If you’ve looked into whether to cold plunge before or after sauna, you’ve hit the same advice everywhere: always end on cold. The instruction traces back to a single study, and the internet adopted it as a universal rule. But it answered one specific question about metabolism, and most people using contrast therapy aren’t chasing that outcome. They want better sleep, sharper mornings, or faster recovery. The right ending changes with the goal.
What the Søberg Principle Actually Showed
In 2021, Dr Susanna Søberg, a metabolism researcher at the University of Copenhagen, and colleagues published a study in Cell Reports Medicine examining eight habitual winter swimmers against eight controls. The swimmers, who regularly combined cold-water immersion with sauna, displayed enhanced cold-induced thermogenesis and improved thermoregulation. What followed became the Søberg Principle: end your contrast session on cold and your body must reheat itself without external help, activating brown adipose tissue (the metabolically active fat that burns energy to generate warmth).
Fair enough: the finding is real, the inference reasonable. But the study didn’t test sequencing head-to-head, didn’t include women, and the sample was eight people. What happened next was predictable: a narrow finding, amplified by podcasters and wellness media, became blanket advice for everyone doing contrast therapy for any reason. Finnish bathers have never followed a fixed ending – they cycle between heat and cold based on feel, finishing when they’re ready.
For Metabolism: End on Cold, but Calibrate Your Expectations
If metabolic activation is your goal, the Søberg Protocol holds. Ending on cold forces thermoregulatory effort, and that effort recruits brown fat. Over repeated sessions, this may improve your body’s capacity to generate heat from stored energy.
But calibration matters. When Eric Trexler, PhD, examined the practical significance of brief cold exposure for Stronger by Science, the numbers were sobering: the absolute increase in energy expenditure from typical cold-exposure durations amounts to less than 11 kilocalories. A separate review he cited concluded there is little reason to believe any practical and tolerable implementation of cold exposure will lead to meaningful body-composition changes. Legitimate mechanism. Negligible magnitude — at least for fat loss.
For Sleep: End on Heat
This is where the universal “end on cold” advice fails most visibly.
A 2019 meta-analysis in Sleep Medicine Reviews by Haghayegh and colleagues found that passive body heating at 40–42.5°C, scheduled one to two hours before bed, significantly shortened the time it took to fall asleep. Physiologically, the mechanism is straightforward: raising core temperature triggers the body’s heat-dissipation response, flushing blood to the skin’s surface. As core temperature then drops, the body reads it as a signal to initiate sleep.
Ending on cold does the opposite. It constricts peripheral blood vessels, pulls heat inward, and raises alertness. For evening sessions aimed at sleep, the evidence favours finishing in the sauna or a warm shower and letting your body cool naturally over the following hour. If sleep quality is your goal, the contrast therapy approach for sleep is the wrong framework.
For Alertness and Energy: End on Cold, for Different Reasons
A 2000 study in the European Journal of Applied Physiology by Šrámek and colleagues found that cold-water immersion at 14°C increased plasma dopamine concentrations by 250% and norepinephrine by 530%. The contrast therapy protocol (one hour of immersion) is far longer than a typical cold plunge, so the exact magnitude won’t translate directly. But the direction is consistent with what users report: finishing on cold produces a sustained, clear-headed alertness that can last hours.
A completely separate argument from the Søberg Principle. Same recommendation, different reason. Not brown fat, but catecholamine release. If you want to feel sharp and energised after your morning session, cold is the logical ending because of what happens neurochemically, not metabolically.
For Recovery: The Ending Matters Less Than You Think
Recovery is the goal where sequencing dogma has the least to stand on. A 2013 meta-analysis by Bieuzen and colleagues, pooling 18 trials, found that contrast water therapy improved recovery compared to passive rest but showed no clear superiority over other active recovery methods. The studies used varied sequencing, and no consistent pattern emerged favouring either ending temperature.
What appears to matter is the alternation itself. Whether your final immersion is hot or cold seems to be a matter of preference rather than physiology. If recovery is the goal, focus on the quality and duration of the contrast cycles. For runners using contrast therapy or those following CrossFit recovery protocols, the last thirty seconds are not where the work happens.
What Real Users Actually Do
In commercial contrast therapy facilities, a pattern shows up without anyone instructing it. Morning users tend to finish on cold. Evening users tend to finish on heat. They aren’t referencing a study. They’re following the logic of how they want to feel when they step out.
This is observational and self-reported, not clinical. But its alignment with the evidence is hard to ignore: the people who need alertness gravitate toward cold endings, and the people winding down gravitate toward warmth.
The Better Question
A single study about thermoregulation in eight winter swimmers became universal sequencing advice for millions of people with different goals at different times of day. That was always going to break.
The more useful question is simpler: What do I want to feel when I step out? Alert and sharp, end on cold. Calm and ready for sleep, end on heat. Recovering from training, focus on the contrast, not the finale. Use it tonight.
