The short version
- A meta-analysis of eight controlled studies found regular cold-water immersion alongside resistance training had a harmful effect on strength outcomes (SMD -0.60, 95% CI -0.87 to -0.33) and no effect on endurance performance.
- In a 7-week trial of 16 men, type II muscle fibre cross-sectional area increased less with 15 minutes at 10°C after each session, while one-repetition maximum leg press gains were similar between groups.
- Pooling 52 studies, cold-water immersion 24 hours after high-intensity exercise improved muscular power (SMD 0.22), soreness (SMD -0.89), creatine kinase (SMD -0.85) and perceived recovery (SMD 0.66).
- The same 52-study meta-regression found shorter durations and lower temperatures produced larger effects, so longer immersions are not better supported than brief ones.
- In a 12-week trial of 21 men, strength and muscle mass increased more in the active recovery group than in the group doing 10 minutes of cold-water immersion after each session.
Most arguments about ice baths are people talking past each other. One side has felt how much better the next morning is. The other has read the hypertrophy trials. Both are describing something real, and the disagreement dissolves the moment you accept that feeling better tomorrow and building muscle over ten weeks are two different outcomes that cold affects in opposite directions.
What cold genuinely buys you tomorrow
Moore and colleagues pooled 52 studies in Sports Medicine, comparing cold-water immersion against passive recovery after a single hard bout. Twenty-four hours after high-intensity exercise, immersion improved muscular power (SMD 0.22), reduced muscle soreness (SMD −0.89), reduced serum creatine kinase (SMD −0.85) and improved perceived feelings of recovery (SMD 0.66). After eccentric exercise it improved recovery of muscular power (SMD 0.34). It did not significantly influence recovery of strength performance after either.
Their meta-regression also found a dose relationship: shorter durations and lower temperatures were associated with the largest effects on creatine kinase and endurance performance. That is the opposite of how plunges are usually sold, where longer is treated as more virtuous.
So: if the next session or the next match is what matters, cold is a defensible tool with reasonable evidence behind it. Nothing in the rest of this article takes that away.
What it costs across a training block
Now change the question from tomorrow to ten weeks.
Roberts and colleagues put 21 physically active men through 12 weeks of strength training with either 10 minutes of cold-water immersion or active recovery after each session, and found strength and muscle mass increased more in the active recovery group, alongside blunted satellite cell and anabolic signalling responses in the cold arm.
Fyfe and colleagues then ran the cleaner mechanistic version: 16 men, 7 weeks of whole-body resistance training three days a week, each session followed by 15 minutes at 10°C or 15 minutes at 23°C. The result is more interesting than the headline usually allows. Type II muscle fibre cross-sectional area increased less in the cold group (−1,959 µm², effect size −1.37), and post-exercise mTORC1 signalling was blunted while a marker of protein degradation rose. But improvements in one-repetition maximum leg press were similar between groups. Their conclusion was that cold-water immersion blunted fibre hypertrophy but not maximal strength.
Malta and colleagues pooled the chronic studies — eight of them — and found a harmful effect of regular immersion alongside resistance training on one-repetition maximum, maximum isometric strength and strength endurance (overall SMD −0.60, 95% CI −0.87 to −0.33) and on ballistic performance (SMD −0.61). Alongside endurance training, they found nothing: no effect on maximal aerobic power (SMD −0.07) or time-trial performance (SMD 0.00).
So what should you take from this?
The split is unusually clean for this literature. If you are an endurance athlete, the pooled evidence does not show a cost to regular immersion. If you are lifting to get bigger, it does. And the honest nuance from Fyfe is that "will it cost me size" and "will it cost me strength" may have different answers, because you can gain strength without adding fibre area.
Three practical rules follow, and none of them is "never".
- Separate cold from lifting in time. The trials that found blunted adaptation put people in the water within minutes of the last set. If you want a plunge and a hypertrophy block, put hours between them, or put the plunge on a rest day.
- Use it when the next performance outweighs the next adaptation. Two matches in a weekend, a second session that day, a tournament — that is exactly the case the 52-study meta-analysis supports.
- Shorter and colder, not longer and heroic. The dose-response ran that direction, and the trials showing the adaptation cost used 10 to 15 minutes.
A word on why the cold arm keeps losing to the comparison group: in Roberts' study the control was active recovery, not lying down. That comparison says something about cold; it does not, on its own, promote gentle cycling to a growth intervention.
And do not read your wearable as an umpire here. Cold reliably shifts autonomic measures for hours afterwards, so heart rate variability will often look flattering the morning after a plunge in the middle of a block where fibre growth is being blunted. The dashboard and the biopsy disagree, and the biopsy is measuring what you trained for.
The caveat we'd rather you heard from us
Cold water immersion is not risk-free. The cold shock response raises heart rate and blood pressure and drives involuntary gasping, which is a genuine problem if you have cardiovascular disease, uncontrolled hypertension, or a seizure history — and drowning risk is why nobody should be plunging alone or after drinking. If any of that describes you, this is a question for your clinician before it is a question about training adaptation.
If you love the plunge for how it makes you feel, keep it. Just stop believing it is helping the muscle, and keep it out of the weeks whose entire purpose is growth.
Good questions
Do ice baths stop muscle growth?
They can blunt it. Two controlled resistance-training trials found smaller increases in muscle fibre size with post-session cold-water immersion, and a meta-analysis of eight studies found a harmful pooled effect on strength adaptations. Blunt is not block — people in these trials still got stronger, just less so in the measures affected. If hypertrophy is the point of your block, keep the cold away from it.
How long should an ice bath be?
Shorter than most people think. The trials sit around 10 to 15 minutes, and a meta-regression across 52 studies found shorter durations and lower temperatures produced the larger effects on damage markers and endurance performance. There is no evidence supporting long immersions as more effective, and long immersions carry more risk. Extra minutes are buying discomfort, not results.
Are ice baths bad for endurance athletes too?
The pooled evidence says no. In the meta-analysis of chronic use, cold-water immersion alongside endurance training had essentially zero effect on maximal aerobic power or time-trial performance. The adaptation cost showed up specifically in the resistance-training studies. If you run, ride or swim and you like the plunge, the current data does not give you a reason to stop.
Is a cold shower the same as an ice bath?
No, and nobody has shown it is. Every trial discussed here immersed people to the waist or higher in water at or below 15°C for a set number of minutes. A shower delivers a fraction of that thermal load to a fraction of the body. It may well feel good and it is very unlikely to harm your training, but it should not be assumed to carry either the benefits or the costs measured in the immersion literature.
Why does my HRV look better after a cold plunge?
Because cold water strongly affects the autonomic nervous system for hours afterwards, which is what heart rate variability measures. A higher morning number after a plunge tells you your nervous system responded to cold. It does not tell you your muscle repaired better, and in a hypertrophy block the trials suggest the opposite may be happening while the score looks good.
Is cold plunging safe for everyone?
No. The cold shock response raises heart rate and blood pressure and causes involuntary gasping, which is dangerous with cardiovascular disease, uncontrolled high blood pressure, or a seizure history, and it is a drowning risk for anyone plunging alone or after alcohol. Clear it with a clinician if any of that applies. This is one of the few recovery tools with a genuine acute risk profile.
Sources
- Moore E, Fuller JT, Buckley JD, Saunders S, Halson SL, Broatch JR, Bellenger CR. Impact of Cold-Water Immersion Compared with Passive Recovery Following a Single Bout of Strenuous Exercise on Athletic Performance in Physically Active Participants: A Systematic Review with Meta-analysis and Meta-regression. Sports Med, 2022. View study
- Malta ES, Dutra YM, Broatch JR, Bishop DJ, Zagatto AM. The Effects of Regular Cold-Water Immersion Use on Training-Induced Changes in Strength and Endurance Performance: A Systematic Review with Meta-Analysis. Sports Med, 2021. View study
- Fyfe JJ, Broatch JR, Trewin AJ, Hanson ED, Argus CK, Garnham AP, et al. Cold water immersion attenuates anabolic signaling and skeletal muscle fiber hypertrophy, but not strength gain, following whole-body resistance training. J Appl Physiol (1985), 2019. View study
- Roberts LA, Raastad T, Markworth JF, Figueiredo VC, Egner IM, Shield A, et al. Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training. J Physiol, 2015. View study
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