ABSTRACT Endurance competition preparation involves complex psychological, logistical, and sociocultural factors. This study investigated the pre-race nutrition practices of female endurance athletes, by applying a newly developed extended Theory of Planned Behaviour, including behavioural execution to the framework to capture real-world influences (ETPB-X). Using a convergent mixed-methods design, 27 female triathletes competing at the 2024 IRONMAN World Championships completed questionnaires, 48-h food diaries, and semi-structured interviews before and after the race. Quantitative data ( n = 23) were analysed for energy and macronutrient intake, whereas qualitative data were thematically coded using the conceptual ETPB-X framework, incorporating attitudes, subjective norms, perceived behavioural control (PBC), utilitarian drivers, and behavioural execution. Only 26% (6/23) of athletes achieved carbohydrate loading guidelines (8-12 g·kg -1 body mass (BM)·day -1 ), with an overall mean intake of 6.4 ± 2.1 g·kg -1 BM. Higher carbohydrate intake correlated with faster finish times ( r = -0.50, p = 0.035), whereas fibre intake was positively associated with gastrointestinal (GI) symptom severity ( r = 0.85, p < 0.001). Qualitative findings revealed that adherence to diet plans was influenced by PBC, travel logistics, emotional regulation, and athlete identity. This study provides a novel application of the ETPB-X framework to pre-race nutrition in female endurance athletes. Athletes often under-achieve carbohydrate loading targets despite awareness, with success determined as much by psychosocial and contextual factors as by knowledge. Practically, enhancing PBC, improving planning/preparation, and delivering clear goal-aligned education may bridge the intention*behaviour gap. Integrating behavioural frameworks into performance nutrition offers a pathway towards more effective athlete-centred interventions.
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