Purpose and Methods To test whether heat training performed as 5 × 50-min sessions per week for 5 wk in a heat chamber (CHAMBER) or while wearing a heat suit (SUIT), in temperate conditions, increases hemoglobin mass (Hbmass) and endurance performance in elite cyclists, compared with a control group (CON-1). Furthermore, after the 5-wk intervention, we tested whether three sessions per week for 3 wk with heat suit (SUITmain) would maintain Hbmass elevated compared with athletes who returned to normal training (HEATstop) or who continued to be the control group (CON-2). Results During the initial 5 wk, SUIT and CHAMBER increased Hbmass (2.6% and 2.4%) to a greater extent than CON-1 (-0.7%; both P < 0.01). The power output at 4 mmol·L-1 blood lactate and 1-min power output (Wmax) improved more in SUIT (3.6% and 7.3%, respectively) than CON-1 (-0.6%, P < 0.05; 0.2%, P < 0.01), whereas this was not the case for CHAMBER (1.4%, P = 0.24; 3.4%, P = 0.29). However, when SUIT and CHAMBER were pooled this revealed a greater improvement in a performance index (composed of power output at 4 mmol·L-1 blood lactate, Wmax, and 15-min power output) than CON-1 (4.9% ± 3.2% vs 1.7% ± 1.1%, respectively; P < 0.05). During the 3-wk maintenance period, SUITmain induced a larger increase in Hbmass than HEATstop (3.3% vs 0.8%; P < 0.05), which was not different from the control (CON-2; 1.6%; P = 0.19), with no differences between HEATstop and CON-2 (P = 0.52). Conclusions Both SUIT and CHAMBER can increase Hbmass, and pooling SUIT and CHAMBER demonstrates that heat training can increase performance. Furthermore, compared with cessation of heat training, a sustained increase in Hbmass was observed during a subsequent 3-wk maintenance period, although the number of weekly heat training sessions was reduced to 3.
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