Sitting in a hot tub hardly seems like exercise. You're not moving much, your muscles aren't working particularly hard, and the whole point is usually to relax. Yet researchers have been investigating whether spending time in hot water might produce some of the cardiovascular benefits associated with physical activity.
Immersion in hot water increases heart rate, changes circulation and places demands on the cardiovascular system. Some of these responses resemble what happens during exercise, and recent studies have produced some intriguing results. The question is whether those similarities translate into lasting benefits.
Why does hot water make your heart work harder?
When you exercise, your heart pumps more blood to supply oxygen to your working muscles. Your body also generates heat, which it needs to release.
Sitting in hot water presents a different challenge. As your body absorbs heat, blood vessels near the skin widen to help regulate your temperature. Your heart rate increases to support the changes in circulation, even though you're barely moving. The water itself contributes too, as its pressure on the body affects how blood returns to the heart.
Researchers are interested in passive heating because it places certain demands on the cardiovascular system without the muscular effort normally associated with exercise. Whether repeatedly doing so has benefits that last beyond the time spent in the water is the subject of ongoing research.
What did the 2026 research find?
In January 2026, a systematic review and meta-analysis published in Physiological Reports examined 20 studies investigating the cardiovascular effects of hot-water immersion.
One of the clearest findings concerned heart rate. Across ten studies, a single session of hot-water immersion increased heart rate by an average of approximately 28 beats per minute compared with control conditions. That's a substantial change for someone sitting still.
The review also found reductions in certain measures of blood pressure following immersion. In five studies investigating repeated exposure, resting heart rate was approximately three beats per minute lower than in the comparison conditions.
The studies varied considerably, though. Water temperatures, immersion depths, session lengths and treatment schedules were far from consistent, making it difficult to draw firm conclusions about what repeated exposure might achieve. Only one of the 20 studies directly measured cardiorespiratory fitness, leaving a significant gap in our understanding.
The authors concluded that the evidence for beneficial cardiovascular effects remained inconclusive and called for more consistent research, particularly into the effects of repeated immersion.
When sitting in hot water produced a greater response than cycling
A second study, published in September 2026 in the European Journal of Applied Physiology, compared hot-water immersion with moderate exercise.
Researchers recruited 25 middle-aged adults with overweight or obesity. Participants completed two activities on separate occasions: 30 minutes of moderate-intensity cycling and 30 minutes immersed to chest level in water at 40°C.
During hot-water immersion, participants' core body temperature increased by an average of 0.91°C, compared with 0.72°C during cycling. Their heart rates also rose more during immersion: approximately 33 beats per minute, compared with 25 beats per minute on the bicycle.
Under the conditions of this experiment, sitting in hot water produced a greater increase in heart rate than moderate cycling. The study measured immediate responses rather than changes in fitness over time, however, and involved a relatively small group of participants. Different participants or a more demanding exercise session might have produced different results.
Even with those limitations, the comparison demonstrates how strongly the cardiovascular system can respond to hot water when the person immersed is doing very little.
A faster heartbeat doesn't necessarily mean you're getting fitter
It's tempting to look at those figures and assume that making your heart beat faster must be doing it some good. But heart rate alone isn't a reliable measure of exercise benefit.
Your heart also beats faster when you're frightened, anxious or under stress, and nobody would suggest that watching The Exorcist counts as cardiovascular training, however much it makes your pulse race. What matters is why the heart is working harder and how the body responds over time.
During exercise, your muscles demand more oxygen. Repeated physical activity can improve the body's ability to deliver and use that oxygen, producing adaptations that contribute to cardiovascular fitness. In hot water, the increased heart rate is largely a response to heat and changes in circulation. Some of the same cardiovascular mechanisms are involved, but the overall demands on the body are different.
Exercise also does things that sitting in hot water cannot. Depending on the activity, it can develop muscular strength, endurance, balance and coordination. Passive heating may have benefits of its own, but an elevated heart rate isn't enough to establish them.
Could passive heating help people who struggle to exercise?
One reason scientists are investigating this subject is that conventional exercise isn't equally accessible to everyone. Age, injury, mobility difficulties and certain medical conditions can make physical activity challenging. If passive heating could provide some cardiovascular benefits without requiring much movement, it might prove useful for people who struggle to exercise regularly.
The January review primarily examined healthy adults, while the September experiment involved a small group of middle-aged participants with overweight or obesity. Neither establishes that hot-water immersion is an effective alternative to exercise for people with limited mobility or cardiovascular conditions.
There's also a safety consideration. Hot water places demands on the body even when no physical effort is involved. Overheating, dehydration, light-headedness and changes in blood pressure can all be concerns, particularly for people with certain medical conditions or taking particular medications. Anyone considering passive heating for a medical or therapeutic purpose should seek appropriate professional advice.
What does this mean for hot tub owners?
The research involved controlled experimental conditions, which aren't necessarily representative of ordinary hot tub use.
In the January review, water temperatures ranged from 37.5°C to 45°C, with immersion periods ranging from 10 to 120 minutes. The September study used 30 minutes at 40°C, with participants submerged to chest level.
These are descriptions of research protocols, not recommendations for home use. Some of those temperatures and durations would be inappropriate or potentially dangerous in a domestic hot tub.
The cardiovascular response also depends on how much of the body is immersed, the temperature of the water and how long someone stays in it. We therefore can't assume that a typical 15- or 20-minute soak will produce the same results.
There's a distinction between sitting in hot water and exercising in it, too. Gentle movement in a hot tub involves some physical activity, while swimming or undertaking structured aquatic exercise in a swim spa places much greater demands on the muscles and cardiovascular system.
For hot tub owners, the research offers an insight into what happens to the body during immersion. It doesn't establish a new exercise routine.
So, does sitting in a hot tub count as exercise?
Not in the conventional sense. The cardiovascular responses are real, and some are surprisingly substantial, but the evidence doesn't yet establish that repeated hot-water immersion produces the lasting fitness benefits associated with regular physical activity.
It would be easy to take the headline findings from these studies and turn them into a story about hot tubs offering the benefits of exercise. As a company that sells hot tubs, we could certainly see the appeal of that argument. But it would be getting ahead of the science, and we think the research deserves a more careful reading than that.
There's plenty here to be interested in, particularly the possibility that passive heating might one day help people who struggle with conventional exercise. Whether that potential translates into practical health benefits is something further research will need to establish.
In the meantime, relaxation, comfort and taking time out are perfectly good reasons to enjoy a hot tub. If regular soaking eventually proves to offer additional cardiovascular benefits, that would be welcome news. But we'd rather give you an accurate account of what the research says than promise benefits it hasn't yet demonstrated.
