I have watched some Taekwondo practitioners resting their legs inside ice cold water for a specific amount of time:
Also, I noticed Cryotherapy devices being used:
What is the effect of low temperature on muscles? What is the science behind it?
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TL;DR: Results are mixed
The theory behind ice baths is related to the fact that intense exercise causes microtrauma, which is tiny tears in your muscle fibers. This microscopic muscle damage is actually a goal of exercise as it stimulates muscle cell activity and helps repair the damage and strengthen the muscles (muscle hypertrophy). But it is also linked with delayed onset muscle pain and soreness (DOMS), which occurs between 24 and 72 hours after exercise.
The ice bath was believed to:
- Constrict blood vessels and flush waste products, like lactic acid, out of the affected tissues
- Decrease metabolic activity and slow down physiological processes
- Reduce swelling and tissue breakdown
Then, with rewarming, the increased blood flow was believed to speed up circulation, and in turn, improve the healing process.
From "Effects of Cold Water Immersion on Muscle Oxygenation During Repeated Bouts of Fatiguing Exercise" published in January 2016:
As the results show that cold water immersion attenuated decreased tissue oxygenation in subsequent exercise performance, the metabolic response to exercise after cold water immersion is worthy of further exploration.
These findings indicate that cold water immersion is no more effective than active recovery for reducing inflammation or cellular stress in muscle after a bout of resistance exercise.