If we spend an hour working out, that’s one hour less during our day that we can potentially spend being sedentary.

But we may, consciously or not, find other opportunities during the day to move less, undermining our best intentions and the potential health benefits of the exercise, according to an interesting new study of how people use their time, minute by minute, on days when they exercise and when they do not. Time management is always tricky, involving constant trade-offs, not all of which are voluntary or even conscious.

If we shop for groceries, for example, we may not have enough time later to visit the gym. Or if we binge-watch sitcoms, those accumulated hours of sitting cannot be devoted to any other activity.

But while many past epidemiological studies and experiments have looked at how we apportion our days — how many hours we spend, on average, sleeping, sitting, working, eating, exercising and so on — few have closely examined how we balance one activity against another and the extent to which some activities elbow others aside.