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.

There is emerging evidence for the potential of occupational back-support exoskeletons (BSEs) to reduce physical demands, and thereby help control/prevent the risk of overexertion injuries associated with manual material handling. However, it is important to understand whether BSEs also introduce any unintended safety challenges. One potential risk associated with BSE use is increased risk of falls, since their extra weight, rigid structure, and external hip extension torque may increase demands on the postural control system. However, there is currently limited evidence on whether, and to what extent, BSE use alters postural stability and/or fall risk. The primary goal of this work was to understand the effects of exoskeleton use, and quantify the effects of exoskeleton design parameters, on balance and postural stability, with a focus on passive BSEs used for repetitive lifting work. A comprehensive evaluation of BSE use was performed under controlled laboratory conditions, focusing on three classes of human activity that form the basis of maintaining postural balance in diverse real-life scenarios: maintenance of a specified posture, voluntary movement, and reaction to an external perturbation. The first study demonstrated that during quiet bipedal stance, BSE use increased median frequency and velocity of the center of pressure in the anterior-posterior direction. In the second study on level walking, BSE use caused an increase in gait step width and gait variability, and decrease in the margin of stability. BSE use with high supportive torque led to adapted gait patterns in early-stance phase. Hip range of motion and peak hip flexion velocity also decreased, and participants exhibited different strategies to increase mechanical energy for propelling the leg in late-stance phase: these effects increased with increasing torque applied by the exoskeleton. In the final study, BSE use did not alter the maximal lean angle from which individuals could successfully execute single step balance recovery, following a forward loss of balance. However, several recovery responses were negatively affected by BSE use, including increased reaction time, impeded hip flexion, and reduced margin of stability in the high-torque condition. This is the first systematical investigation to quantify the effects of passive BSEs with multiple supportive torque levels on balance and postural stability. While exoskeleton effects on static balance were minimal, more substantial changes in gait spatiotemporal parameters, hip joint kinematics, and dynamic margins of stability were observed in the later studies. Our results indicate that postural stability deteriorated with exoskeleton use in dynamic conditions, and provide mechanistic insight into how stability is altered by different exoskeleton design factors such as added mass, restricted range of motion, and external hip extension torque. While our results are suggestive of increased fall risk, especially in the high-torque condition, fall risk in real life is moderated by a complex combination of individual and environmental conditions. Future work should consider more complex, realistic tasks and also include a more diverse sample that is studied under longer exposure durations, to further elucidate these findings. Our characterizations of a wide variety of postural responses as a function of exoskeleton torque settings are expected to contribute to improving both design and practice guidelines to facilitate the safe adoption of BSEs in the workplace. / Doctor of Philosophy / Occupational back-support exoskeletons (BSEs) – wearable mechanical systems designed to support, augment, and/or assist back extension – are expected to serve as an alternative workplace intervention to control and prevent overexertion injuries related to manual material handling tasks. While recent studies have shown the beneficial effects of BSE use in terms of physical load reduction on the low back, some concerns have also been raised on unexpected or unintended effects of exoskeletons. One potential risk associated with exoskeleton use is increased risk of falls, since a BSE's extra weight, rigid structure, and external hip extension torque are expected to place increased demands on the postural control system. Increase in fall risk is a critical safety concern, as occupational falls are a serious problem in terms of injuries, medical/industrial cost, and lost work time. However, there exists limited evidence on whether the use of a BSE alters postural stability and/or increases fall risk. Hence, the goal of our study was to quantify the effects of BSE use on postural stability in various conditions related to real-life scenarios, such as standing balance, walking stability and how one would respond to a loss of balance following an external perturbation. Our results showed that during quiet standing, BSE use slightly increased postural sway. In level walking tasks, BSE use had adverse effects on step length, step width, and dynamic stability. Furthermore, wearing a BSE with high supportive torque led to adapted gait patterns in early-stance phase, whereas participants showed different strategies to increase mechanical energy for propelling the leg in late-stance phase. In the final study investigating single step balance recovery following a forward loss of balance, we found that BSE use negatively affects balance recovery, mainly by impeding hip flexion. Thus, our work suggests that exoskeleton use can deteriorate balance and/or postural stability in situations of static standing, voluntary walking, and reacting to an external perturbation, thereby potentially leading to an increase in fall risk. These effects may be more pronounced among specific population sub-groups such as older workers, and may also affect individuals more severely under conditions of stress or fatigue. Hence, future studies must include more rigorous testing of BSE use using a variety of challenging and realistic scenarios, and also include more diverse population samples. The findings from this work are expected to contribute to improving design and practice guidelines to facilitate the safe adoption of BSEs in the workplace.