The Physiology of Endurance Running Podcast · Dan Nash and Owain Zerilli

Is passive heat better than altitude?! We examine an exciting new paper with author, Elliott Jenkins

·1 hr 10 min·3 clips

Five weeks of hot water immersion produced a 33-gram rise in hemoglobin mass and a 2.7 ml/kg/min VO2 max gain.

1. The Physiology of Endurance Running Podcast discusses Elliot Jenkins’ hot water immersion study on hemoglobin mass and VO2 max. 2. Elliot Jenkins is a PhD student at Cardiff Met University, and hosts Owen and Jen introduce the paper because they were participants in the study. 3. The episode asks whether passive heat stress can produce altitude-like adaptations without interrupting normal training. 4. Elliot says the idea came from Ronestad and Carson Lumby’s work showing five weeks of exercise in heat could increase hemoglobin mass. 5. He explains that his project tested passive heat acclimation instead of exercise in the heat, using hot baths rather than heat suits or chamber sessions. 6. The protocol used a crossover design with 10 participants, five baths per week, 45 minutes per bath, and water at 40 degrees or more. 7. The control arm matched time and training but removed the hot-water exposure. 8. Elliot describes weekly carbon monoxide re-breathing, pre- and post-intervention testing, and echocardiography before and after each five-week block. 9. He says the study also tracked lactate threshold, exercise economy, sweat rate, tympanic temperature, and perceived thermal discomfort. 10. Owen and Dan describe doing the baths themselves, including one session where Dan’s vision blurred after standing up. 11. Elliot explains that the baths were progressively overloaded by raising tub temperature toward 42 degrees across the five weeks. 12. He says that kept the thermal strain high even as participants adapted. 13. Elliot reports a 33-gram increase in hemoglobin mass, a 280 ml increase in blood volume, and a 10 ml rise in left ventricular end-diastolic volume. 14. He links those changes to a 2.7 ml/kg/min improvement in VO2 max and a higher treadmill speed at VO2 max. 15. Elliot compares the hemoglobin-mass gain to live high-train low studies and says the result is broadly comparable. 16. He explains the likely mechanism as plasma-volume expansion reducing hematocrit and triggering erythropoietin signaling through the kidney. 17. The conversation uses a relaxed interview style, with Owen, Jen, and Elliot moving between methods, personal experience, and applied running implications. 18. The tone stays practical and technical, with recurring references to Cardiff Met baths, Manchester Marathon, and the journal of physiology paper. 19. Runners interested in heat acclimation, altitude alternatives, and endurance physiology will get the most from this episode. 20. Listeners wanting entertainment without technical training or blood-volume detail may skip it.

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