Hot bath and performance - Practical guidelines

The recent blog by Prof Neil Walsh on Train Cool - Bathe Hot covered the scientific aspects of a publication on "heat acclimation through hot baths" (first author Mike Zurawlew). The findings of the study were presented in a very clear way, but often a research paper leaves the reader with a number of practical questions. Research is conducted in a very controlled way and it is sometimes difficult to extrapolate findings to different situations, populations or events. Therefore I caught up with Neil Walsh and Mike Zurawlew and asked them about "the practical stuff that you don't read about in research papers"....

Neil and Mike, the conditions in the study you published were fairly extreme 33°C. How does this compare to conditions athletes may experience? (how extreme or how common is this?)

Yes, the conditions were challenging in the hot trial (33°C, 40% RH) in our study. Nevertheless, we present strong evidence that the intervention also reduces thermal strain in cooler conditions. We observed lower core body temperature, lower core temperature at sweating onset and lower perceived exertion when the participants exercised in ‘temperate’ 18°C conditions after the intervention. So if for example a non-heat-acclimated endurance athlete was performing in Rio (likely 24-28°C) we believe that taking a hot bath after exercise on 6 days (see “How to” guidelines below) would provide heat acclimation – this would in-turn reduce thermal strain during exercise and potentially improve performance, as I discuss below.

The run was approximately 1 hour. Do you expect to find similar benefits for longer events (ironman distance in hot conditions such as Hawaii?)

I see no reason why not. When heat acclimated one would expect self-selection of a higher pace during endurance exercise in the heat (as we have seen, albeit for a short 5 km run). Future studies need to confirm this. We speculated in the paper that had we used a longer running test we may have even seen an improvement in performance in ‘temperate’ 18°C conditions after the intervention: the rise in core temperature during a longer test may become a limiting factor. However, whether heat acclimation improves performance in temperate conditions is controversial, as we discuss in our paper.

Was your study performed in the Welsh winter or summer? What difference would this make?

In North Wales, with average winter temperatures of 3-9°C and summer temperatures of 13-20°C, the season makes little difference (as anyone who lives here will testify!). Although the data collection was performed year round, key is that the number of hot bath and control bath participants was the same in each season; and, none of our participants were heat acclimated; none had been exposed to hot conditions in the preceding 3 months.

How well trained were your runners? They were around 19 min for 5k? Do you expect to see benefits for athletes who are somewhat acclimated? And would these effects be seen in elite runners? Would it be seen in slower runners?

These are excellent questions. Although comparing the level of heat acclimation gained in highly trained vs. recreationally active was not our principal aim we believe our data move us some way towards an answer.