Our lab has previously reported the effects of iron deficiency on physical performance in untrained, IDNA women adapting to an aerobic training program. Hinton et al (5) showed that the effect of iron supplementation on physical performance was mediated by changes in iron status (sFer), and concluded that IDNA reduces the potential benefits of aerobic training on endurance. In that study, subjects who were supplemented with iron for 6 weeks during aerobic training improved their time to complete a 15-km cycling time trial by 3.4 min compared to 1.6 min in the placebo group (p<0.05). Given these convincing results, the study of highly-trained competitive female athletes training at a high volume and intensity was warranted. We expected these significant effects to persist in competitive collegiate athletes. However, we expected the magnitude of these effects to be somewhat less due to collegiate athletes' advanced training status, and thus a smaller margin of improvement in performance due to response of increased body iron stores. The goal of the proposed study was to determine whether marginal iron deficiency (IDNA) impairs the ability of moderately- to highly-trained female collegiate rowers to increase their training quality, as well as their performance in response to 6 weeks of iron supplementation, in addition to their usual endurance training.