This dissertation investigated the effects of iron depletion without anemia (IDNA) on physical performance and training in female collegiate rowers. In a cross sectional study, 165 rowers were screened for iron status at the beginning of a competitive season (10% anemic, 30% IDNA, Hgb>12.0, Hgb>12.0 g/dL and ferritin <20 [MICRO SIGN]g/L). IDNA rowers reported 2K times that were 21 seconds slower compared to rowers with normal iron status (p=0.004). During the first week of training, 48 rowers (n=24 IDNA) had their physical performance assessed (VO2peak, 4K time, gross energetic efficiency) and recorded their training regimen. Compared to rowers with normal iron status, IDNA rowers trained ~10 minutes/d less (p=0.02), and had a 0.3 L/min lower VO2peak (p=0.03). Less highly-trained rowers with poor iron status had a lower VO2peak (-0.32 L/min, p=0.02), and were less energetically-efficient (-1.7%, p=0.09) compared to more highly-trained rowers with poor iron status. In a randomized controlled trial, 43 rowers received 100 mg/d FeSO4 (n=22) or placebo (n=21) for 6 weeks, and completed daily training logs. Iron status, performance, and training quality were assessed at baseline and 6 weeks. Thirty-one rowers (n=15 iron, 16 placebo) completed the trial. Rowers supplemented with iron improved their body iron stores (log ferritin, total body iron, p=0.07), and those with most depleted stores at baseline improved the most. Blood lactate concentration during the first 2000m of a 4K TT and 5 min post-recovery was significantly lower in the iron group (p<0.01), and rowers in the iron group had a greater improvement in work efficiency (p=0.15) compared to placebo. Additionally, the energetic efficiency of those rowers with poorer baseline stores (ferritin <20 [MICRO SIGN]g/L) benefitted more from supplementation. Finally, rowers in the iron group had an improved training quality score (p=0.03) compared to those in the placebo group. We conclude that iron status should be screened at the beginning of a training season, and that iron supplementation (~15 mg iron/d) improves iron stores in female rowers during training, especially in the most deplete. The iron status of those with marginal/low stores should be monitored to prevent detrimental effects on training and performance.