Hot baths boost fitness
New research suggests regular hot baths can raise aerobic fitness and help marathon prep without adding miles — promising for runners trying to boost VO2 adaptations during base phases The Conversation.
A Cardiff Metropolitan University team led by Elliott J. Jenkins and Mike Stembridge published the trial in The Journal of Physiology reporting) a within-subject, counterbalanced crossover study of 10 well-trained runners (nine male) with a baseline V̇O2max of 64.5 ± 8.1 mL·kg−1·min−1. The intervention used five 45‑minute hot‑water immersion sessions per week at ≥40°C for five weeks, performed in standard home bathtubs and with water temperature maintained by thermometer shortly after training described). Measured adaptations included a 33 g increase in haemoglobin mass, a 10 mL rise in left‑ventricular end‑diastolic volume, and a 2.7 mL·kg−1·min−1 improvement in V̇O2max after the hot‑bath period reported). The authors link those gains to plasma‑volume expansion triggering erythropoiesis and concurrent central (cardiac) remodeling, with best‑subset regression showing both haematological and cardiovascular changes contributed to the V̇O2max increase noted). Key constraints include the small sample size (n=10), male predominance (9/10), and a single five‑week dose; the paper explicitly calls for larger, sex‑balanced and dose–response trials to confirm generalisability acknowledged). Safety caveats come from related literature showing hot‑water immersion raises core temperature more than saunas and, in some protocols, has produced core temps near 40°C and heart rates approaching ~160 bpm (with transient blood‑pressure drops reported), highlighting the need for cardiovascular caution in higher‑temperature or clinical populations reviewed).
