Key Points 1. Sex differences in ultramarathon runners have been demonstrated in a number of areas including the predictors of performance, fatigue resistance, susceptibility to injury and illness, and oxidative stress. This indicates that sex-specific approaches to race preparation and recovery could benefit female ultramarathon runners. 2. The evidence base comprises mostly of observational studies, and the level of evidence is generally low. The lack of experimental studies, relatively low number of female subjects, and the heterogeneity inherent in ultramarathon race formats makes it difficult to draw conclusions. Thus, it is not currently possible to formulate evidence-based, sex-specific guidelines for ultramarathon runners. Further interventional studies are required to examine sex differences in the physiological responses to different training, nutrition, and recovery modalities. Furthermore, the effects of these interventions during different phases of the menstrual cycle should be elucidated. Future research should also compare males with both pre- and post-menopausal females, as it is likely that female sex hormones significantly influence many study outcomes. Such research could guide the development of guidelines that could optimise female athlete performance and health.
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