I am a bit confused about the correct breathing technique in lifts that require core strength.
Take the squat as example:
1) Some people say that it is very important to breathe in at the top of the movement, then hold the breath until when you go down until you come up again to the straight position. Then you should breath out. The air should go into the stomach and you should contract the abs at the same time. The reason for this is that the air and the ab contraction increases the intra-abdominal pressure. This leads to a tight core which protects the spine. Additionally this gives you a bit more power for your lift (I guess about 10 percent). However doing this also increases the blood pressure which in turn can lead to cerebrovascular accident or hemorrhoids and similar things concerning the blood vessels. It can also lead to oxygen deficit in the brain...
Because of this risks, the general advice in training is
2) Breathe in on relaxion and breathe out under load. I also found this advice in the German book "Differenzierte Kraftraining" by Axel Gottlob, where squats and deadlifts are also discussed in depth.
3) Sometimes, the variant is suggested to hold the breathe on the bottom and very slowly breath out on the way up.
4) Another variant is to breathe into your stomach as you are standing straight, tighten your abs and let some air go out again, then hold it until you are up again.
5) The last advice I have heard is just not to think about it, but just breathe naturally. If I try this, I end up in breathing multiple times during the lift which feels to be wrong. However, I can keep my abs contracted while breathing, so my spine should still be protected, isn't it?
So I am very confused about this topic and need an authoritative answer how to do it in detail and why, and what about the concerns I have with the different kinds of breathing technique: Better spine protection but higher blood pressure or vice versa...
I guess that the first method is the best for professional power- or weightlifters, but I am interested in training for hypertrophy for general health, and just for fun.
If you don't lift your 1 rep max, and choose instead of it a weight where you can do 8-15 reps (and 4 sets), which technique would be the most healthy one and why?
How does the risk for the spine increases in this case when I don't hold my breath during the lift?
Edit: To understand the subject completely: How does the recommended speed of execution relates to the breathing technique and to the possible dangerous. For example, if you hold your breath, it may be better to execute the lift quickly since this seems to me to reduce the risks associated with holding the breath during the lift...