Well you know I think everyone should be doing pretty much that anyway without a belt. That's the way you squat. Gather air into the diaphraghm, tense your abs and push outwards and downwards. In effect make yourself both tighter and wider. Damn straight it helps. It's called the valsalva maneavour I think (that's right, I'm a geek
). This can however, give you a bigger gut appearance since it will basically promote "gut dumping". A good thing is to counter this method during squatting by sucking in your gut when doing ab strength (ONLY during ab work NEVER while squatting or deadlifting).