Does turning on the underwater massage change what a hot tub soak does for your body and mood? That’s what a recent research study wanted to find out. We know there are numerous health benefits to relaxing in warm water – from stress relief to cardiovascular health. But do the massage jets add more to the experience or is the hot water alone responsible for the improvements to hot tub user’s health?
The Test
The study consisted of three test sessions to measure physiological and psychological changes in the participants taken before, during, and after. Each test session comprised of 30 minutes in a hot tub – one with air jet massage, one with water jet massage, and one with no massage. Each person was submerged up to their armpit, and the water was heated to 39°C.
Each test session was carried out at least 48hrs apart at a similar time of day to prevent crossover effects and manage effects of circadian rhythm.
The Participants
The study was carried out of twenty health individuals. There were 16 males and 4 females with an average age of 37 (+/- 8.4 years). Each participant had no underlying conditions and were not on any medications during the study. Other factors, such as pregnancy and regular smoking, meant a participant would be excluded.
The Conditions and Measures
As mentioned, the hot tub water was heated to 39°C and participants spent 30 minutes in the water. The temperature was maintained with a thermometer throughout each session, and each participant rested for 10 minutes at the beginning. They were given water to drink to stay hydrated throughout the study.
After this rest, baseline blood pressure measurements were taken. They also lay down to have ultrasounds of their femoral arteries. These were also taken after the 30-minute session for each test.
Subjective measurements were also taken. Each participant completed the State-Trait Anxiety inventory before and immediately after each session. They were also asked to rate the thermal comfort and thermal sensation from +5 (very comfortable and very hot respectively) to -5 (very uncomfortable and very cold respectively). Additionally, they provided a score on the feelings scale from +5 (very good) to -5 (very bad). The final scale was a modified version of the physical activity enjoyment scale. Participants were asked to rate their enjoyment from 1-7 (1 is positive, 7 is negative) across the following subcategories:
- Pleasurable
- Fun
- Pleasant
- Invigorating
- Gratifying
- Exhilarating
- Stimulating
- Refreshing
Salivary cortisol levels were also tested before and after the test sessions.
The Results
Results 1: Hot water immersion alone drove most changes
The participants heart rate rose during immersion across all conditions. Blood pressure dopped after immersion and then trended back towards baseline after approximately 30 minutes. This indicates that heat therapy improves circulation.
Results 2: Water-jet massage didn’t significantly change cardiovascular or mood effects
The outcomes were similar to the test session with just hot water immersion and no jets.
Results 3: Air jets blunted some blood-flow benefits
The water temperature dropped more in the air-jet test, making the soak less comfortable. Cardiovascular responses increased less than the control (just soaking in hot water) and water jets.
Results 4: Mood/stress improved after soaking
Participants repeated the tests used for subjective measurements of mood and stress levels after each test session. Overall, anxiety scores improved, cortisol levels decreased modestly, and enjoyment and feelings ratings were broadly positive. This is a sign of reduced stress.
Key Takeaways for Owners
In this study, the hot soak itself drove the biggest changes. Adding water-jet massage didn’t boost cardiovascular or mood benefits beyond immersion alone – but it also didn’t reduce them (unlike air jets, which blunted some vascular responses).
The TL;DR
Method:
20 healthy adults completed three separate hot tub sessions. Each session lasted 30 minutes at 39°C with immersion to their armpits.
Conditions:
First soak – hot water with no jets (the control.
Second soak – hot water with water-jet massage.
Third soak – hot water with air jet massage.
Design:
Everyone soaked in all three conditions, with at least 48 hours between them at a similar time of day.
Measures:
- Cardiovascular: heart rate during immersion, blood pressure before and after, blood flow before and after.
- Mood/stress: anxiety questionnaire, feeling/enjoyment scales, thermal/sensation ratings.
- Hormonal marker: salivary cortisol before and after.
Results:
- Hot water immersion drove the main effects: heart rate increased, blood pressure dropped after, and mood/stress markers improved.
- Water jets had similar results to hot water immersion alone.
- Air jets blunted some blood-flow benefits and people tended to feel less comfortable.
If you’ve ever wondered whether turning on the jets makes a hot tub soak “more effective”, this research suggests a simple answer: the heat is the main driver. Across all sessions, hot water immersion improved key cardiovascular and stress markers, while water-het massage didn’t meaningfully change those outcomes. Because this was a small study in healthy adults and looked only at short-term responses, future research could explore different jet intensities, longer-term use, and clinical populations.
Source: Cullen, T. et al. (2024) ‘The effect of underwater massage during hot water immersion on acute cardiovascular and mood responses’, [Journal Name]. Available at: https://pure.coventry.ac.uk/ws/portalfiles/portal/94013060/Cullen2024VoR.pdf (Accessed: 10 December 2025).
