**Participant 01 · Planned protocol · October 5, 2026**

## Observation

The participant reports daily hot-tub use October 1–5, 2026, at 104°F (40°C). Duration is estimated from recollection at 15–25 minutes per session. Timing relative to runs was not recorded.

## Proposed procedure

Log each session’s date, minutes immersed, water temperature, depth, placement relative to running, and response. If post-run use begins, record the change and approximate delay after exercise. A second daily session is not proposed. Future sessions will be measured rather than reconstructed.

> **Warning**
>
> Research exposures are not a home-use prescription. [CDC guidance](https://www.cdc.gov/healthy-swimming/safety/what-you-can-do-to-stay-healthy-in-hot-tubs.html) limits water to 40°C/104°F and advises against alcohol. Avoid adding heat while overheated or dehydrated; stop if unwell. Drink water.

## Evidence on timing

[Jenkins et al. (2025)](https://doi.org/10.1113/JP289874) studied ten trained runners over five weeks: five 45-minute immersions weekly, initially at 40°C. VO₂max rose approximately 4.4%. Most sessions immediately followed training; comparable benefits from standalone baths remain unresolved.

[Zurawlew et al. (2016)](https://doi.org/10.1111/sms.12638) found better five-kilometre performance in heat, but not temperate conditions, after six days of post-run immersion. [Their 2018 morning study](https://pubmed.ncbi.nlm.nih.gov/29745780/) reduced thermal strain during morning and afternoon exercise. Neither establishes an optimal clock time or validates this participant’s recalled exposure.

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*Source links: [Rosner’s TikTok post](https://www.tiktok.com/t/ZPL83h8Lg/) · [@rosner_performance](https://www.tiktok.com/@rosner_performance) · [Rosner’s website](https://marathonscience.beehiiv.com/foot-calf-strength-guide-new).*