D-11 Free Communication/Slide - Altitude and Hypoxia: MAY 29, 2008 1:00 PM - 2:30 PM ROOM: 122
Erythropoietin (EPO) induced increases in total haemoglobin mass (tHb) are generally thought to explain improvements in endurance performance following 3-4 wks of altitude training. However, the time course of the tHb response to natural altitude in endurance athletes is not well documented.
PURPOSE: To identify when the greatest gains in tHb occur during 3 wks of natural altitude training in elite endurance cyclists.
METHODS: tHb (CO re-breathing), [EPO], reticulocytes, and soluble transferrin receptor (sTfr) were measured throughout 21 nights of structured training in 13 internationally competitive cyclists preparing for the World Championships (Mean±SD Mass, Age, VO2max: 67.9±6.0 kg, 21.0±1.5 y, 73.7±6.1 ml.kg−1.min−1). Eight cyclists (ALT) lived at 2760m and trained for 3-6 h.d−1 at 1000-2760m. Five cyclists (SL) lived and trained at ∼600m. All cyclists completed similar training (600-900 km.wk−1; low intensity with frequent climbing 10,000-15,000 m.wk−1). Duplicate measures for all dependent variables were performed at baseline (D0). Daily iron supplementation (305mg ferrous sulphate + 1000mg Vitamin C) was administered for 1-2 wks prior to and during the study.
RESULTS: Typical Error for tHb was 1.6% (ALT) and 1.8% (SL). tHb at D0 (ALT 946±67 g; SL 991±96 g) increased for ALT (Mean±90%CI; D6 1.2±1.2%, p=.12; D11 2.9%±1.2, p=.01; D19 3.5%±1.6, p=.01; D23 2.0%±1.6, p=.07) but not for SL. [EPO] increased from D0 (15.4±4.0 mU.ml−1) in ALT (D2 66.2%±17.3, p<0.001) but returned to D0 values by D12. [EPO] did not increase in SL. Reticulocytes (%) increased slightly from D0 (0.9% ± 0.2 - absolute value) in ALT (D5 20.3%±11.3 p=.02; D12 23.1%±15.7, p=.05 - relative changes) but were not different than D0 by D20 (p=.57). For ALT, sTfr was higher than D0 (2.9±0.5mg.l−1) at D12 (19.9%±9.9, p=.01) but not different from D0 at D20 (13.2%±11.3, p=.1). For SL, sTfr was only elevated from D0 at D21 (10.3%±4.7, p=.03)
CONCLUSIONS: The greatest gains in tHb in this study occurred over the first 11 d of altitude training. tHb did not noticeably increase with an additional 10 d of exposure. The signal for erythropoiesis appears to be attenuated after ∼12 d as reflected by [EPO], sTfr and reticulocytes. In this instance, we observed that the final week of altitude exposure elicited little benefit on tHb.