Higher body fatness is a likely cause of heart disease, but how the harms of body fat compare with the potential benefits of body muscle – another metabolically active body compartment – is unclear. This project aims to use data on body scanning and metabolism from ALSPAC parents in mid-life to determine which aspects of body muscle – whether higher volume based on body scanning or higher strength based on hand grip tests – most strongly influence a set of detailed traits related to adult heart disease susceptibility. It also aims to determine how the cardiometabolic profile of body muscle compares with the profile of body fat. Together with results from complementary studies, these results should help clarify which aspects of body composition are most important to target with limited public resources in order to prevent the onset of heart disease.