Ideas in ecological dynamics have profound implications for designing environments that offer opportunities for physical activity (PA), exercise and play in sedentary individuals. They imply how exercise scientists, health professionals, planners, designers, engineers and psychologists can collaborate in co-designing environments and playscapes that facilitate PA and exercise behaviours in different population subgroups. Here, we discuss how concepts in ecological dynamics emphasise the person-environment scale of analysis, indicating how PA environments might be (re)designed into qualitative regions of functional significance (affordances) that invite health-enhancing behaviours according to individuals' capacities and skills (effectivities).