Interest in saunas is driving growth in both social wellness and recovery and now a study from the University of Oregon has found hot tubs also have a role to play in the mix, by delivering some superior health benefits.

The study, Hot tubs outperform saunas in boosting blood flow and immune power published in the American Journal of Physiology, found soaking in hot water raises the core body temperature more than dry or infrared saunas.

Higher core temperatures trigger stronger heart, blood vessel and immune responses and can also help to lower blood pressure, stimulate the immune system and, over time, improve the body's response to heat stress.

Researchers monitored body temperature, blood pressure, heart rate, cardiac output (the amount of blood the heart pumps per minute), immune cell populations and blood biomarkers of inflammation. Data was collected before, during and after subjects soaked in a hot tub, sat in traditional dry heat and also in far-infrared saunas.

Lead study author, Jessica Atencio says: "We saw that hot water immersion had the most impactful when it came to increasing core body temperature, which is the main stimulus for these subsequent responses. Increasing body temperature causes an increase in blood flow and the force of blood through across the vessels is beneficial for vascular health."

Of the three types of heat therapy, only hot-water immersion produced an inflammatory response, as measured by the levels of inflammatory cytokines in the blood – an immune signaling molecule that drives immune cell populations.

Atencio says: "Hot water immersion gives the most robust changes in core temperature because you can't effectively dissipate heat in the same way as when you have contact with the air and you're sweating to cool the body.

"When you’re submerged in water, the sweat mechanisms aren’t efficient."

Another member of the research team, Christopher Minson, has studied heat therapies for more than two decades, looking at how heat interacts with factors such as age, exercise and illness in men and women. He says heat therapy is a good option for those who are unable to exercise.

“It can be a very peaceful, sometimes religious, sometimes cultural and sometimes social experience, and I think those aspects contribute to the health benefits and are critically important," he explained.

Liz Terry, editor of HCM, said: "With the massive growth in social wellness and recovery across the fitness, health and spa and wellness sectors, having new inslights that can drive purchasing decisions and business devekopment plans is critical.

"We already know the efficacy of both traditional and infra-red saunas, now research shows that warm water bathing, when done safely, is a powerful part of the mix.

"Giving consumers a range of options that work with their personal preferences and the amount of time they have to spend can only do good, helping the sector to deepen its offering.

"Not everyone has time for a dip after a workout, so the mix between saunas and water bathing will need to reflect the clientele."

The findings bear out those from a study, published in 2021 by HCM in partnership with ACE, following research by Lance Dalleck and his team of researchers in the High Altitude Exercise Physiology Programme at Western Colorado University.

They looked at post-exercise passive heating strategies, with subjects wearing a sauna suit and undertaking hot water immersion, to examine the impact on VO2max, lactate threshold and exercise economy.

It was concluded that passive heating strategies following moderate-intensity continuous training, while keeping the core body temperature below dangerous levels, may lead to statistically significant VO2max and lactate threshold changes.

According to Dalleck, the most important element of the findings is the practicality of the post-exercise passive heating approaches, as the improvements in endurance-related parameters were obtained with minimal additional time and no additional training: “This strategy allows people to augment their training without adding volume or intensity. Performance gains can be achieved without increasing the risk of overtraining or injury,” he said

Dalleck said exercise professionals should have a fundamental appreciation of the three critical performance-defining physiological parameters discussed in this research – VO2max, lactate threshold and economy – as this will provide a foundation on which to design comprehensive training programmes to optimise endurance performance.

Researchers do not know if more is better when it comes to post-exercise passive heating, so individuals should not go beyond the 30 minutes used in the research, as reaching higher core body temperatures can be incredibly dangerous. Staying well hydrated during passive heating is also important.