I've read some things on the 'burn'. I'd have to look into more. I think it partly depends what you are training for and partly what muscles you are training.

Trainging for the Toure de France you'll want to have a high lactic acid treshold.

Training to throw a shot put you don't.

So there are many variables.

Type of muscle too. Fast twitch, slow twitch. Postural, prime mover etc

I can't answer but those are somethings to think about. A marathon runner and a hockey player have different demands on their muscles.

I think (not sure here) that postural and slow twitch muscles you can go for more of a burn with. Not sure though.

One thing is always being able to do with good form. When you loose form other muscles are taking over and you are teaching your brain to recruit the wrong ones.

With the swiss ball curl up most peoples necks will fatigue first. Are you roling up starting with the head and not protruding it? (keep tongue on roof of mouth)

My neck fatigues way before my abs.

I said above I think you should come to about level. I think now that you should come through full range. That doesn't mean coming up too far still. I think abs (rectus abdominus) can go about 30degrees of flexion (45degrees extention I think). So from floor you are getting less than half ROM.

But make sure that you balance out flexion and extention exercises to keep balanced.

Sorry can't really answer. Been taught a couple different things in that area and I'm not too sure about it right now.

But depends what you want and what you are training for and what you are training I think.

-make sure with TVA activation you aren't sucking in your abs like I was. If TVA is in and you breath then the upper abs should bulge with belly button in still.

From years of sit-ups I preobably have 3-6months of retraining my abdominal wall so that it works properly by its self.

Its not just being able to do it its training the brain muscle conections. Its training the right recruitment paterns.

Just like hands and knees
I think the progression they learn in physio is laying down, sitting, hands and knees, standing (could be wrong but thats close). Point is its all about retraining as well as strengthening.

Now cause you do that doesn't mean you can do it when it counts.

The string can give you feed back.

-side point I have never been able to squat-movement patterns, flexibility etc etc Yesterday for the first time I squatted with weight and good form through a full range of motion. :) -trying to focus on TVA activation throughout