Abstract
Much of our daily life, including our physical activities (PA) and our sedentary behaviours (SB), is organized around habitual behaviours that have acquired a high degreeof automaticity. This thesis adopts a multidimensional approach to automaticity (i.e., lack ofintentionality, difficulty in controlling behaviour, efficiency), with the main objectives of: (a)demonstrating validity of measure instruments in French and Spanish, applied to PA and SB,(b) examining the extent to which these properties predict the adoption of PA and SB, (c)studying the evolution of these properties during the adoption of a new behaviour (practiceof a new PA), and following an intervention (reduction of SB at work). To this end, aprogramme of 8 empirical studies has been carried out. The main results indicate that (a) theFrench and Spanish versions of the Generic Multidimensional Scale of Automaticity havesatisfactory psychometric properties (internal validity, external convergent and predictivevalidity); (b) automatic properties contribute significantly to the amount of PA and SB, evenwhen they are assessed by accelerometers; (c) the level of lack of control increases over timewhen a new PA is adopted, and the level and changes in automaticity are influenced by thecharacteristics of the PA performed; (d) lastly, an intervention targeting automatic processesis effective in decreasing sedentary time at work.Key-words: automaticity, triggering, lack of control, efficiency, mode of transport, sitting,health