What is an ice bath good for?
An ice bath helps athletes after hard training: less muscle soreness, faster recovery of explosive power and a reduced sense of fatigue. Outside sport, the indications so far are weak.
Muscle soreness after a hard training session decreases measurably after an ice bath. That effect is present at 24, 48, 72 and 96 hours after exercise, compared with simply resting. The benefit is not large, and the studies are small and heterogeneous, but the effect has been found repeatedly.
In addition to less pain, explosive power, such as jumping or sprinting, recovers more quickly. That benefit is visible 24 hours after training. No significant benefit was found for pure maximum muscle strength. Fatigue also decreases: at 72 hours after team sport, athletes report lower fatigue scores, and people already feel less tired immediately after the bath. Subjective sense of recovery improved 24 hours after exercise. A marker of muscle damage in the blood drops significantly at 24 hours after the bath.
Regarding temperature and duration: water of 10 to 15 degrees Celsius for 10 to 15 minutes produced the best results for muscle soreness and performance recovery. Colder or longer is therefore not necessarily better.
Outside the sports context, the findings are thin. There is an indication that stress is reduced, but only at 12 hours after the bath. At all other measurement points, immediately after, at 1 hour, 24 hours and 48 hours, no effect on stress was found. For sleep and overall well-being there are cautious positive signals. No significant effect on mood was measured. For the immune system there is no proven short-term benefit.
Note the safety point: an ice bath temporarily causes an acute inflammatory response, measurable immediately after and 1 hour after the bath. Most studies did not actively track side effects, so what the risks are for people with cardiovascular disease or other health problems cannot be determined reliably on the basis of current research. Discuss the use of ice baths with your doctor if you have a health condition.
This answer is based on multiple reviews of existing research into cold water immersion, with studies that followed athletes after exercise. The findings on muscle soreness and recovery are reasonably consistent, but the underlying studies are small and of varying quality. The findings outside the sports context (stress, sleep, immune system) come from a single review and are thin: the researchers found no significant effect at most measurement points. Side effects were not systematically tracked in most studies, which represents a genuine gap in the evidence.