Immobility – i.e. no travel outside the home in a 24-hour day – is an important issue because it concerns a large part of the population and tends to recur frequently, as our results show. Two questions related to immobility have been particularly highlighted in the literature: firstly, whether immobility is an artefact of travel surveys; secondly, whether it corresponds to an extreme form of low mobility. In light of the literature review and levels of immobility observed, these two questions seem to be minor, particularly in relation to the activity of individuals, which remains the main factor in immobility. By using Structural Equation Modeling to process UK National Travel Survey data, this work has explored the individual variability of trips as a constituent element of immobility for employees and retirees. The link between immobility and variability manifests itself in two ways in our results. Firstly, immobility is associated with activities that are less constrained in time and space, as is the case with the lower frequency of travel for work and support. Secondly, there are rebound effects on mobile days, with more frequent trips for grocery/medical motives in particular, when there is an episode of immobility during the week.