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

Abstract We sought to determine whether improved cycling performance following ‘Live High-Train Low’ (LHTL) occurs if increases in haemoglobin mass (Hbmass) 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). Hbmass was determined in quadruplicate before LHTL and in duplicate weekly thereafter. After 14 nights, cyclists were pair-matched, based on their Hbmass response (DHbmass) from baseline, to form a response group (Response, n = 5) in which Hbmass was free to adapt, and a Clamp group
(Clamp, n = 6) in which DHbmass 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
(MMP4min) followed by a ride time to exhaustion test at peak power output (Tlim). VO2peak was established during the MMP4min. Following LHTL, Hbmass increased in Response (mean ± SD, 5.5 ± 2.9%). Due to repeated phlebotomy, there was no DHbmass in Clamp (-0.4 ± 0.6%). VO2peak increased in Response (3.5 ± 2.3%) but not in Clamp (0.3 ± 2.6%). MMP4min improved in both the
groups (Response 4.5 ± 1.1%, Clamp 3.6 ± 1.4%) and was not different between groups (p = 0.58). Tlim 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 MMP4min despite blocking an *5% increase in Hbmass, suggest that accelerated erythropoiesis is not the sole mechanism by which LHTL improves performance. However, increases in
Hbmass appear to influence the aerobic contribution to highintensity exercise which may be important for subsequent high-intensity efforts.