Low energy availability (LEA) occurs when an athlete's dietary energy intake is insufficient to support both exercise and normal physiological functions. Prolonged or severe problematic LEA can cause relative energy deficiency in sport (RED-S), a syndrome involving impaired health and sporting performance.
Energy availability is calculated relative to fat-free mass (FFM):
For example, an athlete consuming , expending during exercise, and having of FFM has:
LEA may result from intentional dietary restriction, disordered eating, an eating disorder, increased training without increased food intake, or poor knowledge of fuelling requirements. The body responds by conserving energy and reducing investment in processes that are not immediately essential for survival.
| Concept | Meaning and consequences |
|---|---|
| LEA | The underlying state in which insufficient energy remains after exercise to support normal physiological functions. |
| RED-S | The broader syndrome that may develop from problematic LEA, affecting systems such as reproductive function, bone health, immunity, metabolism, cardiovascular health and psychological health. |
| Performance effects | Reduced endurance, impaired recovery, decreased training response, reduced muscle strength, poor concentration and increased injury risk. |
Consequences often interact: impaired bone formation can increase stress-fracture risk, while suppressed immune function can increase illness and missed training. Early recognition therefore requires attention to dietary intake, training load, recovery, injury patterns and changes in mood or reproductive function.
A common misconception is that RED-S affects only female athletes or is simply the loss of menstruation. It can affect athletes of any sex; menstrual dysfunction is one possible effect, while males may experience reduced testosterone and impaired reproductive function. Not every brief energy deficit produces RED-S; duration, severity and individual susceptibility matter.
Exam technique: For IB SEHS subtopic A.2.2, distinguish the cause from the syndrome: LEA is the energy imbalance, while RED-S describes its wider health and performance consequences. Link inadequate fuelling to at least one physiological effect and one performance effect.