Rules in most powerlifting feds:
1. The lifter must lie on their back with head, shoulders and buttocks in contact with the flat bench surface. Shoes MUST be FLAT on the floor/built up surface. This position MUST be maintained throughout the attempt once the "PRESS" single has been given.
2. To achieve firm footing, the lifter may use plates/blocks. The entire foot MUST be flat on the surface.
3. The lifter may have a lift-off from a spotter/coach which MUST be taken at arms length not down at chest.
4. The spacing of the hands may NOT exceed 81 cm(31 7/8") measured between the forefingers. A reverse grip is permitted provided that the distance between the little fingers does Not exceed 81 cms.
5. After receiving the bar at arms length, the lifter shall lower the bar to the chest and await the signal. Before receiving the signal, the lifter may make position adjustments without penalty.
6. When the bar is MOTIONLESS on the chest, the signal will be given. The signal consist of the audible command "PRESS".
7. After the signal to commence the lift has been given, the bar is pressed upward to straight arms length and HELD MOTIONLESS until the audible command RACK is given.
8. The bar is allowed to stop during the upward motion but is NOT allowed any downward movement of either or both hands.
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Of course like all rules they can be interpretted by the ref.
I think the "keeping the feet on the floor" and "bar is motionless on the chest" would be the hardest rules to adhere to.
Alan