Ice baths, used by the All Blacks and other elite athletes, do "nothing" to fight muscle inflammation, according to a researcher from the University of Auckland.
A study published in the Journal of Physiology tested the assumption that cold water immersion reduces muscle inflammation, and was undertaken in part by researchers from University of Auckland.
No data from humans was available to support the notion, so the researchers compared the effects of ice baths with active recovery.
Auckland University professor David Cameron-Smith was involved in the research, and is sceptical of the effect ice baths have on recovery based on the scientific information.
"Quite frankly it does nothing," he said.
"There's been increasing myths around the use of ice baths and other cold water treatments to the point where it's become pretty much standard for a lot of athletes... there's been very little analysis on what it actually does."
Nine active men took part in the research, which was conducted in Australia. They took part in lower-body resistance training exercises on separate days, one week apart.
On one day they immersed their lower body in 10C water for 10 minutes after exercising, and on the other they cycled at a low intensity for 10 minutes.
Muscle biopsies were collected from the exercised leg before the training and then at 2, 24 and 48-hour intervals afterwards.
Cameron-Smith said the study focused on whether ice baths made a difference to the level of inflammation inside muscles.
"That's white blood cells moving into the muscles... really trying to get to the heart of what is going on in terms of inflammation... and nada, nothing, zero, there is no change.
"The answer is there is no reason why anybody ever should jump in a cold water bath."
The study found changes in inflammatory cells, cytokines, neurotophins and Henoch-Schonlein purpura did not differ significantly between the recovery treatments.
New Zealand Rugby high perfomance player development manager Mike Anthony told the Herald ice baths are "only one of a wide range of recovery methods" that elite rugby players use.
"Since 2003 we have referred to all studies that are published and based on those outcomes have made decisions on what is best for our athletes. One study with only nine subjects, measuring just a few variables, does not provide conclusive evidence for us to alter the use of cold water or ice as part of our recovery strategies.
"As the study itself states, the benefits of ice baths are broader than just at the cellular level.
"There are a large number of studies that show positive effects in a range of variables with large sample sizes that support the use of cold water."
The research's abstract states "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".
Cameron-Smith said it was "hard" to explain why it remained popular among elite athletes as a form of recovery.
"The first is it's quite relaxing, it's a simple part of that relaxation cycle. And you do get short-term reductions in pain, you jump in for a while, you relax, you chill - literally - and then you get a small reduction in pain.
"Often that's really important for athletes to go to sleep. When you think of the guys who are playing games at night, like the All Blacks, winding down and going to sleep is a real pain in the butt, those guys are wired til 3 o'clock in the morning.
"So it might have a role in terms of that, but for everybody else, give it away."
The research was undertaken by universities in Brisbane, Norway and Japan, and included Vandre C. Figueiredo, James F. Markworth and David Cameron-Smith from Auckland University's Liggins Institute.