Iron deficiency (ID) is the most common nutrient deficiency in the United States, affecting 13% of pre-menopausal women, and approximately 30% of physically-active women (1, 2). Iron deficiency anemia (IDA) is clinically defined as hemoglobin (Hgb) less than 12.0 g/dl. Iron depletion without anemia (IDNA), or low iron stores, is defined as Hgb greater than 12.0 g/dl and serum ferritin (sFer) less than 20.0 µg/L. Female athletes are at higher risk of IDNA due to their menstrual status, poor dietary intake, and high training volume and intensity (3). Consequences of IDNA that may be relevant to athletes include reduced work capacity, endurance, and energetic efficiency (4-6); and increased local muscle fatigue (7). The mechanism by which IDNA affects endurance and physical performance remains unclear, and the functional consequences of IDNA are not fully understood in trained individuals, as studies to examine these relationships have been underpowered (8, 9).