Creating an arch in the lower back (where your backside is more or less off of the bench) is a technique usually employed by (competative) powerlifters to decrease the range of motion. This is something that should only be reserved at powerlifting meets, as when you train the idea is to develop a full range of motion in all exercises. Don't try to imitate this person's technique when you are training your bench.
Additionally, below is a "checklist" which may aid in improving your benching technique:
1.Take 2.5-3 seconds to lower the bar to 1-1.5 inch below the nipples.
*2.Make a bridge/arch in your lower back so the bar has less distance to travel (always think decline)
3.Use your lats to help drive the bar off your chest.
4.Then push your upper back into the Bench as hard as you can throughout the whole lift.
5.Keep your elbows tucked in at all times trying to pull the bar apart!
6.Push in a straight line.
7.Drive the bar into lockout as fast as possible.
8.Keep your shoulder blades back at all times.
9.Keep feet planted firmly flat on the floor at all times.
10.Fill your lungs with as much air as possible as you lower the bar and exhale when the bars 2/3's of the way up.
* Powerlfting tip. Employ no.2 only at a meet. Only use a slight arch in the back when training.
- B.A.
