In a previous blog post, we delved into the research surrounding the impact of cold-water baths on muscle protein synthesis, muscle mass, and strength gains after exercise. The findings indicated that cold-water immersion might hinder these desired outcomes. Consequently, if the objective is to promote muscle growth, it was advised against using cold-water immersion as a post-workout recovery strategy following resistance exercise.

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Understanding the Potential of Hot-Water Immersion

While cold-water immersion negatively affects muscle growth due to its ability to reduce muscle temperature and blood flow, it led us to consider whether hot-water immersion could have the opposite effect. The hypothesis arose that increasing muscle temperature and blood flow through hot-water immersion might enhance muscle protein synthesis and contribute to long-term gains in muscle mass and strength.

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Conducting a Muscle Protein Synthesis Experiment

To investigate the effects of hot-water immersion following resistance exercise on muscle protein synthesis, we conducted an experiment involving 12 healthy young male adults experienced in resistance-type exercise. Participants were asked to perform a resistance exercise session, followed by immersing one leg in hot water (46°C) and the other in thermoneutral water (30°C) for 20 minutes. Additionally, immediately after water immersion, they were given a 20-gram protein shake containing intrinsically labeled amino acids. Through tracers, blood samples, and muscle biopsies collected over a 5-hour period post-exercise, we analyzed the destination of the amino acids from the protein shake and monitored muscle protein synthesis.

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Findings

No Discernible Difference in Protein Synthesis: Surprisingly, our results revealed no significant disparity in muscle protein synthesis between the leg subjected to hot-water immersion and the one exposed to thermoneutral water. The increase in muscle temperature and blood flow did not lead to a measurable improvement in protein synthesis.

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Examining Long-Term Effects

While there is limited available data on the effects of hot-water immersion as a heating strategy following resistance exercise training, existing evidence does not support its efficacy in enhancing gains in muscle mass. A recent study investigated the impact of 4 weeks of hot-water immersion (15 minutes at 39°C) after resistance exercise in highly trained rugby athletes during an in-season competition phase.

The study reported no discernible benefits in lean body mass after the 4-week period. Although the study's duration and timing may have influenced the results, it does not lend support to the notion that hot-water immersion significantly contributes to muscle mass gains during weeks of resistance training.

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Additional Evidence of No Benefits

Further unpublished research conducted a 10-week study to determine whether hot-water immersion (10 minutes at 45°C) after each resistance exercise session (2 times per week) would enhance muscle mass and strength gains. Consistent with the acute muscle protein synthesis experiment and the 4-week training study, this investigation failed to observe any advantages of repeated post-exercise hot-water immersion in augmenting muscle mass and strength over the 10-week training period.

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Conclusion

Hot Tubs and Muscle Development: Based on the currently available evidence, it is premature to assume that utilizing a hot tub following resistance exercise will lead to substantial gains in muscle mass and strength. However, the encouraging news is that if you genuinely enjoy a hot tub after exercise, it will not hinder your progress in muscle development. Therefore, you can still indulge in this post-workout ritual without concerns, unlike the potential drawbacks associated with cold-water immersion.

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Scientific references

1. Fuchs, C.J., et al., Hot-water immersion does not increase postprandial muscle protein synthesis rates during recovery from resistance-type exercise in healthy, young males. J Appl Physiol (1985), 2020. 128(4): p. 1012-1022.
2. Horgan, B.G., et al., No effect of repeated post-resistance exercise cold or hot water immersion on in-season body composition and performance responses in academy rugby players: a randomised controlled cross-over design. Eur J Appl Physiol, 2022.
3. McGorm, H., The effects of hot water immersion on recovery, performance and adaptation to resistance exercise. PhD Thesis, 2019