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OK, so everyone (everyone that's fit anyway) alwyas says that if you're fit, 
there's less chance of DCI, right?  Well, actually they are right.  The latest 
info from the Naval Medical Research Institure (that's in the US) suggests that 
pigs conditioned on a treadmill were less likely to have DCI that non-
conditioned pigs.  The pigs were compressed in a chamber  on air to 200 FSW for 
24 min and then decompressed at 60 ft/min. 73.5% of the non-conditioned pigs 
compaired to 41.7% of conditioned pigs developed DCI.  Remember, though, that 
all of these pigs were castrated.  Note also that body weight was not
important.  
The abstract is reproduced below for your education.

Authors
  Broome JR.  Dutka AJ.  McNamee GA.
Title
  Exercise conditioning reduces the risk of neurologic decompression illness
  in swine.
Source
  Undersea & Hyperbaric Medicine.  22(1):73-85, 1995 Mar.
Abstract
  During development of a pig model of neurologic decompression illness
  (DCI) we noted that treadmill-trained pigs seemed less likely to develop
  DCI than sedentary pigs. The phenomenon was formally investigated.
  Twenty-four immature, male, castrated, pure-bred Yorkshire swine were
  conditioned by treadmill running, while 34 control pigs remained
  sedentary. All pigs (weight 18.75-21.90 kg) were dived on air to 200 feet
  of seawater (fsw) in a dry chamber. Bottom time was 24 min. Decompression
  rate was 60 fsw/min. Pigs that developed neurologic DCI were treated by
  recompression. Pigs without neurologic signs were considered
  neurologically normal if they ran on the treadmill without gait
  disturbance at 1 and 24 h postdive. Of the 24 exercise-conditioned pigs,
  only 10 (41.7%) developed neurologic DCI, compared to 25 of 34 (73.5%)
  sedentary pigs (X2 = 5.97; P = < 0.015). Neither mean carcass density
  (adiposity) nor mean age were significantly different between groups. No
  patent foramen ovale was detected at necropsy. An additional control group
  of 24 pigs was dived to clarify the influence of weight. The results
  suggest that the risk of neurologic DCI is reduced by physical
  conditioning, and the effect is independent of differences in age,
  adiposity, and weight.

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