Tissue iron deficiency without anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women.

BACKGROUND We previously showed that iron supplementation significantly improves iron status and maximal work capacity in previously untrained, marginally iron-deficient women with a baseline serum transferrin receptor concentration > 8.0 mg/L. However, the effect of transferrin receptor status on adaptation in endurance capacity after aerobic training in these subjects has not been fully explored. OBJECTIVE Our objective was to examine the effect of baseline serum transferrin receptor status on adaptations in endurance capacity. DESIGN Forty-one untrained, iron-depleted, nonanemic women were randomly assigned to receive either 100 mg FeSO(4) or a placebo for 6 wk in a double-blind trial. All subjects trained on cycle ergometers 5 d/wk for the last 4 wk of the study. Endurance capacity was assessed at baseline and after treatment by using a 15-km time trial conducted on a cycle ergometer. RESULTS Significant treatment effects were observed for time to complete the 15-km time trial, work rate, and percentage of maximal oxygen uptake in subjects with a baseline serum transferrin receptor concentration > 8.0 mg/L. No significant treatment effects were observed in subjects with a normal baseline transferrin receptor concentration. CONCLUSIONS Our findings suggest that, in the presence of overt tissue iron deficiency, iron deficiency without anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women. This impairment can be corrected with iron supplementation.