Why? It must do something because alot of powerlifters and heavy benching bodybuilders use them when benching. Why would you use a weight belt on a bench press?
I've never once felt anything from benching my low back and core muscles.
THey press OUT on the Belt w/ their Gut! Big breath, hold breath. Fills chest, less ROM.
Increase pressure and width of core (NOT Decreased)
Also, the bench shirts. You want it SO tight. Pull the shirt DOWN (Best to have help) and cinche it down in place w/ the Belt. This is a 1 rep sport. Set-up is King.
Your narrow Grip bench form is crying for a bench shirt. Thats how a stiff shirt forces your groove anyway.
Muscle order of import: 1.Tri's 2.Lats (Landing Pad) 3.Delts. Pecs tear easy, thats why many PLers use the elbows in form.
For Leg Drive, Belt=Tight. Tight = Better energy transfer from Leg Drive...
Lay flat on the bench w/ a weight thats very easy to play with on chest, w/ deep arch.
Relax ass and leg muscles ---- suddenly Flex ass and leg muscles, while simultaneously Push toes into front of shoes.
(Like your trying to slide back on the bench by pushing w/ legs)
Bar wants to "Pop" off chest...
Practice get as much Pop off the chest as you can w/ out raise ass off bench.... You can get a lot.