Thanks guys. Every story helps protect life. Who knows who will avoid a shortened lifespan just because he or she watched your video. It's always been my biggest fear in spearfishing. I've done the samba twice. Once in a pool after a monitored 4:55 breath hold, and once on a personal best 105 foot freedive in Monterey, California. I have competed in quite a few national spearfishing championships...have been on the first place team, I think three times, and have been individual vice-champion twice. I also went to the Worlds in Chile back in 2004. I'd like to share something I did as an experiment. Please, if you read anything below, please pay attention to the last point. To me, it is the most disturbing point. I am a retired firefighter. As a firefighter, I had access to a pulse oximeter at the firehouse. It measures the percentage of blood oxygen. I wanted to see the effect pre-breath hold hyperventilation had on oxygen levels and contrast that with a breath hold without hyperventilation. I also wanted to determine what was happening to those percentages as a breath hold progressed. I performed many breath holds with different breathing techniques before the hold (I'm just going to call all the breathing up I did "hyperventilation" since I don't remember every technique I used). Though I wish I had, I did not do any with any attempt at simulating dive level exercise, i.e., I didn't walk on a treadmill or anything like that while I held my breath. I did this experiment, probably 25 years ago, and am trying to remember the results, since I don't have the data in front of me (I'm on vacation in Oahu right now. When I get home, I'll try to dig up the actual record I made.) Anyway, I remember a couple of interesting results. First, I recall that, without any hyperventilation...just taking a breath and holding it for as long as I could, I could get my blood oxygen percentage down into the mid to low 90% level before I had to take a breath. I also noted that recovery to my normal resting level (about 98-99%) took only a few seconds. Then I started doing some hyperventilating before I held it. On some of the hyperventilating, I did long, slow, deep breathing. I would count the number of breaths I took, as well as the nature of the breathing up I did. The more I hyperventilated, the longer I could hold my breath. I even did some crazy hyperventilation sessions, like everyone thinks of when they hear the word "hyperventilate", where I would inhale and exhale rapidly and repeatedly. Now, here's some weird information, but read on, because it isn't the weirdest thing. The more I breathed up, the longer I was able to hold my breath. Yes, everyone knows that and expects that. But the oxygen levels were what astounded me. I was able to get my oxygen percentages into the low 70s, and I think i may even have gotten it down into the high 60% range. (As I recall, this was after well over 3 minutes of breath hold) But that's not all. As I timed each breath hold, I would record the oxygen level every 10 seconds. That allowed me to note when the oxygen started dropping and how fast it dropped. Interestingly, the oxygen % stayed at 98-99% for longer when I hyperventilated before the breath hold. In other words, hyperventilating resulted in oxygen levels staying high for longer. That surprised me. It appeared that breathing up DID have a beneficial effect on oxygen retention. The only thing I can come up with as to why this may have been is that maybe breathing up purges more of the lung spaces of CO2 and replaces it with fresh air. Either that, or perhaps there is a little bit of supersaturation of the tissues that can occur. It would take some kind of expert to research that. But here's the part that really shocked me and disturbs me, and I found this out by accident. I mentioned above that my oxygen level returned to normal very quickly after I started breathing. I had noticed the same thing with my breath holds preceded by hyperventilation too. But at one point I just happened to leave the pulse oximeter on my finger for a while after one of the breath hold sessions was completed (a session where I hyperventilated beforehand), and I saw something that really surprised me. My oxygen level went back to normal, as usual, but then as I watched, it started going back down. I thought, "what the heck is going on here? I'm breathing...I feel fine... why is my oxygen level dropping?" This happened for every breath hold that included hyperventilation beforehand. Also, the more I hyperventilated, the more pronounced the drop. For example, when I really hyperventilated a lot, and then held my breath until the oxygen level was down in the 70% range, the secondary drop was really pronounced. I think it actually dropped back into the 80% range. After that happened, I started watching the meter for a lot longer and found out even more interesting but disturbing info. Not only did the levels drop after I started breathing, but they did it SEVERAL times. I'm probably not making any sense, so let me give an example. Ok, say I hyped up pretty good before starting a breath hold. Now, I hold my breath and start the timer. Every 10 seconds I record my oxygen level. Let's say that at the 1 minute mark, my oxygen level goes from 98%-97. Now, let's say that at every 10 seconds, the oxygen has dropped 2% more. So, I hit the 3 minute mark and my oxygen is at 75%. Now, I start to breathe. Within 10-20 seconds, my oxygen level reads 97%. I keep breathing, and as i do, I notice that the oxygen % starts to drop again. It keeps dropping all the way to, let's say 83%. Now, as I continue breathing, the oxygen climbs back up again to near normal levels. As I KEEP watching, it starts to DROP again. This time it goes down to the high 80s...now it again climbs back up to near normal. As I watch, it drops AGAIN...this time into the low 90s. Finally, it levels off and stays at full oxygenation. Ok, I have no idea what the physiology was that caused that to happen. It may be that it's just me and no one else's results would be the same. Maybe it's because I was an out of shape couch potato (actually, I wasn't, but everything's relative. Compared to Mark Healey, I probably was). One possibility that I came up with is that perhaps the breathing gets blood oxygen up very quickly but that the depleted tissues are still starving for it and have to process out the CO2 and take up oxygen. Maybe that process isn't as fast as the lung to blood transfer. One thing I WILL say, and I feel it's very important. I never FELT any of this as it was happening. In other words, I FELT like I was ready for the next breath hold. In FACT, my body was in an oxygen depleted state. Ever since I did this little experiment, I have changed the way I freedive. Now, when I do anything deep or long (for me now, deep is 50-60, and long is 1.5 minutes. Hey, I'm 61 years old, ok?) I stay on the surface for longer than I feel like I need to between dives. I used to adhere to the philosophy "a minute down, a minute up". No more. Now, it's more like, "a minute down, THREE minutes up." Guys, sorry for being so wordy. I just don't feel like editing this for brevity and all that. It's bed time. I truly hope that someone benefits from my experience with this little experiment.