The definition of relative energy deficiency in sport (REDs) is that low energy availability (LEA) is the cause of a wide range of symptoms that are common amongst athletes. In the current REDs model, low energy availability is depicted at the centre of a wheel with numerous spokes. Each spoke represents a grouping of symptoms or suggested consequences of LEA. Considering LEA is central to the REDs model, this blog asks the question: can we measure LEA?Challenges defining low energy availability