The contribution of haemoglobin mass to increases in cycling performance induced by simulated LHTL

We sought to determine whether improved cycling performance following 'Live High-Train Low' (LHTL) occurs if increases in haemoglobin mass (Hb _mass) are prevented via periodic phlebotomy during hypoxic exposure. Eleven, highly trained, female cyclists completed 26 nights of simulated LHTL (16 h day^-1, 3000 m). Hb_mass was determined in quadruplicate before LHTL and in duplicate weekly thereafter. After 14 nights, cyclists were pair-matched, based on their Hb_mass response (ΔHb_mass) from baseline, to form a response group (Response, n = 5) in which Hb_mass was free to adapt, and a Clamp group (Clamp, n = 6) in which ΔHb_mass was negated via weekly phlebotomy. All cyclists were blinded to the blood volume removed. Cycling performance was assessed in duplicate before and after LHTL using a maximal 4-min effort (MMP_4min) followed by a ride time to exhaustion test at peak power output (T _lim). VO_2peak was established during the MMP_4min. Following LHTL, Hb_mass increased in Response (mean ± SD, 5.5 ± 2.9%). Due to repeated phlebotomy, there was no ΔHb_mass in Clamp (-0.4 ± 0.6%). VO_2peak increased in Response (3.5 ± 2.3%) but not in Clamp (0.3 ± 2.6%). MMP_4min improved in both the groups (Response 4.5 ± 1.1%, Clamp 3.6 ± 1.4%) and was not different between groups (p = 0.58). T _lim increased only in Response, with Clamp substantially worse than Response (-37.6%; 90% CL -58.9 to -5.0, p = 0.07). Our novel findings, showing an ∼4% increase in MMP_4min despite blocking an ∼5% increase in Hb_mass, suggest that accelerated erythropoiesis is not the sole mechanism by which LHTL improves performance. However, increases in Hb _mass appear to influence the aerobic contribution to high-intensity exercise which may be important for subsequent high-intensity efforts.