Negative Dive? "Swording"

[wet]

What is a negative dive, and therefore, what is a positive dive?

I'm assuming a negative dive is feet-first descent (extended toes, arched feet),
while positive or regular dive is face-first descent. Correct?
Please clarify or verify.

From a post by Lungfish, a mention of "negative pressure dive", is that "negative dive"?
"There are also many styles of diving and some have suprizing benefits within their limitations. For example, negative pressure diving or diving while saturated but with empty lungs is an effective technique and probably a more efficient way to dive under 50meters. But nobody is negative pressure diving 100meters....."

ps.
Has anyone ever tried ascending feet first, using thoracic contraction of the diaphragm as an undulating mechanism to propel the linear rigid legs forward?
This would parallel a narwhal or swordfish, where the straight legs and abdomen pierce the water (sword-like) while the upper chest and extended semi-rigid arms pivot with spinal sinuations in rhythm with the diaphragmatic contractions providing thunniform-like propulsion (lunate tail), similar to how a tusked narwhal propels itself and actually like a shark too. I refer to this concept as "swording". It is the equivalent of the Dolphin kick, but in reverse. The significance of it is that it might be more O2 efficient than paddling with arms & legs, since it completely based on contractions. It is a blind ascent, since eyes are looking in wrong direction. Anyway, it would be a "negative ascent", if I understand the terms correctly. DDeden

 

[efattah]

A negative dive is short-hand for negative pressure dive.

A negative pressure dive is a dive done with empty or partially empty lungs.

The word negative pressure comes from the fact that while diving with empty lungs, the pressure in the lungs rapidly becomes negative relative to the ambient pressure.

 

[wet]

Thanks for the clarification, Eric.
My confusion stemmed from having read some posts by Seb Murat, in which he mentions IIRC deep diving with "empty lungs", "wet sinuses" and diving feet first.

PS. Thanks for writing about the eye muscles possibly being vestiges of former more aquatic lifestyle, very interesting! DDeden

 

[wet]

Eric, thanks for the clarification. I've read some posts by Seb Murat regarding "empty lungs", "wet sinuses" and feet first diving, that's where I got confused.

PS. Thanks also for writing about the vestigial eye muscles, very interesting! DDedden