The goal of this clinical trial is to understand how the body responds to short-term, severe low energy availability (LEA) in healthy, weight-bearing endurance athletes aged 18-45 years old. LEA describes a mismatch between an individual's dietary energy intake and the energy cost of their commitments for training and competition. The main questions this trial aims to answer are:
1. What effect does short-term, severe LEA have on sleeping metabolic rate?
2. What effect does short-term, severe LEA have on other body systems identified within the Relative Energy Deficiency in Sport (REDs) Health and Performance Conceptual models?
Researchers will compare a control trial with both a LEA trial achieved through diet restriction and a LEA trial achieved through increased exercise to see if there are differences in the body's response.
Participants will complete three 6-day trials, a minimum of 3-weeks apart, involving:
* Prescribed diet (all food provided)
* Prescribed running and/or cycling exercise
* Two visits to ACU Fitzroy campus for blood tests and exercise testing
* 50 hour stay (two nights and two days) in the ACU metabolic chamber