Thermal & cold · graded by use, three uses
Cold Water Immersion
Sickness absence from work (self-reported).
Grade C: human trials exist, but they are small, mixed or not yet repeated. This is not a finding that it does not work. How to read a grade →
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How this letter has changedLatest: October 2026 · Corrected.
The record had set aside post-exercise recovery trials as a use it did not grade, while the page itself described them. Recovery now has its own row. Bleakley et al. (Cochrane, 2012; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 22336838), Moore et al. (Sports Med, 2022; PMID 35157264), Moore et al. (Sports Med, 2023; PMID 36527593) and Machado et al. (Sports Med, 2016; PMID 26581833) pool randomized trials from independent groups showing less soreness after strenuous exercise; self-reported soreness caps the letter at B under the written definition. Berjisian et al. (Sports Med Open, 2026; PMID 42816732) confirms both the recovery benefit and the harm to strength gains and joins both rows. Ngandeu Schepanski et al. (Front Physiol, 2026; PMID 42819812) joins the Mood row: benefit not established. Heart rate variability after immersion has its own row at C: the pooled acute rise replicates (Jdidi et al., J Therm Biol, 2024; PMID 38663342; Galvez-Rodriguez et al., Physiother Res Int, 2025; PMID 39918163; Almeida et al., J Sci Med Sport, 2016; PMID 26614422; Al Haddad et al., Int J Sports Physiol Perform, 2012; PMID 21941017), but heart rate variability is not an established stand-in for a clinical outcome, which caps it at C. Headline letter unchanged. Applied the written grade definition under the editor's standing instruction of October 2026 (Arnold Sandlow, D.C.).PMID 22336838 PMID 35157264 PMID 36527593 PMID 26581833 PMID 42816732 PMID 42819812 PMID 38663342 PMID 39918163 PMID 26614422 PMID 21941017
The record described in prose that immersion after lifting blunted strength and muscle gains (Roberts et al., J Physiol, 2015; PMID 26174323) and that two pooled analyses agree (Malta et al., Sports Med, 2021; PMID 33146851; Grgic, Eur J Sport Sci, 2023; PMID 35068365), but carried no row for it. Under the written rule a treated arm that did worse than control on the stated endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. is D on Route 2 Human randomized trials have been run and did not show benefit on the stated outcome. One of the two routes to the lowest letter on EBL's scale. with the harm badge, so the finding now has its own row where a reader meets it. The headline C rests on the Cain 2025 pooling (PMID 39879231) and the Buijze 2016 trial (PMID 27631616), pooled randomized evidence, so the not-replicated flag contradicted the record and is removed; the letter is unchanged. Applied the written grade definition under the editor's standing instruction of October 2026 (Arnold Sandlow, D.C.).PMID 26174323 PMID 27631616 PMID 33146851 PMID 35068365 PMID 39879231
The endpoint line listed inflammation and mood; Cain 2025 (PMID 39879231) found inflammation markers rose for an hour after immersion and mood did not change, so the headline endpoint now reads stress at 12 hours, sleep quality and quality of life, and mood and inflammation are each a D Route 2 use. 'Few small RCTs Randomized controlled trial: people are assigned to the treatment or a comparison by chance, so the groups differ only in what they received. It is the design that can show cause and effect.' is corrected: one trial, Buijze 2016 (PMID 27631616), carries 3,018 of the 3,177 pooled participants and is now cited and graded as a C use on self-reported sickness absence. Roberts 2015 (PMID 26174323) showed smaller strength and muscle gains, not only blunted signaling; Grgic 2023 (PMID 35068365) and Malta 2021 (PMID 33146851) replicate it, and the three now sit together as a harm signal for immersion after lifting. 'Signalling' is now spelled signaling. Headline letter unchanged; whether the headline should be split further is for the editor.PMID 39879231 PMID 27631616 PMID 26174323 PMID 35068365 PMID 33146851
Every change to a letter on this site is dated and published. The full evidence log →
Cold water immersion means a cold plunge or ice bath. After hard exercise, it eased muscle soreness and helped short-term recovery. In a large Dutch study, people taking cold showers called in sick less often, though they were not sick fewer days. Used after every weight session, cold baths led to smaller gains in strength and muscle. Mood did not change.
The C belongs to one of the three uses graded on this record. The other two carry their own letters.
As studied, and the trials
Bleakley et al. (Cochrane Database Syst Rev, 2012; PMID 22336838): 17 small trials, 366 participants, low quality; soreness lower than with rest at 24 to 96 hours (SMD -0.55 to -0.93), no better than contrast or warm-water immersion. Moore et al. (Sports Med, 2022; PMID 35157264), 52 studies: after high-intensity exercise, muscular power recovered better at 24 hours (SMD 0.22) and soreness was lower (SMD -0.89); strength recovery was not affected. Moore et al. (Sports Med, 2023; PMID 36527593), 28 studies: lower soreness than other recovery methods. Machado et al. (Sports Med, 2016; PMID 26581833), 9 studies: slightly better than passive recovery, best at 10 to 15 degrees Celsius for 10 to 15 minutes. Berjisian et al. (Sports Med Open, 2026; PMID 42816732): across 15 meta-analyses the recovery benefits hold, with certainty rated low to very low. Replicated The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. pooled randomized evidence from independent groups; self-reported soreness caps the letter at B. The same immersion after strength training reduces strength and muscle gains (the harm row on this record).
As studied, and the trials
Jdidi et al. (J Therm Biol, 2024; PMID 38663342), 24 studies: RMSSD (SMD 0.61) and high-frequency power rose and heart rate fell, for up to 15 minutes after cold, with cold water and cryostimulation pooled together. Galvez-Rodriguez et al. (Physiother Res Int, 2025; PMID 39918163), 12 randomized trials after exercise: all reported parasympathetic reactivation, six significant against passive recovery. Almeida et al. (J Sci Med Sport, 2016; PMID 26614422), 100 participants: only the 15-minute, 14 degree Celsius group differed from control on SDNN. Al Haddad et al. (Int J Sports Physiol Perform, 2012; PMID 21941017), 8 swimmers over one week: higher morning HRV after daily immersion. The acute effect replicates, but heart rate variability is not an established stand-in for a clinical outcome the way blood pressure or LDL Low-density lipoprotein cholesterol, the cholesterol fraction most closely tied to plaque in the arteries. is, so under the written definition it qualifies for nothing above C. Whether daily immersion raises resting HRV over weeks rests on one 8-person, one-week trial, and no trial links the change to heart disease or survival.
As studied, and the trials
Buijze et al. (PLoS One, 2016; PMID 27631616): 3,018 adults without severe comorbidity, randomized to a 30, 60 or 90 second hot-to-cold shower or control for 30 days; self-reported sickness absence fell 29 percent (incidence rate ratio 0.71, P = 0.003), illness days did not change, and 79 percent of the intervention groups completed the 30 days. One large open trial on a self-reported endpoint: C.
As studied, and the trials
As studied, and the trials
As studied, and the trials
Roberts et al. (J Physiol, 2015; PMID 26174323): 21 men, 12 weeks, immersion after each session gave smaller gains in strength and muscle mass than active recovery and smaller rises in satellite cells and anabolic signaling after a single bout. Malta et al. (Sports Med, 2021; PMID 33146851): meta-analysis of 8 studies, harmful effect on strength adaptations (SMD -0.60), no effect on endurance adaptations. Grgic (Eur J Sport Sci, 2023; PMID 35068365): meta-analysis of 10 studies, strength gains attenuated (effect size How large a difference the treatment made, as distinct from whether the difference could be detected at all. -0.23). Tested, and the treated arm did worse on the stated endpoint: D on Route 2 with the harm badge. This row is about regular immersion after lifting; it says nothing about occasional immersion or immersion after endurance training, where the pooled analyses found no effect. Berjisian et al. (Sports Med Open, 2026; PMID 42816732), an umbrella review of 15 meta-analyses, found regular post-exercise immersion impaired strength and hypertrophy gains, the same direction.
Read the grade that matches your goal. How EBL grades by use →
Thermal therapy · Recovery
A letter describes the human evidence, not the product, the manufacturer, or the intervention's worth.
See the full evidence record →Cold water immersion (CWI) has human randomized evidence for reducing muscle soreness after strenuous exercise. It has been enthusiastically adopted by the biohacker community for purported longevity benefits that go well beyond what the evidence supports. Grade C reflects real but limited human trial data primarily for recovery endpoints, with important caveats about timing relative to resistance training and the absence of hard longevity outcome data.
| Protocol | Water temperature 10 to 15°C (50 to 59°F). Duration 10 to 20 minutes. Within 1 hour post-exercise for recovery benefits. Whole-body or lower-body immersion depending on target muscle groups. |
| Key caveat | CWI immediately after resistance training blunts acute muscle protein synthesis and may reduce long-term hypertrophy and strength gains. Pooled trials find that cold-water immersion soon after resistance training can attenuate strength and hypertrophy gains. The interval at which that effect disappears has not been established, so no specific separation time is stated here. |
| Cost | Cold plunge tub: $500 to $5,000. Ice bath: approximately $5 per session in materials. Commercial facility access: $20 to $50 per session. |
| Chronic HRV | Daily cold exposure acutely stimulates vagal tone but the evidence for chronic resting HRV improvement from cold exposure alone is not established in controlled human trials. See the HRV page for detail. |
| Vs. cryotherapy | Whole-body cryotherapy (cryochambers at -110°C for 2-3 minutes) has a separate but overlapping evidence base. CWI has stronger and more replicated evidence overall. |
Muscle soreness scores (VAS) after exercise sessions. Recovery quality (subjective). If combining with resistance training, track strength and hypertrophy separately to confirm the timing protocol is not blunting training adaptations.
Seventeen small trials, 366 participants, low quality. Soreness was lower than with rest at 24, 48, 72 and 96 hours, but results varied between trials, and cold water did no better than contrast or warm-water immersion. Limitation: the outcome was self-reported soreness, not performance or longevity markers.
RCT of 21 men. CWI after resistance training significantly attenuated long-term muscle hypertrophy and strength gains compared to active recovery over 12 weeks. Mechanism: CWI blunts the anabolic signaling (mTOR A signaling pathway that controls cell growth. Turning it down is one proposed mechanism behind several longevity interventions., satellite cell activation) that drives muscle protein synthesis after training. This finding is replicated and has significant implications for anyone combining CWI with muscle-building goals.
Meta-analysis of 9 studies. Cold water was slightly better than passive recovery for muscle soreness, with the best results at 10 to 15°C and 10 to 15 minutes. It does not show an anti-inflammatory effect: the pooled analysis of health trials (Cain et al., 2025; PMID 39879231) found inflammation markers rose for an hour after immersion.
Risk of cold shock response (sudden immersion gasp reflex) can cause water inhalation. A gradual entry blunts that reflex. Deep cold water alone carries a drowning risk. Cardiovascular risk: cold water causes acute blood pressure spike and increased cardiac work, people with cardiovascular disease should consult physician before CWI. Hypothermia risk with extended immersion below 10°C.
Antihypertensives: the acute blood pressure increase from cold immersion may interact with blood pressure management. Alongside antihypertensive therapy, it is a decision for a physician. Beta-blockers blunt the heart rate response to cold but do not eliminate the cardiovascular stress.
CWI is a legitimate recovery tool with real human RCT evidence. It is not a longevity intervention with mortality outcome data. The biohacker community has significantly overclaimed the evidence for cold exposure. The most important finding to know is the timing conflict with resistance training: in the published trials, repeated cold immersion IMMEDIATELY after a resistance session, typically within about fifteen minutes, attenuated the hypertrophy and strength adaptation.
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Primary evidenceFive papers, each linked to its PubMed record.
Cain et al. (PLoS One, 2025; PMID 39879231): systematic review and meta-analysis of 11 randomized trials, 3,177 participants, almost all from one cold-shower trial. Inflammation markers INCREASED immediately (SMD 1.03) and one hour after immersion (SMD 1.26); stress was lower at 12 hours (SMD -1.00) but not immediately, at 1, 24 or 48 hours; immune markers did not change; sleep quality and quality of life improved in the narrative synthesis; mood did not. Buijze et al. (PLoS One, 2016; PMID 27631616): the one large trial, 3,018 Dutch adults randomized to a 30, 60 or 90 second cold shower or control for 30 days; self-reported sickness absence fell 29 percent (incidence rate ratio 0.71), illness days did not change; one author was employed by the insurer that supported the study. Against regular use after lifting: Roberts et al. (J Physiol, 2015; PMID 26174323), 21 men, 12 weeks, found smaller gains in strength and muscle mass with immersion after each session than with active recovery, and smaller rises in satellite cells and anabolic signaling after a single bout; Grgic (Eur J Sport Sci, 2023; PMID 35068365), meta-analysis of 10 studies, found immersion attenuated strength gains (effect size -0.23); Malta et al. (Sports Med, 2021; PMID 33146851), meta-analysis of 8 studies, found a harmful effect on strength adaptations (SMD -0.60) and no effect on endurance adaptations. Grade C: one pooled analysis dominated by one trial, self-report endpoints, mixed direction.
Products carry no letter. The letter belongs to the therapy as the trials studied it, and no trial tested these products unless the entry says so. Listed alphabetically; payment does not affect order.
Home cold plunge tub. No trial has tested this product; the Cold Water Immersion grade describes the modality as studied, and its trials are small and short term.
Home cold plunge that cools to as low as 37°F with the included Pro Chiller, per the manufacturer. Six filters keep the water clean. No trial has tested this product; the Cold Water Immersion grade describes the therapy as studied.
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("cold water immersion"[tiab] OR "cold-water immersion"[tiab] OR "cold shower*"[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt])Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →