Aim To identify how activity and mobility lead to pressure ulcer development, using two objective assessments, one for mobility and one for early pressure ulcer detection. Methods 150 older persons from long-term settings were followed up for 20 days, using an observational, quantitative, prospective study design. The study was conducted in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology statement. Visual skin assessment and sub-epidermal moisture assessments were undertaken daily. Activity was measured using the Braden subscale. Further, a mobility profile of the participants was identified using a piezoelectric motion sensor which provided a "movement score" (mean number of movements/hour). Movement scores from 22 healthy participants were also measured to better understand the mobility profile in a healthy population. Results Pressure ulcer incidence using visual skin assessment was 12.7% (low movers = 6.7%; high movers = 6%) and 78.7% using sub-epidermal moisture assessment (low movers = 40.0%; high movers = 38.7%). Sub-epidermal moisture assessment detected pressure ulcers on average 8.2 days before they appeared visually on the skin's surface. Pressure ulcer detection was 25 times greater using sub-epidermal moisture compared to visual skin assessment. Considering the results of the "movement level" assessment using the motion sensor technology, of all those who were determined to be immobile by Braden, 18.8% were assessed as high movers. Discussion & Conclusion Pressure ulcers occurred both in low and high movers, which was unexpected as a similar finding has not been previously reported in the literature. Relevance to clinical practice The traditional focus on low movers/immobile individuals may detract from the identification of those making an abnormally high frequency of unsafe movements. Pressure ulcer assessment can be enhanced through a combination of sub-epidermal moisture assessment and visual skin assessment, and through the identification of both individuals with impaired mobility and those abnormally high movements, such as among those who are agitated.