- There is limited information regarding the optimal hemoglobin level for physical activity and most studies followed relatively few participants. The object of this study was to assess iron storage levels in a population of healthy young males and their impact on physical fitness. Blood samples were drawn from 358 consenting infantry recruits for hemoglobin, iron, ferritin, transferrin, folic acid, and B 12 levels. A detailed medical and nutritional history was noted. Recruits performed a field fitness test including a 2,000-m run. Mean hemoglobin was 13.8 ± 1.0 g/dl. Level of hemoglobin lower than 14 and 12 g/dl were found in 53.6% and 4.5% of the recruits, respectively. Mean ferritin was 57 ± 34 ng/ml, with 15% of the recruits under 25 ng/ml. On multivariate analysis, after adjusting for pre-induction sports activity (P < 0.001), intermediate pre-induction hemoglobin level (12–14 g/dl) was associated with significantly faster 2,000-m running time (530 ± 69 s, n = 176) than both the lower hemoglobin group (570 ± 77 s, n = 16) and the higher hemoglobin group (552 ± 86 s, n = 166, P < 0.05). The subjects in this study were non-athletic healthy young men. The high rate of abnormally low hemoglobin and ferritin values probably indicates a nutritional deficit in this population. The slower running results in the group with hemoglobin below 12 g/dl are in line with previous work, indicating the need for iron supplementation. The decrease in running ability with increased hemoglobin above 14 g/dl is surprising and will need further evaluation. Am. J. Hematol. 82:128–133, 2007. V C 2006 Wiley-Liss, Inc.