I finally read that paper after having cleaned off my desk and found it under all the other ones I hadn't read.

Sadly the study probably can't tell us anything because they've compared elite UWH players to students who don't exercise more than 5 hours a week. So anything that you do (or don't) find could associated with UWH training or it could just be training in general. The authors do claim, however, that the control subjects were as fit as the French national underwater hockey team on the basis that the maximal output (VO2 max) was not statistically significantly different. This lack of significance could be due to small sample size (10 versus 10) as there is an apparent difference between the groups of about 5 ml/min/kg.

So I'm afraid I didn't really get much of a take-home message for any of you.