Hematological, skeletal muscle fiber, and exercise performance adaptations to heat training in elite female and male cyclists
5 weeks of 5 × 50 min heat sessions: Hbmass +4.0% (F) / +3.5% (M), muscle unchanged, LT, VO₂max and 15-min power up
Participants
n=47 elite cyclists: 20 female (VO₂max 58.2 ± 6.7 mL/min/kg) and 27 male (VO₂max 76.4 ± 7.8 mL/min/kg).
Protocol
5 weeks of randomized control or heat training (HEAT)
HEAT: five sessions per week, each 50 min, of heat exercise training, included in the athletes' normal training regimes
Measured before and after: haemoglobin mass and other hematological parameters, skeletal-muscle fibre characteristics (citrate synthase activity, fibre-type distribution, capillary density), lactate threshold, VO₂max, and mean power in a 15-min all-out test in a thermoneutral environment
Key Findings
Hbmass increased with HEAT: females 650 ± 77 → 675 ± 76 g (+4.0 ± 1.6%), males 1,008 ± 155 → 1,041 ± 147 g (+3.5 ± 2.3%) (P < 0.05); HEAT raised Hbmass and other hematological parameters more than control training
Skeletal muscle did NOT change: citrate synthase activity, fibre-type distribution and capillary density remained unchanged with HEAT
Performance improved in thermoneutral conditions: lactate threshold, VO₂max and mean power during 15-min all-out testing were all enhanced (P < 0.05) after HEAT, in both sexes
Sex comparison: the relative responses to HEAT were largely similar in female and male participants
Authors' conclusion: heat training may be recommended to elite female and male athletes aiming to perform in a thermoneutral environment
Practical Application
In 47 elite cyclists (20 women, 27 men) randomized to 5 weeks of control or heat training — five 50-min heat sessions a week on top of normal training — heat training raised haemoglobin mass by 4.0 ± 1.6% (650 → 675 g) in women and 3.5 ± 2.3% (1,008 → 1,041 g) in men, left muscle citrate synthase, fibre type and capillary density unchanged, and improved lactate threshold, VO₂max and 15-min all-out power in cool conditions, with similar relative responses in both sexes (Lundby et al. 2023). Meaning: the heat-block gain in already-elite riders is a blood adaptation, not a muscle one — a central lever that works even at the top, and equally for women.
Heat training works at elite level — not just for sub-elite athletes
Dose that worked here: 5 × 50 min per week for 5 weeks, integrated into normal training; the passive alternative (hot-water immersion) is in REF-135
Plan a heat block as a deliberate periodized component, e.g. before a thermoneutral goal event (the base's own practice; the study tested thermoneutral performance after the block)
Limitations
Single protocol (5 × 50 min/wk, 5 wk) — generalization to other heat doses is limited
Elite cohort — sub-elite response may differ in magnitude
Group sizes per arm and the heat-session temperature are not in the abstract
Performance tested in a thermoneutral environment only
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: well-powered RCT, n=47, single study
Content correction 2026-09-27
"Skeletal muscle fiber adaptations also observed" -> abstract: citrate synthase activity, fibre-type distribution and capillary density remained UNCHANGED with heat training; corrected.
"Plasma volume" -> abstract says "other hematological parameters"; wording corrected. Added the abstract's numbers: n=47 (20 F / 27 M), VO₂max 58.2 / 76.4, Hbmass 650→675 g (+4.0 ± 1.6%) and 1,008→1,041 g (+3.5 ± 2.3%), 5 × 50 min/wk × 5 wk, LT / VO₂max / 15-min power all improved.
Level A -> A- (single RCT, n=47); added Tier/Sport lines and an abstract-based lead.
Cross-reference labels pointed at the wrong entry or named the wrong author (checked against each cited entry's byline); repointed to the entry the label describes, or removed where the base holds no such paper.