Sauna, cold baths, red light and compression boots are arriving in spas, although the evidence behind them carries very different weight.

Why it matters

The advanced guest has often heard of them, sometimes with promises attached. They expect a serious venue to know how to distinguish what rests on decades of observation from what remains a lead.

Classifying these practices honestly is the first thing a hotel can offer. It is also what protects it.

What science establishes

Regular sauna use is associated with lower mortality. In a Finnish cohort of 2,315 men aged 42 to 60 followed for around twenty years, those who took a sauna four to seven times a week had a lower risk of sudden cardiac death than those who took one only once a week, after adjustment for risk factors (hazard ratio 0.37). Comparable associations were observed for cardiovascular and all-cause mortality. Laukkanen et al., 2015. Established as an association; it is not proof of cause. The population is male, Finnish, middle-aged, with a cultural practice of sauna.

Cold after exercise reduces muscle soreness, nothing more. A synthesis of fifteen meta-analyses (161 studies) concludes that immersion for 10 to 15 minutes in cold water reduces muscle soreness for up to 96 hours and helps recover muscle power at 24 or 48 hours. It does not improve strength. The quality of the meta-analyses is judged to be low. Berjisian et al., 2026. Established for muscle soreness, in healthy adults, often athletes.

Cold straight after strength training holds back gains. In 21 active men trained for twelve weeks, ten minutes of cold water after each session reduced gains in strength and muscle mass, compared with active recovery. Roberts et al., 2015. The 2026 synthesis confirms this effect with repeated use. Established, young men. For a guest aged 55 and over who is working on muscle mass, timing matters.

What is emerging

Red light, or photobiomodulation. Applied before exercise, it reduces muscle soreness and improves performance at 24 hours, with a low level of certainty. Canez et al., 2025. A meta-analysis of 24 trials in athletes points in the same direction, while stating that the effect has not yet been definitively demonstrated. Luo et al., 2021. Protocols (wavelength, dose, duration) vary greatly from one study to another. Emerging, heterogeneous evidence, young and athletic populations.

Pneumatic compression. A meta-analysis of 17 studies finds a trivial to small benefit on muscle function, and a trivial to moderate one on perceived pain. Maia et al., 2024. Another meta-analysis finds no reduction in muscle soreness at 24 hours, with a moderate level of certainty. Canez et al., 2025. Emerging, limited and contradictory evidence.

Sauna beyond the heart. An overview links regular sauna use to blood pressure, arterial flexibility and other markers, mainly on the basis of Finnish observational studies. Laukkanen et al., 2018. Emerging.

What we refuse to say

We do not say that the sauna lengthens life. We say that in Finland, those who use it often live longer, and that we do not yet know why.

We do not say that cold “strengthens immunity” or “burns fat”. The studies cited do not show it.

We do not say that red light regenerates the skin or cells. We say that trials on muscle recovery are encouraging, and still fragile.

We point out that intense heat and cold place demands on the heart. Medical advice is recommended in case of cardiovascular disease.

What a hotel can do

Why the current offer disappoints. Many spas have a sauna, but nothing tells the guest how to use it, nor why the cold bath is placed differently depending on whether they have just been running or lifting weights.

Minimum baseline (often already in place). An existing sauna, with a clear notice: duration, frequency, hydration, precautions. A cold shower or cold bath, with the instruction to keep it away from strength-training sessions. Access at extended hours.

Optimised baseline. Devices from the IO8 stack lent by the night, such as a red light panel or compression boots: catalogue price 750 € per device, made available at 50 € per night against a card pre-authorisation, paid off in fifteen nights at catalogue price, fewer than ten at the volume rate. And the longevity menu: around ten services, from 60 to 150 € per session, integrated into the existing spa, each presented with its level of evidence.

The target. A guest who knows what they are doing, why, and with what level of evidence. The amounts are indicative and to be confirmed by quote.

What the Living Lab measures

Measurement planned. The Living Lab, near Lisbon, is being equipped in waves. We will measure the temperature of the cold water and the sauna, the durations actually practised, and heart rate and its variability before and after each session.

We will also track the order of sessions in relation to strength training. The readings will be dated and published here.

Sources

• Laukkanen T et al. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Intern Med, 2015. doi:10.1001/jamainternmed.2014.8187
• Laukkanen JA et al. Cardiovascular and other health benefits of sauna bathing: a review of the evidence. Mayo Clin Proc, 2018. doi:10.1016/j.mayocp.2018.04.008
• Berjisian E et al. Strategic application of post-exercise cold-water immersion to enhance performance recovery and adaptation: an umbrella review of 15 published systematic reviews with meta-analysis. Sports Med Open, 2026. doi:10.1186/s40798-026-01116-8
• Roberts LA et al. Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training. J Physiol, 2015. doi:10.1113/JP270570
• Canez MS et al. Effects of photobiomodulation, intermittent pneumatic compression and neuromuscular electrical stimulation on muscle recovery: systematic review with meta-analysis. J Bodyw Mov Ther, 2025. doi:10.1016/j.jbmt.2025.06.021
• Luo WT et al. Effects of low-level laser therapy on muscular performance and soreness recovery in athletes: a meta-analysis of randomized controlled trials. Sports Health, 2021. doi:10.1177/19417381211039766
• Maia F et al. Effects of lower-limb intermittent pneumatic compression on sports recovery: a systematic review and meta-analysis. Biol Sport, 2024. doi:10.5114/biolsport.2024.133665

The longevity audit for venues  ·  The Research Journal

IO8 Living Lab, near Lisbon. Measured, never promised.

← Previous articleSeries 1Next article →