Iron supplementation improves progressive fatigue resistance during dynamic knee extensor exercise in iron-depleted, nonanemic women.
BACKGROUND
Tissue iron depletion may negatively affect endurance performance and muscle fatigability.


OBJECTIVE
We investigated tissue-level iron depletion and progressive fatigue of the quadriceps during dynamic knee-extension exercise in young women.


METHODS
Twenty iron-depleted (serum ferritin < 20 micro g/L), nonanemic (hemoglobin > 110 g/L) women (macro x +/- SEM age: 29.1 +/- 1.2 y) received iron (iron group) or placebo (placebo group) for 6 wk in a randomized, double-blind trial (n = 10 per group). A protocol integrating 2-3-s maximal voluntary static contractions (MVCs) with dynamic knee extensions was used to assess fatigue.


RESULTS
No significant differences between the groups in baseline iron status, MVC at rest, or MVC at the end of the protocol were observed. After treatment, serum iron and transferrin saturation increased significantly in the iron group (P = 0.02 and P = 0.03, respectively). Serum transferrin receptor concentrations increased significantly in the placebo group (P < 0.01) but not in the iron group. After treatment, the rate of decrease in MVC was attenuated in the iron group but not in the placebo group (P = 0.01). In the iron group, MVC at the sixth minute of the fatigue protocol and MVC at the end of the protocol were approximately 15% (P = 0.04) and approximately 27% higher (P < 0.01), respectively, after treatment. These improvements were not related to changes in iron-status indexes or tissue iron stores, although power was low (< 0.50) to detect these relations.


CONCLUSIONS
Iron supplementation was associated with a significant improvement in muscle fatigability. Interpretation regarding the direct role of tissue iron status is limited by the study's low power to detect relations between tissue iron improvement and decreased muscle fatigue.
Brutsaert
Tom D
TD
Department of Anthropology, the State University of New York at Albany, 12222, USA. tbrutsae@csc.albany.edu
Hernandez-Cordero
Sonia
S
Rivera
Juan
J
Viola
Tracey
T
Hughes
Gail
G
Haas
Jere D
JD
D000293:Adolescent; D000328:Adult; D019587:Dietary Supplements; D004311:Double-Blind Method; D004909:Erythrocyte Indices; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007501:Iron / Q000097:blood; D000090463:Iron Deficiencies; D019266:Iron, Dietary / Q000008:administration & dosage*; D008875:Middle Aged; D018763:Muscle Fatigue / Q000187:drug effects*; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000187:drug effects* / Q000502:physiology; D011990:Receptors, Transferrin / Q000097:blood / Q000187:drug effects; D014168:Transferrin / Q000378:metabolism*
D019266:Iron, Dietary; D011990:Receptors, Transferrin; D014168:Transferrin; D007501:Iron