The Welsh rugby team might want to ditch cryotherapy sessions ahead of their match against Fiji on Thursday, say medical experts who have evaluated this deep freeze aid for tired muscles.
The Cochrane team found no good evidence that the therapy works.
Cryotherapy chambers - where players are exposed to air temperatures of minus 160C - were credited with being a big factor in Wales' run to the semi-finals of the World Cup in 2011.
And the team is using them this year.
One spokesman for the Welsh Rugby Union said it was aware that there wasn't much evidence around cryotherapy but said it "thinks it works and that's why we use it."
I'm sure we would accept that the jury is still out, he said.
Another spokesman said it was unhelpful to get into this sort of debate ahead of an important match - if Wales, who are second in Pool A behind Australia, beat Fiji they will top the group.
The Cochrane work compared the effects of whole-body cryotherapy with simple rest and no treatment or another treatment, called far-infrared therapy, in 64 athletic young adults.
There was no proof that spending short spells in sub-zero temperatures reduced muscle soreness or improved recovery. Based on the findings, the researchers say there is insufficient evidence to recommend whole-body cryotherapy.
Lead researcher Dr Joseph Costello, from Portsmouth University's Department of Sport and Exercise Science, said: "We did an exhaustive research of the literature and found only four studies that assessed the effects of this treatment, which is amazing when you consider that sports teams are investing in it.
"That's not to say it couldn't work, but there's no good evidence that it does."
He is also concerned that there could be side-effects. "Very few studies recorded any negative or adverse effects. There was one report of an elite rugby player getting a small frost injury to the thigh.
"But the research is lagging behind current practice."
He said individuals must wear socks, shorts, a mask, ear protection and gloves while in the cryotherapy chamber to protect vulnerable body parts.
People with blood pressure and heart problems should avoid it entirely, he advised.