A slow burn: Revisiting cross‐adaptation through long‐term heat acclimation

Heat acclimtion has long been used to improve athlete tolerance and performance ahead of competition in warm–hot environments. Typically conducted across 5–14 days, repeated heat exposures improve thermoregulation while attenuating cardiovascular and perceptual strain. In recent years, research has shifted attention towards longer-term heat acclimation interventions (≥5 weeks), which elicit additional physiological adaptations, most notably elevations in haemoglobin (Hb) mass that might contribute to improvements in maximal oxygen uptake (
) after 5 weeks of exercise in the heat (Lundby et al., 2023). The concept of cross-adaptation, whereby adaptation to one environmental stressor (e.g., heat) induces beneficial physiological responses to another (e.g., hypoxia), has also garnered growing scientific interest. Previous research investigating cross-adaptation has typically involved <10 heat exposures, demonstrating consistent reductions in physiological strain during submaximal exercise in hypoxia.