Belial said:
Easy. Valsalva maneuver. During every rep.
Also, don't drink any water before you go.
Uhh...no.
I'm very good about breathing. When I first started lifting I accidentally did the Valsalva maneuver while doing leg-presses. It didn't make me nauseous, but did give me horrible throbbing pain in the back of my skull due to the astronomic rise in blood pressure. And I am always quite well hydrated, though I'm not aware how merely not drinking water before lifting could cause nausea. Severe dehydration might do it though.
DaCyper-
I really think intensity is a mindset. When I first started doing HIT, I had only been training about 3-4 months. I was doing laughably high volume: 2-hour full body workouts 3X a week, and running 3 miles and doing push-ups and sit-ups on my off days. When I first read about HIT on Cyberpump I didn't understand how it differed from normal lifting. 1-3 sets. Full body workouts. What the hell makes this "high-intensity", I wondered. It really is the mindset with which you approach each set. Approach each set as if you're life depended on it. I'm not sure I can explain any better than that. I still focus 110% on each set; the biggest difference in how I currently train is that I rest much longer between sets, waiting until I feel fully recovered before performing any work set. I used to race between machines only pausing to load and unload bars, maybe giving myself 20-30 seconds to catch my breath, and then doing the next exercise(1 set each) I remember once doing leg-presses for 20, rushing to do lat-pulldowns, and BAM it was over. I had to lie down, I physically couldn't complete the rest of my workout--well, I could have but it would have resulted in the gym floor being covered in vomit. Before squatting I would always read Sean Toohey's "The Battle for 20" about 20 rep squatting, which I had printed out and kept in my workout log book. Read the accounts on Cyberpump. Everytime I went into the gym I would compare myself with those guys, and I realized I cut a pretty poor figure. When your just sort of flinging the weights around(and I even call 2-4 cadences flinging) your mind isn't totally on the current set. The easiest way I know to achieve absolute intensity is to use SuperSlow(Though they've amended the cadence to 10-10 I still use 10-4. 10-10 only works on very high quality machines that have very low friction.) Do leg-presses at a 10-4 cadence (Squats are near impossible at this speed due to considerations of balance.) and aim for a 6-8 reps. When your body starts to shutdown and the pain becomes unbearable just focus on contracting the muscle, keep moving. For me thought ceases at this point, there is no longer I, only the weight. Breath. Focus. Contract the muscle. Only stop when you've been pushing for a good 15 seconds without budging the weight stack. If you can stand after this you did something wrong. You most likely will also feel nauseous, although maybe not. Approach EVERY set like this, and you will achieve the sort of intensity of which I spoke about above. Of course, I only ever had the severe nausea occur with full body workouts, which I used to do exclusively, or on leg days. I don't personally agree with the Jones quote about arm curls I posted above. You really have to be stimulating quite a large quantity of muscle mass to get the pukey feeling--or as I like to call it the "God, let me die" feeling.
If you try any of this, tell me what happens.