Pre-exercise hot water immersion increased circulatory heat shock proteins but did not alter muscle damage markers or endurance capacity after eccentric exercise.
Level 2 - randomized trial
Small human crossover trial
PubMed 38846523 · doi:10.1080/23328940.2024.2313954
What was done
Eleven recreational male athletes completed two trials: hot water immersion (41°C for up to 60 min or until rectal temperature reached 39.5°C) and a control immersion (34°C). Six hours after immersion, participants performed a 1-hour downhill run (-4% gradient) to induce muscle damage. An endurance capacity test at 75% VO2max was performed 18 hours later. Blood markers including plasma heat shock proteins (eHSP70, eHSP27), leukocytic p-HSP27, creatine kinase, and lactate dehydrogenase were measured alongside heart rate and time to exhaustion.
What was found
Hot water immersion increased post-immersion plasma eHSP70 (1.3 ± 0.4 vs 1.1 ± 0.4; p = 0.005), pre-endurance eHSP27 (p = 0.049), post-endurance eHSP27 (p = 0.015), and 18-hour leukocytic p-HSP27 (0.97 ± 0.14 vs 0.67 ± 0.11; p = 0.04). However, creatine kinase (3-fold increase) and lactate dehydrogenase (1.5-fold increase) did not differ between conditions (p > 0.05). Mean heart rates were higher during both the eccentric run and the endurance test after hot water immersion (p < 0.05). Endurance capacity was not significantly different between hot water immersion and control (57.3 ± 11.5 min vs 55.0 ± 13.5 min; p = 0.564).
Why it matters
Despite prior rodent evidence showing that pre-exercise heat confers myoprotection via heat shock protein induction, this study indicates that acute hot water immersion does not prevent exercise-induced muscle damage or enhance recovery and endurance capacity in humans.
Limits
The study is limited by a very small sample size (n = 11) restricted to male recreational athletes. Only circulatory markers were assessed rather than direct muscle biopsies for tissue-level HSP expression or histology, and the abstract does not state whether the crossover order was randomized.
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