Hot Tubs, Saunas and Ice Baths: The Science of Recovery

Hot, cold, and the case for both

Heat and cold do different things to your body, and a remarkable amount of what they do is the opposite of what your phone, your office chair and your sleep schedule are doing to you the rest of the week.

Two thousand years of bathing, thirty years of data.

Your nervous system was built for stress that arrives and ends

Comfort can drain your energy. Your body responds well to brief, intense bursts of thermal stress, like a sauna or an ice bath, which train your cardiovascular system and give you a reset from the daily routine.

The technical name is hormesis: a brief, controlled stress that triggers a recovery response much larger than the stress itself.¹ Twenty minutes at 85°C, three minutes at 4°C, and your body answers each with cardiovascular conditioning and a hormonal response.

None of this is exotic. It is what humans did for two thousand years before central heating, and what a generation of researchers have been quietly measuring for the last thirty.

A woman's face split between icy water on one side and a steamy sauna on the other, showing cold and heat

Four doors, one nervous system

Each works on its own. Together they cover the full thermal range, supporting recovery and long-term cardiovascular health.

Way in	Temperature	Session	What it does
Hot tub	37–40°C	20–30 min	Buoyancy off-loads joint pressure and blood flow to the legs rises.
Sauna	70–95°C	15–20 min	A cardiovascular response from passive heat, with heat-shock proteins that help repair cells.
Ice bath	2–5°C	2–4 min	Noradrenaline and dopamine both rise sharply.
Swim spa	26–32°C	30–60 min	Full-body aquatic workouts, and swimming and relaxing all year round.

A woman relaxing in a hot tub on a garden patio

Warm water is passive cardio for a stationary body

Hot tub · Hydrotherapy

Stiff joints and back pain? Warm water takes much of gravity's pressure off your spine, while the heat increases blood flow to help muscles recover and ease daily stress.

Hydrotherapy has measurable effects across the body's systems.² In water up to the neck, buoyancy lifts about 90% of your body weight off your joints and spine,³ while heat raises your heart rate and increases blood flow to the legs.⁴ The result is a cardiovascular dose without the impact.

−5 mmHg

Drop in mean arterial blood pressure after 8 weeks of regular hot-water immersion, 4 to 5 sessions a week, in young sedentary adults.⁵

+95%

Improvement in flow-mediated dilatation, a measure of how well arteries widen, from 5.6% to 10.9% in the same 8-week study.⁵

Ready to bring hydrotherapy into your daily routine? Explore the hot tub collection.

The most-studied longevity habit nobody talks about

Sauna · Heat therapy

Feeling sluggish or struggling to switch off? Deep heat acts like a passive workout, relaxing tension and helping you wind down at the end of the day.

More than two thousand Finnish men were followed for over twenty years, and the pattern was clear: the more sauna sessions per week, the lower the risk of death from any cause.⁶ Researchers are still mapping the mechanisms behind it.¹

−40%
Lower risk of death from any cause in men using a sauna 4–7 times a week, compared with once a week.⁶
−63%
Lower risk of sudden cardiac death in the same group of men.⁶
−66%
Lower risk of dementia in the same Finnish cohort, over about 20 years.⁷

Understand the mechanics? Choose your heat source from the sauna range.

A woman relaxing on a towel inside an infrared sauna cabin

Traditional · 80–95°C

Low humidity. Heats the air via a stove and stones. Suits social bathing and the deepest sweat.

Infrared · 45–60°C

Ambient humidity. Heats the body directly using far-infrared panels, at a lower air temperature.¹

A man sitting in a compact ice bath in a tiled indoor room

+250%

Rise in plasma dopamine during a one-hour immersion in 14°C water.⁸

−29%

Fewer days of sickness absence from work among people who took a hot-to-cold shower every day for 30 days, in a trial of 3,018 adults.¹⁰

Three minutes of cold, a clearer head after

Ice bath · Cold therapy

Need a mental reset? A quick plunge sets off a surge of natural stress chemicals, leaving you alert and energised.

Cold immersion at 2–5°C is the shortest and most demanding of the four. In laboratory studies, cold-water immersion produces a large rise in noradrenaline and dopamine, two chemicals linked with focus and mood.⁸

A three-minute plunge, moment by moment

0:00
Skin contacts water. Blood vessels in the skin narrow and blood shifts towards the core.
0:30
Cold-shock response: a sharp inhale and a raised heart rate. Practice slows the gasp, and the response fades after about four immersions.⁹
1:30
Noradrenaline, linked with focus, mood and pain modulation, climbs. In a one-hour immersion at 14°C it rose by 530%.⁸
3:00
Exit. Re-warming begins. Dopamine also rises in cold-water immersion, by 250% in the same study.⁸

Prepared for the plunge? Discover the ice bath collection.

The ultimate environment for family fun, fitness and relaxation

Swim spa · Aquatic fitness

Want a pool without the massive footprint? Get a full-body aquatic workout against an adjustable current, then recover in the heated hydrotherapy seats. Year-round swimming, sorted.

Swim spas combine swimming with the hydrotherapy features of a luxury hot tub. Adjustable water currents let you swim in place for a full-body workout, while powerful jets provide hydrotherapy for muscle recovery.

365 days

Heated water for year-round aquatic fitness.

Low impact

Water carries most of your body weight while you swim against the current.³

Secure the best of both fitness and recovery in a single footprint with the swim spa range.

A swimmer swimming against the current in a swim spa in a garden

The case for contrast

Heat dilates. Cold constricts.

Cycling between the two, which Nordic bathers call contrast bathing, puts your blood vessels through the full widen-and-narrow cycle. It is a workout for the blood vessels themselves.

Heat or cold, alone

Trains one half of the vascular response.
Single-direction stress on the autonomic nervous system.
Strong, well-documented cardiovascular benefits.
Easier entry point: start with whichever fits the day.

Hot and cold, contrast

Trains the full dilate-and-constrict response of your blood vessels.
Strength and power return faster after hard exercise than with passive rest.¹¹
Heat and cold in one session: a few rounds of each.

One week, kept simple

In the research, the strongest sauna results come at four to seven sessions a week.⁶ Here is a balanced schedule designed for someone with full access.

Monday

Sauna2 × 15 min

Start the week with a solid cardiovascular load and build a steady routine.

Tuesday

Hot tub25 min

Passive recovery. Off-load the spine and let hydrotherapy soothe muscular tension.

Wednesday

RestFull day

Adaptation day. Allow your nervous system to absorb the thermal stress of the previous days.

Thursday

Contrast3 rounds

Sauna (12 min) to ice bath (2 min). Extreme vascular expansion followed by rapid constriction.

Friday

Sauna2 × 15 min

End the working week with a good sweat to release accumulated stress.

The weekend

Contrast and socialActive recovery, family time

Saturday contrast rounds, Sunday reserved for active aquatic recovery in the hot tub or swim spa.

Figures on this page are drawn from peer-reviewed research and represent average effects across study populations. Individual response varies. This page is general information, not medical advice. If you are managing a heart condition or pregnancy, speak to your GP before starting heat or cold therapy.¹²

Sources

Paul Margerison

Managing Director & Founder, Outdoor Living

Heat, cold and water are old habits with a growing body of research behind them. This guide sets out what the studies measured, so you can choose what suits your routine.

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Your nervous system was built for stress that arrives and ends

Four doors, one nervous system

Warm water is passive cardio for a stationary body