Cold water immersion (CWI) has been used a recovery method since man began to exercise. Ancient Chinese, Greek, Russian, Indian and Persian athletes, soldiers and monks all made use of it and cited it repeatedly in their texts as a method of recovery. Today, we look for measurable evidence rather than simply repeating what our predecessors did.

In response to the idea that cold water immersion improves muscular recovery immediately, Parouty et al 2010 had 100m swimmers perform a max effort 100m sprint, take a 30min break (with 5 min immersion in 14C water) and then perform another 100m sprint. They performed 1.8% slower, HR was 1.9% slower. This clearly was not enhancing immediate performance.

Al Hadad 2012 had half an elite swim team add 5 min of CWI (15C) to their daily training regime for 2 weeks. Heart rate variability was measured by Ln rMSSD. By day 4, the swimmers in the experimental group demonstrated improved heart rate variability by 30.4%. This tends to indicate a chronic effect on the parasympathetic nervous system. Similarly, Buchheit et al 2009, that CWI (5min in 14C water) demonstrated improved heart rate variability p<0.05. Again, we see this chronic parasympathetic effect.

Bleakley and Davison 2010 completed a review of the CWI evidence as it currently stands. Of 3971 studies found related to CWI, only 16 met inclusion criteria (<15C for <5min, in trunks or naked, with measures of heart rate, blood pressure, blood flow, respiratory response). Studies had to be RCTs, randomized cross-over trials, cohort trials, or cross-sectional trials.

The included studies demonstrate that HR increases immediately after the 1st minute of CWI but by minute 3 it has begun to drop off. During immersion, systolic bp increased 15mm Hg within 1 minute but within 30 min post immersion had returned to baseline. In one cited study, middle cerebral artery blood flow was measured by transcranial Doppler imaging and demonstrated 43% reduction in total volume.

Respiratory minute volume increased from 16.4l/min to 32l/min within 2 min of CWI. After 3 min in a separate study, it had reached 94.6l/min.

Skin temperature decreased by 0.42C/s but core temperature dropped 0.1C total in 3 min.

Oxygen consumption rose from 0.417 l/min and 0.676 l/min in 3 min.

Interestingly, total radical antioxidant of plasma increased p<.05 for 35min after CWI before returning to baseline. This can have implications for long-term health. Uric acid dropped by more than half from time of immersion to 1h post-immersion and returned to normal 24hr later.

One study found an increase in cortisol for 1h post immersion while another found a drop in cortisol and a spike in norepinephrine. This bears further investigation.

Men who engaged in cold water swimming for >1yr had higher baseline levels of GSH (a naturally occurring anti-oxidant), catalyse, and superoxide dismutase (all P <.01).

Conflicting reports on its effects on thyroid hormone, luteinising hormone, growth hormone and several others exist and thus are inconclusive though in those who participate in studies of more than 3months, catecholamine response to CWI appears to be reduced through chronic adaptation to the acute stimulus.

At this time, while it is clear CWI has a profound effect on the parasympathetic system and by extension some endocrine elements, it is unclear what the total effect on acute or chronic recovery may be.