Bilateral upper-limb coordination is an important ability for our living independency, since most of our daily tasks, such as lifting a box or using knife and fork, require the simultaneous use of both arms (Waller et al., 2006). However, bilateral coordination decline has been observed in both healthy aging and neurological groups (Pollock et al., 2014; Maes et al., 2017) , which often results in decreased quality of life (Broeks et al., 1999; Franceschini et al., 2010). Therefore, this dissertation sought to understand the characteristics and mechanisms of bilateral coordination and its impairments. The two fundamental bilateral movements in human upper limbs, i.e., in-phase (homologous muscles from bilateral arms activate simultaneously) and anti-phase (different muscle groups from bilateral arms activate simultaneously) movements, have been found to show different characteristics in behavioral and neural measurements (Swinnen and Wenderoth, 2004). Behaviorally, anti-phase movements are found to be performed with lower movement accuracy and higher phase variability between hands compared to in-phase movements (Wuyts et al., 1996; Byblow et al., 2000; Pollok et al., 2007). On the neural level, fMRI studies demonstrated that the left hemisphere shows larger task-related BOLD signal changes compared to the right hemisphere during in-phase movements (Aramaki et al., 2006), while the BOLD signal changes between the two hemispheres are similar during anti-phase movements (Walsh et al., 2008). These results suggest a left-dominated control of in-phase movements. However, a critical limitation in the literature is the lack of causal evidence supporting hemispherical specialization in bilateral coordination. Therefore, it is unclear whether the observed behavioral differences between anti-phase and in-phase movements were truly due to distinct hemispheric control. Another limitation of the literature is the design of existing paradigms. While most of our daily activities involve movements engaging multiple joints at the same time (Keenan et al., 2006; Murphy et al., 2006), previous studies mostly investigated single joint movements (e.g. index finger tapping, forearm pronation-supination). Contrary to single joint movements, bilateral movements engaging multiple joints require not only inter-limb coordination, but also additional intra-limb coordination. Therefore, it is unclear whether the previous findings from single joint movements could be directly applied to multiple joint movements. In this dissertation, we used a bilateral coordination paradigm involving both shoulder and elbow joints to investigate the neural mechanisms behind bilateral coordination and its decline. We designed three studies focusing on 1) the differences between bilateral in-phase and anti-phase movements from a human motion perspective, 2) how aging affects different bilateral coordination patterns and its neural correlates, as well as 3) how lesioned hemisphere affects bilateral coordination impairments and whether distinct rehabilitation treatments are needed after a left or right hemispheric stroke. In Study 1, we examined the two basic bilateral coordination modes, in-phase and anti-phase movements, in healthy young right-handed participants. We used a bilateral circle drawing task involving both shoulder and elbow joints. During the movements, we measured participants’ hand positions with high temporal and spatial precision, and developed intra-limb and inter-limb measures to differentiate movement characteristics during the two basic movement modes. For intra-limb coordination, we quantified trajectory variability of each hand during the movements. For inter-limb coordination, we computed the phase synchronization between hands. We found that intra-limb coordination was worse in the non-dominant hand during anti-phase compared to in-phase movements. In contrast, intra-limb coordination in the dominant hand did not differ between anti-phase and in-phase movements. Second, participants showed worse inter-limb synchronization during anti-phase compared to in-phase movements. Moreover, we examined the hand acceleration profile of both hands, and found that participants’ bilateral hands accelerated and decelerated in an in-phase manner during in-phase movements. In contrast, the acceleration and deceleration of the two hands were unrelated during anti-phase movements. These inter-limb acceleration profiles support the idea of differential neural mechanisms behind bilateral anti-phase and in-phase movements: during in-phase movements, the hands are governed by a common neural generator, while during anti-phase movements, the two hands are controlled by both hemispheres more independently. Taken together, Study 1 showed that the current experimental setup is able to differentiate the performance between bilateral in-phase and anti-phase movements engaging multiple joints. Therefore, we used the same paradigm combined with electroencephalography (EEG) to examine the presumed decline of bilateral coordination in aging. In Study 2, we investigated the effect of aging on the two basic bilateral movement modes. We used intra- and inter-limb measures as the behavioral measures, and EEG as a neural measure. Behaviorally, we found that older adults only showed significant impairments in anti-phase movements, but not in-phase movements, compared to young adults. On the neural level, we found that older adults showed different neural responses during anti-phase and in-phase movements compared to young adults. Specifically, during in-phase movements, young adults showed a more pronounced decrease of alpha power (8-12 Hz) over the left compared to the right hemisphere, while older adults showed similar levels of alpha power decrease over both hemispheres. Furthermore, in the older adults, we found a marginal correlation between the change in alpha power over the right hemisphere and the behavioral performance, which indicated a compensatory brain response. As for the anti-phase movements, we found that participants with stronger directional inter-hemispheric connectivity in the beta band (15-25 Hz) showed worse behavioral performance, and this effect was more pronounced in the older adults. This result implies that a balanced inter-hemispheric contribution is essential for executing a successful anti-phase movement. Our findings therefore show that the two hemispheres are differentially involved in the two basic bilateral coordination modes. These different neural characteristics may explain the distinct decline patterns of in-phase and anti-phase movements in older adults. However, causal evidence to support hemispherical specialization is needed to confirm our findings. Therefore, we conducted Study 3, where we used stroke as a lesion model to examine the influence of the lesioned hemisphere on bilateral coordination. In Study 3, we examined the bilateral coordination ability in patients with left (LHS) and right hemispheric stroke (RHS), as well as healthy controls. Given that healthy young participants show a left-dominant control in in-phase movements in Study 2 and in the previous literature (Aramaki et al., 2006; Maki et al., 2008), we expected that LHS patients would display a more pronounced impairment of in-phase movements compared to RHS patients. In contrast, since anti-phase movements require a more balanced inter-hemispheric contribution as shown in Study 2, and RHS patients show larger inter-hemispheric inhibition compared to healthy participants and LHS patients (Lewis and Perreault, 2007b), we expected that RHS patients would show more impairment in anti-phase movements compared to LHS patients. As predicted, we found that patients with RHS patients exhibited greater impairment during anti-phase movements (both intra- and inter-limb parameters) and LHS patients showed greater impairment during in-phase movements (intra-limb parameters only). Though LHS patients did not show greater impairment in inter-limb coordination during in-phase movements compared to RHS patients, our regression analysis revealed that only LHS patients swapped hand dominance during the task. We interpreted this result as a compensatory mechanism whereby bilateral in-phase movements in the LHS group switched from a left-dominated cortical control to a right-dominated cortical control. Our findings not only provide causal evidence for hemispheric specialization in bilateral movement coordination, but also characterize the differential impairments in bilateral coordination after a left or right hemispheric stroke. Taken together, this dissertation highlighted differential neural control processes involved in bilateral in-phase and anti-phase movements, and demonstrated how these distinct mechanisms lead to impaired bilateral coordination in aging and stroke. The present results could therefore advance the development of therapeutic strategies that seek to counteract bilateral coordination decline, such as differential treatment for patients with left and right hemispheric lesions, or the use of noninvasive brain stimulation at a target hemisphere.:List of abbreviations List of figures List of tables Chapter 1. General introduction 1.1. Introduction 1.2. Bilateral coordination in human upper extremities 1.3. Age-related motor decline 1.4. Stroke-induced motor impairments Chapter 2. Rationale of the Dissertation Chapter 3. Study I: Human motion characteristics during bilateral in-phase and anti-phase movements 3.1. Introduction 3.2. Materials and methods 3.3. Results 3.4. Discussion 3.5. Conclusion Chapter 4. Study II: The effect of aging on bilateral coordination 49 4.1. Introduction 4.2. Materials and methods 4.3. Results 4.4. Discussion 4.5. Conclusion Chapter 5. Study III: Effects of lesioned side on bilateral coordination after strokes 5.1. Introduction 5.2. Materials and methods 5.3. Results 5.4. Discussion 5.5. Conclusion Chapter 6. General discussion 6.1. Summary of research 6.2. Contributions and clinical implications 6.3. Outlook for future research Chapter 7. Summary of the dissertation References Appendix Appendix 1. Supplementary information for study 1 Appendix 2. Supplementary information for study 2 Appendix 3. Supplementary information for study 3 Appendix 4. Declaration of authenticity

Thesis (M Sport Sc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Many children experience developmental problems without being aware thereof. In a school setting these developmental delays mostly remain unnoticed and are scarcely remediated sufficiently, if at all. Children with developmental deficits often experience movement difficulties and are labelled as clumsy, sloppy or having two left feet. The development of, and proficiency in specific motor skills have been found to play a critical role in the participation of physical activity in children, as well as the maintenance of health and well-being later in life, when entering adulthood. There are, however, countless other factors that affect the optimal development of motor skills and physical activity participation. One such factor is ascribed to instances where children experience problems associated with their environment or the circumstances in which they grow up. Poor socio-economic circumstances and a culturally poor environment, lacking sufficient developmental opportunities, may hinder a child‟s motor skills development and skill learning to such an extent that they cannot reach their full developmental potential. Research suggests that the school environment can provide ample opportunity for the development of motor skills and that all schools should consider implementing motor skills development programmes during the Physical Education (PE) time slots. The mastery of motor skills may influence and benefit the participation in various school sports and may also enhance the ability of children to learn and master new and more complex movement skills within and outside the classroom environment. Thus, due to the fact that children spend a great part of their day at school and in the classroom setting, teachers, especially those facilitating PE, have the opportunity to play a vital role in the acquisition and mastery of important motor skills and subsequently affect the physical activity and developmental future of children. The purpose of this study was to design and implement a motor skills development programme to improve the balance and bilateral coordination of children between the ages of 10 and 12 years in the Stellenbosch region. Two existing classes, from a previously disadvantaged school, were recruited and randomly selected as an experimental (n=35) and control group (n=32). The children completed the Short Form as well as all the Long Form activities for the balance and bilateral coordination subtests of the Bruininks-Oseretsky Test of Motor Proficiency-2 (BOT-2). This was done to provide an overview of the overall motor proficiency and more specifically the level of balance and bilateral coordination. A 12-week motor skills development programme, with a specific focus on balance and bilateral coordination, was designed and implemented by the researcher. The effect of this programme was determined by statistically analysing and comparing the pre- and post-test results with the use of Statistica 2010. The main findings of this study indicated that the intervention programme had a positive, although not statistically significant, effect on the overall motor proficiency and balance and significantly improved bilateral coordination. This study suggests that some of the children, between the ages of 10 and 12, from a previously disadvantaged school in the Stellenbosch region and with access to an established school PE programme, experienced movement difficulties. Consequently, there is great room for improvement and motor skill development in these children. This study can, therefore, be a stepping stone into future research regarding further motor skills research in primary school children, the implementation of expanded motor skills intervention programmes and to improve all the motor skills as opposed to selected motor skills as in this study. / AFRIKAANSE OPSOMMING: Ontwikkelingsprobleme word, sonder dat ʼn mens daarvan bewus is, deur vele kinders ervaar. In die skool-omgewing bly hierdie ontwikkelingsagterstande meestal ongesiens en word min kinders, indien enige, voldoende geremedieer. Kinders met ontwikkelingsagterstande ervaar gereeld bewegingsprobleme en word as lomp, slordig of as iemand met twee linkervoete beskryf. Daar word beweer dat die ontwikkeling van, en vaardigheid in, spesifieke motoriese vaardighede van kinders ʼn kritieke rol in hul deelname aan fisieke aktiwiteit, asook die onderhoud van gesondheid en welstand tydens volwassenheid, speel. Daar is egter talle ander faktore wat die optimale motoriese ontwikkeling en fisieke aktiwiteit deelname van kinders kan beïnvloed. ʼn Voorbeeld van so ʼn faktor word toegeskryf aan gevalle waar kinders probleme, wat met hulle omgewing of die omstandighede waarin hul grootword geassosieer word, ervaar. Swak sosio-ekonomiese omstandighede en ʼn kultureel-arme omgewing, wat tekort skiet aan voldoende ontwikkelingsgeleenthede, mag die motoriese ontwikkeling en die aanleer van nuwe vaardighede tot so ʼn mate inhibeer dat kinders nie in staat is om hulle volle ontwikkelingspotensiaal te bereik nie. Navorsing dui daarop dat die skoolomgewing vele geleenthede vir die ontwikkeling van motoriese vaardighede kan bied en dat daar onderneem moet word om motoriese vaardigheid-ontwikkelingsprogramme tydens Liggaamlike Opvoeding (LO) periodes te implementeer. Die bemeestering van motoriese vaardighede mag die deelname aan verskeie skoolsporte beïnvloed en bevoordeel, asook die vermoë om nuwe en meer komplekse bewegingsvaardighede binne en buite die klasomgewing aan te leer en te bemeester, bevorder. Dus, aangesien kinders ʼn groot gedeelte van hul dag by die skool en in ʼn klasomgewing deurbring, het onderwysers, veral die wat LO fasiliteer, die geleentheid om ʼn noodsaaklike rol in die aanleer en bemeestering van belangrike motoriese vaardighede, en vervolgens fisieke aktiwiteit, asook die toekomstige ontwikkeling van kinders te beïnvloed. Die doel van hierdie studie was om ʼn motoriese vaardigheid-ontwikkelingsprogram, wat balans en bilaterale koördinasie bevorder, vir 10 tot 12-jarige kinders in die Stellenbosch omgewing te ontwerp en implementeer. Twee bestaande klasse vanuit ʼn voorheenbenadeelde skool was gewerf en lukraak verkies as ʼn eksperimentele- (n=35) en kontrolegroep (n=32). Kinders het die kort vorm- asook al die lang vorm-aktiwiteite vir balans en bilaterale koördinasie sub-toetse van die Bruininks-Oseretsky Test of Motor Proficiency-2 (BOT-2) voltooi. Hierdie toetse is afgelê om ʼn oorsig van die algehele motoriese vaardigheidsvlak, en meer spesifiek die vlak van balans en bilaterale koördinasie, te bepaal. ʼn 12-week motoriese vaardigheid-ontwikkelingsprogram, met ʼn spesifieke fokus op balans en bilaterale koördinasie, is deur die navorser ontwerp en geïmplementeer. Die effek van hierdie program is bepaal deur die pre- en post-toets resultate met behulp van Statistica 2010 statisties te analiseer en vergelyk. Die primêre bevindinge van hierdie studie dui daarop dat die intervensieprogram ʼn positiewe, alhoewel nie statisties beduidende, effek op die bevordering van algehele motoriese vaardigheidsvlak en balans, asook ʼn statisties beduidende effek op bilaterale koördinasie gehad het. Hierdie studie dui daarop dat kinders, tussen die ouderdomme van 10 en 12, vanuit ʼn voorheenbenadeelde skool in die Stellenbosch omgewing en wat toegang tot ʼn gevestigde LO program het, steeds bewegingsprobleme ervaar. Dus, is daar groot ruimte vir die verbetering en ontwikkeling van motoriese vaardighede by hierdie kinders. Hierdie studie kan dus as ʼn beginpunt vir toekomstige navorsing in verdere motoriese vaardigheids-navorsing van laerskool kinders, die implementering van uitgebreide motoriese intervensieprogramme, asook die bevordering van alle motoriese vaardighede in vergelyking met geselekteerde motoriese vaardighede soos in die huidige studie dien.

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