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Bieuzen, Bleakley and Costello ran a systematic review with meta-analysis, published in PLoS ONE in 2013, on contrast water therapy after muscle damage from exercise. The modality is alternating warm and cold water immersion, not sauna. With a search to February 2013, 18 controlled trials qualified, 13 of them poolable, covering 356 healthy participants, 301 men and 55 women, 19 per study on average. Cold water ranged from 8 to 15 degrees, mean 11.1, and warm water from 35.5 to 45 degrees, mean 39.3. Cold phases lasted 1 minute in all but one trial, warm phases 1 to 3 minutes, sessions 6 to 24 minutes, and most protocols ended cold.
Compared with passive recovery, muscle soreness was lower at all five time points, with standardised mean differences of 0.62 under 6 hours, 0.51 at 24, 0.58 at 48, 0.40 at 72 and 1.21 beyond 96 hours. Against the same passive recovery, strength loss was smaller as well, with differences of 0.95, 0.75, 0.56, 0.62 and 1.38 in that order. Against cold water immersion alone there was no robust difference in soreness at any point; against warm water alone contrast bathing did better at 24 and 96 hours; against active recovery, compression and stretching there was little or no difference.
Every one of the 18 trials was rated at high risk of bias. Randomisation was described in 3, adequate allocation concealment in 2, no trial blinded participants or therapists, and only 1 blinded outcome assessment. The outcomes are soreness and short-term strength loss after induced damage, not health or long-term performance.
The comparison belongs with the result: better than doing nothing, not better than other common measures. The authors see the effect sizes as relevant mainly to competitive sport, and nothing here transfers to a Finnish sauna with a plunge pool.