory (capacity and processing) contribute towards the variance observed in listening effort and to determine if the pattern of working memory predictor variables changes with age. Results of a sequential regression analysis for young adults indicated that a measure of auditory capacity (span size) was related to listening effort whereas a measure of auditory processing (alphabetical recall) was related to the cost associated with word recognition accuracy performance under dual task conditions. However, these relationships did not extend to older adults or to the data obtained when the speech recognition tasks were performed audiovisually. Further research is required to determine what cognitive factors underlie listening effort – especially for older adults.

Depuis une vingtaine d’années, la littérature scientifique traitant de la capture attentionnelle a mis en évidence, à l’aide de paradigmes expérimentaux testés en laboratoire, un certain nombre de processus attentionnels fondamentaux. Bien que les résultats obtenus « en laboratoire » à partir de stimuli visuellement « simples » méritent encore d’être investigués, depuis quelques années se pose la question de la « transposabilité » de ces observations à des objets et des situations issus du monde réel. Les phénomènes observés en laboratoire à partir d’un matériel visuellement simple sont-ils transposables à des situations, complexes, de la vie quotidienne ? Afin de répondre à cette question, nous avons créé et testé différentes conditions proches de celles du monde réel,notamment en expérimentant en situation de double-tâche, en utilisant un matériel visuellement complexe extrait du monde réel (c.-à-d. des photographies de conduite automobile), en faisant varier la fréquence d’apparition de l’élément distracteur ou bien encore en testant une nouvelle caractéristique du distracteur, la dimension sémantique. Nos résultats révèlent les conditions d’apparition du phénomène de capture attentionnelle dans des situations s’approchant de celles du monde réel. Nous avons tout particulièrement détaillé dans cet ouvrage le cas de l’effet de capture attentionnelle contingente, phénomène majeur et robuste de la capture attentionnelle, y compris dans des situations visuellement complexes. / During the last two decades, studies about attentional capture revealed some major basic attentional processes by using several experimental paradigms. While further investigations need to be conducted by using simple visual stimuli, a raising question concerns the possibility to generalize laboratory findings to much more complex real-world situations. Indeed, basic attentional capture studies usually use simple stimuli while real-world displays are generally rich in visual information. To answer this issue, we conducted several experiments under close to real-world conditions, such as testingdual task situations, using complex visual stimuli from real-world situations (e.g. driving-scenes photographs), modulating the distractor frequency or testing attentional capture at a semantic and conceptual dimension. Our results revealed the conditions in which the attentional capture phenomenon occurs in close to real-world situations. We particularly discussed in our work the contingent attentional capture phenomenon which appears to be a strong and robust effect, in both laboratory and close to real-world situations.

Female athletes exhibit three- to six-fold greater incidence of noncontact anterior cruciate ligament (ACL) injury relative to their male counterparts. The increased risk appears to stem from interactions between several risk factors, that can roughly be categorized as anatomic, biomechanical, hormonal, and neuromuscular. Neuromuscular risk factors have recently gained a greater focus, and include differences in the timing and magnitude of activation of lower extremity and trunk musculature. In addition to neuromuscular risk factors, the incidence of ACL injury is not evenly distributed across the menstrual cycle, suggesting that hormonal fluctuations may influence neuromuscular control. Finally, it is known that even well-trained athletes experience decrements in performance and postural control when forced to attend to multiple sensory stimuli, which is common in many sports. PURPOSE: To explore neuromuscular differences in the ways healthy and ACL-injured women respond to a secondary task requiring fine motor control and sustained mental focus (typing task). Our investigation encompassed three broad aims. First, we sought to determine whether ACL-injured individuals demonstrated similar reflex profiles to healthy individuals, as well as to determine whether the ACL-involved limb was similar to its uninvolved counterpart. Our second aim was to determine whether the typing task resulted in attenuated Hoffmann (H) reflex amplitudes, and to investigate whether any observed changes were similar in healthy and ACL-injured groups. Finally, our third broad aim was to utilize more complex H reflex analysis techniques to determine whether differences in spinal excitability existed at different points in the menstrual cycle. METHODS: Thirty nine recreationally active women (20 with prior unilateral noncontact ACL injury: 24.0 ± 4.5 years; 23.8 ± 4.5 kg•m⁻²; 4.1 ± 2.6 years post-injury; 19 with no history of knee injury: 23.8 ± 4.5 years; 23.1 ± 2.3 kg•m⁻²) agreed to participate, and were tested during days 2-5 (follicular phase) of the menstrual cycle. A sub-set of this original group (n=8; 24.0 ± 4.8 years; 22.0 ± 2.1 kg•m⁻²) also agreed to return for a second testing session 24-96 hours after ovulation (early luteal phase), in order to assess H reflex differences across the menstrual cycle. During each testing session, H reflex testing was used to explore spinal-level control mechanisms of the lower extremity musculature under both Rest and Task conditions. In the control group, the dominant limb was tested (CON-D) while in the ACL group, both the uninvolved (ACL-UN) and involved (ACL-INV) limbs were assessed. Differences between groups (Control vs. ACL) and within-groups (ACL-UN vs. ACL-INV) were explored. RESULTS: At rest, H reflex parameters in ACL-INV were generally similar to ACL-UN and to CON-D. However, differences in presynaptic inhibition were apparent in ACL-INV that imply reduced reflex plasticity. During the typing task, both the Control and ACL groups experienced attenuated H reflex parameters. In the sub-set of participants who were tested twice during the menstrual cycle, a significant increase in presynaptic inhibition was observed during the early luteal phase compared to the follicular phase. CONCLUSION: While individuals with prior ACL injury display similar H reflex profiles to healthy individuals, the ACL-involved limb may demonstrate less reflex plasticity in response to environmental changes. This lack of plasticity may potentially increase the risk of re-injury. In addition, an upper extremity task requiring fine motor control and sustained mental focus attenuates the H reflex in both groups. This attenuation has implications for lower-extremity neuromuscular control in dual-task environments. Finally, the increase in presynaptic inhibition observed during the early luteal phase may provide insight into why ACL injuries are not evenly distributed across the menstrual cycle. / Graduation date: 2012

Falls and their consequences among older people are a serious medical and public health problem. Identifying individuals at risk of falling is therefore a major concern. The purpose of this thesis was to evaluate measurement tools of balance control and their predictive value when screening for fall risk in physically dependent individuals ≥65 years old living in residential care facilities, and physically independent individuals ≥75 years old living in the community. Following baseline assessments falls were monitored during six months in physically dependent individuals based on staff reports, and during one year in physically independent individuals based on self reports. In physically dependent individuals test-retest reliability of the Timed Up&amp;Go test (TUG) was established in relation to cognitive impairment. Absolute reliability measures exposed substantial day-to-day variability in mobility performance at an individual level despite excellent relative reliability (ICC 1.1 &gt;0.90) regardless of cognitive function (MMSE ≥10). Fifty-three percent of the participants fell at least once during follow-up. Staff judgement of their residents’ fall risk had the best prognostic value for ruling in a fall risk in individuals judged with ‘high risk’ (positive Likelihood ratio, LR+ 2.8). Timed, and subjective rating of fall risk (modified Get Up&amp;Go test, GUG-m) were useful for ruling out a high fall risk in individuals with TUG scores &lt;15 seconds (negative LR, LR- 0.1) and GUG-m scores of ‘no fall risk’ (LR- 0.4), however few participants achieved such scores. In physically independent individuals balance control was challenged by dual-task performances. Subsequent dual-task costs in gait (DTC), i.e. the difference between single walking and walking with a simultaneous second task, were registered using an electronic mat. Forty-eight percent of the participants fell at least once during follow-up. A small prognostic guidance for ruling in a high fall risk was found for DTC in mean step width of ≤3.7 mm with a manual task (LR+ 2.3), and a small guidance for ruling out a high fall risk with DTC in mean step width of ≤3.6 mm with a cognitive task (LR- 0.5). In cross-sectional evaluations DTC related to an increased fall risk were associated with: sub-maximal physical performance stance scores (Odds Ratio, OR, 3.2 to 3.8), lower self-reported balance confidence (OR 2.6), higher activity avoidance (OR 2.1), mobility disability (OR 4.0), and cautious walking out-door (OR 3.0). However, these other measures of physical function failed to provide any guidance to fall risk in this population of seemingly able older persons. In conclusion – Fall risk assessments may guide clinicians in two directions, either in ruling in or in ruling out a high fall risk. A single cut-off score, however, does not necessarily give guidance in both directions. Staff experienced knowledge is superior to a single assessment of mobility performance for ruling in a high fall risk. Clinicians need to consider the day-to-day variability in mobility when interpreting the TUG score of a physically dependent individual. DTC of gait can, depending on the type of secondary task, indicate a functional limitation related to an increased fall risk or a flexible capacity related to a decreased fall risk. DTC in mean step width seems to be a valid measure of balance control in physically independent older people and may be a valuable part of the physical examination of balance and gait when screening for fall risk as other measures of balance control may fail to provide any guidance of fall risk in this population.