This thesis is presented as an investigation into the movement integration, performance processes and effects of anxiety on the skill acquisition of individuals diagnosed with Down syndrome or DS as it will be referred to in this thesis (a full description of this genetic condition is presented in the thesis introduction). The investigation of several features of motor control and performance pressure in individuals with DS is carried out through several related research projects which will be rationalised and outlined throughout. In both everyday life and in sporting situations, people are required to perform tasks quickly and accurately and these tasks vary in complexity. Some of these actions consist of one segment movements (e.g. turning on a light switch), whilst other actions have multiple segments (e.g. making a cup of tea) and the need to be fast whilst maintaining a high degree of accuracy is very important. Therefore understanding the basic principles behind these actions in individuals with DS and how performance pressure may affect speed and accuracy of movements will not just have theoretical implications, but also practical importance such as designing practice protocols to enhance functional independence. Motor skill control, learning and performance are imperative for everyday activities such as signing one’s name, dressing oneself and personal hygiene. The capability to perform these motor skills with or without support is of the upmost importance for individuals with DS. Discovering new channels of enhancement in motor skill control, learning and performance for individuals with DS is extremely important and vital step on the pathway to improving functional independence for personal and professional gains. 1.2 Outline of thesis This thesis attempts to investigate the issues relating to the programming of movements and the affects of anxiety on the motor skill learning of individuals with DS. The first experimental chapter focuses on the underlying mechanisms responsible for the planning, control and integration of multiple target aiming extension movements in individuals with DS. The aim of this chapter was utilise to the One Target Advantage (OTA) phenomenon in sequential extension movements to see if individuals with DS utilise similar movement planning and control strategies to typically developing (TD) individuals and individuals with an undifferentiated intellectual disability (UID). The second experimental chapter was designed to further understand the control of multiple directional movement actions in the DS population and the possible central and peripheral movement deficits. This experimental chapter aims to examine both the directional requirement of the second movement together with the effects of practice on the OTA phenomenon in persons with DS. Specifically, as in the first experimental chapter, we compare single-target movements with two-target extension sequences when the two-target responses are performed with a single arm and when there is a switch between the arms used to execute the first and second movement segments. However, in this chapter we also include sequences where the second movement in the sequence requires a reversal in direction to that of the first movement. The purpose of the third experimental chapter was to investigate the effects of environmental characteristics outside of those associated with the number of targets within a sequence. Specifically, the effects of performance pressure on the speed and accuracy of the movements of persons with DS. 1.3 Thesis format This thesis consists of a review of the literature, three research papers and a general discussion. All three manuscripts were written as stand-alone research articles and have been or are currently being prepared to be submitted for publication in international disability research journals. For consistency, all manuscripts have been written in the style of the American Psychological Association Publication Manual (Deckers, 2001) and the current recommendations adopted by the School of Sport, Health and Exercise Sciences, Bangor University for thesis preparation. For this purpose, all illustrations are numbered consecutively and citations are included in a single section at the end of this thesis. For ease of reading, all abbreviations are defined at their first appearance within each chapter of the thesis. Any contribution of co-authors is detailed in the ‘acknowledgements’ section of this thesis. All experimental chapters of this thesis are independent but linked, therefore at times there may be a necessary overlap in content between chapters.