Longitudinal haematological responses to training load and heat acclimation preceding a male team pursuit cycling World Record.

This evaluated relationships between changes in training load, haematological responses, and endurance exercise performance during temperate and heat acclimation (HA) training preceding a male team cycling pursuit world record (WR). Haemoglobin mass (Hb mass ) and concentration ([Hb]), plasma volume (PV) and blood volume (BV) were assessed in nine male track endurance cyclists (∼3 occasions per month) training in temperate conditions (247 to 142 days prior to the WR) to establish responses to differing acute (ATL) and chronic (CTL) training loads. Testing was performed again pre- and post-HA f(22 to 8 days prior to the WR). Endurance performance (V̇O₂ max, 4MMP, lactate threshold 1 and 2) was assessed on three occasions (238-231, 189-182 and 133-126 days prior to the WR). In temperate conditions, CTL was associated with Hb mass (B=0.62, P=0.02), PV (B=4.49, P=0.01) and BV (B=6.51, P=0.04) but not [Hb] (B=-0.01, P=0.17). ATL was associated with PV (B=2.28, P<0.01), BV (B=2.63, P=0.04) and [Hb] (B=-0.01, P=0.04) but not Hb mass (B=0.10, P=0.41). During HA, PV increased 8.2% (P<0.01), while Hb mass , CTL and ATL were unchanged. Hb mass and [Hb] were associated with all performance outcomes (P<0.05), except V̇O 2max . PV and BV were not associated with performance outcomes. During temperate training, changes in Hb mass were most strongly associated with changes in CTL. Both CTL and ATL were associated with changes in PV, but HA was associated with increased PV and maintainenance of Hb mass without increasing ATL or CTL. In practical terms, maintaining high CTL and high Hb mass might be beneficial for improving endurance performance.Highlights Changes in haemoglobin mass were associated with endurance exercise performance and changes in chronic training load in temperate conditions.Heat acclimation increased plasma volume and maintained haemoglobin mass independently of chronic training load.Chronic training loads and haemoglobin mass should be increased to improve endurance exercise performance.Heat acclimation may optimise haematological adaptations when training load is reduced.