Depth of Cold Water Immersion and Sleep Architecture in Well-Trained Runners
Protocol
Randomized, counterbalanced design: 12 well-trained male endurance runners (VO2max 66.0 ± 3.9 ml/min/kg) performed a simulated trail (≈18:00) of high-intensity, intermittent running on a motorized treadmill (from the abstract).
Then 10 min of cold water immersion at 13.3 ± 0.2°C: whole-body including the head (WHOLE; n = 12), partial-body up to the iliac crest (PARTIAL; n = 12), or an out-of-water control (CONT; n = 10).
Measures: maximal voluntary isometric contraction, countermovement jump, plasma creatine kinase and subjective ratings until 48 h after the trail; nocturnal core body temperature; sleep and heart rate variability by polysomnography.
Key Findings
n=12 well-trained male runners; post-exercise CWI at 13.3°C × 10 min; polysomnography.
Whole-body CWI (incl. head) increased SWS proportion during the FIRST ~180 min of the night vs partial-body immersion (p < 0.05) — a within-night, between-condition effect. No "d=1.36" effect size was reported (that figure was fabricated in the prior entry).
Whole- and partial-body CWI reduced nocturnal arousals vs control; whole-body also reduced limb movements.
No difference between conditions for any marker of fatigue/muscle damage over 48 h — the authors explicitly state overall recovery benefit is unproven.
Practical Application
CWI in the evening after hard endurance work MAY improve early-night deep sleep; treat as a modest, provisional benefit (single small study), not an established large effect.
Do NOT cite a specific effect size for the sleep benefit — none is validated.
Limitations
Single study, n=12, male-only, well-trained runners; not generalizable without replication.
SWS effect is early-night and condition-relative; no demonstrated performance/recovery outcome.
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How this entry was checked and changed
Why this level
(n=12, single study)
Content correction 2026-09-27
2026-09-28: added Protocol from the abstract (Europe PMC PMID 33870188).