Cold plunges have gone from an obscure athlete ritual to something with a queue outside it. The research is genuinely interesting, and almost none of it says what the marketing says. Two findings in particular should change how you use one.
Yes, it reduces soreness. With three caveats.
A Cochrane review pooled 17 trials covering 366 participants and found cold water immersion did reduce muscle soreness compared with doing nothing — at 24 hours (SMD −0.55, 95% CI −0.84 to −0.27), 48 hours (−0.66, −0.97 to −0.35), 72 hours (−0.93, −1.36 to −0.51) and 96 hours. Runners did particularly well: the reviewers noted that studies using running-based exercise showed significantly larger effects.
Now the caveats, in ascending order of importance.
First, the evidence is weak. The reviewers’ own summary of it: “Study quality was low.” Most trials also failed to actively look for adverse events, so the safety data largely was not collected.
Second, it was no better than a warm bath. This is the finding that rarely survives into popular articles. Across the studies that compared cold water against contrast or warm water immersion, there was no evidence of a difference at any follow-up point. Sitting in a bath helped. The bath being cold added nothing measurable.
Third, a placebo matched it. In a 2014 trial, 30 active men were given either cold immersion (10.3°C for 15 minutes), a thermoneutral bath, or a thermoneutral bath presented convincingly as a “recovery oil” treatment. The placebo group recovered strength as well as the cold group, and both beat the plain thermoneutral bath. The authors concluded the benefits are “at least partly placebo related”.
It does not reduce inflammation. It raises it.
“Reduces inflammation” is probably the most repeated claim about cold plunges, and a 2025 meta-analysis of 11 studies covering 3,177 people found the opposite: inflammatory markers rose significantly straight after immersion (SMD 1.03, 95% CI 0.37 to 1.68) and were still elevated an hour later (SMD 1.26, 95% CI 0.59 to 1.94).
That is not necessarily bad — a short inflammatory signal is part of how tissue adapts. But it is the reverse of what the marketing says, and it may be part of why regular plunging interferes with training gains.
The same review found stress reduction at only one of five measurement points (12 hours post), with null results immediately, at one hour, at 24 hours and at 48 hours. And no effect on immune function. One significant result in five timepoints is a thin basis for a claim.
The finding that should actually change your behaviour
If you do strength training — and as a runner you should — regular post-exercise cold immersion appears to reduce the adaptations you are training for.
In a 12-week controlled trial, 21 physically active young men did lower-body strength training twice a week. Half took a 10-minute cold plunge at 10°C after every session; half did light cycling instead. Both groups gained muscle. But the cold group gained 103 g of muscle against the active-recovery group’s 309 g — a difference the authors describe with an effect size of d = 4.1. Type II fibre cross-sectional area rose significantly in the active recovery group and not in the cold group. Leg press and knee extension strength both ended up significantly higher without the ice.
This is not one study. A 2021 meta-analysis of eight controlled studies found regular cold immersion alongside resistance training had a harmful effect on strength outcomes: SMD −0.60 (95% CI −0.87 to −0.33, p < 0.0001). A separate 2019 trial replicated the blunted hypertrophy, though in that one maximal strength was unaffected — so the muscle-size finding is more consistent than the strength finding.
The authors of the 2015 trial put it plainly: anyone using strength training to improve performance, recover from injury or maintain health “should therefore reconsider whether to use cold water immersion”.
For endurance training, it is neither help nor harm
The same meta-analysis found no effect of cold immersion on endurance outcomes — time-trial power (SMD −0.07, 95% CI −0.54 to 0.53) or time-trial duration (SMD 0.00, −0.58 to 0.58). Those intervals are wide, so read it as “no evidence of an effect” rather than proof of none.
You may also have seen the claim that cold exposure boosts mitochondria. That traces to a single study of eight men using a one-leg-immersed design, in which the headline markers — p38, PGC-1α, PPARα — did not reach statistical significance, and a better-designed follow-up failed to reproduce the signalling effect. It is not a basis for the claim.
And in runners specifically: a trial of 30 recreational runners after a 10 km road run found 10 minutes at 10°C was no better than room-temperature immersion or plain rest on any measure. With only 10 per group that study is underpowered, so treat it as weak evidence rather than a verdict.
What the studies actually tested
Worth knowing before you follow a protocol off social media. Essentially every trial above used around 10°C for 10 to 15 minutes. That is the entire evidence base. There is no research identifying an optimal temperature or duration, and advice citing much colder water or much longer exposures is extrapolating past anything that has been tested.
Before you get in
Cold water immersion triggers a large, immediate cardiovascular response — an involuntary gasp, a spike in heart rate and blood pressure. Physiologists have proposed that simultaneous activation of opposing branches of the nervous system can cause arrhythmias in vulnerable people.
The dose matters, and the numbers are worth knowing. Sitting in cold water, head out, breathing freely, produces arrhythmias in roughly 2% of immersions. The variable that changes everything is breath-holding, not depth: releasing a breath-hold in cold water produced arrhythmias in around 60% of head-out immersions, and in about 80% of full submersions — in one series, 29 of 36 breath-hold submersions in twelve healthy volunteers. So a tub plunge is safe on this count only if you keep breathing. Never hold your breath, never put your face in, and get in slowly enough that the gasp does not force a breath-hold on you.
Being straight about the gap: no study has quantified cardiovascular risk from recreational post-exercise cold plunging. The safety literature is about open-water immersion and drowning. That is a reason for caution, not reassurance.
- Talk to your doctor first if you have any heart condition, arrhythmia, high or low blood pressure, Raynaud’s, or are pregnant. Specific risk has been documented in long QT syndrome, in people on medications that prolong the QT interval, and in atherosclerosis — if you do not know whether that includes you, that is itself a reason to ask.
- Never submerge your face or hold your breath, and never plunge alone.
- Do not combine with alcohol.
- Get out for chest pain, palpitations, dizziness or numbness that does not settle.
So should you use one?
- Racing or in a hard block with sessions close together? Reasonable. When the next session matters more than long-term adaptation, feeling recovered has real value — even if some of that is placebo. Placebo is not nothing.
- Building strength? Skip it, or leave several hours between lifting and plunging. This is where the evidence says you are working against yourself.
- Just want to feel better after a long run? A warm bath performed as well in the trials, costs nothing, and carries none of the caveats.
The honest summary: cold plunges are not useless, but almost every specific claim made for them is either untested or contradicted, and the one well-replicated finding is a downside.
References: Bleakley C, et al. Cold-water immersion for preventing and treating muscle soreness after exercise. Cochrane Database Syst Rev, 2012. doi:10.1002/14651858.CD008262.pub2 · 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 · Malta ES, et al. The Effects of Regular Cold-Water Immersion Use on Training-Induced Changes in Strength and Endurance Performance. Sports Med, 2021. doi:10.1007/s40279-020-01362-0 · Broatch JR, et al. Postexercise cold water immersion benefits are not greater than the placebo effect. Med Sci Sports Exerc, 2014. doi:10.1249/MSS.0000000000000348