Hey North, nice to meet you. I didn't see your post for some reason, and I usually try to let other's answer before I step in.
Although we are of course all limited to some extent by our individual physiologies, there is much that can be done to improve that physiology and the capability to resist high CO2 levels and low O2 levels.
First, be in damn good shape. Second, get a notebook, and write down as much as you think is relevant about your training: static and whatever else you do.
This is the routine that got me over 6 minutes....
Do whatever works for you to get the body loosened up and relaxed. For me, this is about a half hour of yoga, and 20 minutes of meditation.
Without breathing up, hold your breath for as long as possible, to the point where you just have to breathe.
Rest and breath deeply and slowly for 2 minutes.
Hold your breath again, as long as possible....this time you might be able to hold a little longer.
2 minute breathe up, then hold again.
Now breathe up for 3 or 4 minutes, but not too long. I experimented with up to a 10 minute breathe up, but it did not help.
Now, for the last 10 seconds of your breathe up, do some quick breathing, then go for the BIG hold.
That's it...simple, but effective. There are some stipulations, and many variables, depending on the individual....eat lots of anti-oxidants: vegetables, fruits, maybe a supplement. Take some extra iron every day that you do this.
Try doing it a lot, say every day, or 3 times a week, and see if you are improving. If your times start to drop, or you get sick, then back off.
Another thing is "belief" encouragement. I will give you an example. Before March 15th of this year, I had never been able to hit 4 minutes on the first hold, no matter what. It just never registered in my head that I should try. On the 14th, I talked to a guy who was asking advice about statics on a chat line, and he said that with hyperventilation, he had hit 4 minutes on his first hold once.
The next day, when I started my static training for the evening, I hit 4:10 on the first hold, and since then, I have been able to do that any day, at almost any time. The point is that once I had heard it could be done, I was able to do it! Psychology is 90% of this sport I believe. So believe, my friend!
If you are serious about it, and put the time in, your body will begin to change, and the times will improve, guaranteed.
Good luck, and please let us know how your training goes,
Erik (Norwegian spelling
) Young