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Blood volume (BV) is an important clinical parameter and is usually reported per kg of body mass (BM). When fat mass is elevated, this underestimates BV/BM. One aim was to study if differences in BV/BM related to sex, age, and fitness would decrease if normalized to lean body mass (LBM). The analysis included 263 women and 319 men (age: 10-93 years, body mass index: 14-41 kg/m 2 ) and 107 athletes who underwent assessment of BV and hemoglobin mass (Hb mass ), body composition, and cardiorespiratory fitness. BV/BM was 25% lower (70.3 ± 11.3 and 80.3 ± 10.8 mL/kg BM ) in women than men, respectively, whereas BV/LBM was 6% higher in women (110.9 ± 12.5 and 105.3 ± 11.2 mL/kg LBM ). Hb mass /BM was 34% lower (8.9 ± 1.4 and 11.5 ± 11.2 g/kg BM ) in women than in men, respectively, but only 6% lower (14.0 ± 1.5 and 14.9 ± 1.5 g/kg LBM )/LBM. Age did not affect BV. Athlete's BV/BM was 17.2% higher than non-athletes, but decreased to only 2.5% when normalized to LBM. Of the variables analyzed, LBM was the strongest predictor for BV (R 2  = .72, p < .001) and Hb mass (R 2  = .81, p < .001). These data may only be valid for BV/Hb mass when assessed by CO re-breathing. Hb mass /LBM could be considered a valuable clinical matrix in medical care aiming to normalize blood homeostasis., (© 2023 The Authors. American Journal of Hematology published by Wiley Periodicals LLC.)

New Findings: What is the central question of this study? Do haemoglobin mass and red blood cell volume increase in elite cyclists training in a hot environment compared to a control group training at normal temperature? What is the main finding and its importance? Five weeks of heat training increases haemoglobin mass in elite cyclists. There are small to intermediate effect sizes for exercise parameters favouring heat training., Abstract: In this study we tested the hypothesis that performing 1 h of regular light exercise in a heat chamber (HEAT; 37.8 ± 0.5°C; 65.4 ± 1.8% humidity) 5 times week -1 for a total of 5 weeks increases haemoglobin mass (Hb mass ) and exercise performance in elite cyclists ( V ̇ O 2 max  = 76.2 ± 7.6 ml min -1  kg -1 ). Twenty-three male volunteers were assigned to HEAT (n = 11) or CON (n = 12; 15.5 ± 0.1°C; 25.1 ± 0.0% humidity) training groups. Hb mass was determined before and after the intervention period in conjunction with an extensive exercise test protocol (conducted at 16-19°C). HEAT increased (P < 0.05) Hb mass by 42 g from 893 ± 78 to 935 ± 108 g whereas Hb mass remained unchanged (+6 g) in CON. Furthermore, statistical analysis revealed a time-group interaction (P < 0.05). The greater increase in Hb mass in HEAT, however, did not manifest in a greater increase in V ̇ O 2 max (225 ± 274 ml min -1 in HEAT and 161 ± 202 ml min -1 in CON). While HEAT reduced (P < 0.05) lactate levels during some of the submaximal exercise tests, there was no statistical difference between other performance parameters. There were, however, small to intermediate effect sizes favouring HEAT for lactate threshold power output (2.8 ± 3.9 vs. -0.4 ± 5.1% change, effect size (ES) = 0.34), gross economy in the fatigued state (0.19 ± 0.42 vs. -0.12 ± 0.49%-point change, ES = 0.52) and 15 min mean power (6.9 ± 8.4 vs. 3.4 ± 5.1% increase, ES = 0.22). This study demonstrates an increase in Hb mass and small to intermediate effect sizes on exercise variables in elite cyclists following a 5-week heat training intervention., (© 2020 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Purpose: The primary purpose was to test the effect of heat suit training on hemoglobin mass (Hbmass) in elite cross‐country (XC) skiers. Methods: Twenty‐five male XC‐skiers were divided into a group that added 5 × 50 min weekly heat suit training sessions to their regular training (HEAT; n = 13, 23 ± 5 years, 73.9 ± 5.2 kg, 180 ± 6 cm, 76.8 ± 4.6 ml·min−1·kg−1) or to a control group matched for training volume and intensity distribution (CON; n = 12, 23 ± 4 years, 78.4 ± 5.8 kg, 184 ± 4 cm, 75.2 ± 3.4 ml·min−1·kg−1) during the five‐week intervention period. Hbmass, endurance performance and factors determining endurance performance were assessed before and after the intervention. Results: HEAT led to 30 g greater Hbmass (95% CI: [8.5, 51.7], p = 0.009) and 157 ml greater red blood cell volume ([29, 285], p = 0.018) post‐intervention, compared to CON when adjusted for baseline values. In contrast, no group differences were observed for changes in work economy, running velocity, and fractional utilization of maximal oxygen uptake (V̇O2max) at 4 mmol·L−1 blood lactate, V̇O2max or 15‐min running distance performance trial during the intervention. Conclusion: HEAT induced a larger increase in Hbmass and red blood cell volume after five weeks with five weekly heat suit training sessions than CON, but with no detectable group differences on physiological determinants of endurance performance or actual endurance performance in elite CX skiers. [ABSTRACT FROM AUTHOR]

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 (W max) 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, W max, 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. [ABSTRACT FROM AUTHOR]