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 (%Delta Training) and changes in Hb(mass) (%Delta Hb(mass)), and between %Delta Hb(mass) and changes in MMP (%Delta MMP) 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 %Delta Training on %Delta Hb(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 similar to 1% change in Hb(mass). The relationship between %Delta Hb(mass) and %Delta MMP was similar to 0.5:1 for MMP(1min,10min) and (25min) and similar to 1:1 for MMP(4min), respectively. Hb(mass) varies by similar to 3% in female cyclists during a competitive season. Some of the variation may be related to oscillations in chronic training load.