Hi there. Most of us get contractions from a certain point on in a dive. When I do a static dive, after some time I feel how the muscles in my belly tense up (I guess the diaphragm?) and then I feel micro contractions for some time before I hit the first real one. This phase from the first feeling of unease to the first contraction, I can influence by will and prolong it a bit. I wonder if this is a good idea or not. I assume that contractions are muscle movement, which costs oxygen, so delaying them is worth it?