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Table 7 Changes of haematological variables related to thermal acclimation protocols

From: Factors Confounding the Athlete Biological Passport: A Systematic Narrative Review

Authors Subjects Interventions [Hb] Ret% OFFs Hct PV
Heat acclimation/acclimatisation        
Costa et al. [50] Runners (n = 6) Three running exercise-heat exposures were performed at 30 °C (T1), followed by three running exercise-heat exposures at 35 °C (T2). Each running exercise-heat exposure was separated by 48 h ↓ (T1) ↓ (T1) ↑ + 7% (T1)
Loeppky [51] Recreational athletes (n = 18) PV variations were reported after 10 d of heat acclimation from studies in winter (WIN, n = 8) and summer (SUM, n = 10). In both studies, heat acclimation and dehydrating ergometer exercise were performed at 50 °C dry bulb and 26 °C wet bulb at 30% of each subject’s VO2max = ↓ − 2% (10 d) =/= (10 d) = ↑ + 5% (10 d)
Scoon et al. [52] Runners (n = 6) Six male distance runners completed 3 weeks of post-training sauna bathing and 3 weeks of control training with a 3-week washout. During the sauna period, subjects sat in a humid sauna at 90 °C immediately post-exercise for 30 min on 12 occasions ↓ − 1.3% (3 weeks) ↓ − 2% (3 weeks) ↑ + 7% (3 weeks)
Stanley et al. [53] Cyclists (n = 7) Seven well-trained male cyclists were monitored for 35 consecutive days (17 d baseline training, 10 d training plus sauna and 8 d training). Sauna exposure consisted of 30 min (87 °C, 11% relative humidity) immediately following normal training ↓ (4 d) ↓ (4 d) ↑ + 18% (4 d)
Tebeck et al. [54] Cyclists (n = 11) Eleven cyclists completed each of two 5-d blocks of short-term heat acclimation matched for heat index (44 °C) and total exposure time (480 min). The blocks were separated by 30 d. Two protocols were applied: dry (D/43 °C and 20% humidity) and humid (H/32 °C and 80% humidity) ↓/↓ (5 d) ↓/↓ (5 d) ↑ + 5%
↑ + 5% (5 d)
Oberholzer et al. [55] Cyclists (n = 21) Participants completed the 5½-week heat acclimation period, after which blood sampling was repeated. Blood sampling was conducted after 2 weeks into the intervention period prior to an exercise training session = (NS) = (NS) *Ret count = (NS) ↑ + 7% (2 weeks)
Cold acclimation/acclimatisation        
Banfi et al. [56] Rugby players (n = 10) Ten athletes were exposed daily to whole-body cryotherapy for 5 d at the Center of Spała, Poland. During this period, moderate training (3 h daily) continued for all athletes ↓ − 2% (5 d) = (NS) = (NS)
Checinska-Maciejewska et al. [57] Swimmers (n = 34) Thirty-four healthy subjects (18 men and 16 women) aged 50 years swam in cold seawater during the winter season at least twice a week. The average water temperature was 10 °C in October (T1), 1 °C in January (T2) and 4 °C at the end of April (T3) ↑ + 9% (T3) = (NS)
  1. Numbers represent the relative changes during the most significant measurement: haemoglobin concentration ([Hb]), reticulocytes percentage (Ret%), OFF-Score (OFFS), haematocrit (Hct) and plasma volume (PV). Values in italics correspond to absolute variations