Headholio
New member
Always keep your back flat on the bench (no arch), and feet flat on the floor. This is the correct form for bench and how it is supposed to be done. If at heavier weights you begin to arch your back, you need to either do less reps or less weight. Good form is crucial and also lessens the risk of injury
Butt on the bench is the usual guideline. Some people can make a pretty good arch while still keeping the butt down, but in general, if your butt is on the bench, the arch isn't going to be excessive. Powerlifters try to maximize arch while keeping their butt on the bench because this gives a mechanical advantage and is what is legal in competition. I agree that normal lordosis is a good and safe position.
Also, keep your feet flat on the ground. As you guessed, some gyms won't allow feet on the bench because if you start to tip to the side, you can't stop yourself.
A good solid base for bench is what you want. No wiggly squirlyness. If you watch a powerlifer bench, you see his legs and butt contract, and force is transfered from his legs to the contact point of his back with the bench. The whole body should be tense and solid and the back of the head should remain down keeping contact with the bench.