Cold water immersion and cryotherapy shift heart rhythm control toward parasympathetic dominance

A 2024 systematic review and meta-analysis pooled data from 24 studies to examine how cold water immersion and whole- or partial-body cryostimulation affect blood pressure, heart rate, and heart rate variability in healthy adults. Across these studies, cold exposure was consistently associated with measurable shifts in cardiac autonomic balance, including higher heart rate variability indices and a modest reduction in heart rate, alongside a small rise in mean blood pressure.

What the study found

Cold exposure was associated with statistically significant increases in several heart rate variability measures reflecting parasympathetic nervous system activity. Specifically, the time-domain measure RMSSD and the high-frequency spectral band — both considered markers of vagal tone — rose meaningfully after cold exposure, as did the average interval between heartbeats.

At the same time, measures associated with sympathetic or mixed autonomic influence — the low-frequency spectral band and the ratio of low-to-high frequency power — declined significantly. These autonomic shifts were detectable for at least 15 minutes following the cold exposure session.

Heart rate itself fell modestly but significantly, while mean blood pressure showed a small but statistically significant increase. The authors interpret the overall pattern as consistent with a shift toward parasympathetic dominance following cold exposure, though effect sizes varied across the included studies.

The authors note that both the type of cooling technique used and individual participant characteristics appear to moderate these responses, and they flag that the scientific literature on how personal factors shape cold-induced physiology remains limited.

Limits worth knowing

The meta-analysis drew on 27 reviewed articles, of which 24 contributed quantitative data — a relatively modest evidence base given the heterogeneity of cooling methods (whole-body cryostimulation, partial-body cryostimulation, and cold water immersion were pooled). All included studies were conducted in healthy individuals, so findings do not extend to clinical populations. The review does not report a pooled sample size, making it difficult to assess total participant numbers. Study durations, immersion depths, and measurement timing varied across the included trials. The authors acknowledge sparse data on how individual characteristics such as age, sex, or fitness level influence outcomes, and meta-regression was used to probe but not fully resolve these sources of variability. Funding disclosures are not detailed in the available abstract.

About this entry. The Heartwood Review summarizes published, peer-reviewed research in its own words and links to the original source. It is not medical advice; consult a physician before beginning or changing any thermal or recovery practice. Findings summarized here describe the study cited, not any product sold by Teak & Marble Atelier. Corrections.