hi gianpaoloc,
Even though I know nothing about your diving skill or the depths you are currently diving to, I think we should all be careful with the logic that what works for Pipin should work for you.
Pipin has had a ton of experience with rapid descents and no limits in general. I would say that his chest/lungs must be more adapted than most (or more scarred than most!) Loic even more so (see my article about Loic's training methods and frequency). I wouldn't be comfortable in the assertion that because Pipin can do such a fast variable weight dive that you can without risk of injury. The heads up position indeed could be a factor in minimizing negative pressures in the trachea.
From personal experience, I think the safest method for improving chest/lung readiness for depth is FRC dives in the 10-25m range done extremely slowly and doing your inhale dives without packing, especially if you are relatively new to packing or have had squeezes before.
FRC dives (see other threads for info) should be done such that you sink very slowly from the surface (or after only one kick or two), with a descent speed of less than 0.5 m/s in the first 10-15m. I believe this trains the body to redirect plasma the fastest to the core to protect the lungs and also allows enough time for vasoconstriction. A mouthfill at the surface or 5-8m is necessary to keep the chest relaxed.
But as Wishbone points out, there is never any guarantee that any method is completely safe, since we're dealing with pressure and a relatively fragile human body. The advantage with doing slow FRC versus fast variable dives and negative pressure dives is that I had enough time to feel the changes in my body and stop the dive if I felt tight or uncomfortable or any pain in the chest. And results: in 3 weeks I went from diving FRC to 15m in complete comfort to 35m and my negative pressures (used as a way to judge progress only) went from 8m to 15m. This is great, but if you use packing and making fast descents, I don't think you'll fully benefit from the changes that FRC make in your body.
My opinion only.
Pete
Even though I know nothing about your diving skill or the depths you are currently diving to, I think we should all be careful with the logic that what works for Pipin should work for you.
Pipin has had a ton of experience with rapid descents and no limits in general. I would say that his chest/lungs must be more adapted than most (or more scarred than most!) Loic even more so (see my article about Loic's training methods and frequency). I wouldn't be comfortable in the assertion that because Pipin can do such a fast variable weight dive that you can without risk of injury. The heads up position indeed could be a factor in minimizing negative pressures in the trachea.
From personal experience, I think the safest method for improving chest/lung readiness for depth is FRC dives in the 10-25m range done extremely slowly and doing your inhale dives without packing, especially if you are relatively new to packing or have had squeezes before.
FRC dives (see other threads for info) should be done such that you sink very slowly from the surface (or after only one kick or two), with a descent speed of less than 0.5 m/s in the first 10-15m. I believe this trains the body to redirect plasma the fastest to the core to protect the lungs and also allows enough time for vasoconstriction. A mouthfill at the surface or 5-8m is necessary to keep the chest relaxed.
But as Wishbone points out, there is never any guarantee that any method is completely safe, since we're dealing with pressure and a relatively fragile human body. The advantage with doing slow FRC versus fast variable dives and negative pressure dives is that I had enough time to feel the changes in my body and stop the dive if I felt tight or uncomfortable or any pain in the chest. And results: in 3 weeks I went from diving FRC to 15m in complete comfort to 35m and my negative pressures (used as a way to judge progress only) went from 8m to 15m. This is great, but if you use packing and making fast descents, I don't think you'll fully benefit from the changes that FRC make in your body.
My opinion only.
Pete