Background: As a component of the physical education curriculum, Health-Related Exercise (HRE) has been subject to intensive critique in terms of its status, organisation and expression in schools. Concerns and questions have also been raised about physical education teachers' professional knowledge of health and the extent to which HRE features within their continuing professional development (CPD) profiles. Aims: This paper presents findings from a research project which investigated English secondary physical education teachers' experiences, views and understandings of HRE and related CPD (HRE-CPD). It also draws upon existing research, sociological theory and the concept of "philosophies" in order to present an explanatory model (the HRE conundrum) which may help the physical education profession better understand the often problematic organisation and expression of HRE in schools. Methods: The research was undertaken via a two-phase, mixed-method study. Phase one consisted of a survey questionnaire, which was completed by 112 secondary physical education teachers. Phase two involved semi-structured interviews with 12 teachers from the phase one sample. Results and discussion: The survey revealed that approximately half of the physical education teachers who participated in the study reported to have had no prior professional experience of HRE before teaching it, and most had not taken part in any CPD related to health and lifelong physical activity in the previous 12 months (80%) or 3 years (70%). Further, the teachers' responses to both the survey and the interviews suggest that HRE within physical education continues to be characterised by incoherence and misunderstanding. The interdependent and emerging themes which provided an explanation for this include: i) the tendency for the teachers' philosophies to bear the hallmark of sport- and fitness-related ideologies; ii) the teachers' often narrow understandings of HRE and how best to teach it; iii) the teachers' largely misguided confidence in their ability to teach HRE; iv) a general lack of teacher engagement with any CPD related to health and lifelong physical activity. Conclusions: With regard to HRE, both the "I" in ITE and the "C" in CPD appear to have been overlooked, and this inevitably raises questions about the degree to which teachers are prepared to teach this area of the curriculum. It is argued that now is the time for action, and that relevant, effective and ongoing CPD has the capacity to address the problematic teaching of HRE and develop in teachers the knowledge, skills and understandings that are necessary to promote healthy, active lifestyles among young people. Many physical education teachers are not engaging in HRE-CPD but in order to disturb common and often narrow understandings of HRE it is arguably necessary. (Contains 9 notes and 2 figures.)