If you do it right, CWI can be effective, says John Cronin, the director of the Sports Performance Research Institute New Zealand at AUT University.

"There is pretty good evidence out there suggesting changes in cardiac responses, peripheral resistance, blood flow and that if you toy with the temperature and hydrostatic pressure, it's good," says Cronin.

Hydrostatic pressure is the pressure exerted by water due to the force of gravity. The pressure increases in proportion to the depth due to the increasing weight of the water.

Cronin believes the technique can aid recovery but the question is, how much? Does it do more than, say, going for a light jog? "There is a lot of uptake in cold water immersion but, again, over and above other types of strategies?" asks Cronin.