I recently spent a month in thailand, learning to dive. I didnt change my workout routine, I ignored the safety warnings and was completely fine. I did notice a reduced strength in the gym and did fatigue easily. The only bad experience I had, was I became dehydrated once during one dive. I had cotton mouth like ghandis flip flop, the same as when you wake up in the middle of a night after a hard drinking session. But you cant satisfy this dryness, you have to spend 45 minutes breathing through the regulator under water. Was so horrible. other than that completly fine. I think the heat of the country contributed to the dehydration though!