The Physiology of Endurance Running Podcast Is passive heat better than altitude?! We examine an exciting new paper with author, Elliott Jenkins
Nov 21, 2025
Elliott Jenkins, PhD student researching heat acclimation and endurance performance, discusses a new study on long-term passive hot baths. He explains why baths might boost hemoglobin mass and VO2max without disrupting training. The conversation covers study design, cardiac remodeling, time course of hematological changes, safety and practical bath protocols for runners.
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Passive Heat Matches Active Heat Benefits
- Passive hot water immersion can produce similar hematological benefits to exercise-in-heat protocols without disrupting training.
- Elliott Jenkins designed a five-week, five-days-per-week bath protocol to test this practical alternative.
Follow The 45×5 Protocol Used In Study
- Do 45-minute hot water immersions at ~40°C five times per week alongside normal training to elicit adaptations.
- Monitor hemoglobin mass, blood volume and cardiac measures before and after to track responses.
Participant Fainting Scare During Baths
- Dan experienced a severe lightheaded episode after a bath and had to lie down until his vision returned.
- Elliott and others recommend having supervision early and learning hydration/nutrition routines to avoid such events.