Seasonal variation of haemoglobin mass in internationally competitive female road cyclists

In order to quantify the seasonal variability of haemoglobin mass (Hb_mass) in cyclists during a competitive season, and investigate whether variability is associated with changes in training load or performance, Hb_mass was measured in 10 internationally competitive female road cyclists approximately once per month for 2–10 months via CO-rebreathing. Power meters were used to quantify daily load (Training Stress Scores) during training and racing, from which cumulative training load units for 7, 14, 28 and 42 day were calculated. Maximal mean power (MMP) for 1, 4, 10 and 25 min, performed during training or racing was used as a surrogate for performance. The relationship between changes in training load (%ΔTraining) and changes in Hb_mass (%ΔHb_mass), and between %ΔHb_mass and changes in MMP (%ΔMMP) was established via regression analysis. Individual coefficients of variation (CV) in Hb_mass ranged from 2.0 to 4.4%. The weighted mean CV in Hb_mass was 3.3% (90% Confidence Limits: 2.9–3.8%) or 23 g over the average 6.6 ± 2.3 month monitoring period. The effect of %ΔTraining on %ΔHb_mass was small for 7 and 14 day (r = 0.22 and 0.29), moderate for 42 day (r = 0.35) and large for 28 day (r = 0.56). The regression slope was greatest for 42 day, with a 10% change in training associated with a ~1% change in Hb_mass. The relationship between %ΔHb_mass and %ΔMMP was ~0.5:1 for MMP_1min,_10min and _25min and ~1:1 for MMP_4min, respectively. Hb_mass varies by ~3% in female cyclists during a competitive season. Some of the variation may be related to oscillations in chronic training load.